CA2425934C - A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and coexistence of multiple physical layer modulation schemes - Google Patents
A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and coexistence of multiple physical layer modulation schemes Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
- H04W28/24—Negotiating SLA [Service Level Agreement]; Negotiating QoS [Quality of Service]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
- H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
- H04L1/0025—Transmission of mode-switching indication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
- H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
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Abstract
One aspect of the invention provides a method of communication in a medium, for a communication network having a number of stations, using Medium Access Control protocol that incorporates quality of service capabilities wherein at least one of the stations is capable of generating a (repetitive) beacon for assigning priority levels for each priority station on the network, wherein a station, before transmitting information on the network, attempts to detect the presence of a beacon for the network, and if the presence of a beacon is not detected, adopts the status of a beacon and transmits a beacon message to other stations in the network. In another aspect of the invention interference is reduced in communication in a medium using carrier modulation, for a communication network having a plurality of stations, using access control protocol wherein at least one of the stations is capable of generating a control message (SOD) that can be transmitted to other stations on the network to change the method of modulation being used, wherein communication between stations in the network is being performed using a first modulation method, by initiating a change in the modulation method being used by sending a control message containing identification of a second modulation method to other stations to inform them of the second modulation method; allowing the other stations to change the modulation method used to the second modulation method. The control message further includes a direction to thaw other stations not charging modulation to the second modulation method to instruct them not to transmit using the first modulation method.
Description
A METHOD OF ADDING QUALITY OF SERVICE CAPABILITIES TO CSMA-CA
BASED PROTOCOLS FOR THE PURPOSE OF ISOCHRONOUS COMMUNICATION
AND COEXISTENCE OF MUI,TIPLF, PHYS1CAI~ LAYER MODULATION SCHEMES
Field of the Invention This invention relates to the field of netwi>rking using Medium Access Control (MAC), and more particularly slotted Carrier Sense Multiple Access (CSMA) protocol, also called CSMA-CA
(Collision Avoidance) protocol, and also to networks that use carrier modulation.
Background To address some problems of the prior art, the- utility of the invention is in the field of guaranteed Quality of Service (QOS) parameters, with specific attention to guaranteed latency and bandwidth (also known as isochronous) parameters and in case of wireless networks deals with hidden node issues.
I S Brief Description of the Drawings Figure I shows the International Standards Organization's (ISO) conceptual reference model of a network device, called the Open Systems lnterconnection (05I) reference model;
Figure 2 illustrates 2 overlapping wireless networks;
Figure 3 illustrates the block level architecture of the embodiment of the coexistence and interpretation of multiple physical layer modulations.
The conceptual model of a network can be represented in the OSI reference model which is depicted in Figure 1 in which it can be seen that a network can be considered as a layered structure, including an Application Layer 1, Presentation Layer 2, Session Layer 3, Transport 2_5 Layer 4, Network Layer 5, Data Link Layer G, M.AC Sublayer 7, and Physical Layer 8. This model of a network is well known in the art and can be referred to during a review of the description below.
CA9-1998-0023CA2 l In a typical CSMA based network each device or staticm in the network is required to carrier sense the medium (detect the presence of a physical carrier generated in the medium generated by a station transmitting information in the medium) before it begins to transmit. The amount of time required to detect the presence of a carrier is dependent upon the modulation method of the electronic design of the underlying physical implementation of devices in the network.
If a station using a CSMA MAC protocol detects a carrier (generated by another CSMA MAC
station) the- particular CSMA MAC: protocol followed will do one of two things; persistent type carrier sensing CSMA MAC stations will continuously monitor the carrier signal from a station that wants to transmit and transmit as soon as the carrier disappears; non-persistent type CSMA
MAC station will wait a finite period of time and carrier sense once again. If a carrier is present then the. process is repeated. To avoid collision that would occur if 2 or more MACs were presented with data to transmit at the same time when following a persistent CSMA MAC
protocol, a station may or may not transmit when no carrier signal is detected. Such CSMA
MAC protocols are referred to as CSMA MAC protocols with collision avoidance, CSMA-CA
MAC protocols. The decision to transmit is based on a protocol dependent probability of transmitting. If the probability is very high (closer to 100~'l0) then the device is more likely to transmit when an idle channel is detected that a device with a lower probability of transmitting.
Another concept that can be applied to CSMA MAC protocols is that of slotring.
If certain actions followed by the CSMA MAC protocol can only occur after certain fixed periods of time the CSMA MAC is referred to as a slotted CSMA MAC. For example if interval of time between cagier sensing the medium in (non-persistent) CSMA MAC protocols or CSMA-CA
MAC protocols is made up of multiple fixed duration time periods (referred to as slots), then these CSMA protocols would be referred to as slotted CSMA c.~r slotted CSMA-CA
MAC
protocols.
Regardless of the- nature of the CSMA MAC protocol, it is possible that 2 or more stations in the network will eventually attempt to transmit their data at the same time. If the devices do not detect the collision, the bandwidth of the medium consumed during the combined transmissions is wasted. If the devices are able to detect the collision then the amount of bandwidth wasted due CA9-1998-002~CA2 2 to the collision is limited to the amount of time required for the devices to detect the collision.
This further enhancement, collision detection, is employed by CSMA-CD
(Collision Detection) MAC protocols.
The referenced prior art CSMA MAC. protocols share a basic common problem. It is extremely difficult to determine how long it will take a station using these CSMA MAC
protocols to transmit a given block of data. The amount of tinne to transmit a given block of data depends on at least 2 factors: the time required to access the channel and the time to place the data on a channel. The amount of time required to place the data on the channel is deterministic and can easily be calculated by those skilled in the art based on the size of the data block, the base baud rate (measured in bits per second) of the channel and the modulation employed in encoding the data on the channel. The other component, channel access time, is dependent upon the number of other devices simultaneously contending for the channel, the amount of data these devices place on the channel, and the nattGre of the particular C'.SMA MAC protocol being employed.
These dynamic parameters of the second component are simply unknown to a device that is attempting to gain access to the channel. Thus the channel access time, or transmit latency time, may be statistically bound, but is not deterministic.
Therefore, in prior art CSMA networks it is virtually impossible to guarantee the amount of time required to transmit a given block of data. But this parameter is fundamental in providing a known quality of service for isochronous communications over a link between stations in the network.
The specific QOS parameters that are sought to be supported are:
1) A time-to-live parameter associated with a given block of data (the maximum amount of time that the data is considered valid)
BASED PROTOCOLS FOR THE PURPOSE OF ISOCHRONOUS COMMUNICATION
AND COEXISTENCE OF MUI,TIPLF, PHYS1CAI~ LAYER MODULATION SCHEMES
Field of the Invention This invention relates to the field of netwi>rking using Medium Access Control (MAC), and more particularly slotted Carrier Sense Multiple Access (CSMA) protocol, also called CSMA-CA
(Collision Avoidance) protocol, and also to networks that use carrier modulation.
Background To address some problems of the prior art, the- utility of the invention is in the field of guaranteed Quality of Service (QOS) parameters, with specific attention to guaranteed latency and bandwidth (also known as isochronous) parameters and in case of wireless networks deals with hidden node issues.
I S Brief Description of the Drawings Figure I shows the International Standards Organization's (ISO) conceptual reference model of a network device, called the Open Systems lnterconnection (05I) reference model;
Figure 2 illustrates 2 overlapping wireless networks;
Figure 3 illustrates the block level architecture of the embodiment of the coexistence and interpretation of multiple physical layer modulations.
The conceptual model of a network can be represented in the OSI reference model which is depicted in Figure 1 in which it can be seen that a network can be considered as a layered structure, including an Application Layer 1, Presentation Layer 2, Session Layer 3, Transport 2_5 Layer 4, Network Layer 5, Data Link Layer G, M.AC Sublayer 7, and Physical Layer 8. This model of a network is well known in the art and can be referred to during a review of the description below.
CA9-1998-0023CA2 l In a typical CSMA based network each device or staticm in the network is required to carrier sense the medium (detect the presence of a physical carrier generated in the medium generated by a station transmitting information in the medium) before it begins to transmit. The amount of time required to detect the presence of a carrier is dependent upon the modulation method of the electronic design of the underlying physical implementation of devices in the network.
If a station using a CSMA MAC protocol detects a carrier (generated by another CSMA MAC
station) the- particular CSMA MAC: protocol followed will do one of two things; persistent type carrier sensing CSMA MAC stations will continuously monitor the carrier signal from a station that wants to transmit and transmit as soon as the carrier disappears; non-persistent type CSMA
MAC station will wait a finite period of time and carrier sense once again. If a carrier is present then the. process is repeated. To avoid collision that would occur if 2 or more MACs were presented with data to transmit at the same time when following a persistent CSMA MAC
protocol, a station may or may not transmit when no carrier signal is detected. Such CSMA
MAC protocols are referred to as CSMA MAC protocols with collision avoidance, CSMA-CA
MAC protocols. The decision to transmit is based on a protocol dependent probability of transmitting. If the probability is very high (closer to 100~'l0) then the device is more likely to transmit when an idle channel is detected that a device with a lower probability of transmitting.
Another concept that can be applied to CSMA MAC protocols is that of slotring.
If certain actions followed by the CSMA MAC protocol can only occur after certain fixed periods of time the CSMA MAC is referred to as a slotted CSMA MAC. For example if interval of time between cagier sensing the medium in (non-persistent) CSMA MAC protocols or CSMA-CA
MAC protocols is made up of multiple fixed duration time periods (referred to as slots), then these CSMA protocols would be referred to as slotted CSMA c.~r slotted CSMA-CA
MAC
protocols.
Regardless of the- nature of the CSMA MAC protocol, it is possible that 2 or more stations in the network will eventually attempt to transmit their data at the same time. If the devices do not detect the collision, the bandwidth of the medium consumed during the combined transmissions is wasted. If the devices are able to detect the collision then the amount of bandwidth wasted due CA9-1998-002~CA2 2 to the collision is limited to the amount of time required for the devices to detect the collision.
This further enhancement, collision detection, is employed by CSMA-CD
(Collision Detection) MAC protocols.
The referenced prior art CSMA MAC. protocols share a basic common problem. It is extremely difficult to determine how long it will take a station using these CSMA MAC
protocols to transmit a given block of data. The amount of tinne to transmit a given block of data depends on at least 2 factors: the time required to access the channel and the time to place the data on a channel. The amount of time required to place the data on the channel is deterministic and can easily be calculated by those skilled in the art based on the size of the data block, the base baud rate (measured in bits per second) of the channel and the modulation employed in encoding the data on the channel. The other component, channel access time, is dependent upon the number of other devices simultaneously contending for the channel, the amount of data these devices place on the channel, and the nattGre of the particular C'.SMA MAC protocol being employed.
These dynamic parameters of the second component are simply unknown to a device that is attempting to gain access to the channel. Thus the channel access time, or transmit latency time, may be statistically bound, but is not deterministic.
Therefore, in prior art CSMA networks it is virtually impossible to guarantee the amount of time required to transmit a given block of data. But this parameter is fundamental in providing a known quality of service for isochronous communications over a link between stations in the network.
The specific QOS parameters that are sought to be supported are:
1) A time-to-live parameter associated with a given block of data (the maximum amount of time that the data is considered valid)
2) A guaranteed latency time for data transmission
3 j A guaranteed bandwidth.
The time-to-live QOS parameter ensures that if the MAC is unable to begin transmitting a given block of data within a given period o f time that the MAC will simply discard the data instead of C'A9-1998-002:iC'A2 3 exceeding the time-to-live parameter and transmitting the data. This is useful when the data arrives periodically and is invalidated by the next periodic update. If the given data block can not be sent before the next periodic update of the information, then then°e is no value in having the MAC consume network bandwidth for the purpose of transmitting stale data.
The guaranteed latency QOS parameter ensures that the MAC will be able to send the given block of data on the network within the latency interval specified. The MAC
determines what range of latencies is supportable and must fail any request to provide guaranteed latency with too small a latency parameter.
Finally, the guaranteed bandwidth QOS of service ensures that a network layer above the MAC
will have access to the medium for some guaranteed interval of time during which it will always be able to transmit a precise amount of data. Therefore, by dividing the maximum amount of data that can be transferred by the guaranteed access period gives the guaranteed bandwidth parameter.
The hidden node problem arises as a result of the limited range of wireless devices. Two devices out of range of each other may simultaneously attempt to communicate with a device in range of both of them thus causing interference hampering successful communications.
Communication networks are made up of the following components, a medium, signal, a modulation technique, a physical layer and a data link layer that may or may not contain a Medium Access Control (MAC.) sublayer and higher network layers. A medium is a physical or spatial entity that is able to transfer one or more signals. A signal is a recognizable pattern that in the context of this invention refers to a single carrier. .A modulation scheme is a method of encoding information into the signals) that the medium is able to transfer. A
network physical layer translates data, in the form of packets, from upper network layers into modulated information carrying signals that can be efficiently transferred across the medium. The physical layer must be able to submit modulated information to the medium and be able to extract the modulated information from the medium. In computer networks this involves the translation of CA9- l 998-0023CA2 4 data bits into the modulated signals sent over the medium. For efficient network performance, the MAC needs to coordinate the physical layer's activities to ensure that multiple physical layers do not attempt to simultaneously submit signals onto the medium if that process will cause interference rendering each signal unintelligible to other physical layer entities. In networks where there are only 2 valid signals, the cornrr~on carrier and silence, this is essential.
The decision to only employ a single carrier wave allows for a simple, cost efficient implementation of the network physical layer hardware. Since the carrier is switched on and off as a result of a particular pulse modulation technique, such networks are only able to transfer a serial stream of binary (on/ off) information. The°.refore such networks are ideally suited to the serial transmission of binary data from a computing device. The method of mapping binary information to the presence or absence of the common carrier is determined by the particular pulse modulation technique employed. The simplest technique would encode a binary 1 as a pulse, and a binary 0 as silence. Under such a modulation scheme, the maximum baud rate that could be supported over the medium depends on how fast the hardware used to generate the pulses is clocked. This is a complex decision that is dependent upon many factors, power, heat, the time required for a receiver to lock on to the carrier and regenerate a binary pulse, cost and others. As technology advances, it may be possible to increase the clock rate of the pulse stream, or more efficient methods may be found to encode the binary data stream. These effects will result in different modulation techniques that can be applied to the Gammon carrier. If the carrier frequency is much higher than the marginal improvements in the data rate brought about by better modulation methods, then the common carrier itself will not need to change as often as the modulation techniques. This means that enhancements in the modulation methods employed in these networks require changes in physical layer hardware but not necessarily the medium through which the common carrier is sent. This is obviously the case in wireless networks.
Modulation enhancements are also commonly followed by new physical layer and MAC layer protocols to take advantage of those enhancements. The end result is a collection of hardware components that share a common carrier signal that employ different modulation techniques using different physical and MAC layer protocols. This means it is impossible for devices listening for and modulating the common carrier to inter-operate. Even worse, the different networks must employ different mediurms or else they will interfere with one another since they all share a common carrier. For mediums that require physical conduits through which to transmit the common carrier, the problem is easy to resolve: Simply ensure that the different networks employ different physical conduits to transfer the common carrier.
However, in wireless networks the problem is harder to resolve since the medium is typically free space. Therefore if devices employing different modulations of the same carrier are in range of one another the interference problem can not be resolved. Devices belonging to the different networks must be spatially separated or temporally separated. Either solution will solve the interference problem but do not address the inceroperability problem.
Both inventions mention concepts employed in Time Division Multiplexing (TDM) and Time Division Multiple Access (TDMA) networks. TDM is the process in which entities are given access to a shared resource in a simple round robin fashion. In reference to networks, TDMA
networks employ the concept of 'rDM to allow stations a period of time in which they are exclusively permitted to send data in the medium in round robin order. One of the problems in basic TDMA networks is that medium bandwidth is often wasted. This occurs as a result of each station usually being allotted the same fixed period of time in which to transfer their data. If the station does not have enough data to comloletely fill its allocated time slice, or does not have any data to send at all. In the period of tinge allocated to that station in the TDMA, little or no data is transmitted. This under utilizes the medium and wastes bandwidth.
Summary of the Invention One aspect of the invention provides a method of communication in a medium, for a communication network having a plurality of stations, using Medium Access Control protocol (having slotted carrier sensing or collision avoidance ) that incorporates quality of service capabilities wherein at least one of the st~utions is capable of generating a beacon for assigning priority levels for each priority station on tl~e network, wherein:
a station, before transmitting information on said network, attempts to detect the presence of a beacon for the network, and if the presence of a beacon is not detected, adopts the status of a beacon and transmits a beacon message to other stations in the network.
Another embodiment of the invention svnchroni~.es the count down of collision avoidance slots in CSMA-CA MAC protocol by the transmission of a MAC layer control frame that is uniquely distinguishable from upper network layer data frames. This frame is called a beacon. The information contained in the beacon frame identifies the MAC layer addresses of a set of devices which have been allocated exclusive use of priority contention slots within the range of the device transmitting the beacon. 'the beacon also contains information to tell these priority devices the maximum amount oi' time they may transmit priority data in the medium, the maximum time between beacons and the tune duration of the beacon. This information allows the priority devices to determine certain quality of service parameters that they may offer to network clients. The beacon also contains information that the non-priority devices within the cell use to determine the minimum number of contention slots that they are required to wait upon detecting an idle channel before these non-priority devices are permitted to transmit on the medium. The invention discloses the process by which stations are assigned priority slots and how the device that generates the beacons is determined. The invention is able to reduce the potential interference caused by hidden nodes in wireless networks that employ the methods described in the invention.
C.A9-1998-002'~CA2 7 Another aspect of the invention provides a method of reducing interference in communication in a medium using carrier modulation, for a communication network having a plurality of stations, using access control protocol wherein at least one of the stations is capable of generating a control message (SOD) that can be transmitted to other stations on the network to change the method of modulation being used, wherein, communication between stations in said network is being performed using a first modulation method, including:
initiating a change in the modulation method being used in the network by sending a control message containing identification of a second modulation method to other stations on the network to inform the other stations of the second modulation method;
allowing the other stations to change the modulation method used by them to the second modulation method; the control message further including a direction to those other stations not changing to the second modulation method to instruct them not to transmit using the first modulation method.
Yet another aspect of the invention ~.~ses very short temporal separation through Time Division Multiplexing (TDM) to reduce interference when devices using different pulse modulation techniques of a common carrier and different physical and MAC layer protocols are in physical proximity. The invention creates unique periods of time in the medium for the explicit use of one of the modulation techniques. This allows for the coexistence of the various modulation techniques and their accompanying protocols.
C,A9-1998-0023CA2 8 Under certain circumstances the invention will also allow limited interoperability between these devices provided that the devices involved in the interoperation are able to communicate with at least one other modulation technique in the area of the devices employing the different modulation technidues. One modulation technique is used as the controlling modulation for one or more subordinate modulation techniques. The protocols of the controlling modulation are used to ensure that all devices using that modulation remain idle for a period of time during which another modulation technique may be used in the medium. The invention adds a special MAC control frame, called a Stmt of Data (SOD) frame, to the protocol of the controlling modulation. The SOD frame is used to inform all devices using the controlling modulation of the next subordinate modulation technique to be used in the medium and the period of time that the subordinate modulation technique will be used on the medium (called the modulation time, or MT). After sending or receiving a SOD frame in the controlling modulation, no devices using the controlling modulation are permitted to transfer data in the controlling modulation.
tf the device employing the controlling modulation is also able to understand the particular subordinate modulation indicated in the S()D frame, then that device may switch to the subordinate modulation for the MT time period specified in the SOD frame.
Additionally, if that device contains a protocol stack that uses the subordinate modulation technique, and the device contains a link manager entity described in the invention, then that device will be able to interoperate with other devices using the protocols of the subordinate modulation.
The invention requires that the MAC layers in the devices using the controlling modulation are able to generate jamming signals in the subordinate modulation techniques that will prevent protocols using those modulartions from ehfectively transmitting in the medium.
This invention uses several building blocks that can be employed by a slotted CSMA (-CD) or C'SMA-CA MAC. protocol to provide a quality of service to network layers above the MAC layer that will allow isochronous communication within a network. The invention is applicable to _'i0 non-persistent CSMA MAC protocols and as well is applicable persistent CSMA MAC protocols if the carrier sense interval is extended to include a contention slot. The following sections describe each of the building blocks and the final section shows how the blocks can be used in a specific embodiment of the- invention to lorovide improved QOS for isochronous servi<:e. The combination of the building blocks used provide an embodiment of the invention.
Priority Queuing Scheme : A building block used in the invention is a mechanism by which a MAC protocol must be able to reorder data for transmission on a channel. Most MAC protocols employ a simple FIFO queuing where the first block of data sent to the MAC for transmission is actually the first block of data to be sent on the channel. To provide isochronous service, the MAC protocol needs to ensure that isochronous data blocks are given higher priority than standard blocks of data that are not time sensitive. The MAC protocol requires a method to <rllow it to transfer the priority data blocks ahead of all non-priority data blocks. The priority data blocks are then sent in FIFO order on the channel. One of the simplest methods of achieving priority queuing is to simply abort any pending non priority data queued for transmission at the time priority data is submitted to the MAC layer for transmission. The ability to move priority l5 data ahead of non-priority data in the CSMA MAC layer does not itself ensure that a minimum transmit latency can be provided. The next packet to be transmitted (priority or not) is still subject to indeterminate latency as discussed under the prior art.
Maximum Contention Interval Scheme : As already discussed, the indeterminate latency of any transmit request submitted to the CSMA MAC layer is mainly due to the number of other devices simultaneously contending for the channel, the amount of data these devices place on the channel, and the nature of the particular CSMA MAC protocol being employed. In order to provide time-to-live latency QOS, a station using the MAC protocol must abort its attempt to transmit a given block of data if the time required to gain access to the channel exceeds the time-to-live latency parameter of the QOS. This can be achieved by starting a timer (that measures the same units of time as the time-to-live latency QOS parameter) in the MAC layer at the same time it begins contending for medium access. Once. the timer exceeds, the time-to-live QOS parameter, the eurre.nt transmit request must to aborted. Although this invention is most useful for slotted CSMA (and CSMA-(;A) MAC protocols. the maximum contention interval timer can be employed in other- CSMA MAC anon slotted as well as persistent CSMA MAC) protocols to provide the time-to-live QOS parameter.
Priority Slots : CSMA-CA MAC protocols incorporate the concept of contention slots. A
contention slot is simply defined as the amount of time required to detect if a station is transmitting on the network. In theory, on an infinitely fast network, the contention slot duration is simply the amount of time required to detect a carrier signal. However, no physical medium is infinitely fast. Therefore, a finite amount of tune is required fc>r a signal to pass from one end of the network to the other. To guarantee that a station does not transmit just before a signal from the farthest point in the network reaches it, the minimum contention slot is usually defined as the amount of time for a round trip signal to propagate between the extreme end points of a network.
In wireless networks, stations often employ a MAC layer handshake (e.g. RTS, CTS) to avoid collisions with nodes that are out of range, or hidden, with respect to the sender. In these situations, the contention slot must also include the amount of time to transmit one half of the handshake signals, as well as the worst case processing time of the handshake at the responder and the. amount of time to carrier sense the responder's handshake. One concept behind CSMA-CA MAC protocols is that if an idle channel is sensed the CSMA-CA MAC
protocol will require the stati<.m to either wait a random number of contention slots, or a predetermined number of contention slots before attempting to transmit. Of course, even after this wait, the station will have to once again carrier-sense the medium before transmitting. While the device waits, it is possible that another device begins transmitting if that device happens to choose to wait a smaller number of contention slots. In some CSMA-CA networks a station will send a jamming signal/
or frame before it intends to transmit to allow synchronization of all CSMA-CA
MACS.
However, the methods we referred to are unable to avoid all collisions. This is because it is possible that stations will choose the carne number of contention slots to wait or may send jam signals at the same time as other jam signals are sent or at the same time a data frame is sent. The use of priority slots can reduce the probability of collision in CSMA-CA MAC
protocol networks. Priority contention slots should be used by priority CSMA-CA devices for tr;~nsferring priority data. Given that there are 'j' priority CSMA-CA devices in the network, then 'n' CSMA-CA priority slots are reserved for their exclusive use (n <= j). For the purposes of this discussion each priority device is assigned one, or more, of the priority slots (m), where. the assignments begin at 0 for the first priority device and end at n-1 for the nth priority device (0<=rn<= n-1<j). If' a device is not assigned one of the 'n' priority slots, then upon sensing an idle channel, the priority device must choose to wait a number of contention slots that is at least ns large as 'n'. If a device is assigned cme of the 'n' priority slots, then upon sensing an idle channel, the non-priority device may either choose to wait a number of contention slots that is at least as large as 'n', or to wait a number of contention slots exactly equal to 'm'. Therefore, even though the device has a priority slot, it does not have co use the priority slot for sending non-priority data. That is, priority slots should only be used to transfer priority data.
Beacons Scheme : Priority slots themselves will not avoid collisions if the CSMA-CA devices begin counting down contention slots at exactly the same time. For example, a device using contention slot 6 will collide with a device using contention slot 8 if the device using slot 8 begins counting down contention clots exactly 2 contention slot times before the device using I S slot 6. To avoid collisions a synchronization event is required to ensure all devices begin counting down contention slots at the same instant. In this invention, the synchronization event is provided by a unique MAC frame that indicates that priority traffic will follow the frame (if there is any present in the priority devices). This synchronization frame is called a Beacon. The beacon is distinguishable from regular MAC data frame and is used by the MAC
protocol for synchronization not for the communication of upper layer data. F'or CSMA-CA
MAC protocols that use separate MAC control and MAC' data frame formats, this application of the invention is straightforward - the beacon is seat as MAC control frame. MAC protocols that do not employ control frames may use a special multicast address for the purpose of QOS
management. Some CSMA-CA protocols may employ similar concepts but are very limited in their scope of 2.5 operation. Some send special non data synchronization pulses, and some will send small frames to announce the desire to transmit, or small frames announcing that synchronized data transfer is about to commence. Although these prcotocols may work well in a wired network, they begin to break down in wireless networks because of hidden nodes and overlapped network cells. For example consider the wireless networks depicted in Figure 2 ire which a device 26 in a network cell 21 (P1 in the left cell) is assigned the same. priority slot as another device 24 in an overlapped cell 20 (P1 in right cell). Since wireless devices are highly mobile, it is possible that device 26,P1, from the left cell 21 will move from a region where it is unable to hear (or interfere with) devices in the right cell 20 to a region 22 where it is able to hear (and interfere with) devices in both cells 20 and 21. Suppose now that the left device 26 moves into overlapping region 22. If device P0, 23, in the right cell 20 initiate a standard CSMA-CA
contention period, then both devices 26 and 24 will send their data at the same time resulting in a collision.
'The beacon is able to solve this problem because either PI device 26 or 24 is able to distinguish between a beacon sent from within its own cell as opposed to a beacon heard from another cell.
This is achieved by 2 mechanisms inherent in the format of the beacon. First, since the beacon is a special MAC (control) frame, it will carry a Source Address (SA), like all other MAC (control) frames. Since the invention requires that the device that is responsible for generating the beacon is also responsible for assigning any priority device its priority slot (discussed later), every priority device knows the identity of the device to whose beacons it should respond. Second the data contained in the beacon is an ordered list of the MAC layer addresses of the n priority devices in the cell that are the n registered users of that device's beacon.
The ordinal position of the MAC address in the list dictates the priority slot that that MAC address is able to use for its priority data.
The 2 mechanisms employed in the beacon that allow a priority device to ensure that it only transmits its priority data at the appropriate time also allow the device generating the beacon to dynamically reassign priority slots. The ability to dynamically reassign priority slots means that the generator of the beacon can minimize the number of priority slots used within the cell which reduces non-priority device's channel access latency times. For example, if there were j 2S registered priority devices in the cell, where j is some integer multiple, x, of n (i.e. j = x * n), then the device generating the beacon could simply generate 1 beacon announcing j slots to all j priority devices. Or the device could generate x successive beacons, each announcing n unique MAC addresses that are able to transmit their priority data in the appropriate contention slot. In the tirst case, on average, all non-priority devices will experience a longer transmit latency time.
In the seccmd case, on average, the non-priority devices will experience a shorter transmit latency but the priority devices will, on average, experience a longer latency time.
Isochronous Implementation Scheme This section gathers information from the previous sections to present the steps required to ensure that once devices in the network are assigned unique priority slots from a unique device, deterministic latency periods can be provided. The next section describes how the priority slots are assigned and the process by which a station is elected to generate the beacons. Networks operating in this manner are referred to as CSMA-CA with Beacon MAC protocols, (CSAM-CAB).
1 ) An isochronous device must have the ability to send priority data, in FIFO
order when required, ahead of all non-priority data by means of priority queuing. It is not necessary to abort a non-priority transmission in progress when priority data is submitted to the MAC.
2) Every contention slot used in every station (priority as well as non-priority) must be of a fixed length and large enough to accommodate the worst case time to detect an active channel and all stations must be using contentions slots of equal duration.
3) Any device that does not have a priority slot must wait a minimum number of contention slots that is equal to, or greater than, the number of priority slots currently distributed in the network before attempting to transmit when the channel is detected as idle.
The time-to-live QOS parameter ensures that if the MAC is unable to begin transmitting a given block of data within a given period o f time that the MAC will simply discard the data instead of C'A9-1998-002:iC'A2 3 exceeding the time-to-live parameter and transmitting the data. This is useful when the data arrives periodically and is invalidated by the next periodic update. If the given data block can not be sent before the next periodic update of the information, then then°e is no value in having the MAC consume network bandwidth for the purpose of transmitting stale data.
The guaranteed latency QOS parameter ensures that the MAC will be able to send the given block of data on the network within the latency interval specified. The MAC
determines what range of latencies is supportable and must fail any request to provide guaranteed latency with too small a latency parameter.
Finally, the guaranteed bandwidth QOS of service ensures that a network layer above the MAC
will have access to the medium for some guaranteed interval of time during which it will always be able to transmit a precise amount of data. Therefore, by dividing the maximum amount of data that can be transferred by the guaranteed access period gives the guaranteed bandwidth parameter.
The hidden node problem arises as a result of the limited range of wireless devices. Two devices out of range of each other may simultaneously attempt to communicate with a device in range of both of them thus causing interference hampering successful communications.
Communication networks are made up of the following components, a medium, signal, a modulation technique, a physical layer and a data link layer that may or may not contain a Medium Access Control (MAC.) sublayer and higher network layers. A medium is a physical or spatial entity that is able to transfer one or more signals. A signal is a recognizable pattern that in the context of this invention refers to a single carrier. .A modulation scheme is a method of encoding information into the signals) that the medium is able to transfer. A
network physical layer translates data, in the form of packets, from upper network layers into modulated information carrying signals that can be efficiently transferred across the medium. The physical layer must be able to submit modulated information to the medium and be able to extract the modulated information from the medium. In computer networks this involves the translation of CA9- l 998-0023CA2 4 data bits into the modulated signals sent over the medium. For efficient network performance, the MAC needs to coordinate the physical layer's activities to ensure that multiple physical layers do not attempt to simultaneously submit signals onto the medium if that process will cause interference rendering each signal unintelligible to other physical layer entities. In networks where there are only 2 valid signals, the cornrr~on carrier and silence, this is essential.
The decision to only employ a single carrier wave allows for a simple, cost efficient implementation of the network physical layer hardware. Since the carrier is switched on and off as a result of a particular pulse modulation technique, such networks are only able to transfer a serial stream of binary (on/ off) information. The°.refore such networks are ideally suited to the serial transmission of binary data from a computing device. The method of mapping binary information to the presence or absence of the common carrier is determined by the particular pulse modulation technique employed. The simplest technique would encode a binary 1 as a pulse, and a binary 0 as silence. Under such a modulation scheme, the maximum baud rate that could be supported over the medium depends on how fast the hardware used to generate the pulses is clocked. This is a complex decision that is dependent upon many factors, power, heat, the time required for a receiver to lock on to the carrier and regenerate a binary pulse, cost and others. As technology advances, it may be possible to increase the clock rate of the pulse stream, or more efficient methods may be found to encode the binary data stream. These effects will result in different modulation techniques that can be applied to the Gammon carrier. If the carrier frequency is much higher than the marginal improvements in the data rate brought about by better modulation methods, then the common carrier itself will not need to change as often as the modulation techniques. This means that enhancements in the modulation methods employed in these networks require changes in physical layer hardware but not necessarily the medium through which the common carrier is sent. This is obviously the case in wireless networks.
Modulation enhancements are also commonly followed by new physical layer and MAC layer protocols to take advantage of those enhancements. The end result is a collection of hardware components that share a common carrier signal that employ different modulation techniques using different physical and MAC layer protocols. This means it is impossible for devices listening for and modulating the common carrier to inter-operate. Even worse, the different networks must employ different mediurms or else they will interfere with one another since they all share a common carrier. For mediums that require physical conduits through which to transmit the common carrier, the problem is easy to resolve: Simply ensure that the different networks employ different physical conduits to transfer the common carrier.
However, in wireless networks the problem is harder to resolve since the medium is typically free space. Therefore if devices employing different modulations of the same carrier are in range of one another the interference problem can not be resolved. Devices belonging to the different networks must be spatially separated or temporally separated. Either solution will solve the interference problem but do not address the inceroperability problem.
Both inventions mention concepts employed in Time Division Multiplexing (TDM) and Time Division Multiple Access (TDMA) networks. TDM is the process in which entities are given access to a shared resource in a simple round robin fashion. In reference to networks, TDMA
networks employ the concept of 'rDM to allow stations a period of time in which they are exclusively permitted to send data in the medium in round robin order. One of the problems in basic TDMA networks is that medium bandwidth is often wasted. This occurs as a result of each station usually being allotted the same fixed period of time in which to transfer their data. If the station does not have enough data to comloletely fill its allocated time slice, or does not have any data to send at all. In the period of tinge allocated to that station in the TDMA, little or no data is transmitted. This under utilizes the medium and wastes bandwidth.
Summary of the Invention One aspect of the invention provides a method of communication in a medium, for a communication network having a plurality of stations, using Medium Access Control protocol (having slotted carrier sensing or collision avoidance ) that incorporates quality of service capabilities wherein at least one of the st~utions is capable of generating a beacon for assigning priority levels for each priority station on tl~e network, wherein:
a station, before transmitting information on said network, attempts to detect the presence of a beacon for the network, and if the presence of a beacon is not detected, adopts the status of a beacon and transmits a beacon message to other stations in the network.
Another embodiment of the invention svnchroni~.es the count down of collision avoidance slots in CSMA-CA MAC protocol by the transmission of a MAC layer control frame that is uniquely distinguishable from upper network layer data frames. This frame is called a beacon. The information contained in the beacon frame identifies the MAC layer addresses of a set of devices which have been allocated exclusive use of priority contention slots within the range of the device transmitting the beacon. 'the beacon also contains information to tell these priority devices the maximum amount oi' time they may transmit priority data in the medium, the maximum time between beacons and the tune duration of the beacon. This information allows the priority devices to determine certain quality of service parameters that they may offer to network clients. The beacon also contains information that the non-priority devices within the cell use to determine the minimum number of contention slots that they are required to wait upon detecting an idle channel before these non-priority devices are permitted to transmit on the medium. The invention discloses the process by which stations are assigned priority slots and how the device that generates the beacons is determined. The invention is able to reduce the potential interference caused by hidden nodes in wireless networks that employ the methods described in the invention.
C.A9-1998-002'~CA2 7 Another aspect of the invention provides a method of reducing interference in communication in a medium using carrier modulation, for a communication network having a plurality of stations, using access control protocol wherein at least one of the stations is capable of generating a control message (SOD) that can be transmitted to other stations on the network to change the method of modulation being used, wherein, communication between stations in said network is being performed using a first modulation method, including:
initiating a change in the modulation method being used in the network by sending a control message containing identification of a second modulation method to other stations on the network to inform the other stations of the second modulation method;
allowing the other stations to change the modulation method used by them to the second modulation method; the control message further including a direction to those other stations not changing to the second modulation method to instruct them not to transmit using the first modulation method.
Yet another aspect of the invention ~.~ses very short temporal separation through Time Division Multiplexing (TDM) to reduce interference when devices using different pulse modulation techniques of a common carrier and different physical and MAC layer protocols are in physical proximity. The invention creates unique periods of time in the medium for the explicit use of one of the modulation techniques. This allows for the coexistence of the various modulation techniques and their accompanying protocols.
C,A9-1998-0023CA2 8 Under certain circumstances the invention will also allow limited interoperability between these devices provided that the devices involved in the interoperation are able to communicate with at least one other modulation technique in the area of the devices employing the different modulation technidues. One modulation technique is used as the controlling modulation for one or more subordinate modulation techniques. The protocols of the controlling modulation are used to ensure that all devices using that modulation remain idle for a period of time during which another modulation technique may be used in the medium. The invention adds a special MAC control frame, called a Stmt of Data (SOD) frame, to the protocol of the controlling modulation. The SOD frame is used to inform all devices using the controlling modulation of the next subordinate modulation technique to be used in the medium and the period of time that the subordinate modulation technique will be used on the medium (called the modulation time, or MT). After sending or receiving a SOD frame in the controlling modulation, no devices using the controlling modulation are permitted to transfer data in the controlling modulation.
tf the device employing the controlling modulation is also able to understand the particular subordinate modulation indicated in the S()D frame, then that device may switch to the subordinate modulation for the MT time period specified in the SOD frame.
Additionally, if that device contains a protocol stack that uses the subordinate modulation technique, and the device contains a link manager entity described in the invention, then that device will be able to interoperate with other devices using the protocols of the subordinate modulation.
The invention requires that the MAC layers in the devices using the controlling modulation are able to generate jamming signals in the subordinate modulation techniques that will prevent protocols using those modulartions from ehfectively transmitting in the medium.
This invention uses several building blocks that can be employed by a slotted CSMA (-CD) or C'SMA-CA MAC. protocol to provide a quality of service to network layers above the MAC layer that will allow isochronous communication within a network. The invention is applicable to _'i0 non-persistent CSMA MAC protocols and as well is applicable persistent CSMA MAC protocols if the carrier sense interval is extended to include a contention slot. The following sections describe each of the building blocks and the final section shows how the blocks can be used in a specific embodiment of the- invention to lorovide improved QOS for isochronous servi<:e. The combination of the building blocks used provide an embodiment of the invention.
Priority Queuing Scheme : A building block used in the invention is a mechanism by which a MAC protocol must be able to reorder data for transmission on a channel. Most MAC protocols employ a simple FIFO queuing where the first block of data sent to the MAC for transmission is actually the first block of data to be sent on the channel. To provide isochronous service, the MAC protocol needs to ensure that isochronous data blocks are given higher priority than standard blocks of data that are not time sensitive. The MAC protocol requires a method to <rllow it to transfer the priority data blocks ahead of all non-priority data blocks. The priority data blocks are then sent in FIFO order on the channel. One of the simplest methods of achieving priority queuing is to simply abort any pending non priority data queued for transmission at the time priority data is submitted to the MAC layer for transmission. The ability to move priority l5 data ahead of non-priority data in the CSMA MAC layer does not itself ensure that a minimum transmit latency can be provided. The next packet to be transmitted (priority or not) is still subject to indeterminate latency as discussed under the prior art.
Maximum Contention Interval Scheme : As already discussed, the indeterminate latency of any transmit request submitted to the CSMA MAC layer is mainly due to the number of other devices simultaneously contending for the channel, the amount of data these devices place on the channel, and the nature of the particular CSMA MAC protocol being employed. In order to provide time-to-live latency QOS, a station using the MAC protocol must abort its attempt to transmit a given block of data if the time required to gain access to the channel exceeds the time-to-live latency parameter of the QOS. This can be achieved by starting a timer (that measures the same units of time as the time-to-live latency QOS parameter) in the MAC layer at the same time it begins contending for medium access. Once. the timer exceeds, the time-to-live QOS parameter, the eurre.nt transmit request must to aborted. Although this invention is most useful for slotted CSMA (and CSMA-(;A) MAC protocols. the maximum contention interval timer can be employed in other- CSMA MAC anon slotted as well as persistent CSMA MAC) protocols to provide the time-to-live QOS parameter.
Priority Slots : CSMA-CA MAC protocols incorporate the concept of contention slots. A
contention slot is simply defined as the amount of time required to detect if a station is transmitting on the network. In theory, on an infinitely fast network, the contention slot duration is simply the amount of time required to detect a carrier signal. However, no physical medium is infinitely fast. Therefore, a finite amount of tune is required fc>r a signal to pass from one end of the network to the other. To guarantee that a station does not transmit just before a signal from the farthest point in the network reaches it, the minimum contention slot is usually defined as the amount of time for a round trip signal to propagate between the extreme end points of a network.
In wireless networks, stations often employ a MAC layer handshake (e.g. RTS, CTS) to avoid collisions with nodes that are out of range, or hidden, with respect to the sender. In these situations, the contention slot must also include the amount of time to transmit one half of the handshake signals, as well as the worst case processing time of the handshake at the responder and the. amount of time to carrier sense the responder's handshake. One concept behind CSMA-CA MAC protocols is that if an idle channel is sensed the CSMA-CA MAC
protocol will require the stati<.m to either wait a random number of contention slots, or a predetermined number of contention slots before attempting to transmit. Of course, even after this wait, the station will have to once again carrier-sense the medium before transmitting. While the device waits, it is possible that another device begins transmitting if that device happens to choose to wait a smaller number of contention slots. In some CSMA-CA networks a station will send a jamming signal/
or frame before it intends to transmit to allow synchronization of all CSMA-CA
MACS.
However, the methods we referred to are unable to avoid all collisions. This is because it is possible that stations will choose the carne number of contention slots to wait or may send jam signals at the same time as other jam signals are sent or at the same time a data frame is sent. The use of priority slots can reduce the probability of collision in CSMA-CA MAC
protocol networks. Priority contention slots should be used by priority CSMA-CA devices for tr;~nsferring priority data. Given that there are 'j' priority CSMA-CA devices in the network, then 'n' CSMA-CA priority slots are reserved for their exclusive use (n <= j). For the purposes of this discussion each priority device is assigned one, or more, of the priority slots (m), where. the assignments begin at 0 for the first priority device and end at n-1 for the nth priority device (0<=rn<= n-1<j). If' a device is not assigned one of the 'n' priority slots, then upon sensing an idle channel, the priority device must choose to wait a number of contention slots that is at least ns large as 'n'. If a device is assigned cme of the 'n' priority slots, then upon sensing an idle channel, the non-priority device may either choose to wait a number of contention slots that is at least as large as 'n', or to wait a number of contention slots exactly equal to 'm'. Therefore, even though the device has a priority slot, it does not have co use the priority slot for sending non-priority data. That is, priority slots should only be used to transfer priority data.
Beacons Scheme : Priority slots themselves will not avoid collisions if the CSMA-CA devices begin counting down contention slots at exactly the same time. For example, a device using contention slot 6 will collide with a device using contention slot 8 if the device using slot 8 begins counting down contention clots exactly 2 contention slot times before the device using I S slot 6. To avoid collisions a synchronization event is required to ensure all devices begin counting down contention slots at the same instant. In this invention, the synchronization event is provided by a unique MAC frame that indicates that priority traffic will follow the frame (if there is any present in the priority devices). This synchronization frame is called a Beacon. The beacon is distinguishable from regular MAC data frame and is used by the MAC
protocol for synchronization not for the communication of upper layer data. F'or CSMA-CA
MAC protocols that use separate MAC control and MAC' data frame formats, this application of the invention is straightforward - the beacon is seat as MAC control frame. MAC protocols that do not employ control frames may use a special multicast address for the purpose of QOS
management. Some CSMA-CA protocols may employ similar concepts but are very limited in their scope of 2.5 operation. Some send special non data synchronization pulses, and some will send small frames to announce the desire to transmit, or small frames announcing that synchronized data transfer is about to commence. Although these prcotocols may work well in a wired network, they begin to break down in wireless networks because of hidden nodes and overlapped network cells. For example consider the wireless networks depicted in Figure 2 ire which a device 26 in a network cell 21 (P1 in the left cell) is assigned the same. priority slot as another device 24 in an overlapped cell 20 (P1 in right cell). Since wireless devices are highly mobile, it is possible that device 26,P1, from the left cell 21 will move from a region where it is unable to hear (or interfere with) devices in the right cell 20 to a region 22 where it is able to hear (and interfere with) devices in both cells 20 and 21. Suppose now that the left device 26 moves into overlapping region 22. If device P0, 23, in the right cell 20 initiate a standard CSMA-CA
contention period, then both devices 26 and 24 will send their data at the same time resulting in a collision.
'The beacon is able to solve this problem because either PI device 26 or 24 is able to distinguish between a beacon sent from within its own cell as opposed to a beacon heard from another cell.
This is achieved by 2 mechanisms inherent in the format of the beacon. First, since the beacon is a special MAC (control) frame, it will carry a Source Address (SA), like all other MAC (control) frames. Since the invention requires that the device that is responsible for generating the beacon is also responsible for assigning any priority device its priority slot (discussed later), every priority device knows the identity of the device to whose beacons it should respond. Second the data contained in the beacon is an ordered list of the MAC layer addresses of the n priority devices in the cell that are the n registered users of that device's beacon.
The ordinal position of the MAC address in the list dictates the priority slot that that MAC address is able to use for its priority data.
The 2 mechanisms employed in the beacon that allow a priority device to ensure that it only transmits its priority data at the appropriate time also allow the device generating the beacon to dynamically reassign priority slots. The ability to dynamically reassign priority slots means that the generator of the beacon can minimize the number of priority slots used within the cell which reduces non-priority device's channel access latency times. For example, if there were j 2S registered priority devices in the cell, where j is some integer multiple, x, of n (i.e. j = x * n), then the device generating the beacon could simply generate 1 beacon announcing j slots to all j priority devices. Or the device could generate x successive beacons, each announcing n unique MAC addresses that are able to transmit their priority data in the appropriate contention slot. In the tirst case, on average, all non-priority devices will experience a longer transmit latency time.
In the seccmd case, on average, the non-priority devices will experience a shorter transmit latency but the priority devices will, on average, experience a longer latency time.
Isochronous Implementation Scheme This section gathers information from the previous sections to present the steps required to ensure that once devices in the network are assigned unique priority slots from a unique device, deterministic latency periods can be provided. The next section describes how the priority slots are assigned and the process by which a station is elected to generate the beacons. Networks operating in this manner are referred to as CSMA-CA with Beacon MAC protocols, (CSAM-CAB).
1 ) An isochronous device must have the ability to send priority data, in FIFO
order when required, ahead of all non-priority data by means of priority queuing. It is not necessary to abort a non-priority transmission in progress when priority data is submitted to the MAC.
2) Every contention slot used in every station (priority as well as non-priority) must be of a fixed length and large enough to accommodate the worst case time to detect an active channel and all stations must be using contentions slots of equal duration.
3) Any device that does not have a priority slot must wait a minimum number of contention slots that is equal to, or greater than, the number of priority slots currently distributed in the network before attempting to transmit when the channel is detected as idle.
4) If a device loses access to the medium in while contending, it can resume counting down contention slots from where it left off before the another device began transmitting if the remaining contention slot count is still larger than the current number of priority slots distributed in the network; otherwise the device must chose a new contention slot according to rule 3.
5) Devices using a priority slot are only bound by rule 4 when transmitting non-priority data.
When attempting to transmit priority data, they may continue counting down contention slots as soon as the medium is once again sensed as idle.
When attempting to transmit priority data, they may continue counting down contention slots as soon as the medium is once again sensed as idle.
6) The device using priority slot 0 must send the Beacon frame at regular intervals (determined by the minimum latency and guaranteed bandwidth QOS parameters). The beacon contains the MAC layer addresses of the n devices that have been granted priority slots. The ordinal position of those MAC addresses determines which priority slots) each device has been assigned. The Beacon must be sent hefore any priority data from Device 0 is sent.
7) A station that recognizes its MAC address in the beacon, and the beacon SA
as the MAC
address of the station that assigned its priority slot, will transmit its priority data in the slot indicated by the ordinal position of its MAC address in the beacon. If this differs from the previously allocated priority slot for that device, then the device has been assigned a new priority slot.
as the MAC
address of the station that assigned its priority slot, will transmit its priority data in the slot indicated by the ordinal position of its MAC address in the beacon. If this differs from the previously allocated priority slot for that device, then the device has been assigned a new priority slot.
8) In order to keep using a priority slot, other than slot 0, a non-beacon generating priority device must be able to hear the broadcast beacon frame from the device using priority slot 0.
Once a device using priority slot n hears the beacon, and that device has priority data to transfer, it will use it's assigned slot to transfer up to a pre determined amount of priority data. This ensures that all priority data will be transferred in the first n-1 contention intervals after the beacon.
In the absence of any interference, these steps would be sufficient to ensure that a device using a priority slot will be able access the medium in a finite, deterministic period of time. Step 3) guarantees that if a device using a priority slot and a device not using a priority slot are both given data to transmit at the exact same time, then the device using the priority slot will win access to the medium before the other device. Steps 2) to 4) ensure that even when there are other devices that have previously lost a reservation any device using a priority slot will still win access to the medium before all other device, not using priority slots.
?0 Suppose the particular MAC protocol requires that no single station can transmit non-priority data on the medium for any more than the Non-Priority Access Time (NPAT).
Also, suppose that each priority device can only tranamit priority data on the medium for no mode than the Priority Access Time (PAT). Suppose the Beacon required BT time to transmit and is sent every Beacon Interval Time (BfT). Finally suppose there are 'n' priority slots allocated in the, network.
Note that in the equations that follow the duration of the contention slot is not taken into account.
This scheme ensures that no matter how many devices there are in the network, nor how much data those devices are transmitting, the worst case maximum transmit latency for a priority device (in the. absence of interference) is always deterministic and given by the following formula:
(1) Latency = BIT - n * I'AT -BT+ NPAT + BT + (n- I ) ~' PAT
= BIT + NPAT - PAT
On average, over time, each priority device is able to get access to the medium for a period of time of PAT every BIT period. Therefore, on average, over time, every priority device is guaranteed PATBIT* l00 % of the channel's base baud rate.
(2) Priority bandwidth = PAT / BIT * channel bandwidth Extensions The definition of the beacon can be extended to include the cell parameters BIT, NPAT', BT and PAT. This allows the beacon generator to dynamically change the cell parameters. In addition, to an ordered list of MAC addresses, the beacon definition can further be enhanced to include unique PA'T times for every MAC in the beacon list. This would allow the beacon generator to dynamically modify the bandwidth allocated to each priority device and allow the priority devices to request varying guaranteed bandwidths. With this beacon definition the worst case transmit latency is:
(3) Latency; = BIT - sum(for j=0 to n-1 )of(PAT~) -B'T+ NPAT + BT
+ sum(for j=0 to n-I, j != i)of(PAT;) = BIT + NPAT - P,AT;
And the bandwidth allocated to device i i:~:
(4) Priority bandwidth; = PAT; / BIT * channel bandwidth Finally, if the cell were operated in a TDMA manner than NPAT in equation 1 would be 0. The BIT would also be specified in terms o1 the number of priority devices in the cell, BIT = n PAT. (The registration process defined in the next section would also need to be enhanced.) 'Therefore equation 1 could be reduced to:
(5) Latency = (n-1 ) '~ PAT
if every station were assigned varying amounts of bandwidth according to equation 4, then the worst case latency is:
(6) Latency; = sum(for j=0 to n-l,j!=i)of(PA'Ta) Allocating and ReleasingPriori~ Slots Another aspect of CSMA-CA.B networks in accordance with this invention involves acquiring use of a priority slot(s), releasing a priority slots) and determining which device will use slot 0.
To simplify the discussion, the device using priority slot n will be referred to as Device n. The broadcast frame that Device 0 must transmit every BIT period will be called the (isochronous) Beacon. These frames must be consumed at the MAC layer without being passed up to the network or higher layers. As previously mentioned, this may be achieved through MAC layer control frames or through a special multicast MAC address reserved for CSMA-CAB networks.
IS In the following text the beacons are assumed to be transmitted as MAC
control frames.
Establishing the Presence of a Beacon Generator in the Cell We have found that for advantageous performance, before a device is permitted to transmit on the network, it must first wait a period of time at least 2 default BIT
periods long to allow ~0 sufficient time to detect a beacon. (A guaranteed minimum bandwidth and maximum frame size determine the default maximum BIT, see equation 4.) If a beacon is heard within this interval, them the new device will know the number of allocated priority slots within the network and hence the minimum number of contention slots it must wait before attempting to transmit when the medium is sensed as idle. If the number of allocated priority slots changes as successive ?5 beacons are heard then so too does the ~ninirnum number of contention slots that a ncm-priority device (or a priority device sending non-priority data) is required to wait before attempting to transmit when the medium is sensed as idle.
On the other hand, if after having listened for a period of time at least 2 default BIT periods long, the Beacon is not heard, then the local device must start issuing the beacon and assume that it is Device 0. (This is required even if the device does riot wish to transfer priority data.) The first beacon generated by Device 0 must not be sent using a priority slot. In the case where the device assuming Device 0 responsibility never heatrd a previous beacon, at must waif one contention slot before sending its first beacon. In the case where the device is no longer able to hear the beacons of the device from which it was previously allocated a beacon, it must wait a minimum number of contention slots equal to the priority slot it was assigned on the last beacon heard. This helps to eliminate beacon collisions when the previous beacon generator suddenly stops beaconing in a cell with allocated priority slots.
Note that this process ensures that before any device in the network begins transmitting, there will already be 1 allocated priority slot for Device 0. Therefore the minimum number of contention slots that a non-priority device must wait before attempting to transmit when the medium is sensed as idle is always at least 1.
If a device that does not wish to transfer priority data becomes the beacon generator, it may transfer Device 0 status to the first device that registers it's desire to allocate a priority slot (see below).
?0 Requesting a Priority Slot From Device U
A device that wishes to acquire a priority slot must send a special MAC
control frame to Device 0, informing Device 0 that it wants to use a priority slot.. The device must now wait for the next Beacon. If the Beacon identifies the device as Device n, then the local device knows it has ?5 acquired priority slot n. If the Beacon does not contain the MAC address of this device, then this device has not been assigned a priority slot. In this case, the device resends the control frame requesting the use of a priority slot. ffhis may be done automatically in the MAC or at the explicit request of the upper network layer.
If there were multiple devices simultaneously requesting priority slots, their requests will most likely collide meaning that the beacon generator would not receive either request. Therefore the next beacon will be void of either requesting device's MAC address and they will have to resubmit their requests. (Again this may be done aurtomatically in the MAC or at the: explicit _5 request of the upper network layer.) 1f the beacon generator does happen to receive both requests the next beacon generated will indicate that one device is Device x, and the device is Device y.
Multiple Beacons Generators in a Cell In the embodiment of this invention described herein, it is assumed that in each network cell, 1() there is only 1 beacon generator (you will recall that device with priority level 0, P0, is used as the beacon generator). However, in a wireless network, where devices are mobile, it is possible that one beacon generator will move into a region where it will be heard by another beacon generator. This is an unstable configuration and may defeat the algorithm if the beacon generators attempt to transmit their beacons at exactly the same time all the time.
In the situation where Device 0 hears another Beacon, the MAC with the higher numeric MAC
address will stop sending Beacons. This may mean that some devices in the cell will no longer be able to hear any beacons (i.e. those devices that are only able to hear the beacons from the beacon generator that just stopped sending beacons). The rules for beacon generation will ensure that one or more of those devices that are unable to hear a beacon will automatically start beaconing themselves. This may in turn lead to beacons being heard by beacon generators. After some period of time, the new beacon generators will be determined and the network will once again return to the default, stable, condition whereby each cell has only 1 beacon generator.
An enhancement to the basic algorithm that may reduce the contention for Device 0 status just described. Once the beacon generator detects another beacon generated by a device with a numerically smaller MAC address requiring it to stop generating beacons of its own, it may inform all Devices that had requested priority slots with it that they can no longer use their priority slots and inform them of Device ()'s MAC address in a special control frame. It is expected that either approach will cause some disruption in the isochronous transfers until the new priority slots are allocated from the new Device 0(s).
Devices in the Overlapping Region of Overlapping Network Cells In networks where all devices are able to hear all other devices, the previous rules on beacon generation and priority slot registration ensure that all priority slot assignments in the network are unique. As such, there will only be one beacon generator (Device 0). However, when these concepts are extended to wireless networks, it is possible that one group of devices may not be able to hear all other devices that are in the; area of the entire network.
For example, if a wireless device has a range of 100 meters, than if 3 devices, A, B and C were in a line each ~~0 meters apart, than all devices are in range of a subset of all devices in the wireless network. But the devices at the end points will be unable to hear' each other. This phenomenon is referred to as the hidden node problem.
In the context of this invention, a cell is defined as all devices that are able to communicate with Device 0. However, even if the beacon generators are far enough apart to ensure that they do not hear each other (and can therefore form their own cell), devices at the cell boundaries can be in a position where they are able to hear devices in the other cell. In situations where a priority device is in a position where it is able to hear multiple beacons and the beacon generators are unable to hear each other, it is possible that the beacons will all collide at this device if they are transmitted at the same time. When this happens, the device will not be able to hear a beacon and may not transfer any data.
If a non-priority device is able to hear multiple beacons it must not attempt to transmit in a contention slot lower than the largest priority slot allocation indicated in the multiple; beacons.
This ensures that non-priority devices in overlapped network cells do not interfere with any pri<»-ity data in either cell.
Devices Not in the Overlapping Region of Overlapping Network Cells Devices that are not present in the overlapping region of overlapped cells are considered hidden nodes with respect to the cells) from which they are absent. These devices can interfere with priority and non-priority traffic in the cwerlapped cell(s). This invention does not provide a mechanism to etirninate the interference caused by multiple hidden nodes in every Situation;
however, the invention will significantly reduce the hidden node interference for priority data transmissions originating from or destined to the overlapping region of overlapping cells (see the wireless extension in the next section) Extension: Beacon Splitting Wireless for the Purpose of Reducing Hidden Node Interference In the discussion of the previous section it was stated that so long as the beacon generators in overlapped cells do not continually simultaneously generate their beacons, devices in the overlapping regions would be able to detect that they are in an overlapping region. Therefore, these devices would know the number of allocated priority slots in each cell because of the information contained in the beacon frames. A device in the overlapping region would then do the following. First it would tell the beacon generators) in the cell(s), in which fewer priority slots were allocated, to artificially allocate dummy priority slats (i.e.
priority slots assigned to the NULL MAC address, which is used as a dummy address). Secondly, each priority device in the overlapping region would inform its own beacon generator that it is in an overlapping region.
This information would be; conveyed in MAC control frames.
This would allow the beacon generator of the priority device in the overlapping region the opportunity to send multiple beacons to service the priority devices in its cell. In some vases, this beacon generator may be able to use ibis information to alert potentially hidden nodes of a pending priority transfer. For example, in wireless networks where hidden nodes are a problem, the MAC protocol often employs a handshake mechanism (e.g. RTS CTS) to eliminate interference from hidden nodes. Suppose that a beacon generator realizes that its n priority devices are split in x (x >= 2) overlapped cells (as a result of feedback from these devices).
Instead of generating a single beacon with priority slot information for all priority devices in the cell, the beacon generator could generate multiple beacons where each is meant to serve the subset of the n priority devices in the cell that acre in a specific overlapping region. By performing the MAC protocol handshake: with a device in the overlapping region, hidden nodes in the vicinity of the overlapping region would be required to remain idle for a number of contention slots equal to the allocated number of slots in its own cell. But since the device in the overlapping region previously informed the beacon generator of the overlapped cell to allocate dummy slots, the hidden node will not attempt to transmit for x contention slots, where x is the greater of the number of allocated priority slots in each cell. Therefore the hidden node will not be able to interfere with the priority data transfer initiated by priority devices in the overlapping region until after the priority transfers authorized by the beacon completed.
If the split beacon indicated that the number of priority slots in the cells was reduced, then the beacon generator in the overlapped cell would again be informed of this and could eliminate some of its dummy priority slat allocations. Once a steady state condition was reached, hidden nodes would not be able to interfere with the priority transfer in the overlapping region. This process could be repeated for all overlapped cells.
Wireless Extension: Resolving Beacon Contention in Overlapping It was noted that if Device Os in overlapped cells transmitCed beacons at the same tune all the time that devices in the overlapping regi«n would not be able to detect they are in an overlapping region. But even if this did not initially occur and the process described above was followed, problems would occur if the beacon generators in the overlapped cells attempted MAC
handshakes with different devices in the same overlapping region. To prevent this a method is needed to ensure that devices in an overlapping region register with the same beacon generator.
This can be achieved by requiring a priority device in an overlapping region to release its priority slot if it was ncot gained from the highest MAC address of the beacon generators heard. Before releasing the priority slot, the affected priority device would request a priority slot from the beacon generator with the highest MAC address (some.what arbitrary decision, important point is that all devices in the overlapping region are registered with the same beacon generator).
Finally, it should be noted that because this method coordinates the priority transfer in overlapped cells, the. maximum latency times are extended by the aI110Unt of priority data transfer in the overlapped cell(s).
Releasing Priority Slots When a station no longer wishes to use a priority slot the reverse process is followed. A MAC
control frame is sent to Device 0, to release slot n. Upon hearing the next Beacon if slot n is marked as idle or owned by another device than the local device no longer owns priority slot n.
When Device 0 no longer wishes to use priority slot 0, it sets the 'pass beacon' field to some other priority slot device (This is not essential since beacon generators will be created in a cell by the nature of the protocol followed to establish a beacon generator in the cell. This extra step reduces the disruption to priority data tra.rnsfer). When the Device using this slot heart; the next Beacon identifying it as the new beacon generator, that device will changes its identity to Device 0 and will be responsible for sending Beacons from that point on. If the.
original Device 0 does not hear a Beacon within 2, or more default BIT intervals, it must reassign the Beacon. The decision of which priority device to pass the beacon generating responsibility to can be arrived at by heuristical methods, or arbitrarily chosen. The exact method used is not key to the invention but may disrupt operation (for example it would be undesirable to pass beacon generating to a device in the overlapping region of overlapped cells since this may alter the identity of many beacon generators.
Other Consideration In situations where Device 0 simply vanishes, Device 1 (or the device using the smallest priority slot) will usually assume the responsibility of generating the Beaccm after at least 2 BIT periods by nature of the method of establishing a beacon generator. In doing so, Device 1 will become Device 0 remove all other entries i~rom the list of MAC addresses sent in the beacon.
Periodically Device 0 should reassign priority slots to ensure that there are no gaps in the Beacon.
This also has the effect of reducing the maximum number of allocated priority slots and affords non-priority device a lower average transmit latency time.
Detailed Description of the Preferred Embodiment of another Aspect of the Invention Referring to Figure 3 this embodiment of the invention is demonstrated though a coexistence scheme designed into a controlling modulation MAC protocol layer, 33, that will allow it to coexist with an arbitrary subordinate modulation MAC protocol layer, 30. The invention will allow the 2 MAC protocol layers, 30 and 33, to interoperate with other such devices employing both MAC' protocol layers or other devices employing one or the other .MAC
protocol layers.
Both physical layers, 34 and 35, employ different pulse modulation techniques of a common infrared carrier signal. Without using the methods in this invention, these protocols will interfere with one another if they are placed within range of each other. Because each protocol uses a different modulation encoding of the a c<:>mmon carrier, they are not able to directly communicate with one another.
In this embodiment, the controlling physical layer, 34, is able to generate a jamming signal in the modulation of the subordinate physical layer, 35. The jamming signal so generated ensures that other subordinate MAC physical layers in other devices in the networks will be prevented from transmitting data in the medium for a certarin period of time, called the Idle From Jam time. The controlling MAC protocol, 33, directs the controlling physical layer, 35, to generate the jamming signal. The jamming signal will 'have to be retransmitted if the controlling modulation MAC
protocol, 33, remains in control of tlne modulation for a period of time greater than the Idle_From Jam Time. The controlling modulation MAC protocol manager, 33, will therefore direct the controlling modulation physical layer, 34, to generate jamming signals at the appropriate interval.
The controlling modulation MAC protocol layer, 33, sends a SOD frame in its own modulation to inform other controlling rnodulatiorr MAC protocol layers when the modulation will be changed to that of (one of) the subordinate modulation. The SOD frame also informs the control modulation MAC protocol layers of the amount of time the subordinate modulation will be used in the medium.
'The link manager, :i2, uses the services of the. controlling modulation MAC
protocol layer, 33, to generate the SOD from with the required MT value when the subordinate MAC
protocol manager, 31, deternnines that the subordinate modulation MAC layer, 30, requires access to the medium. 'The subordinate MAC protocol manager, 31, is able to determine this by knowing the protocol flow of the subordinate modulation MAC layer protocol, 30. The subordinate MAC
protocol manager, 31, queues data frames from the subordinate MAC protocol manager-.. 30, until sufficient data has been queued to warrant a transfer on the medium, or until such time as it realizes the subordinate modulation MAC protocol flow will break down because of being blocked from the medium while the controlling modulation is being used.
I () The subordinate MAC protocol manager, 31, is able to block data transfer between the subordinate modulation MAC protocol layer, 30, and the subordinate modulation physical layer, 35, by placing itself in the path of this data flow. When the controlling modulation is being used in the medium, the subordinate MAC protocol manager, ~ 1, may either queue any data requests from the subordinate modulation MAC protocol layer, 30, or simply discard the data. Similarly when the controlling modulation is used the subordinate MAC'. protocol manager, 31, will discard any data the subordinate rrrodulation physical layer believes it is receiving.
When the subordinate MAC protocol manager, 31, determines that its subordinate modulation MAC protocol layer, 30, requires medium access it requests the link manager, 32, to request the controlling modulation MAC protocol layer, 33, generate the SOD frame indicating the use of the subordinate modulation for a certain period of time. When this frame has been transmitted in the controlling noodulation, the contrcalling modulation MAC protocol layer, 33, wil stop directing the controlling modulatir~n physical layer tc~ generate jarnrning signals. The controlling modulation MAC protocol layer, 33, will also indicate the new modulation in effect in the medium to the link manager, 32; which in turn will convey the information to all subordinate modulation protocol managers, 31. After the subordinate modulation protocol manager, 3 t, is informed that its subordinate modulation is in effect, it will no longer block communication between the subordinate modulation MAC protocol layer, 30, and the subordinate rrrodulation physical layer, 35. This will allow commr.rnications in the subordinate modulation to occur between subordinate modulation MAC protocol layers, 30 for the period of time specified in the SOD frame.
After the period of time during which the subordinate modulation may be used in the medium, which was contained in the SOD frame of the controlling modulation, the controlling modulation MAC protocol layer, 33, will inform the. link manager, 32, that the controlling modulation is once again in control of the medium. 'fhe link manager, 32, will then inform all subordinate modulation protocol manager, 31, that it must once again resume blocking the transfer of data between the subordinate modulation MAC protocol layer, 30 and the subordinate modulation physical layer, 35.
Pseudo Code For the First Aspect of the Invention Notes: The pseudo cc)de that follows illustrates an embodiment of the basic invention. None of 1S the enhancements to the. base algoritlun have been included. In particular, the wireless extensions dealing with hidden nodes and some overlapping cell details are not shown in the implementation. Also the implementation uses:
- A fixed value for PAT, NPAT, BIT
- Only a single priority slot is assigned to any 1 MAC address - The beacon generator does not partition beacons for sets of priority devices.
It will be appreciated that when appropriately licensed the pseudo code may be used in the implementation of the invention in software recorded on a medium that may be used by stations of a network or in circuitry such as rrLicro code used in the stations.
Init Routine:
i Bcuc<mHcurd = FALS1:;
MinitnumContcntionSlot = 0;
MuximurnContenrionSlot = MAXIMUM NUMBER of Cc)NTENTIO N SL.()TS;
3~ NurttbcrAasignulPrioritySl«ts=.(l;
RenrtiningContrtnionSlots = 0;
MvPrioritvSlot = (1:
MisscdBeuconCuunt = 0;
Bcucunldentitr = NULL;
pendingrransmitFramcType = NULL;
pendingTran,mitData= Nlll~l.;
physicalCarricrStatc= NO. CARRIER:
SIotClock'1'imerHandle = Nlll,l.;
NPAT = Maximum time a non-priority device may send data on the channel;
1'A'1'= Maximum time a priority device may send data;
BIT= Beacon Interval 1'imc BT='1'imc to transmit beacon WaitingForNhysicalTransmitCompletc = FAL SE;
ReyuestTimeouU interval = BIT, timecxu Routine= Beacon'1'imeoutHandler ):
output: Integer RandomIntel;er input: L.owestValucInSelectionRange, input: HighcstValueInSeIcctionRange local variable: ReturnV<tlue;
RcturnValue _ chooae a number at random at least as large as the I~westValueInSetectionRange and no larger than IiighestValueInSelectionRan,;e at random;
return( RetumValue );
I'hsicalLayerC.'arrierSense('allback input: C:arricrState C
/*
*'Lhis MAC callback routine is called by the phtaical layer when it dctectc a * change in the carrier signal static in 1h c medium. Whm the medium i; idle and a carrier is detected (i.e. another station is starting to transmit), thi, * routine will he called with CarricrState=AC'1'bVEC'ARRIFR. When the * trammitting station completes ils rran,,mission this routine is called again * with Carrier;St<ne=N<) CARRIER
*i phpsicaICarTierState = CarricrStaW ;
IF( CarrierStatc==NO_.C'ARRIER ) I
CA9-1998-0023CA2 2~
IF( I'entlingTr<utsmitFr;tmc'I'ypc != Nlll.l_ ) I
Start_Slot CI<>Lk_Timer();
_5 ) ELSE
f Cancel Slot,C.lock Timer():
IF( Rcntaining('ontentionSlotv < MinimuntC"tmtentionSlot ) IF( PendingTransmitFrame'1'ype =:.- NON_ 1'RIORITY_DATA ) l RentainingContcntionSlots=Itandont__InUger( MinintutnC,'ontentionSlut, MaximuntC'ontentionSlol );
l5 ) Start Slot Cluck 'Timer /*
* All transmit reyueats must eventually votne through this routine.
?5 * We cue not allowed to transmit until n beacon i, heard. 'I'tterefore the slut clock is only actually stated * it we have recently heard the beacon. Iha bcaam has not been heard rerentlv, then tltu current xmit * data is held pending until we once again start haring beacons (or start grneralin g them ) if( licaconHeard ) i1( RcntainingContentionSlots > 0 ) f SIotCIockTimerliandler= ReyueatTimeout( interval=CONTEN'rl(')N__SL,OT 'TIME, timeout Routine=Sleri Clock Timeout );
f else 40 ) Slut_Cloc:k Timeaut();
Cancel Slot Clock 'Timer i call into operating system to disable timer W ivitv on handle SIutCk>LkTirnerHandler Slut ('lock Tinreout _5 t ,, *'Htisroutine is called every CONTENTION SLO'T_'1'IME period while there is a pending.
*'fhe slot clock timer period is a constant fir the particular MAC' protocol hcin~! usrd.
* W'hcnever the slot clock tuner is enaMcd, it will always count a complete slot clrxk * intervals. It the slot cluck timer is started with a 0 value to count down, thin routine * i, innnediatelv called.
*/
IFt RemainingC'untentionSluts==0 ) i WaitingForPhysiealTransnit('onrplete = TRUE:
I,,smPhysicalLayer Transmit( t'endin~rransmitl~ata ):
}
ELSE
f 20 RemainingContcntionSlots = RemainingC_'onlcntionSlots - I
SIotClockTimerHandler-- RcquestTintcout( interval=CONT'ENTION_SL(»' TIME.
timeout Ruutinr = Slcri Clock T'inrcout ):
25 }
Send_Frame Complete C
/*
30 * This routine is called by the physical layer when it has completed transmitting * the frame data Iron the Issue_F'hysiecil__L.ttyerTransmit physical layer routine.
*/
WaitingForPhysicalTransrnitConplcte= FALSE:
.35 IF( there is a queued Beacon for transmit ) /*
* This check is really only necessary ;I the station does nut choose to abort a transmit in progress * when a Beacon needs to he transnntted.
*/
remove beacon data Team the beacon queue Send Frame Ruutincl 13EA<'ON, BcnconDatu ):
l:I.SE;
IF( PcndingTransmitFrameTylx, = BE ACON ) I
/*
* The beacon has just been transmitted by this station.
Therefore thin station is using * priority atot (.). 'fherufore any <lucued priority data rut now be ,ant = there is no need * to contenttl, everyone else will Ix waiting fmr at Ieast on a contention slot.
;/
IF( there is more priority data queued ) 1 n I'en<lin~~ rran,mitF'rame'I'ype -- PRIURfI'Y ..I)A'TA:
I'endingTransmitData = deyueue up to 1'AT of priority data from the priority data queue;
WaitingForPhyswalTrausmitComplete = TRUE;
Isxue I'hy;ical_ Laycr'franamit( I'mdiugTransmitDat<t );
) ELSE
C
PendingTransmi tFrante'1'ypc = N l! LL:
I
ELSE
f PcndingTrammitFranteType = NlIL.L;
IF( there is more non-priority datalucued ) I
Send_.frtmea_Routine( NON _PRI()RfT'YDATA.
dcywue upto NPAT o1' non priority data from nun-priority data queue);
I
) J
Send Frames Routine ~5 input: franWype.
input: Irant~ data 1*
4U * It is assumed that the HW/ Physical layer can transfer multiple frames at once. The Irantedata tnay actually wunain muhiplc frames. The re.stricuon ort the; data sire is that Ior a (non)priority transfer, frantedata in bytes * ii bits per byte i channel bandwidth e= (NP)A'f * I, another fr;tme already pending fctr transmit.' 45 m IFI Ntnding'1'ransmitFrameTypc != NULL r I
1*
* rlborl it we're trying to send priority data or a beacon *!
IF( li~ametype != NON,. PRIQRITY DATA ) i ('anccl Slot Clock Timvr();
rcqucuc the pm<ling data at tlic head of the non priority transmit qwue;
) EL.,SE
/*
*'rhia should not occur. More error handling should by added.
*/
internal error => priority data and heacom should wver overlap;
Cancel Slot Clock Tirnert):
PcndingTransmitFramcType=frame type;
1'cndingTransitData = franydata;
/*
* Ch<Krse the nurnber of contention slots to wait based cm livme typr.
* The pending transmit data needs to be lbrmatcd into an appropriate physical layer Ibrmat and the MAC
* needs to distinguish between control frames (sent beUVern MAC layers an<t upper layer data framvs_ */
e:hoose( ft'amz type ) as one of:
t BEACON ):
I
RemainingContentionSlots : U;
PendingTransmitData is 1i>rntatted a, MAC control frame:
);
.~ S ( PR IOR 11'Y DATA ):
RemaingContcntionSlots = A,sigwd_Priority_Slot;
PendingTrammill>ata is li>rmattetl as upper layer data frame;
):
N()N_PRIORITI'_I)AT.A j:
i IZcmainingContcntionSlots =Random Irrtcgcr( 0, MaximumContcntionSlot )+MinimumContentionSlot PendingTransmitl)ata is ti>rmatted as upper layer data f~antc:
):
4S i REQUES'I-PRIORITY_SLOTCONTKOI,FRAME ) CA9-1 y98-0023CA2 31 i RELEASE NRIORITY_ SLO'I'_C()NT(t()L_FKAME Y.:
f Renrtinin~~ContentionSlnta = Random_Inte~erl (1. MaxirnuntContentiunSlot ) +
MininmmC'ontentiunSlut Pending fransmitData is tbrm:uted a. MAC cttntrul fr;nne:
* Check for a valid eurricr. We only begin ccxmtin,: down contention slots once the rncdium is fret.
1 n */
IF( Phy,ical<'arricrStale = N()..._CARRIER
Sutrt_Slot__Clock Timer( RemainingContentionSlots t;
;
MAC 'Transmit Non 1'rioritv Data I
input: data frame i ( queue the daW frame on the non-t~riority data queue;
IF( Vv'aitingF'orl'hyaical7'ran,mit('ompleW =-- FAL ,1E ) i Send__FrauteRoutinet NONpRl()Rl'lY I).A'fA, dequeuc upto NPAT of nun priority data faun non-priority data queue);
i MAC.Reyuest Priority_.Slut 1*
5 * In thin sample implementation, each MAC station is only ably to have 1 priority slot.
* An enhanced implementation would allow multiple priority slots to be used by any station.
*/
IF( Myl'rioritySlcn == 0 ) ANI) f Beaconldcntity '= N(.!l.,L ) AND ( Rcaronldentity != MyMACAddress ) 40 {
Format MAC control Frame to request a priority slot from the Bcacunldentity Send Frames_Jtoutinc( REQUEST_pRl<)Rll'Y_SL,OT,<'ON'pROL. FRAME, formatted control frame ):
IF( Myl'rioritySlut != U o OIZ ( licaconldcntity .-__- MyMAC'Adtlrcss ) indicate that priority slot alrwdy assitned I
ELSE
fail the rcyuest I
I
MAC_Release Priority- Slut IS I
/*
~' Th a MAC could track the amount of time between successive calls to MAC
TransmitPriority_IW to * and automatically release the priority slut (by calling this routine>. In this simple implementation, * once the priority slot has been alkxated, it is Icli open until the upper layer explit:itly releases iL
IF( MyprioritySl<ri != 0 ) C
Format MAC control frame to release priority .lot from the Bcaconldcntity Scnd_FrantesRoutinc( RELfi;ASF 1'RIORITI'_SLO'f_C.'ONTROL_FRAML;.
RntnatlcdCOnlrol frame );
/*
* This simple implementation does not reassign the beacon responsibility *l MAC 'Transmit I'rioritv Data input: data frame ~5 ;
IF( MyprioritySlot != 0 ) OR ( Beaconldentity = MIyMAC'Addrt;ss ) queue the data frame on the priority data yuew;
40 !*
* Must u~ait for the next beercon to send priority data.
*/
EL..SI3 CA9-1998-0023CA2 3 y /*
* Faile the request. This should indicate to the upper layer that this device duc> nut own a * priority slut an<i thcrel're can not .,en<1 piurity data. 'this will cttuae the upper Ittyer to (re)request t * a priority ,lot.
*/
fteacon TimeoutHandler i local variable: slot_delay_on_first., beacon:
IF( Bcacunldetttity - MyMACAddrexa ) I
IF( Waitin~ForPhyaicalTranstnitContplcte == FALSE 1 I
SendFrame( BEACON FRAME, Bcaconl.ist );
E1..SE
I
yucue beacon data Be~tconList;
EL.sE
I
1F( ReaconHeurd == FALSE t THEN
i MiasedBe<tconCouttt:=Mis~edBeaconCormt+ 1;
IF( MissedBcaconCount >= MAX MISSEn...BEACON C'pUNT
I
MissedBeuconC'ount = t);
/*
* The Beacon 1~mcralor hasn't hven hcartl in awhile.
* Assume ownership of the beacon.
:/
IF( MyPrioritySlot !-1> J
i slut_clelay on_firat beacon = Myl'rioritySIuU
else s slot delay un fin;t beacon - I
IFI pendingTransmitFrameTypc '= Nl II,L ) l 1*
* (RclF:nahle transmit opcnuion */
Start Siot Clrxk(l:
remove <tny pm<'ling or ymucd Rcyuestf'rioritySl<n control (names Bcaconlticntity =- f~IyMAC'Addrcss;
Bcaconl.ist== I cnilxy ):
MinimutnContentionSlot = I;
MyPrioritySlot = 11;
NumherAssigncdl'rioritySluts= 1;
f RequcstTimeout( interval = BIT+ ( slot_dclay_on_ first "heacon *
C()NTFNTION_.SL.O'I'.'fIME, timcout Routine = Beacon'1'imeoutHandler );
20 ) Receive ('allback Routine t 2S input: data t /*
* Dctcnninr if this is upper layer data or a MAC layer f onirol frame.
30 * Note: Received data must be transtnormed from physical layer data into mac layer dale. Only non * MAC voutrol frames are sent to the upper layer,.
*/
IFI data is formatted as an upper layer data packet I
I
3 S transfer data to upper network layer for processing Et_SE
f J*
40 * This is a MAC. control frantc.
*/
~h~x~se( frame type 1 as one ~>f:
f ( BEACON CO'1'ROL_FR.4ME ):
BcaconHcard ='1'R t iE:
Process Beacon( I>cacon duty ):
1:
S ( REQIIEST_I'KIOK1TY_SLOT CONTR()L_FkAME >:
IF( Keaconldentity = Ivty~1ACAJdre" ) S
~, * Add the requester to the and of the Beaconl.ist BcaconLisy NumberAssitnedPrioritySluts ] = MAC address of rcyuester;
NumbcrAs,i~nedPrioritySlota = NumberAssignedprioritySlots + 1;
15 ;
t RELEASE PRIOkITY._SLt)T_C'<)NTROL FRAME ):
IF( Bcaconldcntiy~ = MyMACAddrws ) i IF( MAC address of myustee fuund in the t3eaconList =at index x) BeaconList( x ~ = NULL Muc address;
~:E:
25 * 'This step dc'tes not have to be dune every time a device releases a priority slot...
Reorder BeamnList so all NULL MAC addresses at end of list.
NumberAssignedPrioritySlots = NumberAssignedPrioritySlots - J
f I'roeess Beacon ) input: BeaconUaW
IF( Beaconldentitv = NULL ) I
Beacunldcntitv = source MAC address of the Beacon;
I
CA9- I 99~-0023CA2 3E~
IF'l MvMA('Addrws == Beaeonldcntity ) * -This device is generating and receiving beacons. This is n<n permitted.
* Stop sending beacons if the device heard has a numerically sntallcr M.AC' athlress.
*/
IFf Mv~~1AC'Addrc~s > source tviAC a<ldicss ol'thc Beacon /*
* In this wimple implcntentahon, hcmon generation by this device ix simply stopped.
*'phc procesx of Establishinl_~ tithe Presence of a Bcactm Generator in the Cell * will be followmi to establish mw beacon generatonsl instead of vending a special MAC' control frantc infixn,ing all devices in the BcaconLi.st of Ibe identity of the new bcaCi>n gcncrator-'~'/
MyPrioritySlot = 0;
Bcaconldentity = source address of the Beacon;
inform the upper layer that the Iwiority slot is no longer available (it will be rc-rcyucsted if still needed).
IF( source MAC address of the Beacon == Beaconldentity ) If'( MyMACAddt~as is in the BeaconD;ua ) I
MyPrioritySlot = ordinal pcmition of MyMACAddress in lhc BcaconDat:r if( MyPrior itySlot =---- 0 1 /*
* We have been passed responsibility of beacon generation */
Bcaconldcntity = MyMACAd'.tress;
5 BeamtnLi st = Bcucon I )ata:
ELSE
S
/,:
40 * Cancel any pending transmit and submit priority tr:dtic instead.
*/
Send Frantc Routine( N()NPRI<)RITY DATA, deqmuc upto NPAT of non priority data fiom non-priority dale queue):
CA9-1998-0023CA2 3 i ELSE
/>:
We have lost the use c:f'our priority slot. Sine this implententatiun does not use split * beacons this should only oc;wr as a result of a release priority clot request. In tire case '" where the release priorty alm rcyuest wan issued but not honoured by the bc:tcon generator.
* it is assented that the upper layer will tirncont on the rcclucst cunt7rmation and resubmit it.
;:/
inform upper layer that the priority plot is no longer available.
1 ~~
/*
* Note in this wimple implementation the beacon generator always generates a single beacon indicating the MAC addresses oFall <Icvices assigned priority sluts.
*1 1 5 IFt MinintumCuntentictnSlut < number ~~f entries in llcaCOtt Data ) MinimumCuntentionSlot = number uf_entries in BeucunData;
NumherAssignedprioritySiots = MinimnmContentionSlot;
20 s ELSE:
I
/.,.
* This simple implementation does not inform beacon gwerauns in overlapped cells of the largest nunther of allocated priority slots in the overlapped cells, Similarly this implcmentution does not require priority devices in the overlap to register with the beacon generator using the numerically * hi~her MAC' :tddrcas. 'rhe prc,,cesainl, ler these (wireless) enhancements would he perfornted here.
However, we ntuy need to increase the minimum contention slot value used if this beacon generator has more * allocated priority slots.
*/
IF( MinimumConrentietnSlot < number of entries in Beacon Data ) I
MinimumCuntentionSlot = nutnhcr of entries in 8cacunData;
35 t NuntherAssignedYrioritySlots - MininmntCctntentiunSlot;
40 Pseudo Code ror the Second Aspect of the Invention Pseudo code is not shown for the operation of the subordinate modulation physical layer or the subordinate modulation MAC protocol layer since this operation is unaffiected by this invention.
Subordinate Modulation Protocol Manager Operation C'urrcntModulation=CON'1"ROLLING MODIILA'1'ION:
'When rcyuested to transmit data t?y the subordinate rncxlulate MAC: protocol layer:
L
IF( CurrcntModulation == My__SUf3ORl )INATG__MODULATION ) l wend data to the suh~rrdinate modulation physical layer;
y EE.SE
I
<lueue data for transmissicm t~.> the subordinate modulation physical layer;
L;pon receiving data from the subordinate modulaOOn physical layer:
i IF'( GurremModulation==My SUf3ORDINA~EG MODULATION ) zo I
transfer received dala to the subordinate modulation MAC' prokxol layer;
E;LSI
i 25 d~,~ard the daw;
) EJpon receiving an indication of a modulation chaugc from the link utana~;er:
('urrentModulation = modulation indi.:atcd by the link manager;
IF( C'urrentModulatictn == My_SU13()IZf)INATE_MODIJLATION 1 i wend all queued subordinate modulation MA(' pnUocol to the subordinate modulation physical layer;
EJpun determining that the subordinate mctdulatimn MAC' prot<xol layer rcyuires accecs to the medium:
I
reyucst the link manager to swil,eh to My_ 511130R1>INA'I'E_MODL.1LATION for a period of tithe = MT;
CA9-1998-00?3CA2 39 Link Manager Operation ('urrentMcxlulation --- CON'J'ROLLINC~ Mt)DULA'11()N:
S When requested to change nu>dulation to subordinatc_nt<xhtlation for time pericxl ~~1T by a suhordinctte prottxol manager:
i IF( CurrentModulation != auhordin<ttemudulation J
I
request the controlling modulation MAC protocol Jaycr to generate a SOD frame using( suhordinate nxxlulation and M'1' ):
1 _5 Upon indication front the mntrollin~ mo<luJation MAC' protocol that the current modulation ix Modulation:
I
CnrrcntModulation = Modulation Indicate current modulation to all protocol managers;
?~
Contrullinf;_Mudulation MAC_Protocol Operation y 2.5 1*
* Only the operation of the MAC required in the context of this invention are shown.
*!
C'uwentMtxiulation = CONTKOLLING MCtDULATION:
pc,ic,tlically gcnarate jatnminp signals in all suhoalinate modulations;
J'encfin~Modulation =N(JL,LL,;
PendingModulationTintc - 0:
lVhm requested to send SOD frame li,r sufiordinate nwdulation = Modulation.
<tnd time = MT
IF( pcndingModulatiutn = NI ILf, ) AND ( C.'urrcntModulution =CONTROL,LING_M(>I,)ULATION ) Pcndin~;Modulatiun =mouulation:
PcndingModulationTinte= MT:
Send SOD Frante( modulation. MT );
i ELSE
qucur modulation change request;
When SOD franc indicated as trunsntittvd:
s CnrrcntMcxlul<4ion = PendingMixlulation;
PcndingMcxlulation= NULL;
Stop generating jamming ,ignals in current nxxlulation;
se( Mcxlulation'fintcr to expire in MT;
Inilicatc CurrentMo<lulation to Link Manager;
I
r 5 When Modulation Tirner expires:
I
resume periodically generating jamrttinp~ signals in CurrentModulation;
CurrwtModulatictn = ('ONTROLLIN(i Mt)Dl ~LATI( )N:
Indicate CuwentM<xlulation to Link Manager:
IF( queued modulation change request/ ) I
deyueuc modulation change, 5 PendingModulation = mcxlulation:
PendingModulationTimc = MT;
Send. _S01 >_Framc( rnrx[ulation, M'r ):
f Cuntrollin~_Modulation__I'hysical Layer Operation:
( />:
* Only the operation of the physical (aver requin;d in the context of this invention arc shown.
*/
When requested to generate.jamming aignal in modulation=Modulation generate jamming signal in modulali~m;
Once a device using priority slot n hears the beacon, and that device has priority data to transfer, it will use it's assigned slot to transfer up to a pre determined amount of priority data. This ensures that all priority data will be transferred in the first n-1 contention intervals after the beacon.
In the absence of any interference, these steps would be sufficient to ensure that a device using a priority slot will be able access the medium in a finite, deterministic period of time. Step 3) guarantees that if a device using a priority slot and a device not using a priority slot are both given data to transmit at the exact same time, then the device using the priority slot will win access to the medium before the other device. Steps 2) to 4) ensure that even when there are other devices that have previously lost a reservation any device using a priority slot will still win access to the medium before all other device, not using priority slots.
?0 Suppose the particular MAC protocol requires that no single station can transmit non-priority data on the medium for any more than the Non-Priority Access Time (NPAT).
Also, suppose that each priority device can only tranamit priority data on the medium for no mode than the Priority Access Time (PAT). Suppose the Beacon required BT time to transmit and is sent every Beacon Interval Time (BfT). Finally suppose there are 'n' priority slots allocated in the, network.
Note that in the equations that follow the duration of the contention slot is not taken into account.
This scheme ensures that no matter how many devices there are in the network, nor how much data those devices are transmitting, the worst case maximum transmit latency for a priority device (in the. absence of interference) is always deterministic and given by the following formula:
(1) Latency = BIT - n * I'AT -BT+ NPAT + BT + (n- I ) ~' PAT
= BIT + NPAT - PAT
On average, over time, each priority device is able to get access to the medium for a period of time of PAT every BIT period. Therefore, on average, over time, every priority device is guaranteed PATBIT* l00 % of the channel's base baud rate.
(2) Priority bandwidth = PAT / BIT * channel bandwidth Extensions The definition of the beacon can be extended to include the cell parameters BIT, NPAT', BT and PAT. This allows the beacon generator to dynamically change the cell parameters. In addition, to an ordered list of MAC addresses, the beacon definition can further be enhanced to include unique PA'T times for every MAC in the beacon list. This would allow the beacon generator to dynamically modify the bandwidth allocated to each priority device and allow the priority devices to request varying guaranteed bandwidths. With this beacon definition the worst case transmit latency is:
(3) Latency; = BIT - sum(for j=0 to n-1 )of(PAT~) -B'T+ NPAT + BT
+ sum(for j=0 to n-I, j != i)of(PAT;) = BIT + NPAT - P,AT;
And the bandwidth allocated to device i i:~:
(4) Priority bandwidth; = PAT; / BIT * channel bandwidth Finally, if the cell were operated in a TDMA manner than NPAT in equation 1 would be 0. The BIT would also be specified in terms o1 the number of priority devices in the cell, BIT = n PAT. (The registration process defined in the next section would also need to be enhanced.) 'Therefore equation 1 could be reduced to:
(5) Latency = (n-1 ) '~ PAT
if every station were assigned varying amounts of bandwidth according to equation 4, then the worst case latency is:
(6) Latency; = sum(for j=0 to n-l,j!=i)of(PA'Ta) Allocating and ReleasingPriori~ Slots Another aspect of CSMA-CA.B networks in accordance with this invention involves acquiring use of a priority slot(s), releasing a priority slots) and determining which device will use slot 0.
To simplify the discussion, the device using priority slot n will be referred to as Device n. The broadcast frame that Device 0 must transmit every BIT period will be called the (isochronous) Beacon. These frames must be consumed at the MAC layer without being passed up to the network or higher layers. As previously mentioned, this may be achieved through MAC layer control frames or through a special multicast MAC address reserved for CSMA-CAB networks.
IS In the following text the beacons are assumed to be transmitted as MAC
control frames.
Establishing the Presence of a Beacon Generator in the Cell We have found that for advantageous performance, before a device is permitted to transmit on the network, it must first wait a period of time at least 2 default BIT
periods long to allow ~0 sufficient time to detect a beacon. (A guaranteed minimum bandwidth and maximum frame size determine the default maximum BIT, see equation 4.) If a beacon is heard within this interval, them the new device will know the number of allocated priority slots within the network and hence the minimum number of contention slots it must wait before attempting to transmit when the medium is sensed as idle. If the number of allocated priority slots changes as successive ?5 beacons are heard then so too does the ~ninirnum number of contention slots that a ncm-priority device (or a priority device sending non-priority data) is required to wait before attempting to transmit when the medium is sensed as idle.
On the other hand, if after having listened for a period of time at least 2 default BIT periods long, the Beacon is not heard, then the local device must start issuing the beacon and assume that it is Device 0. (This is required even if the device does riot wish to transfer priority data.) The first beacon generated by Device 0 must not be sent using a priority slot. In the case where the device assuming Device 0 responsibility never heatrd a previous beacon, at must waif one contention slot before sending its first beacon. In the case where the device is no longer able to hear the beacons of the device from which it was previously allocated a beacon, it must wait a minimum number of contention slots equal to the priority slot it was assigned on the last beacon heard. This helps to eliminate beacon collisions when the previous beacon generator suddenly stops beaconing in a cell with allocated priority slots.
Note that this process ensures that before any device in the network begins transmitting, there will already be 1 allocated priority slot for Device 0. Therefore the minimum number of contention slots that a non-priority device must wait before attempting to transmit when the medium is sensed as idle is always at least 1.
If a device that does not wish to transfer priority data becomes the beacon generator, it may transfer Device 0 status to the first device that registers it's desire to allocate a priority slot (see below).
?0 Requesting a Priority Slot From Device U
A device that wishes to acquire a priority slot must send a special MAC
control frame to Device 0, informing Device 0 that it wants to use a priority slot.. The device must now wait for the next Beacon. If the Beacon identifies the device as Device n, then the local device knows it has ?5 acquired priority slot n. If the Beacon does not contain the MAC address of this device, then this device has not been assigned a priority slot. In this case, the device resends the control frame requesting the use of a priority slot. ffhis may be done automatically in the MAC or at the explicit request of the upper network layer.
If there were multiple devices simultaneously requesting priority slots, their requests will most likely collide meaning that the beacon generator would not receive either request. Therefore the next beacon will be void of either requesting device's MAC address and they will have to resubmit their requests. (Again this may be done aurtomatically in the MAC or at the: explicit _5 request of the upper network layer.) 1f the beacon generator does happen to receive both requests the next beacon generated will indicate that one device is Device x, and the device is Device y.
Multiple Beacons Generators in a Cell In the embodiment of this invention described herein, it is assumed that in each network cell, 1() there is only 1 beacon generator (you will recall that device with priority level 0, P0, is used as the beacon generator). However, in a wireless network, where devices are mobile, it is possible that one beacon generator will move into a region where it will be heard by another beacon generator. This is an unstable configuration and may defeat the algorithm if the beacon generators attempt to transmit their beacons at exactly the same time all the time.
In the situation where Device 0 hears another Beacon, the MAC with the higher numeric MAC
address will stop sending Beacons. This may mean that some devices in the cell will no longer be able to hear any beacons (i.e. those devices that are only able to hear the beacons from the beacon generator that just stopped sending beacons). The rules for beacon generation will ensure that one or more of those devices that are unable to hear a beacon will automatically start beaconing themselves. This may in turn lead to beacons being heard by beacon generators. After some period of time, the new beacon generators will be determined and the network will once again return to the default, stable, condition whereby each cell has only 1 beacon generator.
An enhancement to the basic algorithm that may reduce the contention for Device 0 status just described. Once the beacon generator detects another beacon generated by a device with a numerically smaller MAC address requiring it to stop generating beacons of its own, it may inform all Devices that had requested priority slots with it that they can no longer use their priority slots and inform them of Device ()'s MAC address in a special control frame. It is expected that either approach will cause some disruption in the isochronous transfers until the new priority slots are allocated from the new Device 0(s).
Devices in the Overlapping Region of Overlapping Network Cells In networks where all devices are able to hear all other devices, the previous rules on beacon generation and priority slot registration ensure that all priority slot assignments in the network are unique. As such, there will only be one beacon generator (Device 0). However, when these concepts are extended to wireless networks, it is possible that one group of devices may not be able to hear all other devices that are in the; area of the entire network.
For example, if a wireless device has a range of 100 meters, than if 3 devices, A, B and C were in a line each ~~0 meters apart, than all devices are in range of a subset of all devices in the wireless network. But the devices at the end points will be unable to hear' each other. This phenomenon is referred to as the hidden node problem.
In the context of this invention, a cell is defined as all devices that are able to communicate with Device 0. However, even if the beacon generators are far enough apart to ensure that they do not hear each other (and can therefore form their own cell), devices at the cell boundaries can be in a position where they are able to hear devices in the other cell. In situations where a priority device is in a position where it is able to hear multiple beacons and the beacon generators are unable to hear each other, it is possible that the beacons will all collide at this device if they are transmitted at the same time. When this happens, the device will not be able to hear a beacon and may not transfer any data.
If a non-priority device is able to hear multiple beacons it must not attempt to transmit in a contention slot lower than the largest priority slot allocation indicated in the multiple; beacons.
This ensures that non-priority devices in overlapped network cells do not interfere with any pri<»-ity data in either cell.
Devices Not in the Overlapping Region of Overlapping Network Cells Devices that are not present in the overlapping region of overlapped cells are considered hidden nodes with respect to the cells) from which they are absent. These devices can interfere with priority and non-priority traffic in the cwerlapped cell(s). This invention does not provide a mechanism to etirninate the interference caused by multiple hidden nodes in every Situation;
however, the invention will significantly reduce the hidden node interference for priority data transmissions originating from or destined to the overlapping region of overlapping cells (see the wireless extension in the next section) Extension: Beacon Splitting Wireless for the Purpose of Reducing Hidden Node Interference In the discussion of the previous section it was stated that so long as the beacon generators in overlapped cells do not continually simultaneously generate their beacons, devices in the overlapping regions would be able to detect that they are in an overlapping region. Therefore, these devices would know the number of allocated priority slots in each cell because of the information contained in the beacon frames. A device in the overlapping region would then do the following. First it would tell the beacon generators) in the cell(s), in which fewer priority slots were allocated, to artificially allocate dummy priority slats (i.e.
priority slots assigned to the NULL MAC address, which is used as a dummy address). Secondly, each priority device in the overlapping region would inform its own beacon generator that it is in an overlapping region.
This information would be; conveyed in MAC control frames.
This would allow the beacon generator of the priority device in the overlapping region the opportunity to send multiple beacons to service the priority devices in its cell. In some vases, this beacon generator may be able to use ibis information to alert potentially hidden nodes of a pending priority transfer. For example, in wireless networks where hidden nodes are a problem, the MAC protocol often employs a handshake mechanism (e.g. RTS CTS) to eliminate interference from hidden nodes. Suppose that a beacon generator realizes that its n priority devices are split in x (x >= 2) overlapped cells (as a result of feedback from these devices).
Instead of generating a single beacon with priority slot information for all priority devices in the cell, the beacon generator could generate multiple beacons where each is meant to serve the subset of the n priority devices in the cell that acre in a specific overlapping region. By performing the MAC protocol handshake: with a device in the overlapping region, hidden nodes in the vicinity of the overlapping region would be required to remain idle for a number of contention slots equal to the allocated number of slots in its own cell. But since the device in the overlapping region previously informed the beacon generator of the overlapped cell to allocate dummy slots, the hidden node will not attempt to transmit for x contention slots, where x is the greater of the number of allocated priority slots in each cell. Therefore the hidden node will not be able to interfere with the priority data transfer initiated by priority devices in the overlapping region until after the priority transfers authorized by the beacon completed.
If the split beacon indicated that the number of priority slots in the cells was reduced, then the beacon generator in the overlapped cell would again be informed of this and could eliminate some of its dummy priority slat allocations. Once a steady state condition was reached, hidden nodes would not be able to interfere with the priority transfer in the overlapping region. This process could be repeated for all overlapped cells.
Wireless Extension: Resolving Beacon Contention in Overlapping It was noted that if Device Os in overlapped cells transmitCed beacons at the same tune all the time that devices in the overlapping regi«n would not be able to detect they are in an overlapping region. But even if this did not initially occur and the process described above was followed, problems would occur if the beacon generators in the overlapped cells attempted MAC
handshakes with different devices in the same overlapping region. To prevent this a method is needed to ensure that devices in an overlapping region register with the same beacon generator.
This can be achieved by requiring a priority device in an overlapping region to release its priority slot if it was ncot gained from the highest MAC address of the beacon generators heard. Before releasing the priority slot, the affected priority device would request a priority slot from the beacon generator with the highest MAC address (some.what arbitrary decision, important point is that all devices in the overlapping region are registered with the same beacon generator).
Finally, it should be noted that because this method coordinates the priority transfer in overlapped cells, the. maximum latency times are extended by the aI110Unt of priority data transfer in the overlapped cell(s).
Releasing Priority Slots When a station no longer wishes to use a priority slot the reverse process is followed. A MAC
control frame is sent to Device 0, to release slot n. Upon hearing the next Beacon if slot n is marked as idle or owned by another device than the local device no longer owns priority slot n.
When Device 0 no longer wishes to use priority slot 0, it sets the 'pass beacon' field to some other priority slot device (This is not essential since beacon generators will be created in a cell by the nature of the protocol followed to establish a beacon generator in the cell. This extra step reduces the disruption to priority data tra.rnsfer). When the Device using this slot heart; the next Beacon identifying it as the new beacon generator, that device will changes its identity to Device 0 and will be responsible for sending Beacons from that point on. If the.
original Device 0 does not hear a Beacon within 2, or more default BIT intervals, it must reassign the Beacon. The decision of which priority device to pass the beacon generating responsibility to can be arrived at by heuristical methods, or arbitrarily chosen. The exact method used is not key to the invention but may disrupt operation (for example it would be undesirable to pass beacon generating to a device in the overlapping region of overlapped cells since this may alter the identity of many beacon generators.
Other Consideration In situations where Device 0 simply vanishes, Device 1 (or the device using the smallest priority slot) will usually assume the responsibility of generating the Beaccm after at least 2 BIT periods by nature of the method of establishing a beacon generator. In doing so, Device 1 will become Device 0 remove all other entries i~rom the list of MAC addresses sent in the beacon.
Periodically Device 0 should reassign priority slots to ensure that there are no gaps in the Beacon.
This also has the effect of reducing the maximum number of allocated priority slots and affords non-priority device a lower average transmit latency time.
Detailed Description of the Preferred Embodiment of another Aspect of the Invention Referring to Figure 3 this embodiment of the invention is demonstrated though a coexistence scheme designed into a controlling modulation MAC protocol layer, 33, that will allow it to coexist with an arbitrary subordinate modulation MAC protocol layer, 30. The invention will allow the 2 MAC protocol layers, 30 and 33, to interoperate with other such devices employing both MAC' protocol layers or other devices employing one or the other .MAC
protocol layers.
Both physical layers, 34 and 35, employ different pulse modulation techniques of a common infrared carrier signal. Without using the methods in this invention, these protocols will interfere with one another if they are placed within range of each other. Because each protocol uses a different modulation encoding of the a c<:>mmon carrier, they are not able to directly communicate with one another.
In this embodiment, the controlling physical layer, 34, is able to generate a jamming signal in the modulation of the subordinate physical layer, 35. The jamming signal so generated ensures that other subordinate MAC physical layers in other devices in the networks will be prevented from transmitting data in the medium for a certarin period of time, called the Idle From Jam time. The controlling MAC protocol, 33, directs the controlling physical layer, 35, to generate the jamming signal. The jamming signal will 'have to be retransmitted if the controlling modulation MAC
protocol, 33, remains in control of tlne modulation for a period of time greater than the Idle_From Jam Time. The controlling modulation MAC protocol manager, 33, will therefore direct the controlling modulation physical layer, 34, to generate jamming signals at the appropriate interval.
The controlling modulation MAC protocol layer, 33, sends a SOD frame in its own modulation to inform other controlling rnodulatiorr MAC protocol layers when the modulation will be changed to that of (one of) the subordinate modulation. The SOD frame also informs the control modulation MAC protocol layers of the amount of time the subordinate modulation will be used in the medium.
'The link manager, :i2, uses the services of the. controlling modulation MAC
protocol layer, 33, to generate the SOD from with the required MT value when the subordinate MAC
protocol manager, 31, deternnines that the subordinate modulation MAC layer, 30, requires access to the medium. 'The subordinate MAC protocol manager, 31, is able to determine this by knowing the protocol flow of the subordinate modulation MAC layer protocol, 30. The subordinate MAC
protocol manager, 31, queues data frames from the subordinate MAC protocol manager-.. 30, until sufficient data has been queued to warrant a transfer on the medium, or until such time as it realizes the subordinate modulation MAC protocol flow will break down because of being blocked from the medium while the controlling modulation is being used.
I () The subordinate MAC protocol manager, 31, is able to block data transfer between the subordinate modulation MAC protocol layer, 30, and the subordinate modulation physical layer, 35, by placing itself in the path of this data flow. When the controlling modulation is being used in the medium, the subordinate MAC protocol manager, ~ 1, may either queue any data requests from the subordinate modulation MAC protocol layer, 30, or simply discard the data. Similarly when the controlling modulation is used the subordinate MAC'. protocol manager, 31, will discard any data the subordinate rrrodulation physical layer believes it is receiving.
When the subordinate MAC protocol manager, 31, determines that its subordinate modulation MAC protocol layer, 30, requires medium access it requests the link manager, 32, to request the controlling modulation MAC protocol layer, 33, generate the SOD frame indicating the use of the subordinate modulation for a certain period of time. When this frame has been transmitted in the controlling noodulation, the contrcalling modulation MAC protocol layer, 33, wil stop directing the controlling modulatir~n physical layer tc~ generate jarnrning signals. The controlling modulation MAC protocol layer, 33, will also indicate the new modulation in effect in the medium to the link manager, 32; which in turn will convey the information to all subordinate modulation protocol managers, 31. After the subordinate modulation protocol manager, 3 t, is informed that its subordinate modulation is in effect, it will no longer block communication between the subordinate modulation MAC protocol layer, 30, and the subordinate rrrodulation physical layer, 35. This will allow commr.rnications in the subordinate modulation to occur between subordinate modulation MAC protocol layers, 30 for the period of time specified in the SOD frame.
After the period of time during which the subordinate modulation may be used in the medium, which was contained in the SOD frame of the controlling modulation, the controlling modulation MAC protocol layer, 33, will inform the. link manager, 32, that the controlling modulation is once again in control of the medium. 'fhe link manager, 32, will then inform all subordinate modulation protocol manager, 31, that it must once again resume blocking the transfer of data between the subordinate modulation MAC protocol layer, 30 and the subordinate modulation physical layer, 35.
Pseudo Code For the First Aspect of the Invention Notes: The pseudo cc)de that follows illustrates an embodiment of the basic invention. None of 1S the enhancements to the. base algoritlun have been included. In particular, the wireless extensions dealing with hidden nodes and some overlapping cell details are not shown in the implementation. Also the implementation uses:
- A fixed value for PAT, NPAT, BIT
- Only a single priority slot is assigned to any 1 MAC address - The beacon generator does not partition beacons for sets of priority devices.
It will be appreciated that when appropriately licensed the pseudo code may be used in the implementation of the invention in software recorded on a medium that may be used by stations of a network or in circuitry such as rrLicro code used in the stations.
Init Routine:
i Bcuc<mHcurd = FALS1:;
MinitnumContcntionSlot = 0;
MuximurnContenrionSlot = MAXIMUM NUMBER of Cc)NTENTIO N SL.()TS;
3~ NurttbcrAasignulPrioritySl«ts=.(l;
RenrtiningContrtnionSlots = 0;
MvPrioritvSlot = (1:
MisscdBeuconCuunt = 0;
Bcucunldentitr = NULL;
pendingrransmitFramcType = NULL;
pendingTran,mitData= Nlll~l.;
physicalCarricrStatc= NO. CARRIER:
SIotClock'1'imerHandle = Nlll,l.;
NPAT = Maximum time a non-priority device may send data on the channel;
1'A'1'= Maximum time a priority device may send data;
BIT= Beacon Interval 1'imc BT='1'imc to transmit beacon WaitingForNhysicalTransmitCompletc = FAL SE;
ReyuestTimeouU interval = BIT, timecxu Routine= Beacon'1'imeoutHandler ):
output: Integer RandomIntel;er input: L.owestValucInSelectionRange, input: HighcstValueInSeIcctionRange local variable: ReturnV<tlue;
RcturnValue _ chooae a number at random at least as large as the I~westValueInSetectionRange and no larger than IiighestValueInSelectionRan,;e at random;
return( RetumValue );
I'hsicalLayerC.'arrierSense('allback input: C:arricrState C
/*
*'Lhis MAC callback routine is called by the phtaical layer when it dctectc a * change in the carrier signal static in 1h c medium. Whm the medium i; idle and a carrier is detected (i.e. another station is starting to transmit), thi, * routine will he called with CarricrState=AC'1'bVEC'ARRIFR. When the * trammitting station completes ils rran,,mission this routine is called again * with Carrier;St<ne=N<) CARRIER
*i phpsicaICarTierState = CarricrStaW ;
IF( CarrierStatc==NO_.C'ARRIER ) I
CA9-1998-0023CA2 2~
IF( I'entlingTr<utsmitFr;tmc'I'ypc != Nlll.l_ ) I
Start_Slot CI<>Lk_Timer();
_5 ) ELSE
f Cancel Slot,C.lock Timer():
IF( Rcntaining('ontentionSlotv < MinimuntC"tmtentionSlot ) IF( PendingTransmitFrame'1'ype =:.- NON_ 1'RIORITY_DATA ) l RentainingContcntionSlots=Itandont__InUger( MinintutnC,'ontentionSlut, MaximuntC'ontentionSlol );
l5 ) Start Slot Cluck 'Timer /*
* All transmit reyueats must eventually votne through this routine.
?5 * We cue not allowed to transmit until n beacon i, heard. 'I'tterefore the slut clock is only actually stated * it we have recently heard the beacon. Iha bcaam has not been heard rerentlv, then tltu current xmit * data is held pending until we once again start haring beacons (or start grneralin g them ) if( licaconHeard ) i1( RcntainingContentionSlots > 0 ) f SIotCIockTimerliandler= ReyueatTimeout( interval=CONTEN'rl(')N__SL,OT 'TIME, timeout Routine=Sleri Clock Timeout );
f else 40 ) Slut_Cloc:k Timeaut();
Cancel Slot Clock 'Timer i call into operating system to disable timer W ivitv on handle SIutCk>LkTirnerHandler Slut ('lock Tinreout _5 t ,, *'Htisroutine is called every CONTENTION SLO'T_'1'IME period while there is a pending.
*'fhe slot clock timer period is a constant fir the particular MAC' protocol hcin~! usrd.
* W'hcnever the slot clock tuner is enaMcd, it will always count a complete slot clrxk * intervals. It the slot cluck timer is started with a 0 value to count down, thin routine * i, innnediatelv called.
*/
IFt RemainingC'untentionSluts==0 ) i WaitingForPhysiealTransnit('onrplete = TRUE:
I,,smPhysicalLayer Transmit( t'endin~rransmitl~ata ):
}
ELSE
f 20 RemainingContcntionSlots = RemainingC_'onlcntionSlots - I
SIotClockTimerHandler-- RcquestTintcout( interval=CONT'ENTION_SL(»' TIME.
timeout Ruutinr = Slcri Clock T'inrcout ):
25 }
Send_Frame Complete C
/*
30 * This routine is called by the physical layer when it has completed transmitting * the frame data Iron the Issue_F'hysiecil__L.ttyerTransmit physical layer routine.
*/
WaitingForPhysicalTransrnitConplcte= FALSE:
.35 IF( there is a queued Beacon for transmit ) /*
* This check is really only necessary ;I the station does nut choose to abort a transmit in progress * when a Beacon needs to he transnntted.
*/
remove beacon data Team the beacon queue Send Frame Ruutincl 13EA<'ON, BcnconDatu ):
l:I.SE;
IF( PcndingTransmitFrameTylx, = BE ACON ) I
/*
* The beacon has just been transmitted by this station.
Therefore thin station is using * priority atot (.). 'fherufore any <lucued priority data rut now be ,ant = there is no need * to contenttl, everyone else will Ix waiting fmr at Ieast on a contention slot.
;/
IF( there is more priority data queued ) 1 n I'en<lin~~ rran,mitF'rame'I'ype -- PRIURfI'Y ..I)A'TA:
I'endingTransmitData = deyueue up to 1'AT of priority data from the priority data queue;
WaitingForPhyswalTrausmitComplete = TRUE;
Isxue I'hy;ical_ Laycr'franamit( I'mdiugTransmitDat<t );
) ELSE
C
PendingTransmi tFrante'1'ypc = N l! LL:
I
ELSE
f PcndingTrammitFranteType = NlIL.L;
IF( there is more non-priority datalucued ) I
Send_.frtmea_Routine( NON _PRI()RfT'YDATA.
dcywue upto NPAT o1' non priority data from nun-priority data queue);
I
) J
Send Frames Routine ~5 input: franWype.
input: Irant~ data 1*
4U * It is assumed that the HW/ Physical layer can transfer multiple frames at once. The Irantedata tnay actually wunain muhiplc frames. The re.stricuon ort the; data sire is that Ior a (non)priority transfer, frantedata in bytes * ii bits per byte i channel bandwidth e= (NP)A'f * I, another fr;tme already pending fctr transmit.' 45 m IFI Ntnding'1'ransmitFrameTypc != NULL r I
1*
* rlborl it we're trying to send priority data or a beacon *!
IF( li~ametype != NON,. PRIQRITY DATA ) i ('anccl Slot Clock Timvr();
rcqucuc the pm<ling data at tlic head of the non priority transmit qwue;
) EL.,SE
/*
*'rhia should not occur. More error handling should by added.
*/
internal error => priority data and heacom should wver overlap;
Cancel Slot Clock Tirnert):
PcndingTransmitFramcType=frame type;
1'cndingTransitData = franydata;
/*
* Ch<Krse the nurnber of contention slots to wait based cm livme typr.
* The pending transmit data needs to be lbrmatcd into an appropriate physical layer Ibrmat and the MAC
* needs to distinguish between control frames (sent beUVern MAC layers an<t upper layer data framvs_ */
e:hoose( ft'amz type ) as one of:
t BEACON ):
I
RemainingContentionSlots : U;
PendingTransmitData is 1i>rntatted a, MAC control frame:
);
.~ S ( PR IOR 11'Y DATA ):
RemaingContcntionSlots = A,sigwd_Priority_Slot;
PendingTrammill>ata is li>rmattetl as upper layer data frame;
):
N()N_PRIORITI'_I)AT.A j:
i IZcmainingContcntionSlots =Random Irrtcgcr( 0, MaximumContcntionSlot )+MinimumContentionSlot PendingTransmitl)ata is ti>rmatted as upper layer data f~antc:
):
4S i REQUES'I-PRIORITY_SLOTCONTKOI,FRAME ) CA9-1 y98-0023CA2 31 i RELEASE NRIORITY_ SLO'I'_C()NT(t()L_FKAME Y.:
f Renrtinin~~ContentionSlnta = Random_Inte~erl (1. MaxirnuntContentiunSlot ) +
MininmmC'ontentiunSlut Pending fransmitData is tbrm:uted a. MAC cttntrul fr;nne:
* Check for a valid eurricr. We only begin ccxmtin,: down contention slots once the rncdium is fret.
1 n */
IF( Phy,ical<'arricrStale = N()..._CARRIER
Sutrt_Slot__Clock Timer( RemainingContentionSlots t;
;
MAC 'Transmit Non 1'rioritv Data I
input: data frame i ( queue the daW frame on the non-t~riority data queue;
IF( Vv'aitingF'orl'hyaical7'ran,mit('ompleW =-- FAL ,1E ) i Send__FrauteRoutinet NONpRl()Rl'lY I).A'fA, dequeuc upto NPAT of nun priority data faun non-priority data queue);
i MAC.Reyuest Priority_.Slut 1*
5 * In thin sample implementation, each MAC station is only ably to have 1 priority slot.
* An enhanced implementation would allow multiple priority slots to be used by any station.
*/
IF( Myl'rioritySlcn == 0 ) ANI) f Beaconldcntity '= N(.!l.,L ) AND ( Rcaronldentity != MyMACAddress ) 40 {
Format MAC control Frame to request a priority slot from the Bcacunldentity Send Frames_Jtoutinc( REQUEST_pRl<)Rll'Y_SL,OT,<'ON'pROL. FRAME, formatted control frame ):
IF( Myl'rioritySlut != U o OIZ ( licaconldcntity .-__- MyMAC'Adtlrcss ) indicate that priority slot alrwdy assitned I
ELSE
fail the rcyuest I
I
MAC_Release Priority- Slut IS I
/*
~' Th a MAC could track the amount of time between successive calls to MAC
TransmitPriority_IW to * and automatically release the priority slut (by calling this routine>. In this simple implementation, * once the priority slot has been alkxated, it is Icli open until the upper layer explit:itly releases iL
IF( MyprioritySl<ri != 0 ) C
Format MAC control frame to release priority .lot from the Bcaconldcntity Scnd_FrantesRoutinc( RELfi;ASF 1'RIORITI'_SLO'f_C.'ONTROL_FRAML;.
RntnatlcdCOnlrol frame );
/*
* This simple implementation does not reassign the beacon responsibility *l MAC 'Transmit I'rioritv Data input: data frame ~5 ;
IF( MyprioritySlot != 0 ) OR ( Beaconldentity = MIyMAC'Addrt;ss ) queue the data frame on the priority data yuew;
40 !*
* Must u~ait for the next beercon to send priority data.
*/
EL..SI3 CA9-1998-0023CA2 3 y /*
* Faile the request. This should indicate to the upper layer that this device duc> nut own a * priority slut an<i thcrel're can not .,en<1 piurity data. 'this will cttuae the upper Ittyer to (re)request t * a priority ,lot.
*/
fteacon TimeoutHandler i local variable: slot_delay_on_first., beacon:
IF( Bcacunldetttity - MyMACAddrexa ) I
IF( Waitin~ForPhyaicalTranstnitContplcte == FALSE 1 I
SendFrame( BEACON FRAME, Bcaconl.ist );
E1..SE
I
yucue beacon data Be~tconList;
EL.sE
I
1F( ReaconHeurd == FALSE t THEN
i MiasedBe<tconCouttt:=Mis~edBeaconCormt+ 1;
IF( MissedBcaconCount >= MAX MISSEn...BEACON C'pUNT
I
MissedBeuconC'ount = t);
/*
* The Beacon 1~mcralor hasn't hven hcartl in awhile.
* Assume ownership of the beacon.
:/
IF( MyPrioritySlot !-1> J
i slut_clelay on_firat beacon = Myl'rioritySIuU
else s slot delay un fin;t beacon - I
IFI pendingTransmitFrameTypc '= Nl II,L ) l 1*
* (RclF:nahle transmit opcnuion */
Start Siot Clrxk(l:
remove <tny pm<'ling or ymucd Rcyuestf'rioritySl<n control (names Bcaconlticntity =- f~IyMAC'Addrcss;
Bcaconl.ist== I cnilxy ):
MinimutnContentionSlot = I;
MyPrioritySlot = 11;
NumherAssigncdl'rioritySluts= 1;
f RequcstTimeout( interval = BIT+ ( slot_dclay_on_ first "heacon *
C()NTFNTION_.SL.O'I'.'fIME, timcout Routine = Beacon'1'imeoutHandler );
20 ) Receive ('allback Routine t 2S input: data t /*
* Dctcnninr if this is upper layer data or a MAC layer f onirol frame.
30 * Note: Received data must be transtnormed from physical layer data into mac layer dale. Only non * MAC voutrol frames are sent to the upper layer,.
*/
IFI data is formatted as an upper layer data packet I
I
3 S transfer data to upper network layer for processing Et_SE
f J*
40 * This is a MAC. control frantc.
*/
~h~x~se( frame type 1 as one ~>f:
f ( BEACON CO'1'ROL_FR.4ME ):
BcaconHcard ='1'R t iE:
Process Beacon( I>cacon duty ):
1:
S ( REQIIEST_I'KIOK1TY_SLOT CONTR()L_FkAME >:
IF( Keaconldentity = Ivty~1ACAJdre" ) S
~, * Add the requester to the and of the Beaconl.ist BcaconLisy NumberAssitnedPrioritySluts ] = MAC address of rcyuester;
NumbcrAs,i~nedPrioritySlota = NumberAssignedprioritySlots + 1;
15 ;
t RELEASE PRIOkITY._SLt)T_C'<)NTROL FRAME ):
IF( Bcaconldcntiy~ = MyMACAddrws ) i IF( MAC address of myustee fuund in the t3eaconList =at index x) BeaconList( x ~ = NULL Muc address;
~:E:
25 * 'This step dc'tes not have to be dune every time a device releases a priority slot...
Reorder BeamnList so all NULL MAC addresses at end of list.
NumberAssignedPrioritySlots = NumberAssignedPrioritySlots - J
f I'roeess Beacon ) input: BeaconUaW
IF( Beaconldentitv = NULL ) I
Beacunldcntitv = source MAC address of the Beacon;
I
CA9- I 99~-0023CA2 3E~
IF'l MvMA('Addrws == Beaeonldcntity ) * -This device is generating and receiving beacons. This is n<n permitted.
* Stop sending beacons if the device heard has a numerically sntallcr M.AC' athlress.
*/
IFf Mv~~1AC'Addrc~s > source tviAC a<ldicss ol'thc Beacon /*
* In this wimple implcntentahon, hcmon generation by this device ix simply stopped.
*'phc procesx of Establishinl_~ tithe Presence of a Bcactm Generator in the Cell * will be followmi to establish mw beacon generatonsl instead of vending a special MAC' control frantc infixn,ing all devices in the BcaconLi.st of Ibe identity of the new bcaCi>n gcncrator-'~'/
MyPrioritySlot = 0;
Bcaconldentity = source address of the Beacon;
inform the upper layer that the Iwiority slot is no longer available (it will be rc-rcyucsted if still needed).
IF( source MAC address of the Beacon == Beaconldentity ) If'( MyMACAddt~as is in the BeaconD;ua ) I
MyPrioritySlot = ordinal pcmition of MyMACAddress in lhc BcaconDat:r if( MyPrior itySlot =---- 0 1 /*
* We have been passed responsibility of beacon generation */
Bcaconldcntity = MyMACAd'.tress;
5 BeamtnLi st = Bcucon I )ata:
ELSE
S
/,:
40 * Cancel any pending transmit and submit priority tr:dtic instead.
*/
Send Frantc Routine( N()NPRI<)RITY DATA, deqmuc upto NPAT of non priority data fiom non-priority dale queue):
CA9-1998-0023CA2 3 i ELSE
/>:
We have lost the use c:f'our priority slot. Sine this implententatiun does not use split * beacons this should only oc;wr as a result of a release priority clot request. In tire case '" where the release priorty alm rcyuest wan issued but not honoured by the bc:tcon generator.
* it is assented that the upper layer will tirncont on the rcclucst cunt7rmation and resubmit it.
;:/
inform upper layer that the priority plot is no longer available.
1 ~~
/*
* Note in this wimple implementation the beacon generator always generates a single beacon indicating the MAC addresses oFall <Icvices assigned priority sluts.
*1 1 5 IFt MinintumCuntentictnSlut < number ~~f entries in llcaCOtt Data ) MinimumCuntentionSlot = number uf_entries in BeucunData;
NumherAssignedprioritySiots = MinimnmContentionSlot;
20 s ELSE:
I
/.,.
* This simple implementation does not inform beacon gwerauns in overlapped cells of the largest nunther of allocated priority slots in the overlapped cells, Similarly this implcmentution does not require priority devices in the overlap to register with the beacon generator using the numerically * hi~her MAC' :tddrcas. 'rhe prc,,cesainl, ler these (wireless) enhancements would he perfornted here.
However, we ntuy need to increase the minimum contention slot value used if this beacon generator has more * allocated priority slots.
*/
IF( MinimumConrentietnSlot < number of entries in Beacon Data ) I
MinimumCuntentionSlot = nutnhcr of entries in 8cacunData;
35 t NuntherAssignedYrioritySlots - MininmntCctntentiunSlot;
40 Pseudo Code ror the Second Aspect of the Invention Pseudo code is not shown for the operation of the subordinate modulation physical layer or the subordinate modulation MAC protocol layer since this operation is unaffiected by this invention.
Subordinate Modulation Protocol Manager Operation C'urrcntModulation=CON'1"ROLLING MODIILA'1'ION:
'When rcyuested to transmit data t?y the subordinate rncxlulate MAC: protocol layer:
L
IF( CurrcntModulation == My__SUf3ORl )INATG__MODULATION ) l wend data to the suh~rrdinate modulation physical layer;
y EE.SE
I
<lueue data for transmissicm t~.> the subordinate modulation physical layer;
L;pon receiving data from the subordinate modulaOOn physical layer:
i IF'( GurremModulation==My SUf3ORDINA~EG MODULATION ) zo I
transfer received dala to the subordinate modulation MAC' prokxol layer;
E;LSI
i 25 d~,~ard the daw;
) EJpon receiving an indication of a modulation chaugc from the link utana~;er:
('urrentModulation = modulation indi.:atcd by the link manager;
IF( C'urrentModulatictn == My_SU13()IZf)INATE_MODIJLATION 1 i wend all queued subordinate modulation MA(' pnUocol to the subordinate modulation physical layer;
EJpun determining that the subordinate mctdulatimn MAC' prot<xol layer rcyuires accecs to the medium:
I
reyucst the link manager to swil,eh to My_ 511130R1>INA'I'E_MODL.1LATION for a period of tithe = MT;
CA9-1998-00?3CA2 39 Link Manager Operation ('urrentMcxlulation --- CON'J'ROLLINC~ Mt)DULA'11()N:
S When requested to change nu>dulation to subordinatc_nt<xhtlation for time pericxl ~~1T by a suhordinctte prottxol manager:
i IF( CurrentModulation != auhordin<ttemudulation J
I
request the controlling modulation MAC protocol Jaycr to generate a SOD frame using( suhordinate nxxlulation and M'1' ):
1 _5 Upon indication front the mntrollin~ mo<luJation MAC' protocol that the current modulation ix Modulation:
I
CnrrcntModulation = Modulation Indicate current modulation to all protocol managers;
?~
Contrullinf;_Mudulation MAC_Protocol Operation y 2.5 1*
* Only the operation of the MAC required in the context of this invention are shown.
*!
C'uwentMtxiulation = CONTKOLLING MCtDULATION:
pc,ic,tlically gcnarate jatnminp signals in all suhoalinate modulations;
J'encfin~Modulation =N(JL,LL,;
PendingModulationTintc - 0:
lVhm requested to send SOD frame li,r sufiordinate nwdulation = Modulation.
<tnd time = MT
IF( pcndingModulatiutn = NI ILf, ) AND ( C.'urrcntModulution =CONTROL,LING_M(>I,)ULATION ) Pcndin~;Modulatiun =mouulation:
PcndingModulationTinte= MT:
Send SOD Frante( modulation. MT );
i ELSE
qucur modulation change request;
When SOD franc indicated as trunsntittvd:
s CnrrcntMcxlul<4ion = PendingMixlulation;
PcndingMcxlulation= NULL;
Stop generating jamming ,ignals in current nxxlulation;
se( Mcxlulation'fintcr to expire in MT;
Inilicatc CurrentMo<lulation to Link Manager;
I
r 5 When Modulation Tirner expires:
I
resume periodically generating jamrttinp~ signals in CurrentModulation;
CurrwtModulatictn = ('ONTROLLIN(i Mt)Dl ~LATI( )N:
Indicate CuwentM<xlulation to Link Manager:
IF( queued modulation change request/ ) I
deyueuc modulation change, 5 PendingModulation = mcxlulation:
PendingModulationTimc = MT;
Send. _S01 >_Framc( rnrx[ulation, M'r ):
f Cuntrollin~_Modulation__I'hysical Layer Operation:
( />:
* Only the operation of the physical (aver requin;d in the context of this invention arc shown.
*/
When requested to generate.jamming aignal in modulation=Modulation generate jamming signal in modulali~m;
Claims (10)
1. A method of reducing interference in communication in a medium using carrier modulation, for a communication network having a plurality of stations, using access control protocol wherein at least one of said stations is capable of generating a control message (SOD) that can be transmitted to other stations on said network to change the method of modulation being used, wherein, communication between stations in said network is being performed using a first modulation method, comprising:
monitoring interference to determine if quality of service is acceptable and if unacceptable;
initiating a change in the modulation method being used in said network by sending a 15 control message containing identification of a second modulation method to other stations on said network to inform said other stations of said second modulation method;
allowing said other stations to change the modulation method used by them to said second modulation method; and said control message further including a direction to those other stations not changing to said second modulation method to instruct them not to transmit using said first modulation method.
monitoring interference to determine if quality of service is acceptable and if unacceptable;
initiating a change in the modulation method being used in said network by sending a 15 control message containing identification of a second modulation method to other stations on said network to inform said other stations of said second modulation method;
allowing said other stations to change the modulation method used by them to said second modulation method; and said control message further including a direction to those other stations not changing to said second modulation method to instruct them not to transmit using said first modulation method.
2. The method of claim 1 wherein said control message includes information identifying the duration of time for which said second modulation method will be used.
3. The method of claim 2 wherein at least one of said network stations sends a jamming signal using said second modulation method when said first modulation method is in use.
4. The method of claim 3 wherein said network stations sending jamming signals on said second modulation stop sending said jamming signals upon receiving a modulation control message directing said second modulation method be used for communication.
5. The method of claim 4 wherein said jamming signals are resumed when said duration of time for the use of said second modulation technique expires.
6. The method of claim 1 wherein a selected communication protocol is associated with each modulation method used wherein when a modulation method in use is changed at a station said station will change to the appropriate communication protocol associated with said changed modulation.
7. Apparatus for reducing interference in communication in a medium using carrier modulation, for a communication network having a plurality of stations, using access control protocol wherein at least one of said stations is capable of generating a control message (SOD) that can be transmitted to other stations on said network to change the method of modulation being used, wherein, communication between stations in said network is being performed using a first modulation method, comprising:
means for monitoring interference in communication to determine if quality of service is acceptable to determine if a change in the method of modulation is preferable;
means for initiating a change in the modulation method being used in said network by sending a control message containing identification of a second modulation method to other stations on said network to inform said other stations of said second modulation method;
means for allowing said other stations to change the modulation method used by them to said second modulation method;
said control message further including a direction to those other stations not changing to said second modulation method to instruct them not to transmit using said first modulation method.
means for monitoring interference in communication to determine if quality of service is acceptable to determine if a change in the method of modulation is preferable;
means for initiating a change in the modulation method being used in said network by sending a control message containing identification of a second modulation method to other stations on said network to inform said other stations of said second modulation method;
means for allowing said other stations to change the modulation method used by them to said second modulation method;
said control message further including a direction to those other stations not changing to said second modulation method to instruct them not to transmit using said first modulation method.
8. The apparatus of claim 7 wherein a selected communication protocol is associated with each modulation method used said apparatus being adapted so that when a modulation method in use is changed at a station said station will change to the appropriate communication protocol associated with said changed modulation.
9. Apparatus comprising a computer readable medium storing computer readable code for use in stations in a communications network in accordance with claims 7 or 8.
10. Apparatus comprising a computer readable medium storing computer readable code for use in stations in a communications network to perform the methods of any of claims 1 to 6.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2242985 CA2242985A1 (en) | 1998-07-14 | 1998-07-14 | A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and co-existence of multiple physical layer modulation schemes |
| CA2,242,985 | 1998-07-14 |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2242985 Division CA2242985A1 (en) | 1998-07-14 | 1998-07-14 | A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and co-existence of multiple physical layer modulation schemes |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2425934A1 CA2425934A1 (en) | 2000-01-14 |
| CA2425934C true CA2425934C (en) | 2004-04-20 |
Family
ID=4162649
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002425934A Expired - Fee Related CA2425934C (en) | 1998-07-14 | 1998-07-14 | A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and coexistence of multiple physical layer modulation schemes |
| CA 2242985 Abandoned CA2242985A1 (en) | 1998-07-14 | 1998-07-14 | A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and co-existence of multiple physical layer modulation schemes |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2242985 Abandoned CA2242985A1 (en) | 1998-07-14 | 1998-07-14 | A method of adding quality of service capabilities to csma-ca based protocols for the purpose of isochronous communication and co-existence of multiple physical layer modulation schemes |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2425934C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101873710B (en) * | 2009-04-23 | 2013-08-14 | 厦门星网锐捷软件有限公司 | Optimization method of non-channel way CSMA-CA (Carrier Sense Multiple Access-Conflict Avoidance) algorithm based on IEEE802.15.4 standard |
-
1998
- 1998-07-14 CA CA002425934A patent/CA2425934C/en not_active Expired - Fee Related
- 1998-07-14 CA CA 2242985 patent/CA2242985A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| CA2242985A1 (en) | 2000-01-14 |
| CA2425934A1 (en) | 2000-01-14 |
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