Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W28/00—Network traffic management; Network resource management
  • H04W28/02—Traffic management, e.g. flow control or congestion control
  • H04W28/10—Flow control between communication endpoints
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/30—Flow control; Congestion control in combination with information about buffer occupancy at either end or at transit nodes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/39—Credit based
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W28/00—Network traffic management; Network resource management
  • H04W28/02—Traffic management, e.g. flow control or congestion control
  • H04W28/0278—Traffic management, e.g. flow control or congestion control using buffer status reports
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W28/00—Network traffic management; Network resource management
  • H04W28/02—Traffic management, e.g. flow control or congestion control
  • H04W28/10—Flow control between communication endpoints
  • H04W28/14—Flow control between communication endpoints using intermediate storage
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W80/00—Wireless network protocols or protocol adaptations to wireless operation
  • H04W80/02—Data link layer protocols
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/12—Access point controller devices

Definitions

• the present invention relates in general to the field of communications systems, and in particular, by way of example but not limitation, to handling potential buffer overflows resulting from users overloading a communications system.
• wireless networks Access to and use of wireless networks is becoming increasingly important and popular for business, social, and recreational purposes. Users of wireless networks now rely on them for both voice and data communications. Furthermore, an ever increasing number of users demand both an increasing array of services and capabilities as well as greater bandwidth for activities such as Internet surfing. To address and meet the demands for new services and greater bandwidth, the wireless communications industry constantly strives to improve the number of services and the throughput of their wireless networks. Expanding and improving the infrastructure necessary to provide additional services and higher bandwidth is an expensive and manpower-intensive undertaking. Moreover, high-bandwidth data streams will eventually be demanded by consumers to support features such as real-time audiovisual downloads and live audio-visual communication between two or more people. In the future, it will therefore become necessary and/or more cost-effective to introduce next generation wireless system(s) instead of attempting to upgrade existing system(s).
• the wireless communications industry intends to continue to improve the capabilities of the technology upon which it relies and that it makes available to its customers by deploying next generation system(s).
• Protocols for a next-generation standard that is designed to meet the developing needs of wireless customers is being standardized by the 3 rd Generation Partnership Project (3GPP).
• 3GPP 3 rd Generation Partnership Project
• the set of protocols is known collectively as the Universal Mobile Telecommunications System (UMTS).
• UMTS Universal Mobile Telecommunications System
• the network 100 includes a core network 120 and a packet data convergence protocol (GSM) network.
• UMTS Universal Mobile Telecommunications
• the network 100 includes a core network 120 and a packet data convergence protocol (GSM) network.
• the UTRAN 130 is composed of, at least partially, a number of Radio Network Controllers (RNCs) 140, each of which may be coupled to one or more neighboring Node Bs 150.
• RNCs Radio Network Controllers
• Each Node B 150 is responsible for a given geographical cell and the controlling RNC 140 is responsible for routing user and signaling data between that Node B 150 and the core network 120. All of the RNCs 140 may be directly or indirectly coupled to one another.
• a general outline of the UTRAN 130 is given in Technical Specification TS 25.401 V2.0.0 (1999-09) of the 3rd Generation Partnership Project, 3GPP, which is hereby incorporated by reference in its entirety herein.
• the UMTS network 100 also includes multiple user equipments (UEs) 110.
• UE may include, for example, mobile stations, mobile terminals, laptops/personal digital assistants (PDAs) with wireless links, etc.
• a set of Radio Access Bearers is provided to make radio resources and services available to user applications.
• RABs Radio Access Bearers
• RABs Radio Link Control
• RLC Radio Link Control
• the RLC entities buffer the received data segments and map the RABs onto respective logical channels.
• a Medium Access Control (MAC) entity receives data transmitted in the logical channels, and further maps the data from the logical channels onto a set of transport channels.
• the transport channels are, in turn, mapped to a single physical transport channel having a specified total band width allocated to it by the associated network.
• a MAC entity connected to a dedicated transport channel is known as MAC-d
• MAC-c a MAC entity connected to a common transport channel
• GPS Generalized Processor Sharing
• an arrangement is made available which provides data flow from a number of different MAC-d entities, respectfully associated with different logical channels, with a fair share of the data rate between the Mac-d entities and a common MAC-c entity, and which also maintains the MAC-c buffer at or close to a desired fill level. This is achieved by sharing MAC-c buffer free space between active data flows of Mac-d entities according to a sequential, round robin or flow activity principle and using available information pertaining to the buffer fill levels of the respective RLC/MAC-d entities.
• the invention is directed to a method for providing flow control in a wireless communications system which comprises the steps of providing a receiver entity and one or more transmitter entities, a given transmitter entity transmitting when it receives credit from the receiver entity.
• the method further comprises the step of determining whether to give credit to respective transmitter entities.
• the method comprises transmitting packets of data from respective transmitter entities to the receiver entity in a sequential or round robin fashion.
• the receiver entity comprises a common Medium Access Control Entity (MAC-c) having a receiver buffer
• each of the transmitter entities comprises a dedicated Medium Access Control (Mac-d) entity, each transmitter entity bearing associated with another buffer.
• MAC-c Medium Access Control Entity
• Mac-d Medium Access Control
• the determination of the determining step is based, at least in part, on the fill level of the receiver buffer, and also on the fill levels of one or more buffers associated with respective transmitter entities.
• determination is based, at least in part, on the fill level of the receiver buffer, but not on the fill levels of any of the buffers associated with transmitter entities.
• Another embodiment of the invention includes the steps of ascertaining if a first active transmitter entity has a current credit which is less than the buffer fill level of an associated buffer, and if so, increasing the current credit of the first active transmitter entity by one and decreasing the available credit amount by one.
• Such ascertaining step is repeated for each active transmitter entity until either the available credit amount is exhausted, or all active transmitter entities have their corresponding current credits to their corresponding buffer fill levels.
• Such embodiment further includes the step of recording the last active transmitter entity to receive a credit, and making another active transmitter entity immediately following the last active transmitter in a sequence to be the first active transmitter entity to receive a credit on the next occasion when credits are distributed.
• FIG. 1 illustrates an exemplary wireless communications system with which the present invention may be advantageously employed
• FIG. 2 illustrates a protocol model for an exemplary next-generation system with which the present invention may be advantageously employed
• FIG. 3 illustrates a view of an exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention
• FIG. 4 illustrates an exemplary method in flowchart form for allocating bandwidth resources to data flow streams between entities in the exemplary second layer architecture of FIG. 3;
• FIG. 5 illustrates a flow control comprising an embodiment of the invention interconnected between transmit and receive entities.
• FIG. 6 shows a portion of the embodiment of Figure 5 in greater detail.
• FIG. 7 illustrates a buffer for the embodiment of Figure 5.
• FIG. 8 illustrates operation of the flow control of the embodiment shown in
• FIG 9 shows a buffer for a second embodiment of the invention.
• FIG. 10 is a schematic diagram illustrating operation of the second embodiment.
• FIG. 11 is a graph depicting the relationship between buffer fill level and credits for the second embodiment.
• FIGs. 12 and 13 are schematic diagrams for illustrating a third embodiment of the invention.
• FIGS. 1-13 of the drawings like numerals being used for like and corresponding parts of the various drawings.
• Aspects of the UMTS are used to describe a preferred embodiment of the present invention. However, it should be understood that the principles of the present invention are applicable to other wireless communication standards (or systems), especially those in which communication is packet-based.
• a protocol model for an exemplary next-generation system with which the present invention may be advantageously employed is illustrated generally at 200.
• the "Uu” indicates the interface between UTRAN 130 and the UE 110
• ' ub" indicates the interface between the RNC 140 and a Node B 150 (where "Node B” is a generalization of, for example, a Base Transceiver Station (BTS)).
• BTS Base Transceiver Station
• User and signaling data maybe carried between an RNC 140 and a UE 110 using Radio Access Bearers (RABs) (as illustrated hereinbelow with reference to FIG. 3).
• RABs Radio Access Bearers
• a UE 110 is allocated one or more RABs, each of which is capable of carrying a flow of user or signaling data.
• RABs are mapped onto respective logical channels.
• MAC Media Access Control
• a set of logical channels is mapped in turn onto a transport Channel, of which there are two types: a "common” transport Channel which is shared by different UEs 110 and a "dedicated” transport Channel which is allocated to a single UE 110 (thus leading to the terms “MAC-c" and "MAC-d”).
• One type of common Channel is the FACH.
• a basic characteristic of a FACH is that it is possible to send one or more fixed size packets per transmission time interval (e.g., 10, 20, 40, or 80 ms).
• transport channels e.g., FACHs
• S-CCPCH Secondary Common Control Physical CHANNEL
• the serving RNC 140 may subsequently differ from the controlling RNC 140 in a UMTS network 100, but the presence or absence of this condition is not particularly relevant here.
• the RNC 140 both controls the air interface radio resources and terminates the layer 3 intelligence (e.g., the Radio Resource Control (RRC) protocol), thus routing data associated with the UE 110 directly to and from the core network 120.
• RRC Radio Resource Control
• the MAC-c entity in the RNC 140 transfers M AC- c Packet Data Units (PDUs) to the peer MAC-c entity at the UE 110 using the services of the FACH Frame Protocol (FACH FP) entity between the RNC 140 and the Node
• the FACH FP entity adds header information to the MAC-c PDUs to form FACH FP PDUs which are transported to the Node B 150 over an AAL2 (or other transport mechanism) connection.
• An interworking function at the Node B 150 interworks the FACH frame received by the FACH FP entity into the PHY entity.
• an important task of the MAC-c entity is the scheduling of packets (MAC PDUs) for transmission over the air interface.
• UMTS defines a framework in which different Quality of Services (QoSs) maybe assigned to different RABs. Packets corresponding to a RAB that has been allocated a high QoS should be transmitted over the air interface at a high priority whilst packets corresponding to a RAB that has been allocated a low QoS should be transmitted over the air interface at a lower priority. Priorities maybe determined at the MAC entity (e.g., MAC-c or MAC-d) on the basis of RAB parameters .
• QoSs Quality of Services
• UMTS deals with the question of priority by providing at the controlling RNC 140 a set of queues for each FACH.
• the queues may be associated with respective priority levels.
• An algorithm which is defined for selecting packets from the queues in such a way that packets in the higher priority queues are (on average) dealt with more quickly than packets in the lower priority queues, is implemented. The nature of this algorithm is complicated by the fact that the FACHs that are sent on the same physical Channel are not independent of one another. More particularly, a set of Transport Format Combinations (TFCs) is defined for each S-CCPCH, where each TFC includes a transmission time interval, a packet size, and a total transmission size (indicating the number of packets in the transmission) for each FACH. The algorithm should select for the FACHs a TFC which matches one of those present in the TFC set in accordance with UMTS protocols.
• TFCs Transport Format Combinations
• a packet received at the controlling RNC 140 is placed in a queue (for transmission on a FACH), where the queue corresponds to the priority level attached to the packet as well as to the size of the packet.
• the FACH is mapped onto a S-CCPCH at a Node B 150 or other corresponding node of the UTRAN 130.
• the packets for transmission on the FACH are associated with either a Dedicated Control CHANNEL (DCCH) or to a Dedicated Traffic CHANNEL (DTCH).
• DCCH Dedicated Control CHANNEL
• DTCH Dedicated Traffic CHANNEL
• each FACH is arranged to carry only one size of packets. However, this is not necessary, and it may be that the packet size that can be carried by a given FACH varies from one transmission time interval to another.
• the UE 110 may communicate with the core network 120 of the UMTS system 100 via separate serving and controlling (or drift) RNCs 140 within the UTRAN 130 (e.g., when the UE 110 moves from an area covered by the original serving RNC 140 into a new area covered by a controlling/drift RNC 140) (not specifically shown).
• RNCs 140 within the UTRAN 130 (e.g., when the UE 110 moves from an area covered by the original serving RNC 140 into a new area covered by a controlling/drift RNC 140) (not specifically shown).
• the UE 110 are received at the MAC-d entity of the serving RNC 140 from the core network 120 and are "mapped" onto logical channels, namely a Dedicated Control Channel (DCCH) and a Dedicated traffic CHANNEL (DTCH), for example.
• the MAC-d entity constructs MAC Service Data Units (SDUs), which include a payload section containing logical channel data and a MAC header containing, inter alia, a logical channel identifier.
• the MAC-d entity passes the MAC SDUs to the FACH FP entity.
• This FACH FP entity adds a further FACH FP header to each MAC SDU, where the FACH FP header includes a priority level that has been allocated to the MAC SDU by an RRC entity.
• the RRC is notified of available priority levels, together with an identification of one or more accepted packet sizes for each priority level, following the entry of a UE 110 into the coverage area of the drift RNC 140.
• the FACH FP packets are sent to a peer FACH FP entity at the drift RNC 140 over an AAL2 (or other) connection.
• the peer FACH FP entity decapsulates the MAC-d SDU and identifies the priority contained in the FRAME FP header.
• the SDU and associated priority are passed to the MAC-c entity at the controlling RNC
• the MAC-c layer is responsible for scheduling SDUs for transmission on the FACHs. More particularly, each SDU is placed in a queue corresponding to its priority and size. For example, if there are 16 priority levels, there will be 16 queue sets for each FACH, with the number of queues in each of the 16 queue sets depending upon the number of packet sizes accepted for the associated priority. As described hereinabove, SDUs are selected from the queues for a given FACH in accordance with some predefined algorithm (e.g., so as to satisfy the TFC requirements of the physical channel).
• the scheme described hereinbelow with reference to FIGS. 3 and 4 relates to data transmission in a telecommunications network and in particular, though not necessarily, to data transmission in a UMTS.
• the 3 GPP is currently in the process of standardizing a new set of protocols for mobile telecommunications systems.
• the set of protocols is known collectively as the UMTS.
• FIG. 3 a view of an exemplary second layer architecture of an exemplary next-generation system in accordance with the present invention is illustrated generally at 300.
• the exemplary second layer architecture 300 illustrates a simplified UMTS layer 2 protocol structure which is involved in the communication between mobile stations (e.g.
• the RNCs 140 are analogous to the Base Station Controllers (BSCs) of existing GSM mobile telecommunications networks, communicating with the mobile stations via Node Bs 150.
• BSCs Base Station Controllers
• the layer 2 structure of the exemplary second layer architecture 300 includes a set of Radio Access Bearers (RABs) 305 that make available radio resources (and services) to user applications.
• RABs Radio Access Bearers
• Data flows (e.g., in the form of segments) from the RABs 305 are passed to respective Radio Link Control (RLC) entities 310, which amongst other tasks buffer the received data segments.
• RLC Radio Link Control
• RABs 305 are mapped onto respective logical channels 315.
• a Medium Access Control (MAC) entity 320 receives data transmitted in the logical channels 315 and further maps the data from the logical channels 315 onto a set of transport channels 325.
• MAC Medium Access Control
• the transport channels 325 are finally mapped to a single physical transport channel 330, which has a total bandwidth (e.g., of ⁇ 2Mbits/sec) allocated to it by the network.
• a physical channel is used exclusively by one mobile station or is shared between many mobile stations, it is referred to as either a "dedicated physical channel” or a "common channel”.
• a MAC entity connected to a dedicated physical channel is known as MAC-d; there is preferably one MAC-d entity for each mobile station.
• a MAC entity connected to a common channel is known as MAC-c; there is preferably one MAC-c entity for each cell.
• the bandwidth of a transport channel 325 is not directly restricted by the capabilities of the physical layer 330, but is rather configured by a Radio Resource
• RRC Radio Resource Controller
• TFs Transport Formats
• Transport Blocks For each transport channel 325, the RRC entity 335 defines one or several Transport Block (TB) sizes. Each Transport Block size directly corresponds to an allowed MAC Protocol Data Unit (PDU) and tells the MAC entity what packet sizes it can use to transmit data to the physical layer.
• PDU Protocol Data Unit
• TBS Transport Block Set
• MAC entity can transmit to the physical layer in a single transmission time interval (TTI).
• TTI transmission time interval
• TFC Transport Format Combination
• ⁇ TF1 (80, 80)
• the MAC entity can choose to transmit one or two PDUs in one TTI on the particular transport channel in question; in both cases, the PDUs have a size of 80 bits.
• the MAC entity 320 In each TTI, the MAC entity 320 has to decide how much data to transmit on each transport channel 325 connected to it. These transport channels 325 are not independent of one another, and are later multiplexed onto a single physical channel 330 at the physical layer 330 (as discussed hereinabove).
• the RRC entity 335 has to ensure that the total transmission capability on all transport channels 325 does not exceed the transmission capability of the underlying physical channel 330. This is accomplished by giving the MAC entity 320 a Transport Format Combination Set (TFCS), which contains the allowed Transport Format Combinations for all transport channels.
• TFCS Transport Format Combination Set
• MAC entity 320 which has two transport channels 325 that are further multiplexed onto a single physical channel 330, which has a transport capacity of 160 bits per transmission time interval (It should be understood that, in practice, the capacity will be much greater than 160).
• TF2 (80, 80)
• TF3 (80, 160)
• the RRC entity 335 has to restrict the total transmission rate by not allowing all combinations of the TFs.
• TFCI Transport Format Combination Indicator
• TFCI Transport Format Combination Indicator
• IP Internet Protocol
• ATM Asynchronous Transfer Mode
• GPS Generalized Processor Sharing
• WFQ Weighted Fair Queuing
• the weights calculated for all of the input flows are added together, and the total available output bandwidth is divided amongst the input flows depending upon the weight of each flow as a fraction of the total weight.
• GPS could be applied to the MAC entity in UMTS, with the weighting for each input flow being determined (by the RRC entity) on the basis of certain RAB parameters, which are allocated to the corresponding RAB by the network.
• RAB parameter may equate to a Quality of Service (QoS) or Guaranteed rate allocated to a user for a particular network service.
• MAC entity logical channels in infinitely small blocks. This is not possible in UMTS, as UMTS relies upon Transport Format Combinations Sets (TFCSs) as the basic mechanism defining how much data can be sent in each TTI.
• TFCSs Transport Format Combinations Sets
• GPS is to be employed in UMTS, it is necessary to select the TFC (from the TFCS) which most closely matches the bandwidth allocated to an input flow by GPS.
• the result of this approach is that the actual amount of data sent for an input stream in a given frame either may fall below the optimized rate or may exceed that optimized rate. In the former case, a backlog of unsent data may build up for the input flow.
• MAC Media Access Control
• UMTS UMTS
• the method including the following steps for each frame of an output data flow: computing for each input flow to the MAC entity a fair share of the available output bandwidth of the MAC entity; selecting a Transport Format Combination (TFC) from a TFC Set (TFCS) on the basis of the bandwidth share computed for the input flows, where the TFC includes a Transport Format allocated to each input flow; and for each input flow, if the allocated TF results in a data transmission rate which is less than the determined fair distribution, adding the difference to a backlog counter for the input flow, where the value of the backlog counter(s) is taken into account when selecting a TFC for the subsequent frame of the output data flow.
• TFC Transport Format Combination
• TFCS TFC Set
• Embodiments of this scheme allow the TFC selection process for a subsequent frame to take into account any backlogs which exists for the input flows. The tendency is to adjust the selected TFC to reduce the backlogs. Such a backlog may exist due to the finite number of data transmission possibilities provided for by the TFCS.
• Nodes at which the method of this scheme may be employed include mobile stations (such as mobile telephones and communicator type devices) (or more generally UEs) and Radio
• RNCs Network Controllers
• the input flows to the MAC entity are provided by respective Radio Link Control (RLC) entities.
• RLC Radio Link Control
• each RLC entity provides buffering for the associated data flow.
• RRC Radio Resource Control
• the step of computing a fair share of resources for an input flow is carried out by a Radio Resource Control (RRC) entity.
• RRC Radio Resource Control
• the step of computing a fair share of resources for an input flow includes the step of determining the weighting given to that flow as a fraction of the sum of the weights given to all of the input flows.
• the fair share may then be determined by multiplying the total output bandwidth by the determined fraction.
• this step may involve using the Generalized Processor Sharing (GPS) mechanism.
• the weighting for a data flow may be defined by one or more Radio Access Bearer (RAB) parameters allocated to a RAB by the UMTS network, where the RAB is associated with each MAC input flow.
• RAB Radio Access Bearer
• the method further includes the step of adding the value of the backlog counter to the computed fair share for that flow and selecting a TFC on the basis of the resulting sums for all of the input flows.
• a node of a Universal Mobile Telecommunications System including: a Media Access Control (MAC) entity for receiving a plurality of input data flows; first processor means for computing for each input flow to the MAC entity a fair share of the available output bandwidth of the MAC entity and for selecting a Transport Format Combination (TFC), from a TFC Set (TFCS), on the basis of the bandwidth share computed for the input flows, where the TFC includes a Transport Format allocated to each input flow; second processor means for adding to a backlog counter associated with each input flow the difference between the data transmission rate for the flow resulting from the selected TFC and the determined fair share, if the data transmission rate is less than the determined fair share, where the first processor means is arranged to take into account the value of the backlog counters when selecting a TFC for the subsequent frame of the output data flow.
• MAC Media Access Control
• TFC Transport Format Combination
• TFCS TFC Set
• the first and second processor means are provided by a Radio Resource Control (RRC) entity.
• RRC Radio Resource Control
• a simplified UMTS layer 2 includes one Radio Resource Control (RRC) entity, a Medium Access Control (MAC) entity for each mobile station, and a Radio Link Control (RLC) entity for each Radio Access Bearer (RAB).
• RRC Radio Resource Control
• MAC Medium Access Control
• RLC Radio Link Control
• the MAC entity performs scheduling of outgoing data packets, while the RLC entities provide buffers for respective input flows.
• the RRC entity sets a limit on the maximum amount of data that can be transmitted from each flow by assigning a set of allowed Transport Format Combinations (TFC) to each MAC (referred to as a TFC Set or TFCS), but each MAC must independently decide how much data is transmitted from each flow by choosing the best available Transport Format Combination (TFC) from the TFCS.
• TFC Transport Format Combinations
• the flowchart 400 is a flow diagram of a method of allocating bandwidth resources to, for example, the input flow streams ofa MAC entity of the layer 2 of FIG 3.
• an exemplary method in accordance with the flowchart 400 may follow the following steps. First, input flows are received at RLCs and the data is buffered (step 405). Information on buffer fill levels is passed to the MAC entity (step 410). After the information on buffer fill levels is passed, the fair MAC bandwidth share for each input flow is computed (step 415). The computed fair share of each is then adjusted by adding the contents of an associated backlog counter to the respective computed fair share (step 420). Once the computed fair shares have been adjusted, a TFC is selected from the
• the RLC is next instructed to deliver packets to the MAC entity according to the selected TFC (step 430).
• the MAC entity may also schedule packets in accordance with the selected TFC (step 435).
• the traffic channels may be transported on the physical Channel(s) (step 440) .
• the backlog counters should be updated (step 445). The process may continue (via arrow 450) when new input flows are received at the RLCs, which buffer the data (at step 405).
• the MAC entity on a per Transmission Time Interval (TTI) basis, the optimal distribution of available bandwidth using the Generalized Processor Sharing (GPS) approach (See, e.g., the article by A. K. Parekh et al. referenced hereinabove.) and by keeping track of how far behind each flow is from the optimal bandwidth allocation using respective backlog counters.
• the available bandwidth is distributed to flows by using the standard GPS weights, which may be calculated by the RRC using the RAB parameters.
• the method may first calculate the GPS distribution for the input flows and add to the GPS values the current respective backlogs. This is performed once for each 10ms TTI and results in a fair transmission rate for each flow.
• this rate may not be optimal as it may happen that there is not enough data to be sent in all buffers.
• the fair GPS distribution is reduced so as to not exceed the current buffer fill level or the maximum allowed rate for any logical Channel.
• a two step rating process is then carried out.
• the set of fair rates computed for all of the input flows is compared against possible Transport Format Combinations (TFCs) in turn, with each TFC being scored according to how close it comes to sending out the optimal rate. In practice this is done by simply counting how much of the fair configuration a TFC fails to send (if a given TFC can send all packets at the fair rate, it is given a score of zero) and then considering only the TFCs which have the lowest scores. The closest match is chosen and used to determine the amount of packets sent from each queue. TFCs having an equal score are given a bonus score according to how many extra bits they can send
• the final selection is based on a two-level scoring: the TFC with the lowest score is taken. If there are several TFCs with an equal score, the one with the highest bonus score is chosen. This ensures that the rate for each TTI is maximized. Fairness is achieved by checking that if the chosen TFC does not give all flows at least their determined fair rate, the missing bits are added to a backlog counter of the corresponding flow and the selection is repeated for the next TTI. If any of the flows has nothing to transmit, the backlog is set to zero. This algorithm can be shown to provide bandwidth (and, under certain assumptions, delay bounds) that is close to that of GPS.
• int maxrate int i ; int tfc, tfci, qf, rate, trch; int tfc_to_use;
• FIG. 5 there is shown a portion of the second layer architecture depicted in Figure 3. More particularly, there is shown the MAC entity 320 of Figure 3 comprising a MAC-c entity 500, as described above, connected to a dedicated MAC-d entity 510, as likewise described above.
• Figure 5 further shows RLC entities 515, which receive data in the form of segments from respective RAB's and map the data onto corresponding logical channels 315. Each of the RLC ' s 515 is provided with a buffer 520 for buffering received data segments comprising PDU's.
• MAC-d entity 510 serves a single mobile station (not shown) and data transmitted by the MAC-d entity is directed through transport channel 325 to a dedicated physical Channel DPCH.
• the common MAC-c entity 500 provided with buffers 525 and connected to receive data, or more specifically PDU' s, from MAC-d entity 510 as well as from other MAC-d entities which are not shown, h accordance with the invention, it is desired to provide a flow control mechanism 530 between each of the dedicated MAC-d entities and the common MAC-c entity 500.
• the flow control 530 enables a number of different MAC-d entities which are respectively in an active data flow mode to share the available free space of MAC-c buffer 525.
• the flow control is designed to provide each of the active MAC-d entities with a "fair share" of the additional data flow capacity provided by the MAC-d buffer free space, that is to ensure that all active MAC-d entities are given a reasonable opportunity to use such buffer capacity to enhance their respective data flow rates.
• the available common transfer channel data rate is shared among all the active dedicated logical channels.
• the flow control is further designed to maintain the fill level of the MAC-c entity buffer at or close to a desired optimum fill level.
• data transmitted by MAC-c entity 500 is directed to a transport Channel FACH.
• flow control 530 coupled to regulate data flow into the MAC-c PDU buffers 525 from each of a number RLCs 515, each coupled to a different mobile station or other User Equipment 1-n.
• the flow control operates in accordance with a "round robin" or some other principle, that is, each of the MAC-d entities connected to a given MAC-c entity are enabled to transfer data thereto sequentially, or in turn, or by flow activity (greedy manner), hi this embodiment, credits are assigned to the respective MAC-d entities, in accordance with criteria described hereinafter in further detail.
• a MAC-d entity Upon receiving a credit, a MAC-d entity is entitled to transmit one packet data unit to the MAC-c buffer 525.
• MAC-c buffer 525 which is available for use by dedicated channels associated with MAC-d entities.
• the MAC-c buffer has an optimum level Q copt , which is related to delay and throughput requirements in buffer operation.
• the flow control 530 endeavors to maintain such level, using feedback information received from the MAC-d entities.
• the flow control also functions to keep the MAC-c buffer as low as possible, so that delays related to use of a common channel will be equally distributed among different MAC-d users. If the level of buffer 525 at a particular time is Q c , the available buffer space Q cdiff is equal to Q copt -
• the flow control 530 operates to share this space amongst MAC-d users by assigning equal numbers of credits to them, provided they have PDU's available for transmission.
• the flow control calculates the credit for each MAC-d entity from both
• the flow control establishes credit assignment criteria which is related to buffer level Q copt , as well to levels Q cmax and Q cun , also shown in Figure 7. These criteria are as follows: (1) If Q c , MAC-c buffer fill level, is less than Q cun , an infinite or unlimited credit is given to MAC-d entities. (2) If the current MAC-c buffer fill level Q c is greater than Q cun but less than Q copt , the difference (Q COpt -Q cun ) * s divided among active MAC-d entities. (3) If the current MAC-c buffer fill level Q c is greater than Q copt , no new credits are granted except initial credits. If the credits were previously set to 'unlimited' then they are cleared by sending ofa 'zero' credits to appropriate MAC-d entities.
• an active user is a dedicated channel service that is connected to a common channel, and has data in its RLC-d buffer.
• An active user changes to a passive user when its RLC-d buffer becomes empty.
• the algorithm provides fair sharing of the total available band width between active users which have available band widths.
• the algorithm also minimizes packet delay, which is of particular importance for users operating with small packets in situations when other users have packets of large size.
• hi overload situations the flow control algorithm isolates different data from each other and increases RLC buffer fill level only for dedicated channels with the highest rates. The RLC buffer fill levels of other channels with unchanged rates will not be increased.
• the algorithm supports working of a channel switching function that can identify and switch the overloaded channels toward dedicated transport channels.
• the algorithm stores the user identification where it stops with the calculations, and continues with the next user identification when the flow control algorithm is used again.
• Figure 8 shows steps 600, respectively numbered 1-18, which depict the sequential assignment of credits and corresponding transfer of data about with respect to several dedicated channels, respectively incorporating radio link controls RLC-1, RLC-2, and RLC-3.
• steps 1-12 displays a notation indicating the step number, and also certain count information in parentheses.
• the count information comprises the MAC-c buffer fill level Q c , the fill level Q d of a corresponding one of the dedicated channel buffers, and the available credit count at the conclusion of the step.
• Item 620 shows the notation for step 2, by way of illustration.
• the available data space Q cdiff in MAC-c buffer 525 is equivalent to 12 credits.
• assigning a credit to a dedicated channel enables the channel to transfer a specified amount of data, such as one PDU, to the MAC-c buffer.
• the channel of RLC-1 receives one credit.
• the available space in the MAC-c buffer decreases from 12 to 11, and one PDU, corresponding to the 1 credit, can be transferred from the RLC-1 buffer to the MAC-c buffer. Accordingly, the data contents of the RLC-1 buffer which initially equivalent to 2 credits, diminishes to a Q d count of 1.
• step 2 the RLC-2 channel has received 1 credit, the available Q c count has decreased to 10, and the count Q d of buffer RLC-2 has decreased to 3 from an initial count of 4.
• step 3 associated with the RLC-3 buffer.
• step 4 shows the next-following credit again assigned to the RLC-1 channel.
• the Q d count of the RLC-1 count goes to zero, indicating that the channel has no more PDU's available.
• step 5 directed to the RLC-2 channel, the next credit is assigned to the RLC-2 channel, as indicated in step 7. This is in accordance with criterion (2), set forth above.
• flow control 530 again operates in accordance with a round robin or with flow activity (greedy manner) credit based algorithm.
• MAC-c buffer 525 again used by dedicated channels.
• the Q optimum (Q copt ) dashed line in figure 9 represents the optimum level in regard to unwanted buffer overflow, delay variance and good throughput.
• the flow control endeavors to maintain the buffer at the Q cop , level by means of current buffer queue fill level (Q c) and queue maximum (Q cmax) threshold values, as well as by means of information pertaining to the active users routed to the MAC-c buffer.
• Q c current buffer queue fill level
• Q cmax queue maximum
• an active user is a dedicated channel service that is connected to a common channel and has data in its RLC-d buffer.
• An active user changes to a passive user when its RLC-d buffer becomes empty.
• T h is processing delay/handling delay
• T d is transmission delay
• R cmax is FACH transport channel maximum rate for this buffer.
• N mac . d is the number of active MAC-d entities and Q cmax is a buffer high level. Default value for Q cmax could be 2 * Q copJ .
• the flow control has an associated preprocessing function which can be triggered to run from an incoming PDU, a timer, or both.
• the preprocessor checks the credit status of users, the value of Q c and the number of active users of buffers. The flow control algorithm is not started if the Credit is greater than 0 or other predefined value.
• Figure 11 shows the relationship between Q c and Credits, in accordance with
• Equations (1) - (3) Dashed lines indicate an adjustment which is made to limit C to a maximum value.
• Packets from RLC-d buffers through MAC-d are first transmitted to MAC-c appropriate buffers and then to FACH transport channels.
• the MAC-d packets are transferred with Data Frames that also include RLC-d buffer fill level information, as indicated by path 700 in Figure 12.
• the MAC-c controls user data flow from MAC-d using Control Frames that include credits, i.e., the number of packets the user may transmit, represented in Figure 12 by path 710.
• the credits for the MAC-d user will be set to initial value by the MAC-c entity.
• MAC-c will send a Control Frame message with an Initial Credits parameter to the MAC-d user, shown by path 730.
• sending such message after receiving the last packet from a user increases transmission delay of the next-arriving packets, and also increases the number of Control Frame messages, as shown by Figure 12. hi order to achieve a smaller delay for the next packet from a user after the buffer thereof has become temporarily empty, as well to decrease the number of control messages, an Early Initial Credit granting arrangement is used.
• the flow control algorithm in the MAC-c shall add Initial credit to the calculated credit.
• an initial credit will be sent to the MAC-d in advance, and there will be no need to send any new credit parameter thereto after receiving the last packet.
• Figure 13 shows that by using the Control Frame of path 740 (Credits and Initial Credits) the additional Control Frame of path 730 in Figure 12 is eliminated.

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