KR20040014414A - Multiple Service Subflows within a Cable Modem Service Flow - Google Patents

Abstract

A method for dividing a primary network data flow into a plurality of subflows is disclosed. Each subflow is assigned a unique class or priority value for the service. Tokens are assigned to each of the subflows from the primary flow to regulate the transmission of data over the network. The regulation is made in such a way that the highest priority packets have a higher transmission priority.

Description

Multiple Service Subflows within a Cable Modem Service Flow

Internet access via telephone modems is available today at speeds up to 56kbps. A telephone-based modem modulates data signals for transmission over a voice bandwidth telephone network. In contrast, cable modems provide access to the Internet or other external networks through cable television systems. Cable television systems provide higher bandwidth than telephone systems and thus operate at higher data rates. The cable modem provides a connection between the user computer or other communication device and the cable system headend from which the external network access is possible, for example via a T1 transmission line. In a cable network, data transmitted from a network headend to a user or subscriber is referred to as downstream data, and data transmitted from a user to a network headend is referred to as upstream data.

An exemplary prior art bidirectional cable system is shown in block diagram form in FIG. 1. Prior art cable systems include headend equipment 101, hybrid fiber coaxial (HFC) cable plant 103, a plurality of cable modems 105, 106 (only two are shown), and corresponding communication links 116 and 117. And corresponding subscriber communication devices 107, 108 coupled to cable modems 105 and 106 via. Subscriber communication devices 107 and 108 may include, for example, a computer, a television, or a telephone. As will be appreciated by those skilled in the art, the headend equipment 101 may include a processor, router, broadband downstream transmitter, upstream receiver, splitter, combiner, subscriber database, network management station, dynamic host configuration protocol (DHCP), and Trivial file transfer protocol (TFTP) servers, call agents, media gateways, and billing systems. HFC cable plant 103 includes fiber optic cables, coaxial cables, fiber / coax nodes, amplifiers, filters, and taps, which are cable modems 105 from headend equipment 101 through shared downstream channels 110. And 106, or from the cable modems 105 and 106 to the headend equipment 101 via the shared upstream channel 112.

Downstream channel 110 and upstream channel 112 use respective transport protocols to communicate information. Typically, the modulation method (e.g., 64-ary QAM) used to convey information over the downstream channel 110 is a modulation (e.g., used to convey information over the upstream channel 112). Higher order than Differential Quaternary Phase Shift Keying (DQPSK) or 16-ary QAM], resulting in higher downstream transmission rate than upstream transmission. Cable systems whose upstream transmission rate is lower than the downstream transmission rate are typically referred to as "asymmetric" systems. Cable systems whose upstream transmission rate is substantially the same as the downstream transmission rate are called "symmetrical" systems.

In addition to the particular type of modulation used on each channel 110 and 112, the shared nature of each channel 110 and 112 brings about different protocol requirements. For example, because the downstream channel is shared, the downstream protocol includes addressing information, and each cable modem 105 and 106 monitors the downstream channel 110 to find the information packet addressed to it. . Information packets addressed to a particular cable modem 105 or 106 or attached communication device 107 or 108 or all cable modems 105 or 106 (or all attached communication devices 107 and 108) (e.g., Only broadcast messages are processed by the cable modems 105 and 106 and appropriately forwarded to the associated subscriber communication devices 107 and 108 (e.g., telephones, personal computers, or other terminal devices). Since upstream channel 112 is shared, an upstream channel access protocol is used to reduce the likelihood of collisions of communicated information coming from cable modems 105 and 106. There are a plurality of multiple access protocols for defining upstream channel access, including ALOHA, slotted-ALOHA, CDMA, TDMA collision detection TDMA, CSMA, and the like.

Some bidirectional cable systems adhere to and use the upstream and downstream channel protocols defined in the recently published DOCSIS version 1.0. The upstream protocol defined by the DOCSIS standard is a time-stamp whose timing is controlled by the headend equipment 101 (hereinafter referred to as "cable modem termination device (CMTS)") and transmitted over the downstream channel 110. Is a TDMA approach delivered to cable modems 105 and 106 via configured synchronization messages. Thus, in order for the upstream communication to be aligned and occur in a high quality manner, the time criteria within each cable modem 105 and 106 are such that the modems 105 and 106 transmit the information provided by the subscriber communication devices 107 and 108. Previously, it should be substantially synchronized with a similar time reference within the headend equipment 101. Otherwise, transmissions from one modem 105 may conflict with transmissions from another modem 106.

The headend equipment 101 is an external network, which is a packetized network such as a public switched telephone network (PSTN) or the Internet, through an appropriate communication link 119, such as a Fiber Distributed Data Interface (FDDI) link or a 100 baseT Ethernet link. 114) typically. Thus, the bidirectional cable system provides a communication connection between subscriber communication devices 107 and 108 and other similar devices not shown in FIG. 1 and an internet server, computer network, represented by external network 114.

Headend equipment 101 also receives program signals for broadcast to subscribers (via satellite downlink, terrestrial microwaves, or underground lines). Subscriber data is carried on the 6 MHz channel, which is the spectral size allocated to the cable television channel for broadcasting television signals to all subscribers. At the subscriber's location, program signals are received by the set top box (see FIG. 2) while downstream signals are received separately by the cable modems 105 and 106. The number of upstream and downstream channels in a given cable modem system is designed based on the service area, the number of users, the data rate promised for each user, and the available spectrum.

2 is a block diagram of cable system components at a subscriber or user's location with respect to communication device 108. In the subscriber zone, splitter 134 splits the incoming signal from cable system headend 101. The television program signal is displayed on the television 140 under the control of the set top box 138. The second output from splitter 134 provides a connection to cable modem 105. Downstream signals from the headend equipment 101 are provided to an RF (radio frequency) tuner 142, which is a frequency band assigned to the cable modem 105 during the startup operation or configuration phase of the modem. Are tuned to. As noted above, typically, the downstream channel uses QAM, which is demodulated in demodulator 144. The demodulated signal is input to the media access controller 146. Baseband data signals from the media access controller 146 are input to a data and control logic unit 148 that controls the overall operation of the cable modem 105 and further provides data control functions. The communication device 108 is connected to the data and control logic unit 148 of the cable modem 105 to receive data transmitted in the downstream direction and to transmit data in the upstream direction.

The upstream data eventually arrives and demodulates from the communication device 108 via the data and control logic unit 148, the media access controller 146, and the demodulator 150. Typically either DQPSK or 16-ary QAM modulation is used for upstream data. The choice of modulation type is disclosed in the configuration information provided to each cable modem 105. Upstream data passes through splitter 134 for transmission to headend 101 via hybrid fiber / coaxial cable plant 103. Eventually, the data arrives at the external network 114 as discussed in connection with FIG. 1.

The present invention relates generally to a communication system, and more particularly to a communication system in which a class of service data flow is divided into subflows.

1 is an electrical block diagram of a typical prior art bidirectional cable communication system.

2 is an electrical block diagram of the components of a bidirectional cable communication system within a subscriber area.

3 is a flow chart describing service class assignment and methodology in accordance with the present invention.

In one embodiment, the downstream channel uses 64 or 256 QAM, which can transfer data from 30 to 40 Mbps on a 6 MHz cable channel. The upstream channel uses QPSK or 16 QAM signaling with data rates from 320 Kbps to 10 Mbps available. Both upstream and downstream data rates are configured by the system operator. For example, the cable modem 105 used by a business user may be configured to send and receive information at relatively high data rates in both directions. Resident users, on the other hand, have a wider bandwidth (and higher data rate) in the downstream direction to receive data from the external network 114, while a cable modem (configured to be limited to lower speeds for upstream data transmission). 105). In yet another embodiment, the data rate assignment may vary from time to time (time-of-day sensitive).

However, it should be emphasized that the cable modem operates at a given symbol rate (or data rate) using a predefined modulation type. The priority of individual data packets does not affect the instrumented upstream data rate or bandwidth. All modems transmitting on the upstream channel use the same symbol rate and modulation type. However, the actual amount of bandwidth used by the cable modem may be limited by the software controlling the modem. As noted above, business users may be configured to use 2 Mbps in the upstream direction, while residential users are limited to 1 Mbps. However, cable modems that support business and residential users may operate at the highest system rate, such as 10 Mbps. The priority of individual data packets does not affect the configured symbol rate and modulation type.

When power is supplied to the cable modem 105 or 107, a connection to the headend equipment 101 is created via the hybrid fiber / coaxial cable plant 103. This connection employs Internet Protocol (IP), so that data in IP format received by the headend device 101 from the Internet or the World Wide Web (referred to as external network 114) will be forwarded down to the cable modem 105 or 106. Can be. During the cable modem initialization procedure, the modem obtains an IP address, other IP related operating parameters, and a server address from the modem configuration file from the DHCP server. Many such DHCP servers are available on the network, and the cable modem 105 or 107 simply broadcasts to all DHCP servers. Any DHCP server responds to the broadcast request and can provide the necessary information. The configuration file contains various configuration parameters such as access control information, downstream and upstream channel assignments, security configuration information, and a Trivial File Transfer Protocol (TFTP) server from which modem operation software can be downloaded.

Packet-switched networks, such as the cable system network shown in FIG. 1, typically operate on a best-effort service delivery basis. Unfortunately, Internet protocols with a connection-less best forwarding model do not guarantee sequential, timely delivery of packets or provide them at all. All traffic has the same priority and the same opportunity to be delivered in a timely manner. When the network is congested, all traffic is delayed or missed with the same probability. Among the many types of applications that use the network are mission-critical applications that interface with the World Wide Web, online business-critical applications, and multimedia-based applications (desktop video conferencing or Internet protocols). Used voice conferences). Some network applications are sensitive to bandwidth and delay, requiring a unique class of service requirements on the network. Some applications require real time delivery to the receiving site, while others tolerate some delay. To use real-time applications such as voice over IP (VOIP) or video conferencing using Internet protocols, acceptable levels of quality must be ensured, including bandwidth latency and jitter requirements, and real-time traffic can be The manner of allowing coexistence with data traffic must be satisfied. The adoption of the class of service concept allows network managers to ensure that mission-critical and real-time application traffic is protected from other bandwidth requesting applications, while less important applications use the network in a reasonable manner. To achieve this goal, the network class policy of the service aligns network resources with the purpose of the network user. Without these class of service parameters, network resources may not be used for more important applications and may be quickly exhausted by less important applications. Implementation of the class of service feature enables network devices to recognize and deliver high priority traffic in a predictable manner. When network congestion occurs, the class of service mechanism drops or delays low priority traffic to deliver high priority traffic.

Therefore, there is a need to increase the probability that high priority upstream data reaches its destination in a timely manner by developing a mechanism for establishing and implementing a class of service scheme in a packet-switched cable modem.

DETAILED DESCRIPTION The present invention will be more readily understood with reference to the accompanying drawings and preferred embodiments thereof.

Before describing in detail the specific method and apparatus for assigning and implementing service priority classes for data flows in a two-way cable communication system, it is to be understood that the present invention relates primarily to novel combinations of steps and apparatus related thereto. Accordingly, the hardware components and method steps are represented by conventional components in the drawings, and are not described in the prior art so as not to obscure the disclosure of structural details that will be readily appreciated by those skilled in the art. As regards, only parts relevant to the present invention will be described in detail.

The DOCSIS 1.0 protocol allows cable modems, such as cable modems 105 and 106, to be configured by multiple service flows for carrying data in the upstream direction. However, it is not possible for cable operators to take advantage of this feature, because there is no mechanism in this industry to classify data onto a service flow rather than a primary service flow. Thus, all data flows on the primary upstream data flow. The DOCSIS 1.0 standard includes a classifier feature, which can be activated through configuration settings to instruct the cable modem to send certain packets on a particular service flow. For example, this classifier can be configured to place all voice packets on subflow number 2 while all other data packets are sent on the primary service flow.

According to the present invention, the primary service flow is divided into a plurality of subflows. Each of the plurality of service flows is assigned a service class, which is a relative class that determines the priority for transmitting queued data on a subflow from cable modems 105 and 106 to headend equipment 101. Or a preferential method. Higher priority data is transmitted prior to lower priority data. For example, voice over Internet protocol phone calls must be delivered in near real time to avoid delays and interruption of conversations. Delays above about 300 milliseconds were found to be usually unacceptable to the conversation party. Thus, data representing voice over the Internet protocol will be assigned a high priority class of service. Conversely, text data will be assigned a lower priority class of service.

Service flow parameters (eg transmission priority) for a given modem are disclosed in the configuration file. Subflow parameters are derived from service flow parameters, as described below.

In one embodiment of the present invention, the token bucket method manages upstream subflows carrying data packets to ensure that packets are sent to cable modems 105 and 106 according to their assigned service priority. Each token bucket has three elements. That is, burst size, average speed, and time interval. The average speed specifies how much data can be transmitted per unit time defined by the time interval. The burst size (specified in bits) specifies the amount of data that can be transmitted in one burst that avoids creating network scheduling conflicts. An exemplary token bucket algorithm with a token bucket size of 5 Mb has an average bit rate of 1 Mbps and a time interval of 1 second. The bucket has a maximum capacity of 5 megabits. When the bucket is full (i.e. including 5 megabits of tokens) no more tokens can be added.

Each token indicates that the cable modem allows sending a predetermined number of bits to the headend equipment 101. To send a packet, the cable modem removes the same number of tokens from the bucket as the packet size. If there is not enough token in the bucket to send the packet, the packet waits until the bucket has enough tokens or waits for the packet to be discarded. Therefore, the largest burst or packet the cable modem can ever send into the network is roughly proportional to the bucket capacity.

Further, according to the present invention, packet transmission from cable modems 105 and 106 is controlled by a plurality of buckets, each token bucket being associated with a particular class of service (or subflow) for each cable modem. . Tokens from the primary flow bucket are distributed into a plurality of subflow buckets. As mentioned above, the tokens are periodically replenished in the primary bucket. Each of the subflow buckets is replenished from the primary token bucket. In fact, there are a number of algorithms for replenishing subflow buckets. For example, the primary bucket can be controlled to assign a certain percentage of the received tokens to each of the subflow buckets. For example, the highest priority subflow bucket (bucket 1) may receive 50% of the tokens in the primary bucket over a period of time. The lowest priority subflow bucket (bucket 3) may receive 15% of the primary bucket tokens over the same time interval. Finally, an intermediate priority bucket (bucket 2) may receive 35% of the primary bucket token over the same time interval. Alternatively, when tokens enter the primary bucket, they can be directed to bucket 1 (the highest priority subflow bucket) until bucket 1 is full. This ensures that high priority packets are more likely to receive tokens and therefore more likely to be transmitted. The tokens received later are then directed to bucket 2 until bucket 2 is full (assuming bucket 1 is still full), and finally, the tokens reached are buckets if both of these buckets are full. Headed to 3. Those skilled in the art will appreciate that there are many ways to control the replenishment procedure for both the primary bucket and the plurality of subflow buckets.

An algorithm for recharging the primary bucket and the plurality of subflow buckets may be hard-coded in the cable modems 105 and 106. Alternatively, this algorithm is initiated in the configuration file via vendor-specific TLV parameters and downloaded to the cable modems 105 and 106 during the startup phase. Using a configuration file as a control mechanism allows the cable system operator to change the weighting algorithm for multiple subflows. The cable system operator can also manage each of the cable modems 105 and 106 using network management application software operating under the Simple Network Management Protocol (SNMP). SNMP allows network administrators to modify network parameters by modifying network objects in network devices. For example, the bucket replenishment process can be modified in real time by SNMP based commands.

In one embodiment, each data packet is assigned to one of the subflows via the information contained in the packet header. For example, the packet header identifies the packet as IP data, LLC data, or TCP / UDP data. Based on the data type, data packets are assigned to subflows of appropriate priority. Correlation between data type and priority subflows is initiated in the configuration file or hard-coded in the modem. Alternatively, to identify the data type, the modem may examine the data file for a unique data signature. VOIP data has this unique signature. In another embodiment, the modem may identify the data type and assign a subflow by examining the embedded cable modem software application that generated the packet. For example, a network management application generates SNMP packets. Typically, SNMP packets are assigned a higher priority than data packets.

Instead of the modem checking the header to assign the subflow, the application software generating the packet may assign the subflow and provide that information as a parameter. In another example, a modem may include and packetize a VOIP software application that digitizes audio tones from a telephone. In this example, there is no need to inspect the packet to determine the priority of the packets, because the modem operating software may determine that the packets came from a software application running on voice data. Typically, these packets will be assigned to a high priority subflow.

3 is a software flow diagram illustrating the present invention. Modem 105 or 106 is activated in step 180 to download the configuration file in step 182. In an embodiment of the present invention where a plurality of subflow and bucket replenishment algorithm details are identified in a configuration file, this information is derived from the configuration file and provided to modem operation software that controls replenishment procedures and subflow assignments. In step 186, the packet ready to be sent is examined to determine its associated class of service. As described in other embodiments, the grade of service may be determined by other methods than header checking. In any case, once the grade of service of the packet is determined, processing moves to step 188 where the subflow (or grade of service) bucket associated with this packet is checked. If enough tokens are available in the bucket, processing moves from decision step 190 to step 192 where an appropriate number of tokens are assigned to the packet. In step 194, a packet is sent. The process then returns to step 186 to check for the next packet in the queue. If a sufficient number of tokens are not available at decision step 190, this packet cannot be sent and remains in the queue. The process returns from decision step 190 to step 186 to check the next queued packet. When the subflow token bucket associated with the delayed packet is replenished, this packet will be sent. As noted above, the replenishment procedure periodically places tokens in each subflow bucket. This is not shown in FIG. 3. In one embodiment, the replenishment procedure proceeds as follows. Let R / T be the average speed of the algorithm. Here, R is measured in bits and T is measured in seconds. If R is 1 million bits and T is 1 second, then 1 million bits are added to the bucket every second. Thus, the average speed is 1 Mbps.

As noted above, the cable system operator can modify the operation of the subflow assignment procedure by sending network management control information to the cable modems 105 and 106 (using the SNMP protocol). This arbitrary management information acts as an interrupt to the flowchart of FIG.

Although the invention has been described with reference to its preferred embodiments, those skilled in the art will understand that various modifications may be made and components may be replaced by other equivalent elements without departing from the scope of the invention. In addition, modifications may be made to suit a particular situation without departing from the spirit of the invention. Accordingly, the invention is not limited to the specific embodiments disclosed herein, but includes all embodiments falling within the scope of the appended claims.

Claims (18)

A method for managing packet transmission in a network having a primary service flow including a plurality of network devices for transmitting and receiving packets, the method comprising: Dividing the primary service flow into a plurality of subflows; Assigning priority to each of the plurality of subflows; Assigning priority to each packet; And Transmitting the packet on the subflow associated with the assigned priority. 2. The method of claim 1 wherein each priority is associated with a class of service. 3. The method of claim 2, wherein each class of service is associated with a data transmission priority and each packet is transmitted according to the class of service assigned to the packet. 2. The method of claim 1 wherein the priority is associated with a predetermined transmission bit rate. 2. The packet transfer management of claim 1 wherein each packet is enqueued prior to transmission and said priority is associated with a predetermined maximum time between arrival of said packet in said queue and transmission of said packet on said associated subflow. Way. 2. The method of claim 1, wherein one of the hierarchical network transmission parameters is associated with each priority. The packet transmission of claim 1, wherein the transmission of one packet in each subflow of the plurality of subflows requires assigning a plurality of tokens to the packet, the number of tokens being based on the length of the packet. How to manage. 2. The method of claim 1, wherein a plurality of tokens are assigned to the primary service flow, and the tokens are sequentially assigned among the plurality of subflows. 10. The method of claim 8, wherein the tokens are allocated between the plurality of subflows based on the number of unused tokens in the subflow. 9. The method of claim 8, wherein the tokens are allocated between the plurality of subflows based on a priority associated with the subflows. 9. The method of claim 8, wherein when tokens are assigned to the primary service flow, the tokens are distributed in turn to the plurality of subflows, and the highest priority subflow allocates a predetermined percentage of tokens from the primary service flow. And each lower priority subflow is correspondingly assigned a smaller rate. 10. The system of claim 8, wherein the primary service flow has a token bucket associated with it and each subflow has a token bucket associated with it, the burst size defining a maximum amount of data that can be transmitted within each burst. The average rate defining the maximum amount of data that can be transmitted per defined time interval is defined for each token bucket. 13. The method according to claim 12, wherein tokens of the primary service flow token bucket are replenished periodically and each subflow token bucket is replenished from the primary service flow token bucket. 2. The method of claim 1 wherein the priority of each packet is initiated in the packet header. The method of claim 1, wherein the priority of each packet is determined based on a software application that generated the packet. 2. The method of claim 1 wherein the network device comprises a cable modem. In manufactured goods, A computer usable medium having a computer readable program code for managing packet transmission in a network having a primary service flow and comprising a plurality of network devices for transmitting and receiving a packet, the medium comprising: Computer readable program code configured to cause a computer to divide the primary service flow into a plurality of subflows; Computer readable program code configured to cause a computer to assign priority to each of the plurality of subflows; Computer readable program code configured to cause a computer to assign priority to each packet; And Computer readable program code configured to cause a computer to transmit the packet on the subflow associated with the assigned priority. An apparatus for managing the packet transmission within each of a plurality of network devices that transmit and receive packets over a network having a primary service flow, the apparatus comprising: A first module for separating the primary service flow into a plurality of subflows; A second module for assigning priority to each of the plurality of subflows; A third module for assigning priority to each packet; And And a fourth module for transmitting the packet on the subflow associated with the assigned priority.