Abstract:
A system and method is provided for scheduling transmissions from a plurality of services operating over a widely distributed communications network. A headend communications device (such as a cable modem termination system) arbitrates bandwidth among a plurality of cable modems configurable for bi-directional communications. The headend grants a bandwidth region to a specified cable modem or assigns contention regions for a group of cable modems. Each cable modem contains a local scheduler that sends requests for bandwidth according to local policies or rules. Upon receipt of a grant from the headend, the local scheduler selects packets to be transmitted to best serve the needs of the services associated with the cable modem. Accordingly, a service requesting bandwidth may not be the service utilizing the grant corresponding to bandwidth request. Nonetheless, the local scheduler manages bandwidth allocation among its local services such that all requesting services eventually receive bandwidth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/427,792, entitled “System and Method for Multiplexing Data from Multiple Sources,” filed Oct. 27, 1999, by Limb et al., (still pending), which is incorporated by reference herein in its entirety. This application claims the benefit of the following United States provisional applications: 
     U.S. Patent Application No. 60/182,470, entitled “Intelligent Silence Suppression,” filed Feb. 15, 2000, by Gummalla et al., (abandoned), which is incorporated by reference herein in its entirety; 
     U.S. Patent Application No. 60/247,188, entitled “A Local Scheduling Mechanism for Cable Modems,” filed Nov. 9, 2000, by Sala et al., (abandoned), which is incorporated by reference herein in its entirety; 
     U.S. Patent Application No. 60/254,415, entitled “A Local Scheduling Mechanism for Cable Modems,” filed Dec. 8, 2000, by Sala et al. (abandoned), which is incorporated by reference herein in its entirety; 
     U.S. Patent Application No. 60/262,201, entitled “Voice Scheduling Algorithms,” filed Jan. 17, 2001, by Sala et al. (abandoned), which is incorporated by reference herein in its entirety; and 
     U.S. Patent Application No. 60/262,203, entitled “Concatenation of Requests at CMTS,” filed Jan. 17, 2001, by Sala et al. (abandoned), which is incorporated by reference herein in its entirety. 
    
    
     The following United States utility patent applications have a common assignee and contain some common disclosure: 
     “Voice Architecture for Transmission Over a Shared, Contention Based Medium,” U.S. patent application Ser. No. 09/785,020, by Gummalla et al., filed Feb. 15, 2001, which is incorporated by reference herein in its entirety; 
     “System and Method for Suppressing Silence for Support in Voice Traffic over an Asynchronous Communication Medium,” U.S. patent application Ser. No. 09/783,405, by Gummalla et al., filed Feb. 15, 2001, which is incorporated by reference herein in its entirety; 
     “Cable Modem System and Method for Specialized Data Transfer,” U.S. patent application Ser. No. 09/783,403, by Bunn et al., filed Feb. 15, 2001, which is incorporated by reference herein in its entirety; and 
     “System and Method for Combining Requests for Data Bandwidth by a Data Provider for Transmission of Data Over an Asynchronous Communication Medium,” U.S. patent application Ser. No. 09/783,311, by Gummalla et al., filed Feb. 15, 2001, which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to controlling network transmissions. More particularly, the present invention relates to scheduling transmissions from multiple clients in a network environment. 
     2. Background Art 
     With the advent of the Internet, it has become more commonplace to develop vast communications networks to readily exchange information over remote areas. As modern technology continues to evolve to create new services to be provided over communications media, a greater demand has been generated for bandwidth and improved quality of services. For example, television broadcasts historically involved one-way communication from a broadcast transmitter to a viewer&#39;s home. As interactive or personal television services continue to grow, communications media used to support one-way communications must now contend with an increased demand for bi-directional communications. 
     In a conventional communications network, a communications device (such as a modem) would request bandwidth from a headend prior to transmitting data to its destination. The headend would allocate bandwidth to the cable modem based on availability and competing demands from other modems. The allocation of bandwidth is typically granted to the requesting modem in a MAP. The cable modem would be required to follow the instructions specified in the MAP, and use the grant for the service specified in the MAP. 
     Problems arise when the service specified in the MAP is later determined to no longer require the bandwidth, or require more bandwidth than originally requested. Another problem can occur if another service of equal or higher priority should require immediate bandwidth shortly after the headend&#39;s granting a lower-priority service&#39;s request bandwidth. The cable modem may not be able to use the granted bandwidth to transmit data from the higher priority service, because the grant would be restricted to the lower priority service. For example, a DOCSIS-compliant network system specifies that a cable modem must accept decisions made during the requesting phase. 
     One mechanism that can be implemented to reduce latency would be to utilize piggyback requests for bandwidth. Piggyback requests can be very effective if a cable modem is operating in a contention mode, where the modem transmit packets without a specified grant. Transmitting a signal during a contention mode increases the likelihood of the packets colliding, getting loss or becoming corrupted. 
     However, the conventional way of piggybacking requests is to use variable sized headers. The header can be extended to incorporate the piggyback request when there exist a need to send one. This is a common practice in a DOCSIS-compliant environment. This approach is more effective if the header is very small and/or the size of the request message is also small. Otherwise, piggybacking requests can add excessive packet overhead that require more bandwidth or may cause packet latency. 
     Consequently, a system and method are needed to solve the above-identified problems and provide a simple, efficient and cost-effective way to schedule communications in an classify packets in a dynamic environment. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a system and method for scheduling transmissions from a plurality of services operating over a widely distributed communications network. In an embodiment, a headend communications device (such as a cable modem termination system) functions as a arbitrator of bandwidth among a plurality of cable modem configurable for bi-directional communications. The headend grants a bandwidth region to a specified cable modem or assigns contention regions for a group of cable modems. 
     Each cable modem contains a local scheduler that sends requests for bandwidth according to local policies or rules. Upon receipt of a grant from the headend, the local scheduler selects packets to be transmitted to best serve the needs of the services associated with the cable modem. Accordingly, a service requesting bandwidth may not be the service utilizing the grant corresponding to bandwidth request. Nonetheless, the local scheduler manages bandwidth allocation among its local services such that all requesting services eventually receive bandwidth. 
     In an embodiment, the cable modem contains multiple priority queues for collected packets from different services. The local scheduler is programmable to transmit packets from the priority queues based on the actual priority of the associated service. For example, local rules may specify that voice telephony services have a higher priority than video conferencing. 
     In an embodiment, independent piggybacking is used to request additional bandwidth. The present invention allows single piggybacking, multiple piggybacking and cross-piggybacking. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. 
         FIG. 1  illustrates a data traffic management system according to an embodiment of the present invention. 
         FIG. 2  illustrates an operational flow diagram for the steps involved in scheduling communications according to an embodiment of the present invention. 
         FIG. 3  illustrates a block diagram of an example computer system useful for implementing the present invention. 
         FIGS. 4   a  and  4   b  illustrate an operational flow diagram for the operating states of a cable modem. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Table of Contents 
     
         
         I. Data Traffic Management System Overview 
         II. Cable Modem Scheduling 
         III. Piggybacking Bandwidth Requests 
         IV. Conclusion
 
I. Data Traffic Management System Overview
 
       
    
       FIG. 1  illustrates data traffic management system  100  according to an embodiment of the present invention. System  100  is preferably, but not necessarily, of the type described in U.S. Patent Ser. No. 60,247,188, entitled “A Local Scheduling Mechanism for Cable Modems,” filed Nov. 9, 2000, by Sala et al., (still pending), which is incorporated by reference herein in its entirety. 
     System  100  includes a headend or cable modem termination system (CMTS)  102  that exchanges data with one or more cable modems  104  over a communications interface  110 , which includes wired or wireless local area networks (LAN) or wide area networks (WAN), such as an organization&#39;s intranet, local internets, the global-based Internet (including the World Wide Web (WWW), private enterprise networks, or the like. Communications interface  110  includes wired, wireless or both, transmission media, including satellite, terrestrial (fiber optic, copper, coaxial and the like), radio, microwave and any other form or method of transmission. In an embodiment, CMTS  102  and cable modem  104  can be integrated to support protocols, such as, Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Real Time Transport Protocol (RTP), Resource Reservation Protocol (RSVP), or the like. 
     One or more downstream channels carry information (such as, television signals, IP data packets, control messages in MPEG format) from CMTS  102  to the plurality cable modems  104 . Similarly, one or more upstream channels carry bursts of packets from the cable modems  104  to CMTS  102 . In an embodiment, the bursts are assigned or allocated by mini-slots prior to upstream transmissions. In another embodiment, the bursts are quantified and apportioned by bits, bytes, mini-ticks (such as 2.5 μm per click) or like metrics for apportioning bandwidth regions. The burst includes bandwidth requests from cable modems  104  and transmissions of data from the corresponding services, as discussed in greater detail below. 
     CMTS  102  includes an upstream scheduler  106  that arbitrates bandwidth requirements among multiple cable modems  104 . Map builder  108  also is included within CMTS  102  to transmit a MAP containing upstream slot specifications and grant specifications to cable modems  104 . In an embodiment, MAPs are introduced into the MPEG transport stream of downstream communication as control messages. 
     Bursts from cable modems  104  are received by burst demultiplexer  122 , which forms the physical layer interface between CMTS  102  and the upstream channel from communications interface  110 . Burst demultiplexer  122  sends bandwidth request to request queue  124  and other packets to upper layer  126 , which forwards the packet to another device or application, such as a web browser, another cable modem  104 , or other data receiver. Packets from these other data receivers are collected by output queue  128  for external use. 
     A contention slot allocator (CSA)  130  specifies which areas in an upstream channel are to be used as assigned bandwidth regions for grants and contention transmissions. In an embodiment, if no requests are resident in request queue  124 , the bandwidth region is allocated to contention transmissions. In an embodiment, a piggyback probability metric is sent from request queue  124  to CSA  130  to aid CSA  130  in determining the percentage of bandwidth to allocate for grants and contention transmissions. 
     The state of request queue  124  is sent to call admission controller (CAC)  132  that decides whether to admit more traffic into system  100 . In an embodiment CAC  132  is operable to process voice data and generate a call admission signal if a call is accepted. The call admission signal is sent downstream to the cable modem  104  that is requesting a call admission. However CAC  132  is not limited for use with voice data. CAC  132  can support other forms of media and multimedia. CAC  132  also sends the parameters for establishing queues within upstream scheduler  106 , and upstream scheduler  106  notifies CAC  132  after the queues have been established. Upstream scheduler  106  also received information from CSA  130  representative of the distribution of contention bandwidth regions or contention mini-slots (CMS). Based on information received from CAC  132 , CSA  130  and a collision resolution algorithm device (CRA)  138 , upstream scheduler  106  specifies the bandwidth regions for grants and contention requests. 
     Collision detector  136  monitors contention regions in the upstream channels on a continuous basis to detect a collision immediately if a collision occurs. Collision detector  136  sends a collision/no collision (C/NC) signal to CRA  138 , which uses the C/NC signal to adjust the CRA parameters. This allows the C/NC signal and an acknowledgment/no acknowledgment message to be sent downstream to enable cable modem  104  to resent the collided request. 
     Each cable modem  104  hosts one or more services to a subscriber. The services (typically identified by a service identification or SID) include telephony, television broadcasts, internet communications (e.g., WWW), facsimile, file data transfer, electronic mailing services (email), video conferencing, live or time-delayed feeds (such as, speeches, debates, presentations, news reports, sporting events, concerts, etc.), and the like. Hence, the data exchanged between CMTS  102  and cable modems  104  includes text, video, audio, voice, graphics, other media or a combination thereof (i.e., multimedia). 
     Cable modem  104  includes an output queue  112 , CM scheduler  114  and burst multiplexer  114 . Each service provided by cable modem  104  is mapped to one or more priority queues (not shown) within output queue  112 . CM scheduler  114  is responsible for deciding the order in which packets are sent, and for controlling and balancing the request/grant loop process for all services. At the appropriate time, CM scheduler  114  directs packets to be sent to burst multiplexer  116 , where the packets are multiplexed into a burst. 
     MAP messages from CMTS  102  are recovered with other messages by a demultiplexer  142 . Grants in the MAP messages containing the slot structure and grants for the requesting cable modem  104  are separated and sent to CM scheduler  114  to control the allocation of packets to the granted bandwidth regions. The C/NC signal transmitted downstream and the CRA parameter derived from a control message are sent downstream and used by the downstream CRA  144  to adopt the parameters. CRA  144  sends the count of contention regions to CM scheduler  114 . These counts corresponds to the number of priority CMSs the cable model  104  must wait before it can transmit a request in a contention bandwidth region of the same priority. 
     Input queue  150  stores data received from the upstream until it is ready to be processed by the services. Upper layer  148  receives packets from the services and forwards them to output queue  112 . 
     II. Cable Modem Scheduling 
     Referring to  FIG. 2 , flowchart  200  represents the general operational flow of an embodiment of the present invention. More specifically, flowchart  200  shows an example of a control flow for scheduling data transmissions from cable modem  104  over communication infrastructure  110 . 
     Referring to  FIG. 2 , the control flow of flowchart  200  begins at step  201  and passes immediately to step  204 . At step  204 , output queue  112  receives a data packet from a service (e.g., telephony, cable, and the like) and stores the packet within the appropriate priority queue (not shown). Output queue  112  notifies CM scheduler  114  of its queue state on a periodically scheduled basis. In an embodiment, output queue  112  transmits its queue state each time it is modified. 
     At step  208 , upon notification from output queue  112 , CM scheduler  114  decides whether to send a request message for bandwidth to CMTS  102 , based on internal policies or rules. CMTS  102  prepares a grant specification to allocate bandwidth according to the size specified in the bandwidth request. The grant specification is transmitted to the requesting cable modem  104 . 
     At step  212 , CM scheduler  114  receives the grant specification from CMTS  102 , and at step  216 , CM scheduler  114  evaluates the needs of the service(s) being provided by cable modem  104 . In an embodiment, CM scheduler  114  evaluates the needs by considering the current queue state of the priority queues for each service. The current queue state can be evaluated by measuring the quantity of packets, bandwidth size, byte size, or the like. In an embodiment, CM scheduler  114  evaluates the needs of the service(s) by balancing throughput requirements versus latency. For example, it may become necessary to interrupt or fragment a transmission of text data to allow a voice transmission since voice communication require a lower tolerance for delay. 
     At step  220 , CM scheduler  114  determines which packets to send, based on the needs assessment performed at step  212 . Therefore, CM scheduler  114  is not required to use a grant in the same order that the corresponding requests were sent. CM scheduler  114  functions as a bandwidth manager that decides how to use the received grants according to the current needs of an active service. Since the needs of a service can change from the time of requesting a grant, CM scheduler  114  is programmable to assign a particular granted region (or portion thereof) to a different service than the one specified in the grant specification. 
     In an embodiment, CM scheduler  114  is priority based and will empty the priority queue for a higher-priority service before drawing data from the priority queue for a lower-priority service. For example, a higher-priority service (such as, telephony) and a lower-priority service (such a, web browsing) can request bandwidth from CMTS  102 . The flexible use of grants provided by cable modem  104  allows the higher-priority service (i.e., telephony) to borrow a first arriving lower-priority grant if the grant arrives earlier than its own grant. The lower-priority service (i.e., web browsing) would be permitted to utilize the bandwidth granted to the higher-priority, unless another higher-priority service is judged to require the grant. 
     In an embodiment, each service is registered as being a borrower, lender, both or none. As a borrower, the service is permitted to transmit data in a slot granted to another service. As a lender, the service is permitted to allow another service to transmit data over a slot granted to the lender. If registered as none, the service is not permitted to lend or borrow grants. Finally, as both, the service operates as a lender and borrower. 
     Thus, cable modem  104  is a flexible modem. In other words, CM scheduler  114  is configurable to overwrite a centralized CMTS scheduling decision in a seamless manner, such that the overwriting is virtually undetectable by CMTS  102  or the subscriber receiving the service. As described above, conventional systems (e.g., a DOCSIS-compliant system) must follow the instructions given in a grant. However, CM scheduler  114  decides which priority queues to transmit at the time the data is sent, instead of maintaining the decisions made at the requesting phase. Accordingly, CM scheduler  114  is programmable to change decisions at any time ranging from when CM scheduler  114  first sends a request until it transmits the actual information. 
     Nonetheless, the grant slots must be scheduled such that CMTS  102  detects a matching between the amount of data requested from a service and the actual amount of data the service is transmitting. In other words, CM scheduler  104  must balance the request/grant loop for each individual service. Additionally, each service must request bandwidth even if it has nothing to send in queue  112  but has used the grants apportioned to other services. As a result, the present invention guarantees that a grant for the other services will be available at some future point in time. Moreover, an advantage of the present invention is that cable modem  104  can reduce the latency of higher-priority services, which manifests a substantial improvement in quality of service. Another advantage of the present invention is that cable modem  104  can operate with more services than the ones that CMTS  102  may have recognized at a given point in time. This is a transient advantage because, as discussed, cable modem  104  permits a borrowing service to used the grant of a lending service, only if a bandwidth request will be transmitted for the borrowing service. 
     Referring again to  FIG. 2 , after CM scheduler  114  has selected the packets to be transmitted, the control flow passes to step  224 , where burst multiplexer  116  formats the data packets and transmits a burst to CMTS  102 . After the burst has been transmitted, the control flow ends as indicated by step  295 . 
     III. Piggybacking Bandwidth Requests 
     Referring back to  FIG. 2 , at step  208 , CM scheduler  114  transmits bandwidth requests in either contention or piggyback mode. As discussed above, any request transmitted in contention mode bares the risk of being corrupted or loss due to collision. 
     Piggyback mode can be used to reduce the load of requests in the contention channel. In an embodiment, CM scheduler  114  prepares a piggyback request message that is formatted to have the highest priority for transmissions. Convention piggybacking requests are included as part of an extended header of another message. However, the piggyback request messages of the present invention are separate messages that are transmitted in a contention channel or a reservation channel without making a previous reservation. As used herein, traditional piggybacking is referred to as being piggyback requests in extended headers and independent piggybacking is referred to as being piggyback requests that are sent as separate messages. 
     Since concatenating messages typically do not introduce any additional overhead, the efficiency of independent piggybacking is comparable to the efficiency gained by using traditional piggybacking for systems with smaller header sizes. For example, an implicit convention for voice packets is the specification of very small headers. An advantage of independent piggybacking is that the piggyback request message can be easily sent anywhere in a burst (i.e., between packets) without imposing any processing delays on CMTS  102 , in particularly in cases where headers cannot be easily extended. 
     As discussed with reference to step  220  as shown in  FIG. 2 , CM scheduler  114  has the flexibility to use grant slots to optimize throughput and reduce latency. As such, a piggyback request message can be transmitted at anytime upon receipt of a grant specification or in contention mini-slots. The piggyback request message can be inserted in a burst of voice packets or other data packets (i.e., text, graphics). In an embodiment, CM scheduler  114  uses cross-piggybacking to combine a piggyback request message for one service (i.e., primary piggyback) with a piggyback request messages from one or more other services (i.e., secondary piggyback(s)). Although secondary piggybacks are generally requests from other services, secondary piggybacks can also be from the same service. For example, a service may request more bandwidth than the maximum request size imposed by system  100 . In addition, CM scheduler  114  may decide to send another request before it receives a grant for a previously transmitted request. Therefore, a cable modem  104  can have more than one piggyback request outstanding in CMTS  102 , at any given time. 
       FIGS. 4   a – 4   b  illustrate an operational flow for requesting and granting bandwidth according to an embodiment of the present invention. Referring to  FIG. 4   a,  the operational states of cable  104  are shown as being in either an open state  402  or closed state  404 . Open state  402  indicates that cable modem  104  has one or more requests outstanding. Closed state  404  indicates that cable modem  104  has no outstanding requests. 
       FIG. 4   b  shows the operational flow of the various queue states for cable modem  104 , according to an embodiment of the present invention. More specifically, when cable modem  104  is operating in open state  402 , cable modem  104  can operate in one or more of four queues states, namely requesting state  406 , waiting state  408 , acknowledge state  409  and close state  410 . Requesting state  406  indicates that CM scheduler  114  is requesting bandwidth from CMTS  102 . Once the request has been transmitted, cable modem  104  enters waiting state  408  until feedback is received from CMTS  102 . Acknowledge state  409  indicates that CMTS  102  has received the request or cable modem  104  has received a corresponding grant. If cable modem  104  remains in acknowledge state  409  or waiting state  408  beyond a predetermined time, cable modem  104  generate another request (i.e., re-enter request state  406 ). In other words, if cable modem  104  does not receive an acknowledgment message or grant message within a predetermined time frame, cable modem  104  will generate another request. 
     After all requests have been granted or there are no other pending or outstanding requests, cable modem  104  enters a close state  410 . Close state  410  indicates that either output queue  112  has not recently signaled CM scheduler  114  for additional bandwidth or all requests have been granted or are no longer required. 
     IV. Conclusion 
       FIG. 1  is a conceptual illustration of system  100  that allows an easy explanation of the present invention. That is, one or more of the blocks can be performed by the same piece of hardware or module of software. It should also be understood that embodiments of the present invention can be implemented in hardware, software, or a combination thereof. In such an embodiment, the various components and steps would be implemented in hardware and/or software to perform the functions of the present invention. 
     Additionally, the present invention (e.g., system  100  or any part thereof) can be implemented in one or more computer systems or other processing systems. In fact, in one embodiment, the invention is directed toward one or more computer systems capable of carrying out the functionality described herein. 
     Referring to  FIG. 3 , an example computer system  300  useful in implementing the present invention is shown. The computer system  300  includes one or more processors, such as processor  304 . The processor  304  is connected to a communication infrastructure  306  (e.g., a communications bus, crossover bar, or network). Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or computer architectures. 
     Computer system  300  can include a display interface  302  that forwards graphics, text, and other data from the communication infrastructure  306  (or from a frame buffer not shown) for display on the display unit  330 . 
     Computer system  300  also includes a main memory  308 , preferably random access memory (RAM), and can also include a secondary memory  310 . The secondary memory  310  can include, for example, a hard disk drive  312  and/or a removable storage drive  314 , representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive  314  reads from and/or writes to a removable storage unit  318  in a well-known manner. Removable storage unit  318 , represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to removable storage drive  314 . As will be appreciated, the removable storage unit  318  includes a computer usable storage medium having stored therein computer software and/or data. 
     In alternative embodiments, secondary memory  310  can include other similar means for allowing computer programs or other instructions to be loaded into computer system  300 . Such means can include, for example, a removable storage unit  322  and an interface  320 . Examples of such can include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units  322  and interfaces  320  which allow software and data to be transferred from the removable storage unit  322  to computer system  300 . 
     Computer system  300  can also include a communications interface  324 . Communications interface  324  allows software and data to be transferred between computer system  300  and external devices. Examples of communications interface  324  can include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface  324  are in the form of signals  328  which can be electronic, electromagnetic, optical or other signals capable of being received by communications interface  324 . These signals  328  are provided to communications interface  324  via a communications path (i.e., channel)  326 . This channel  326  carries signals  328  and can be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels. 
     In this document, the terms “computer program medium” and “computer usable medium” are used to generally refer to media such as removable storage drive  314 , a hard disk installed in hard disk drive  312 , and signals  328 . These computer program products are means for providing software to computer system  300 . The invention is directed to such computer program products. 
     Computer programs (also called computer control logic) are stored in main memory  308  and/or secondary memory  310 . Computer programs can also be received via communications interface  324 . Such computer programs, when executed, enable the computer system  300  to perform the features of the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor  304  to perform the features of the present invention. Accordingly, such computer programs represent controllers of the computer system  300 . 
     In an embodiment where the invention is implemented using software, the software can be stored in a computer program product and loaded into computer system  300  using removable storage drive  314 , hard drive  312  or communications interface  324 . The control logic (software), when executed by the processor  304 , causes the processor  304  to perform the functions of the invention as described herein. 
     In another embodiment, the invention is implemented primarily in hardware using, for example, hardware components such as application specific integrated circuits (ASICs). Implementation of the hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s). 
     In yet another embodiment, the invention is implemented using a combination of both hardware and software. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Moreover, it should be understood that the method and system of the present invention should not be limited to transmissions between cable modems and headends. The present invention can be implemented in any multi-nodal communications environment governed by a centralized node. The nodes can include communication gateways, switches, routers, Internet access facilities, servers, personal computers, enhanced telephones, personal digital assistants (PDA), televisions, set-top boxes or the like. Thus, the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.