Delivery of low bit rate isochronous streams over the DOCSIS 1.0 cable television protocol

The Data Over Cable Systems Interface Specification (DOCSIS) 1.0 protocol enables the delivery of Internet Protocol (IP) traffic over cable TV networks with significantly higher data rates when compared to analogue modems and integrated services digital network (ISDN) links. The availability of greater bandwidth enables the delivery of high quality audio and video services. Such services require bounded delay characteristics. This paper evaluates the capacity and performance characteristics of the DOCSIS 1.0 protocol for the delivery of isochronous streams given the limited quality of service (QOS) features of the protocol and a modem population of up to 500 nodes. Stream rates of up to 64 Kbps with different packet size were considered, suitable for compressed audio, voice and low quality video. Packet concatenation for upstream traffic was also considered. Simulation results indicated that such streams, within the given protocol limitations, can be supported for a particular system population with tradeoffs in terms of system throughput and channel utilisation of up to 50%. The network capacity, in terms of the number of simultaneous streams supported and link utilisation, is significantly affected by packet size. Support for concatenation has limited advantages. Performance benefits from concatenation are more evident when delivering higher rate bitstreams