Performance evaluation of a request cluster allocation scheme for multi-channel DOCSIS

DOCSIS is a de facto standard for data transmissions on CATV/HFC networks. In DOCSIS, an upstream channel is shared by many stations, and the stations send out their data PDUs according to the random reservation manner. Before data transmission, the station must send a request in a random access manner during the reservation period called a request cluster. Recently, DOCSIS has introduced a concept in that the multiple upstream channels can be combined together to get greater aggregated bandwidth. However, DOCSIS does not provide a request cluster allocation scheme for the aggregated upstream channel. On the other hand, for single upstream channel, DOCSIS employs the binary exponential back-off scheme for request cluster allocation. But, that provides too small/large request periods which are used in the random reservation, the delay increases rapidly as the offered traffic increases. In this paper, we propose a request cluster allocation scheme for multichannel CATV/HFC networks. Our scheme dynamically changes the request cluster size according to the traffic conditions. In order to evaluate performance of the proposed scheme, we build a queueing model and execute computer simulation. Simulation results present that the proposed scheme provides the smaller delay than the conventional scheme.