Abstract: The contention request mode of upstream bandwidth allocation for HFC (Hybrid Fiber Coax) network access device CM (Cable Modem) was discussed based on the international standard specification for HFC,DOCSIS specification. Firstly, this paper proposed a Markov Chain model for the contention request algorithm of the CM upstream channet. Based on this model, we proposed an M/M/1/K queue model for the data frame sending process of the CM upstream channel,and deduced a theoretical method for estimating the data frame sending buffer size of the CM upstream channel. Finally, we simulated the upstream channel by NS-2 simulator. The simulation results show that our method is able to correctly estimate the relationship between the upstream sending buffer size and the buffer overflow probability.Hence our method can offer a theoretical reference to the setup of the CM upstream sending buffer size.

Key words: DOCSIS, Cable modem, Markov chain, Queue model, Buffer size estimation