Transient analysis of DOCSIS 1.1 cable modem networks

The authors seek to identify the primary factors that determine the time-to-recovery of a network of DOCSIS-compliant cable modems (CMs). DOCSIS, which stands for Data-Over-Cable Service Interface Specifications (L.P. Holdings, 1999), is an emerging industry standard for data services over the cable TV infrastructure. According to the specification, individual cable modems must compete for access to the upstream channel, making it difficult to predict how long it will take for all CMs to initialize. We have developed a high fidelity simulation of the DOCSIS 1.1 upstream channel which allows us to test various upstream channel allocation rules. We have simulated networks of 200, 500, and 1000 CMs, and we have used the results to estimate the distribution function for the time-to-initialize for each topology. We have found that there is a tradeoff between optimizing the initialization process and the steady state operation of the network. In particular, allocation rules that reserve channel capacity for initialization lead to shorter initialization times at the expense of reduced capacity for the transmission of data.