Research Of Upstream Channel Bandwidth Allocation Algorithm In HFC Network

With the rapid development of computer technology and digital technology, our society has stepped into the information age. People's demands for high-speed data services and video services have been increasing continuously. Broad bandwidth and advanced IP technology has been the fundamental character of the new generation telecommunication networks. Three networks merged into one has become the developing trend of future network. HFC(Hybrid Fiber/Coax) network, as the integration of PSTN, computer network and CATV(cable television) network, has gained more and more attentions. Due to its particular mixed topology of star and branch as well as its asymmetric upstream and downstream, the upstream channel's bandwidth allocation algorithm in HFC network has been a research hotspot domestic and abroad.Having referred to a lot of documents, the author analyzed the HFC network's frequency spectrum, topology and channel features. Based on analyzing the upstream channel's description in the DOCSIS protocol, the author profoundly explored the upstream channel's bandwidth allocation algorithm in the HFC network. To increase the slot throughput and shorten the network's delay, the author analyzed all kinds of existent bandwidth allocation algorithm. According to the theoretical deduction, the author concluded the relation between the slot throughput, the number of arrived Request packets and the number of allocated contention slots. Thereout, he put forward an upstream channel bandwidth allocation algorithm based on the estimation of the Request packet's arrival ratio(λ). Meanwhile, the paper analyzed and researched the estimation algorithm of the Request packet's arrival ratio, and presented a concise and effective estimation algorithm. Through theoretical analysis and experimental simulation, the author obtained the value of collusion coefficient under common situation or heave load, and the size of the sample window. The paper also analyzed the request access delay(RAD) when using the bandwidth allocation algorithm, and found that the number of allocated contention slots has little effect on the RAD, however the RAD connected with the length of upstream time segment being depictedby MAP. As for the allocation of data slots, the paper adopts a simple FCFS(First Come First Serve) algorithm. Finally, by constructing a queue model, the paper computed the queue delay and analyzed the effect of the size of serving window on the data access delay(DAD). Aimed at reducing the access delay(AD) on the condition of stable network, the author defined the size of serving window and also simulated it. From the result of simulation, it is found that the algorithm can effectively enhance the slot throughput, and by setting a appropriate serving window size it can also decrease the RAD and the DAD.