Data Services In The Hfc Network Qos Technology Research

HFC network has the special tree-and-branch topology. It decides that the downstream channel is a point-to-multipoint broadcasting channel, and the upstream channel is a multipoint-to-point channel which shared by all the cable modems. Because the upstream and downstream channels are separate from each other in frequency band, the cable modems has the inability to carrier sense, then the inability to detect transmission collision. This leads to the absolute random access to upstream channel for all the cable modems. So an effect upstream channel manage mechanism is needed for HFC network to provide two-way data services. The DOCSIS specification is established as the primary HFC network data communication standard. DOCSIS makes use of upstream channel in TDMA mode. The upstream channel is modeled as a stream of mini-slots, and are allocated by "request-grant"mechanism. This way can well coordinate the upstream channel access of all the CMs, so reduce the collision rate and promote the bandwidth utilization. However, the "request-grant"mechanism do not promise the Quality of Service(QoS) of real-time service, such as VoIP, MPGE video stream, and so on. In order to solve this problem, DOCSIS defines five QoS service flow, i.e. UGS, UGS-AD, rtPS, nrtPS and BE. This paper concentrate on the UGS and rtPS service flow, they are for real-time CBR and VBR service respect. One access admission control algorithm for UGS service flow is offered. This algorithm can reject those service setup requests which can not be serviced with QoS promise. Then proposes a bandwidth allocation algorithm in order to service multiple UGS service flows properly, so as to reduce the QoS Violation. The simulation results reveals that this algorithm excelled the simple...