A Network Simulator model of the DOCSIS protocol and a solution to the bandwidth-hog problem in Cable Networks.

Abstract

A number of broadband access solutions have been developed in the recent years to provide high speed Internet access to the residential users or the ?last-mile?. Some of the prominent technologies include Cable access, Digital Subscriber Loop, Integrated Services Digital Network, Satellite and Wireless. The cable broadband access is gaining widespread popularity. While several approaches to broadband access over cable have been proposed (e.g., DVB/DAVIC and IEEE 802.14), the industry is converging on the architecture developed by the Multimedia Cable Network System (MCNS) group (referred to as the Data-Over-Cable Service Interface Specification or DOCSIS standard). The DOCSIS Radio Frequency Interface specification defines the Media Access Control (MAC) layer as well as the physical communications layer.

The objectives of this thesis were: Design, Implementation and Study of a Network Simulator-2 (NS-2) [1] model of the DOCSIS 2.0 MAC protocol and Design and analysis of an algorithm to solve the bandwidth-hog problem in Cable Networks. It was realized that there is a need for the support of DOCSIS protocol in a publicly available popular simulator to do research on DOCSIS. Network Simulator was chosen as it is widely used by the Internet research community for research of networking protocols and it currently lacks the support for DOCSIS. The Network Simulator implementation is conformant to the DOCSIS RF-interface specifications with support for Quality of Service features.

The second part of this thesis presents a solution for congestion control in cable networks. It has been observed in cable networks that few heavy bandwidth users can cause severe congestion affecting the performance of the other users. Typically, the end user applications incorporate end-to-end congestion control for best-effort traffic (e.g. TCP congestion control). However, with the growth of the Internet, it might no longer be practical to rely on all end-nodes to use end-to-end congestion control. There is a need for the participation of the network itself in controlling the resource utilization. A solution is proposed where the central entity (known as Cable Modem Termination System) in the cable network identifies and restricts the bandwidth of selected best-effort flows in times of congestion. The flows using disproportionate bandwidth during times of congestion are restricted. As outlined in [2], this approach promotes the use of end-to-end congestion control by the end-nodes as it provides an incentive to flows responsive to congestion by not restricting them.