Accessing Internet using Cable modem is one of the recent technological advancements in the field of networking. Cable network has widely deployed infrastructure and is most commonly used to distribute television programs. Utilizing the existing cable network (coaxial cable entering subscribers’ premises) to provide Internet access has opened up a completely new paradigm. Cable modems used in the Cable networks provide line speeds of 300kb/s and above for Internet access in addition to distributing television programs (video). Introducing IP telephony over Cable network introduces many new challenges like quality of service and security. In this research, we evaluate the performance of IP telephony over a Cable network using OPNET network simulator.