By Jonathan Fellows Ph.D., Victor T. Hou, General Instrument Corporation
For many current cable service areas, telephone return cable modems may be a viable long term technology for delivery of high speed data services. The first generation of commercially deployed telephone return cable modems and associated headend equipment have now been installed in multiple cable plants. This system, incorporating 64-QAM transmission in the downstream and telephone return in the upstream, provides high speed access to the Internet and other data applications. Many of the network design issues of telephone return cable modems, such as network addressing schemes, asymmetric bandwidth, and system management, will also apply to two-way systems. Other issues, such as integration with dial-up networks, and asymmetric routing, apply uniquely to one-way systems. Experience with performance tuning of TCP in asymmetric systems is described, as well as field experiences with installation and configuration of the modem in customer PCs.