Impacts of Internet Traffic on LEC Networks and Switching Systems

The past year has seen explosive growth in internet traffic. Currently, the most common way of accessing the internet is via the switching systems and the interoffice trunk facilities of the Public Switched Telephone Network (PSTN). The PSTN was designed to carry voice calls that have an average call holding time of about 3 minutes. The nominal 3 minute call assumption pervades all aspects of telco equipment design such as switch engineering, line concentration ratios, and trunk group sizes. However, internet calls violate this fundamental assumption and have a mean holding time of the order of 20 minutes with some calls lasting for many hours. This long holding time traffic severely taxes the PSTN. It requires additional equipment to be provisioned, without compensating revenues, and potentially affects service performance for all users. Internet traffic, which is packet data in nature, can in principle be carried much more efficiently on data networks. However, since the PSTN currently represents the only nearuniversal access method, any long term solution necessarily involves a staged migration from the present mode of operation towards some packet network solution. This paper reviews the impacts of internet traffic on the PSTN. It summarizes the impact of internet traffic on transmission and switching equipment, the need for comprehensive revisions to existing engineering and planning algorithms, and the implications of these issues for operational practices and operations support systems. It also provides analysis of the cost of supporting internet traffic on the PSTN. Finally, it describes a number of possible solutions. In each case the current barriers to implementing the solution are discussed.