The Communication Network
The world wide communication network has been going through a significant stage of evolution in recent years. For many years the network was devoted to voice communication only.

Over a span of 100 years, it evolved from an analog switched circuit over copper wire system to a primarily digital system using virtual circuits (channels) over copper and fiber. It became known as the Public SwitchedTelephone Network (PSTN). However, in the mid-sixties, networks devoted to data transmission using packet switching techniques began to appear. Eventually, these networks were interconnected to form the world wide Internet. In many cases this interconnection was accomplished by using existing PSTN facilities. The problem with using the PSTN for data transmission is that its circuit switched infrastructure is optimized for voice transmission making it inefficient for bursty data transmission. Since building a completely new network to handle both voice and data was not a viable solution it was determined that the existing network infrastructure must be modified to achieve this objective. This convergence of voice and data traffic onto the traditional voice network has been going on for several years and will continue to go on for many more years. This paper will look at where the communications network is now, and where it is heading.

The Basic Model
It is generally agreed that the communication network divides into three major subdivisions; Access, Metro (also referred to by some as the “Edge”) and Core. The Access subdivision is made up of transport media and application devices that connect directly to the subscribers. It is responsible for aggregating these subscriber connections and interfacing them to the Metro subdivision. The Metro subdivision provides high speed transport media and application devices (routers, switches, gateways, servers, etc.) required to interconnect all of the access subdivisions in its area. From a voice network perspective this is the domain of the Local Exchange Carriers (LECs). The Metro subdivisions are in turn interconnected by the Core subdivision which consists of even higher speed transport media and application devices. From a voice network perspective, the Core subdivision is the domain of the Inter-eXchange Carriers (IXCs). Even though LEC and IXC are voice network terms they are commonly used in conjunction with both voice and Reliable Best Effort (RBE) data networks.