When defining a telecommunications network, the concept of traffic must be considered. The traffic may be conversations, information, or complex video or audio services. It results in a congested and costly network configuration. Alexander Graham Bell was responsible for the direct connect network. Because of Vail, the early railroads were used as the model for development of a new kind of telephone network - the centralized telephone network.
Centralized systems are virtually unlimited in how large they can become.
Their major advantage is that customers can be interconnected through switching centers for worldwide communications. In its simplest form, a transmission facility is a communication between two end points. The local loop is also referred to as the subscriber loop. A simple local loop architecture is depicted in Figure 1.7 . The CPE is connected to the central office by means of the drop wire, distribution cable, and feeder cable which are cross-connected at specific points.