A Study of Non-Blocking Switching Networks

The impact of recent discoveries and developments in the electronic art is being felt in the telephone switching field. This is evidenced by the fact that many laboratories here and abroad have research and development programs for arriving at economic electronic switching systems. In some of these systems, such as the ECASS System,* the role of the switching crossnet array becomes much more important than in present day commercial telephone systems. In that system the common control equipment is less expensive, whereas the crosspoints which assume some of the control functions are more expensive. The requirements for such a system are that the crosspoints be kept at a minimum and yet be able to permit the establishment of as many simultaneous connections through the system as possible. These are opposing require ments and an economical system must of necessity accept a compromise. In the search for this compromise, a convenient starting point is to study the design of crossnet arrays where it is always possible to establish a connection from an idle inlet to an idle outlet regardless of the amount of traffic on the 2system. Because a simple square array with N inputs, N outputs and N crosspoints meets this requirement, it can be taken as an upper design limit. Hence, this paper considers non-blocking arrays 2 where less than N crosspoints are required. Specifically, this paper describes for an implicit set of conditions, crossnet arrays of three, five, * Malthaner, W. A . , a n d H .