The Transmission Performance of Bell System Intertoll Trunks

The Bell System toll network consists of a hierarchy of toll offices interconnected by transmission paths called intertoll trunks. A toll call between two subscribers is built up of a tandem connection of several transmission paths which are joined by switching. At each end of such a connection is a loop t h a t connects the subscriber's telephone set with a local telephone office. T h e local telephone offices connect with toll offices by toll connecting trunks. These toll offices are connected by either a single intertoll runk or by several intertoll trunks through intermediate toll offices. The transmission performance of a toll connection between subscribers is thus influenced by the performance of each trunk and loop in the connection. Systemwide improvement in transmission performance by a category of trunks is directly measured by the corresponding improvement in built-up connections. Systems engineering on transmission objectives, therefore, requires information about the relation between 1561