GB1170040A - Improvements in or relating to Dial-Operated Data Transmission Networks - Google Patents

Abstract

1,170,040. Digital transmission systems. SIEMENS A.G. 30 May, 1968 [31 May, 1967], No. 25905/68. Heading H4P. In an exchange system signals are accompanied by class signals indicative of the priority, speed, terminal equipment, or network, i.e. the group in which a subscriber lies. Terminal and network class signals are evaluated after development of a connection within the originating or destination exchange, but priority and speed class signals are evaluated during development of the connection. If a subscriber calls a subscriber who is restricted to reception only from certain subscribers, after connection to the called subscriber has been developed, one subscriber sends to the other a network class signal. This is compared at the exchange associated with the latter subscriber with the class signal of the former, and only if there is agreement is the connection switched through. If there is no restriction on the called subscriber, no class signals are sent. If a calling subscriber is restricted in the subscribers which he may call his network class signal is transmitted from his local exchange to the destination exchange, via any other exchanges, prior to the transmission of dialling signals. Priority signals, i.e. signals indicating whether a connection must wait for a free line or can break in to an existing connection are evaluated in each exchange as the connection is developed. If, for a given speed of line, no such line is available at an exchange, calls are routed through a higher speed line and a speed signal is added so that at a subsequent exchange a line of the original speed is selected.