Patent GB-1177753-A (GB)
Title: Switching System for Telecommunication Circuits
Inventor: HERTOG MARTINUS DEN
IPC: H04Q3/545
Filed: 1966-01-18
Abstract: 1,177,753. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 13 Jan., 1967 [18 Jan., 1966], No. 2275/66. Heading H4K.  Inter-exchange connections are set up by the random association of separate one-way speech channels from a number of such channels provided between exchanges in association with a separate signalling channel, an exchange seizing a free one-way speech channel to another exchange in response to digital data received from the other exchange over the signalling channel and sending the identity of the seized speech channel to the other exchange over the signalling channel. Inter-exchange speech channels may be grouped, each group being served by an associated signalling channel. An originating exchange may seize a forward oneway channel and, over a signalling channel serving the group from which the one-way channel has been selected, send a seize signal to the forward exchange to obtain a backward one-way channel and to indicate the identity of the selected forward channel. The forward exchange selects a backward channel and reverts a signal over a signalling channel to give the originating exchange the identity of the backward channel so that a both-way connection may be switched forward. In the context of inter-exchange circuits having large propagation times the arrangement is said to avoid double seizures. Separate signalling channels for inter-exchange satellite relayed circuits may be provided by other circuits relayed over the satellite or by earth-bound cable or radio circuits in which latter case a separate signalling channel may need to be established over tandem exchanges to reach an exchange direction accessible to the satellite. Auxiliary signalling link terminal equipment.-As shown in Fig. 2 a separate signalling channel between modulator 303 to demodulator 304 carries signalling units (words of a fixed bit length) from exchange A to exchange B. A separate signalling channel between 309 and 310 similarly provides a data path from B to A. Signalling data compiled at A is set up in a selected or associated storage location in store 301 and is read out in parallel to a shift register 302 from which it is transmitted serially over the signalling channel. A buffer store may be provided between store 301 and the register 302 so as to queue signalling units according to precedence. If a forward speech channel has been selected the identity of that channel is sent forward over the signalling channel along with control data so that data returned in response can be tagged with the channel identity and be associated with transactions on behalf of that channel. Where no speech channel has yet been selected a so-called temporary label is attached to the forward message to identify the transaction until such time as a selected channel identity is available. A forward register can be seized and be given requirements under a temporary label before speech path selection has taken place. Signalling units reverted from B are received at A on a stepping register 311 from which they are passed in parallel to a store 312, if processing of received data is required, or to the store 301 (or a similar such store associated with other signalling channels) if the signalling units are to be passed on unprocessed to a further exchange over an appropriate signalling channel.