Patent GB-1391840-A (GB)
Title: Telecommunications systems
IPC: H04Q11/04
Filed: 1972-05-18
Abstract: 1391840 Automatic exchange systems SIEMENS AG 18 May 1972 [18 May 1971] 23314/72 Heading H4K In a telecommunications system in which data signals relating to speech channels are transmitted in special transmission channels between a pair of exchanges which are connected to one another via a P.C.M. transmission link, a number of the special transmission channels are seizable from either exchange. Two exchanges AB are coupled by two 32 channel P.C.M. links L1, L2, one for each direction of transmission. Thirty channels in each link are reserved for speech communication, one for synchronization purposes, and the final one for transmission of data signals. The time slot of this channel may be divided into two parts to provide two special transmission channels per frame for transmission of data signals relating to two of the speech channels. Data signals relating to the 30 speech channels are therefore transmitted in sequence over fifteen frames and in this sense 30 special transmission channels are provided. Each of the thirty special transmission channels has associated with it at each exchange a signal translator which is coupled to either the incoming (SAan or SBan) or outgoing (SAab or SBab) switching stage of the respective exchange, the term channel being used to cover the arrangement of an outgoing channel in P.C.M. link L1 (L2) paired with a corresponding incoming channel in P.C.M. link L2 (L1). Ten of the special channels are seizable only from exchange A and have associated therewith 10 signal translators represented by K1Aa and K2Aab at exchange A and 10 signal translators represented by K1Ban and K2Ban at exchange B, these 20 signal translators being seizable only from exchange A. Likewise there are provided 10 special channels seizable only from exchange B and having associated therewith 20 signal translators, seizable only from exchange B, represented by K1Bab and K2Bab at exchange B and by K1Aan and K2Aan at exchange A. The further 10 special channels each have associated therewith a pair of signal translators at each exchange, one signal translator of each pair being seizable from exchange A and the other of each pair being seizable from exchange B. The figure shows the signal translators K3Aab, K3Aan, K3Bab, K3Ban associated with one of these 10 special channels together with change over switches S3A, S3B associated therewith, the arrangement rendering these channels seizable by either exchange as follows. Assuming a call is being established from exchange A and that exchange A has already in use all the 10 special channels allotted thereto, one of the 10 outgoing signal translators such as K3Aab associated with one of the 10 further special channels seizable from either exchange, is seized provided all 10 such channels are not already in use. In the idle state of these special channels the change over switches S3A, S3B are switched to connect the signal translator seizable by the exchange in which it is situated to a respective distribution arrangement KVA, KVB which connects the output of the signal translator to the P.C.M. link outgoing from the respective exchange during the ¢ time slot in the frame allotted to the particular special channel in the sequence of 15 frames. In this particular case the output of signal translator K3Aab is connected via P.C.M. link L1 to the input of a change over switch S3B and a change over switch actuating device BStb. The data signal transmitted will include at the beginning thereof a signal that will cause the switch actuating device BStb to operate the change over switch S3B to connect signal translator K3Ban to the distribution arrangement KVB and this signal translator is then seized by exchange A. Once seized the signal translators are capable of relaying signals in either direction, and once data signals have been received by exchange B from exchange A via switching stage SAab, translator K3Aab, P.C.M. link L1, translator K3Ban and switching stage SBan a backwards acknowledgement signal will be transmitted via switching stage SBan, translator K3Ban, P.C.M. link L2, translator K3Aab and switching stage SAab. Means are provided for preventing seizure of a special channel by both exchange simultaneously The P.C.M. interexchange links may be transmission lines or radio links.