Patent GB-829095-A (GB)
Title: Improvements in or relating to equipment for use in automatic telephone systems
Inventor: BAKER GEORGE THOMAS
IPC: H04M3/36
Filed: 1954-11-23
Abstract: 829,095. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. Feb. 23, 1956 [Nov. 23, 1954], No. 33987/54. Class 40 (4). In designing a trunking system to meet probable traffic loads the suggested system is simulated on a traffic analyser and subjected to signals from random pulse generators whereby calls are simulated and the performance is assessed. The simple trunking system of Fig. 4 is set up on a magnetic drum in the manner shown in Fig. 5. The area A represents a first rank of ten cross-bar switches in tracks 0-9, each switch having ten bridges as represented by the unit areas in each track. An auxiliary " relation " track 10 stores information regarding access from a particular switch to bridges located in a track or in a slot of a succeeding portion, such as area B, of the drum. An element such as a representing the bridge connected to subscriber 55, comprises four unit areas NUM containing a number in binary form indicating the track or slot in a subsequent group to which the particular bridge extends a connection. The last unit area F/B indicates whether the bridge is free or busy. A corresponding element b in the relation track 10 has unit areas GRP identifying the group to which bridges in the associated slot have access, the last unit area T/S indicating whether a slot or a track in the subsequent group is concerned. Operation, Fig. 6. A composite random event generator RG supplies calling and called numbers together with instructions to establish or release a call. The numbers are stored in control equipment CC which feeds the position a on the drum corresponding to the calling line. If the related bridge is free CC uses the information stored in area b of the relation track to scan the relevant subsequent group of bridges terminating all the links accessible to the calling line. The identities of the free links are stored on a " delay line " track SL3 (Fig. 9, not shown). From the accessible free bridge positions of the second rank further routing information is read which directs the control equipment to the group corresponding to the next rank of switches and so on eventually to the terminating lines. Testing for free links proceeds from stage to stage until the outlet group is reached containing the called line. As the positions in this group are scanned coincidence is reached between the called-line position and the number stored in the control equipment CC, and the switch on which the line terminates is marked on the delay line track. This track now contains information which indicates free paths between the calling and called lines. If the called line position is marked busy a signal is returned to the control equipment to inhibit the remainder of the cycle. If the called line position is marked idle the first free route is selected from the delay line track. On the next revolution of the drum the control equipment reads the information into the calling line position and the corresponding position on the relation track, proceeding from stage to stage and marking the appropriate areas busy. A pulse is then sent to the output meter OM to indicate a successful call. As each attempted call also operates a meter, comparison of the two meters provides an analysis of the chosen trunking arrangement. When the random generator provides a signal to release a connection the control equipment traces through the connection from the rereleasing station and changes all busy indications to free. Releases are not metered. The trunking arrangement can be altered by a punched-tape device TR. Specification 785,714 is referred to.