GB1400148A - Digital data network interface for datel subscribers - Google Patents

Abstract

1400148 Automatic exchange systems STANDARD TELEPHONES & CABLES Ltd 28 Sept 1972 [4 Oct 1971] 45994/71 Heading H4K An interface arrangement between two dissimilar networks includes means for scanning circuits incoming from a first of the networks which comprises a circuit selector operated in conjunction with a counter, and means for counting signalling impulses and the intervals therebetween comprising a gate responsive to outputs from the circuit selector and the counter whereby predetermined call establishment signals received from said first network are recognized and are converted into a form suitable for use in the second network. The arrangement is used in an interface exchange 10 (Fig. 1) between a telephone network 11 and a data network and is specifically used to enable Datel subscribers on the telephone network to establish connections to subscribers, e.g. computer bureaux on the data network. Referring to Fig. 1 (two-figure references) and Fig. 3 (four-figure references) the interface is associated with a toll centre 1000 which is accessible from local junctors 1001 and national and international trunks 1002-1005. A Datel subscriber requiring a data network subscriber dials a special three digit exhcange code prefixed by an appropriate national or international code to gain access to a signalling terminal 1009 via an auto-auto repeater 1007 and a special group of junction circuits 1008, which are scanned by a circuit 1010 under the control of a counter. The calling subscriber then dials a four digit number the digits and interdigital pauses of which are counted and compared with a 12 bit word supplied by the core store of a processor 1012, 16. A non-decimal code supplied by the processor to a data signalling terminal 1020, 18 for transmission over a special signalling channel 17 to a processor 14 of a first data exchange 12 and thence if necessary to other data exchanges, e.g. 13 over further special signalling channels. Answer signals received from the data subscriber enable a modem 1027 appropriate to the transmission speed to be selected and answer frequency and echo suppressor control frequencies are transmitted back to the Datel subscriber from a data answer set positioned between the modem 1027 and the modem access switch unit 1026. Only two of the four digits may be translated at the interface to give the identity of the required data exchange, the remaining digits being transmitted in a non-decimal code to the appropriate data exchange for translation. Such a numbering arrangement allows traffic for particular data exchanges to be concentrated at the interface. Call charging.-Subscribers on the telephone network are only charged for a call as far as the interface exchange and the data subscribers are expected to pay for the data network part of the call, e.g. by paying a rental charge for their access number from the telephone network. Data subscribers may arrange to be accessible via more than one interface exchange by renting numbers at the appropriate interfaces.