GB1329368A - Digital telecommunications systems - Google Patents

Abstract

1329368 Automatic exchange systems SIEMENS AG 15 Oct 1971 [27 Oct 1970] 47975/71 Heading H4K In a digital transmission network comprising groups of exchanges that utilize different bit rates and modulation modes, tandem calls via an exchange group utilising a modulation mode different from that of the terminal groups are set up without the aid of modulation changers. As shown groups A and B use 2-4 Kb. PCM whereas group B uses 19À2 Kb. delta modulation. A connection from subscriber Alk to C1m is set up via tandem exchanges B1 and B4 over multiplex lines that incorporate bit rate changers GU, i.e. pulse stretchers and shorteners which may be monostables, that serve to match the different bit rates of the three groups but without any change of modulation at the interfaces between the groups. A connection between A1k and say B4n however requires a modulation changer MU. The latter has two appearances on exchange B1's switching network such that it is effectively in series with the transmission path between A1k and B4n. The switching networks may incorporate superhighways with channel stores being provided for time slot changing. The interexchange highways may comprise carrier radio or line transmission systems. Signalling data, e.g. dial signals must be converted so that a tandem exchange can interpret them correctly, appropriate converters may therefore be connected in parallel with the rate changers in each intergroup highway. A mobile subscriber nominally attached to one group, e.g. Co in group C, may be provided with a direct (radio or line) link to an exchange e.g. B4 in another group, this line being equipped with a bit rate changer but a modulation changer only being required if a call involving Co terminates in group B.