GB1458626A - Arrangement for bridging line equipment in communication networks - Google Patents

Abstract

1458626 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 23 May 1974 [7 June 1973] 23049/74 Heading H4K In a system where the transmission quality of a switched communication path determines whether terminal equipment need be incorporated in the path, one end of the path is equipped with a signal generator that transmits a code of a similar format to that to be used in the communication while the other end is equipped with a suitable receiver. If the latter validates the code it causes the local terminal equipment to be short circuited and reverts another code which produces a similar effect at the first end. The system is particularly concerned with cutting-out the need for D/A and A/D converters when switching digital signals through a four-wire tandem exchange. The prior art is depicted in Fig. 1. Therein relays A1, A2 operate to cut-out the converters if battery U2, U1 respectively penetrates the phantom of a switched connection between the terminals LA1 and LA2 In Fig. 3, a common generator KG1 transmits a digital code word or a frequency at the upper end of the, e.g. 52 KHz, band occupied by a digital transmission so that if a switched connection between two terminals is satisfactory, a receiver KE2 can respond and in so doing enable relay A2. The latter bridges both of the converters at its end of the path and applies a holding earth (a25) to the phantom. Simultaneously a generator KG2 (which may be the same as KG1) transmits a signal over the Return path so as to similarly enable a converter-bridging relay A1. The two relays are held over the respective phantoms and both generators are disabled during the connection. In Fig. 4 (not shown) the generator KG2 is dispensed with, the holding contact a25 serving also to actuate relay A1. In Fig. 5 (not shown), the Go and Return paths each incorporate an arrangement similar to Fig. 4 but arranged such that each path is independently controlled by a separate pair of relays and generators.