Codecs with suppression of multiple encoding/decodings across a connection

In a private telecommunications network, a plurality of digital PBXs are interconnected via pairs of codecs. The codecs of each pair, or "tandem", are each operative to encode 64 kilobit/second (kbps) mu-law speech so as to compress it to 16 kbps speech for transmission to the other codec in the tandem. The latter is operative to thereafter decompress the 16 kbps speech back to 64 kbps. Each codec has a second mode of operation in which, rather than decode the encoded speech, it preserves the bits thereof in its own output signal. The codec transitions to this mode whenever it recognizes the presence of another codec on its high-bit-rate side of the connection. As a result, only one encoding/decoding cycle is performed across the connection, thereby minimizing the speech-coding-induced distortion and delay therein. The mechanism enabling a codec to communicate its presence to another codec on its high-bit-rate side of the connection is based on the transmission of predetermined synchronization patterns inserted in the signals it outputs in that direction. In a second embodiment, codecs of the above-described type are used in a cellular mobile radio telecommunications system.