ITU-T Q.121-1989
Signal Code - Specifications of Signalling Systems Nos. 4 and 5 (Study Group XI) 6 pp

Standard No.

ITU-T Q.121-1989

Release Date

1989

Published By

International Telecommunication Union (ITU)

Status

Withdraw

Latest

ITU-T Q.121-1989

Scope

The signals of System No. 4 are signals (binary code signals and their acknowledgement signals) used for the transmission of signal called “line signals” for the so-called supervisory functions;

ITU-T Q.121-1989 history

• 1989 ITU-T Q.121-1989 Signal Code - Specifications of Signalling Systems Nos. 4 and 5 (Study Group XI) 6 pp