Digital signal X is a term for the series of standard digital transmission rates or levels based on DS0, a transmission rate of 64 kilobits per second (Kbps), the bandwidth normally used for one telephone voice channel. Both the North American T-carrier system and the European E-carrier system of transmission operate using the DS series as a base multiple. The digital signal is what is carried inside the carrier system.
DS0 is the base for the digital signal X series. DS1, used as the signal in the T1 carrier, is 24 DS0 (64 Kbps) signals transmitted using pulse-code modulation (PCM) and time-division multiplexing (TDM). DS2 is four DS1 signals multiplexed together to produce a rate of 6.312 Mbps. DS3, the signal in the T3 carrier, carries a multiple of 28 DS1 signals or 672 DS0s or 44.736 Mbps.
Digital signal X is based on the ANSI T1.107 guidelines. The ITU-TS guidelines differ somewhat. The following table summarizes the set of signals and relates them to the T-carrier and E-carrier systems.
|Digital Signal Designator||Data Rate||DS0 Multiple||T-Carrier||E-Carrier|
|-||565.148 Mbps||4 E4 channels||-||E5|