AT&T MERLIN LEGEND Installation & Maintenance Manual page 92

System Description
Common-Channel Signaling
CCS is an out-of-band signaling format that places the signaling
bits for channels 1 through 23 into the 8-bit word of the 24th
channel. This restricts DS1from using the 24th channel for voice
or data transmissions.
D4 framing does not preclude the use of CCS, but CCS is not
compatible with D4 channel banks because the D4 channel
banks recognize only RBS. Coupled with B8ZS coding, CCS can
support digital data up to 64 kbps per channel.
Recommended Framing and
Signaling Formats
ESF framing should be used to take advantage of its improved
maintenance, diagnostic, and testing capabilities (the ESF T1
CSU is required to interface with the network). If the transmission
between two systems is voice-only, RBS should be used for all
24 communication paths. For voice transmission, both ZCS and
B8ZS line coding can be used to satisfy the ones-density
requirement; the preferred line-coding format is B8ZS, which is
needed for 64-kbps digital data.
The framing and signaling formats depend on the network and
interconnection devices (CSUs) used. For example, many CSUs
support only ZCS line coding.
Notes:
Digital data up to 64 kbps is possible only in ISDN-PRI
mode. Also, ESF framing mode, CCS signaling, and B8ZS line
coding are required.
An ESF T1 CSU must be used for interbuilding DS1
connections.
DS1 Capabilities 1-61