Comtech EF Data CDM-600/600L - Manual (Page 177)

CDM-600/600L Open Network Satellite Modem Revision 3
Open Network Operations MN/CDM600L.IOM
12–5
12.4.3 IDR Engineering Service Channel
Bi-directional processing of the components of the ESC channel, including the ADPCM audio
channels, 8 kbps data channel, and fault indications specified by IESS-403 and IESS-308.
Option of using the ADPCM portion of the satellite overhead for a single 64 kbps ESC data
channel in addition to (and with the same format as) the 8 kbps data channel.
When using G.703 format for the primary IDR data path, the P3B primary data interface (25-pin)
is used for the 8kbps overhead channel. If RS-422 or V.35 is used, P3B becomes the primary
interface and the 8kbps channel is unavailable.