T1 CAS Signaling Format

Parameter group

Signaling Type

Access level


Possible values

2-bit AB (SF)
4-bit ABCD (ESF)


2-bit AB (SF)


Specifies the T1 bit-robbing CAS Signaling format (as defined in TIA/EIA-464-B) that is to be used. If the T1 framing mode on the trunk is set to D4, choose 2-bit format. If the T1 framing mode on the trunk is ESF, choose 4 bit.

2-bit format means that only the AB bits are used for signaling: C and D are ignored.

4-bit format means that all the ABCD bits are used for signaling. The C and D bits are normally set to the values of the A and B bits respectively, but this depends on the protocol (for more information, see TIA/EIA-464-B).

Because the signaling format is defined on a channel group basis, the user must ensure that channel groups that span multiple trunks all have the trunks set to use either D4 or ESF; otherwise some signaling problems might occur.