T1 line code, framing mode, and framing format

For T1 trunks, the T1 Line Code system parameter (in the Trunk Interface parameter group) should be set to the correct value, as shown in Table 1. The possible values are:

AMI

Alternate Mark Inversion with Zero-Code Suppression (known as AMI-ZCS). (This is the default.) This does not allow "clear channel", that is 64–kilobit per second operation, whether or not when Robbed-Bit Signaling is used with channel associated signaling (CAS).

B8ZS

Bipolar with 8-Zero Substitution. This is required for 64–kilobit per second channels like ISDN.

The T1 Framing Mode system parameter (in the Trunk Interface parameter group) should be set to the correct value, as shown in Table 1. The possible values are:

D3/D4

Superframe with 12 concatenated frames. (This is the default.)

ESF

Extended Superframe with 24 concatenated frames. This type of framing also has cyclic redundancy checking and a maintenance channel, and is used for common channel signaling (CCS).

The T1 CAS SignalingFormat system parameter (in the Signaling Type parameter group) should be set to the correct value, as shown in Table 1. This specifies the T1 bit-robbing CAS Signaling format (as defined in TIA/EIA-464-B) to be used. The possible values are:

2-bit AB (SF)

Only the AB bits are used for signaling: C and D are ignored. (This is the default.)

4-bit ABCD (ESF)

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, but this depends on the protocol (for more information, see TIA/EIA-464-B ).

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 format.

Because the signaling format is defined by channel group, you 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.