T1 Framing Mode

Parameter group

Trunk Interface

Access level


Possible values





Specifies the frame format that is to be used with T1 trunks. Select D3/D4 for superframe format. Select ESF for extended superframe format.

Superframe format timeshares the framing bit to identify channel framing and signaling channel framing. Channel framing identifies the location of time slot 1 and signaling framing identifies those frames in which signaling bits a and b are transmitted using robbed-bit signaling.

The extended superframe format extends the superframe structure from 12 frames to 24 frames and redefines the 8kbits per second framing bit position. The 8kbits per second ESF channel is divided into 2kbits per second for channel framing and signaling channel framing, 2kbits per second for Cyclic Redundancy Check code (CRC-6) and 4kbits per second for a data link. Four signaling channels, A, B, C, and D, are provided by ESF.

ESF is set automatically when a T1 common channel signaling protocol (such as ISDN) is selected. When a pack is used with a channel associated signaling protocol, you must select D3/D4 or ESF as necessary.

See Setting line code and framing mode parameters for guidance on which value to select.