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Many T-l connections use an in-band signaling method called “robbed bit.” In-band signaling is also known as Channel Associated Signaling (CAS), because line signaling information is carried within each chan­ nel’s data stream. Robbed bit signaling literally “robs” one bit from the data path on each of the 24 DS-0 channels to indicate a hook condition. In the case of a T-l using the D4 Super Frame (D4 SF) framing technique (based on 12 frame increments), every 6th and 12th frames have the Least Significant Bit (LSB) from every 8-bit byte over­ written to indicate the hook state. Because such bits are no longer available for the actual channels, the DS-O’s are now voice grade lines and only transmit at 56Kbps, as compared to the full 64Kbps in out-of-band or clear channel signaling. The bit robbed from the 6th frame is called the “A-bit” and the bit robbed from the 12th frame is called the “B-bit.” Note that in the case of T-ls using Extended Super Framing (ESF), which is based on 24 frames, the LSB of frames 6, 12,18 and 24 are used for signaling purposes.