24 B Channels in D/240SC-T1

From: "Jim Beecher" <jbeecher@dmsgs.com>

Something that might help you all:

1) Old T1s (the original T1 is an ANALOG T1. Meaning, 24B channels. This also required INBAND signaling (control (data) done with frequencies within the voice (bearer) channel.

2) "New" T1s are DIGITAL T1s, and are ISDN. meaning 23B+1D channels. This is OUT-OF-BAND Signalling (control (data) done in its own channel, not in the 23 voice (bearer) channels).

Same bandwidth, either way. Analog T1s are usually D4/AMI. The original, basic mode of signalling on a T1. All other signalling and linecoding patterns were developed to lower the amount of error correction/detection bits used in the bitstream, while giving enough information that a damaged signal could be rebuilt by repeaters, and to ensure that data on the line would not in and of itself destroy the signal (what happens if you transmit all zeroes? Gee-- waveform fails because voltage drops to ZERO, which means the number of zeros can't be counted. No sync, no frame, no data).

The entire signalling methodology is based on a regular counting of 1 bits to keep in "sync". Without regular ones, the signal can't be error corrected, frames can't be measured, etc.

Now you know more than most Telco people, about how it actually works. :P

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Received on Tue May 17 14:41:11 2005