T1 Robbed Bit Signaling Software (RBS) complies with EIA-464B and AT&T TR41458. Robbed Bit Signaling is an older digital signaling protocol that uses (robs or steals) one bit (the least significant bit) from every sixth octet on each voice DS0 on a T1. Using RBS means that data cannot reliably be transmitted in that bit, so a DS0 on a T1 using RBS is limited to 56K transmission.
Each T1 channel carries a sequence of frames, composed of 24 octets (each B channel, or DS0 contributes one octet per frame) and a framing bit. CAS looks specifically at every sixth frame for the channel's associated signaling information, which is carried in the least significant bit of each DS0's octet. In an Extended SuperFrame (ESF) these bits occur in frames 6, 12, 18, and 24 and are called the A-, B-, C-, and D-bits respectively. In other types of framing, the AB bits are repeated in the CD bits, so instead of ABCD, the line is ABAB. Note that RBS is a type of "in-band" signaling protocol.
Because of the fraud that occurred soon after T1 RBS was deployed, several ways to start a phone call were devised. A quality RBS source code will support at least the following starts:
The above starts should configurable on a per-DS0 basis.
The Software should also support
A good Robbed Bit Signaling protocol stack supports "ABCD" and "ABAB" signaling:
A good RBS source code library will also support the following T1 maintenance operations:
Alarms should be supported per: