CAS T1 RBS Protocol Stacks  -- C Source Code

TeleSoft provides many WAN protocol software packages, including T1 Robbed Bit Signaling Software (RBS) That 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.  TeleSoft's RBS source code supports at least the following starts:

• Wink start - E&M support
• Delayed Start - E&M support
• Immediate Start - E&M support
• Ground start - FXS support
• Loop start - FXS support

The above starts are configurable on a per-DS0 basis.

TeleSoft's RBS protocol stack also supports

• DTMF Tone Processing Module 
• Direct Inward Dialing support (DID) for Wink start
• Logging function (tracks line signaling state changes)
  

TeleSoft's Robbed Bit Signaling SDK has a state machine that is shared with TeleSoft's PRI SDK and E1 CAS SDK.

TeleSoft's Robbed Bit Signaling protocol stack supports "ABCD" and "ABAB" signaling:

• ABCD signaling for the following protocols as defined by TIA-464-C:
  • PBX Tie-Trunk (4W E&M)
  • CO / FX / WATS Trunk (SAS / FXS & SAO / FXO)
  • DID (DPT & DPO)
  • OPS (SAO / FXO & SAS / FXS)
  
  
  • Both ends of the interface (PBX end and far end) are required to use the same protocol such that peer-to-peer connections may be established.
  • The protocols are configurable on a per-DS0 basis.
  • Note that Hook Flash Support includes ability to initiate and receive flashes and digits during active call phase using pulse dialing.
    


•  Line encoding for:
  • AMI, B8ZS, CMI
  • Bit oriented messages
  • BOM/BOC per T1.403


• Line framing for:
  • SF (D4)
  • ESF
  • TR-08 (SLC-96)

TeleSoft's RBS source code library supports the following T1 maintenance operations:

• Maintenance operations for:
  •  Remote, local and payload loopbacks
  • ANSI T1.403 Facilities Data Link (FDL) reports
  • AT&T TR54016 Facilities Data Link (FDL) reports


• Performance data per:
  
  • ANSI T1.403
    
  • ANSI T1.231
    
  • AT&T TR54016

TeleSoft's RBS stack supports alarms per:

• ANSI T1.231
  
  • Red Alarm -- Loss of Frame (LOF)
    
  • Red Alarm -- Loss of Signal (LOS)
    
  • Blue Alarm -- Alarm Indication Signal (AIS)
    
  • Yellow Alarm -- Remote Alarm Indication (RAI)
    
• ANSI T1.231 (Declaration & clearing)

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TeleSoft International is the original developer of the TsLink3 range of high performance WAN protocols including ISDN BRI and PRI, QSIG, CAS E1 R2, T1 RBS, AO/DI, ML-PPP, Frame Relay, X.25, and also a range of hardware reference designs. TsLink3 protocol source code is exceedingly well engineered - tightly coded for performance and compact footprint, with a quality that delivers rock-solid stability.

TeleSoft's foundations go back to 1986 when the first ISDN stack was released. Since then TeleSoft's protocols have been proven in use by more than 200 customers worldwide. World leaders, including AT&T, Cisco, D-Link, Digital Equipment, Fujitsu, IBM, Lucent, Matsushita, Multi-Tech, NTT, Polycom, and Vertical Networks have all used the source code for  TeleSoft's proven protocol software.