The robbed bit T1 has 2 signalling bits, but the usually do the same thing, so its really like having just one signalling bit. However, the timing of changes to that signalling bit can follow one of several patterns. You will see the terms immediate start and delayed dial used, as well as the terms LS, GS, etc. These are more descriptive, as they describe what will actually happen to the signalling bit.When we had a MCI ct1, they couldn't send us proper supervised hangup on
a loopstart encoded DS0. They claimed it to be a problem with the
software on their switch. Their solution was to switch to groundstart.
Our end solution was to drop them and switch to Telcove(formerly
Adelphia) and get a PRI where we controlled the signaling with asterisk.
Again, how the hell is switching the supervision type changing anything in the bitstream? You have 193 bits being sent 8000 times a second. There is no grounding or reversing of a battery on any kind of T1 -- that is strictly FXO-side signalling. You have 2 (SF) or 4 (ESF) bits with a CT1 to determine channel state. And with ESF those extra bits are usually just duplicates of the original 2. You have onhook, offhook, ringing and something I can't remember at the present moment.
I am positive I'm showing my T1 newbieness here but again... how does the switch changing their FXO signalling/supervision change the bitstream and "fix" CT1-related issues?
I completely understand E&M, LS, GS and all of that on the actual analog side -- but how does it change a damn thing on the CT1 side?
Immediate start and I want to dial: I raise my signalling bit, wait a moment, then send my DTMF. When the far end answers the exchange's signalling bit is raised. When the far end drops the exchange's signalling bit drops.
Delayed dial and I want to dial: I raise my signalling bit, I wait for the far end to give a little pulse (called a wink) on its signalling bit, I then know it is ready to receive DTMF. I send my DTMF. When the far end answers the exchange's signalling bit is raised. When the far end drops the exchange's signalling bit drops.
Other variants are that only signalling bit A or only bit B changes; the signalling bits are inverted; the line only works during a full moon; etc.
Regards, Steve
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