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T1 CAS and E&M

When we talk about T1 CAS, is E&M the only signal protocol or there is something else? I know T1 CAS is in-band signal. T1 PRI is out-band signal which uses 24 channel as CCS. My problem here is: we have a centralized cluster CCM solution.two sites have T1 CAS, two sites have PRI. I have PRI experience, but no T1 CAS experience. What I should configure on the T1 CAS? Has it be E&M or others? Thanks


Re: T1 CAS and E&M

There are more flavours of T1 CAS than you could poke a stick at ...

In mosts cases you would use e&m wink start with DTMF dnis -

controller t1 1/0

framing esf

linecode b8zs

ds0-group 0 timeslots 1-24 type e&m-wink-start dtmf dnis

The Signalling for a CAS trunk is passed via the ABCD bits, which corresponds to the least significant bit in timeslots 6,12, 18 and 24.

These bit patterns could theoretically represent up to 16 (2 to the 4th) states, but essentially T1 uses just the on hook (idle) and off hook (seized) states.

The most common type of T1 CAS is E&M wink start (sometimes called feature group B) , but there are variants such as E&M immediate start, FXO/FXS loopstart, FXO/FXS groundstart, Feature D and Feature group D EANA amongst others. Just to add to the confusion, you can often get any of these with Multi frequency tone signalling or Dual Tone Multi Frequency tone siganlling - this is the way the digits are passed in band on a particular timeslot.

All of these signalling variants use the ABCD bits to represent the call state for an individual channel in the T1. There is a ABCD bit pattern for each of the 24 timeslots. The bits will be idle, but if a call comes in or is sent out, they changed state to the seized state. The other device then listens for the signalling tones on the timeslot that corresponds to the particular ABCD bits that changed state.

If the signalling is E&M winkstart, the attched device will send a 200msec 'wink' (it sends a idle/sieze/idle) in the backwards direction to indicate it is ready to receive digits - kind of like a clear to send signal.

Here is a bit of light reading on some of the more common variants ...

And if you thought T1 CAS could be complicated (in most cases it isn't) you should try working with E1 R2 CAS signalling and it's 100 different country specific variants !

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