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Re: T-1 Question
Someone with more technical knowledge may answer better or differently but I would put it another way. A T1 with 24 channels is not the same as an ISDN PRI, which would have 23 B channels and 1 D channel for the signalling. A local ISDN PRI can have any number of DIDs assigned to it by your telco, it is not one-for-one with 1 DID assigned to each channel. I have a group of 2 PRIs with 1000 DIDs. I cannot have DIDs assigned to a T1, not with AT&T anyway. I have another group of 3 T1s, or Megacom circuits, for inbound toll free numbers and outbound.
A CO trunk is a Central Office trunk, or some people might call it a copper line or a copper trunk. I would liken it to an analog line and, as far as I know, you can't put DIDs on a CO trunk. At least I never requested that from the telco.
A T1 has 24 channels, inbound and/or outbound
An ISDN PRI has 23 usable channels, inbound and/or outbound
A CO is one line, inbound and/or outbound.
All of the above can be multiple trunks or circuits combined by the telco or you into one trunk group.
Just depends on what calls you have routing in or out on any given circuit or trunk.
An example of one of my systems:
Trunk Group 1 has 8 CO trunks and is used for last choice if all other circuits are down and for outbound 911.
Trunk Group 10 has 2 ISDN PRI circuits used for inbound DID and outbound local.
Trunk Group 11 has 3 T1 circuits for inbound toll free, outbound local toll, national and international.
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 Penelope
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