PBXJoker

On a T-1 you can have up to 24 channels where each channel can be designated as a DID or CO channel. My question is simple:
Is the CO channel simply an outbound line to the Central Office? I know the DID is for calling in and how everything works but I was confused on what the outbound was called a CO.

penelope

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

PBXtech.info

 

PBXJoker

Thanks that does help.

Our case is we have three T-1s for DID, local outbound, and toll free and we also have two T-1s dedicated for long distance. We are trying to figure out since we only have about 300 people that can call long distance if we can get by with only three T-1s that would be divided up for DID and local outbound, and long distance.

Thanks again.

penelope

If you have Avaya Site Administrator (ASA) you can run trunk analysis to see what your usage is. You will need to set up a job that runs once a day and gathers the information. Do a search on ASA for 'trunk analysis' (I am not at work so can't look it up now). The longer you can run it the better. I have ASA set to be able to log on automatically and leave the software up and running on my PC every night. It runs at 10pm. Make sure that all connections are closed and it is totally disconnected or it won't run.

When you have collected the data you can run the Trunk Analysis. It will tell you how many trunks were needed out of each trunk group. Say... you needed 8 of the LD trunks and 40 of the other then you know that in total you needed 48 trunks, which could all be handled by the 3 T1s.

My HQ system is a little over trunked but it is a bit of protection in case a circuit should go down then the others can take up the load. I have had instances where all of the DID trunks were down. I can't do anything about the inbound DID not working but the other 3 trunks can take up the slack. I also have 1 LD trunk from another carrier and the CO trunks as backup.

I have also had the group of 3 T1s go down where all the inbound toll free come in. I have created DIDs that go to the same point as the toll frees would normally go in case I need to have the carrier re-route them to the other trunk group.

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Penelope

martinyoung

Penelope, your answers are very good.

The trunk analysis is on Fault & Performance tab and you should run it every day for at least 30 days. I would recommend at least 45. It will give you a good estimate of your daily needs.

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Marty
Retired Avaya DSIC tech