atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's How many B channels on a PRI

I have 3 PRI's in the same trunk group.
There are 22 B channels on the first one, 20 on the second and 20 on the third.
Should there not be one A channel on each T1 and 23 B channels? It's been a long time since I worked on this stuff and I don't recall exactly how it all works.
I have an old G3siV11, not that it makes any difference.

A PRI should consist of 23 B (bearer) channels and one D (data) channel. There isn't an A channel. I'm a bit confused as to why two of your PRIs have only 20 channels though.

A PRI should be 23B+D (23 B Channels and1 D Channel), unless it's European format, in which case it's 30B +1D.

Sam

Beat me to it, Ed.

Sam

There wouldn't be a limitation due to the card in my Definity would it. Should I redirect this to the Avaya post?

With NFAS it might even be slightly better than 3 D channels, you could probably reclaim one and cut it down to 1D plus one backup timeslot for it.

Those terminate on a TN767 E board. Should I redirect these questions to the Avaya forum?

I have PRI's with 12,16, 20,and 23 B channels. It's popular down here particularly if you different trunk groups and just looking to save a few bucks with the cost of reduced B channels.

According to my AT&T Rep, we don't pay per B channel, just for the T1 ($645/mo). Not sure I understand that, in light of the short number of B channels I'm paying for.
I enailed him to find out why we aren't maxed out on B channels for the T1's and still have no response.

Enailed was an accident, I like it.

Are all the B channels on each PRI enabled in your switch??

I don't buy that. I'm sure you're paying for each termination in the switch as well as the T1

I tried to bring the vacant B channels up and they didn't respond.

Bill, I agree with you, but still have not heard from my AT&T rep. about the enail I sent him. Looks kind of fishy. For one thing, why wouldn't you have the unused B channels at the end of things.
Another thing about this that's curious is that we have way to many B channels. I have it set up so that incoming calls hit the first B channels first and outgoing calls hit the last B channels first. I have never seen one call on the middle T1. So how are we seeing busys (a very few) on my Busy study?
I think our grade of service exceeds AT&T's and those busys are actually their blockage.
This whole thing is curious.

At one time you could buy a fractional T1 or PRI. You can't any more. You lease a PRI nowadays and you get all 24 channels. 23 Bearer channels for Voice or Data and one D or Delta Signaling Channel. Any individual channel blockings or turn downs are accomplished through translations.

Boskerthearkite, we have have a fractional PRI, originally it was 5 B channels and 1 D. Then about 6 months after that we got 16 B and 1 D. However, we seemed to have an unusually amount of busies when all channels weren't busy. Turned out that Windstream created a seperate trunk group at the CO for the added channels instead of rebuilding the original trunk group at the CO. So we were able to make as many outgoing calls as we needed but the first incoming trunk group wasn't forwarding to the second. After many calls and explaining to them what was going on finally I got a switch tech that knew their way around a CO switch and said "Oh all we need to do is forward your first group to your second" and as soon as that was done we were good to go. So I don't know if this is happening at all but you may be having a similar problem.

I've definitely seen fractional PRIs with 16 or 20 Bs, but I, too, don't understand why they wouldn't just give you 16 on the last one and leave the other two full.

I also agree with nortelvoip...ask them about how they handle overflow conditions. You might need to specify a "trunk group overflow" "feature" depending on the LEC -- they won't necessarily provision you by default.

You need to get AT&T to reconfigure your PRI pipes. You need to make sure that all 23 B channels in each pipe is in the same trunk group. You are paying for a full boat PRI, therefore there should be no fractional service.

I don't know what the tariff situation is in Kansas, but, here in PA there are a lot of fractional T-1 and PRI circuits, however, all new circuits are full 23B and 1 D on the PRIs. I haven't seen any T-1 circuits being installed for a while. Everything is PRI.

Rcaman

Audit your T1/PRI's and see what your paying for then go according to Rcaman's suggestions.

In the early days of T1/PRI fractionalizing was a way of providing digital service above 128K to customers who couldn't afford or didn't need 1.544Mb/s. You paid according to the bandwidth needed which equated to a certain number of 64kb/s channels.

I just installed an AT&T IP Flex product. This was a PRI with 15 enabled channels. The rest of the provided bandwidth will be for a secondary data pipeline for their network.

I have asked the AT&T Business Department for an accounting. Obviously the Account Rep is too darned busy for me.
I'd switch to Cox, but they aren't nearly reliable enough here to count on. One good thing to be said for AT&T, the have never gone down with their local service.
Long distance is down about once a year.
Our IT guys say the Cox T1's are down a few times a year, for varying lengths of time.
I'll let you alll knnow how this turns out.

Well, now I have the straight skinny from the Business office.
The spans are working in sequence as we want, I am paying for 22 channels on the first, and 20 channels on each of the other two.
Cost is $337.50 per span and $20.00 per B channel.
That makes more sense.