PRI Question

Unanswered Question
Jul 11th, 2007


i have a question about PRI configurations. most of my customers have T1 CAS and are now going to implement PRI. i have normally configured the main routers as H323 gatways and separated the timeslots according to customer requirements. for example

i have one customer that uses the VM AA as well as the IPCC AA on the same T1. i have two PLARS to the different pilot numbers and thats it. how do i do this with a PRI? can i split it in the same way? i also noticed that most persons configure it as an MGCP gateway. from my limited experience ive always opted to go H323 based on what i saw as instability factors (could simply be my misconfigurations but who knows).

any explanations would be greatly appreciated.

thanks in advance

I have this problem too.
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dgahm Wed, 07/11/2007 - 20:43

Sounds like FXO signalling on the T1 CAS? Do they also have DID service? With PRI the telco is going to send you a number with every call, typically a DID number that will be fewer digits than the full E164 external number. As an example, if you have DID service, and internal DNs with 4 digits, just those digits will be sent. The telco will also be able to send you whatever number you need to see for calls that go to your VM or IPCC pilots. Depending on your dial plan, you may need CCM translation patterns to route calls to the correct phone or route point.

MGCP is very solid, with the benefit of caller ID. You can use MGCP fallback to revert to H323 if SRST is a requirement.

Here are a couple MGCP PRI docs:


Please rate helpful posts.


a.gooding Thu, 07/12/2007 - 03:31

they will be having DID service. so again i normally split the timeslots and i get different voiceports which i then apply a PLAR to. im assuming that would not be the case. also, the telco asked to provide our DID ranges - our dial-plan will range from numbers 1xxx to 2xxx and our VM and IPCC pilots are 9XXX. do i sepcify a DID range for those as well?

basically, its a few services on the PRI that i want to get and normally i split it.

dgahm Thu, 07/12/2007 - 06:56


You won't use PLAR because the telco will be sending you a called number that the Call Manager will route. Let's say the phone on your desk has a DN of 2123 and the outside number is 555-2123. When someone external calls 555-2123 the telco will send call setup on the PRI D channel with a called number of 2123. The actual bearer channel (audio) used can be any one of the 23 available. You will not split timeslots.

Calls to AA pilots are usually a result of someone calling a main listed number in the phone book. The telco can translate and send you whatever number you want on the PRI. If your old PLAR setup rang 9222(as an example), then that is what you should request from the telco.


a.gooding Thu, 07/12/2007 - 14:55

Got it...bear with me for one last time..

my pilot number for my IPCC presently is say 9240 on the call manager side but from the telco side its 800-QUOT (7868) then with PRI i need to CHANGE my pilot number on the CCM side to 7868 right? now say i also have a number 623-2201 which is a pilot FROM THE TELCO SIDE AGAIN (which has say 16 lines associated with it) and i want that pilot to go to my normal AA then i need to also change that pilot to 2201 on my CCM instead of say 9270 as i have right now?

i promise ill get it. first time workig with PRI :(

Paolo Bevilacqua Thu, 07/12/2007 - 15:49


telco can route you toll-free number to any number. So it not said it will be 7868. Ask them which number it will be, or make your request for this. Then you configure all your system to behave appropriately when a call for that number comes in.

dgahm Thu, 07/12/2007 - 16:34


The telco will send you whatever you request, or you can change your pilots, or you can configure a translation pattern in Call Manager and both numbers will work. If they send 7868, you translate that to 9240. But your best bet is to ask for 9240. It will be less confusing in the future for someone else to understand it.

Regards, Dave

a.gooding Thu, 07/12/2007 - 19:45

thanks a lot for all the replies. i think i have the jist of it now. We have one local provider and they are now deploying voice PRI hence my issues with the way it operates especially with this provider. i also spoke to them and they said that they would not be able to provide both 800 numbers and my normal pilot 623-2201 on the same PRI. that made no sense to me whatsoever and im under the assumption that its some type of marketing issue.

again thanks for everything and i can now go ahead with a little more confidence.

a.gooding Fri, 07/13/2007 - 11:23

just an update. spoke to my provider and here is the deal

we cannot have more than one pilot number associated with 1 pri since there is only 1 control channel. therefore i cannot have pilot numbers 623-2201 and pilot numbers 800-7868 on the same PRI. both pilots have about 10 lines associated with them. with T1-CAS this can be done since we can split the channels.

i have a workaround but thats still dissapointing.

dgahm Fri, 07/13/2007 - 11:36


I think you are miscommunicating with your service provider. He is referring to the PRI pilot/billing number which has nothing to do with what you want. Unless you request that they pass your calling number through this billing number will be the caller ID number seen on outbound calls through the PRI.

Just tell them that when someone calls 623-2201 you want to see XXXX as the called number on the inbound (to you) call. Don't use the word pilot.

We have over 40 PRIs from 4 different service providers, and I have never had a problem with getting the forwarding set up to handle multiple main number pilots.

Good Luck, Dave

a.gooding Fri, 07/13/2007 - 12:41

im going around in circles. please bear with me.

I HAVE 2 lines from my provider 623-2201 ( which is a pilot number which has other PSTN lines all in a hunt group. when someone calls from the PSTN side THEY DIAL 623-2201 and the calls comes into the PBX via anyone of the available PSTN lines in the hunt. thats fine.

Now we have another PSTN number 800-QUOT which has 4 PSTN lines associated with it. this is for our call centre. so someone from the PSTN calls 800-quot for a different service. what they are saying is that they cannot combine these two numbers into one PRI.they say that this cannot be done - we have not even spoken about the CCM as yet.

again bear with me. it probably the weather here :)

dgahm Fri, 07/13/2007 - 14:40

What phone company is this? I have done this exact thing (disconnect a MLH or DNH and forward the pilot to a PRI that handles DID calls)with many telcos. Several have been more than a little frustrating to deal with (I have nightmares about Verizon), but all were able to accommadate us.

Since you are getting DID service, ask them if they can forward each of the hunt group pilots to a DID number? Unless they are also saying you can only have one DID number per PRI. That's a joke :-)

a.gooding Fri, 07/13/2007 - 15:26

was i clear with the last comment?. i asked because it was what i asked them and they said no. One one Pilot (eg 623-2201) per PRI. i even have a series of numbers 800-quot, 800-serv and 800-care and they all say that since they are all separate trunk groups they have to be on separate PRI. i have all these on 1 T1-CAS and the only reason we are moving to PRI is for the Caller-ID but we are now thinking this probably isnt worth the cost. and no they asked for us to specify a DID range however they only sell in blocks of 50 which is another thing i wont get into.

rob.huffman Fri, 07/13/2007 - 18:19

Hi Arvind,

Maybe the weather has cooked the telco persons brain :) Just to add a note to the great info you have received from Dave and Paolo.

Many Telcos sell DID Blocks in 100 number increments only so 50 isn't too bad. What if you did this;

Order a new 50 number DID block - lets just say it is 644-5000 to 644-5049 this 50 number block will all route to you via the new PRI.

Ask the Telco to route 623-2201 to 644-5000 and you can put 5000 anywhere you want. The translation for 623-2201 to 644-5000 is all done behind the scene.

For the 800 numbers;

Ask the Telco to term 800-quot on 644-5010

Ask the Telco to term 800-serv on 644-5020

Ask the Telco to term 800-care on 644-5030

You can then install 5010,5020 and 5030 on any devices that you want to.

These are extremely common practices with PRI Services. You may be dealing with a Sales person who doesn't fully understand what is possible. But, as Dave mentioned before, we have many 800 numbers (probably 50 or more) that all route to us via the same set of PRI's. They just need to term on a DID number within our range.

Hope this helps!


a.gooding Sat, 07/14/2007 - 05:29

everyone thats for ALL the great assistance.

so if i order that block, assign 623-2201 to 644-5000 then i understand that. how much calls can i have coming through that number (623-2201)though?. one only? ( since 623-2201 is assigned only 644-5000?). i think this is unclear to me. we want that number to be the main number but have 16 lines associated with it for simultaneous calls into the organization. (basically as it is now 16 PSTN calls can come in simultaneous on the 623-2201 number)

i know this is PRI 101. and this is the last question promise. once i understand this fully i can be a little more confident when speaking to the provider and from the amount of questions i had you guys a probably regretting this :)

thanks again and you wouldnt beleive how helpful this has been

dgahm Sat, 07/14/2007 - 09:45


You can have 23 calls active on a PRI, and all of them could be placed to the same number.

If you only have enough internal capacity (VM ports or wave ports) to handle 16, then the 17th call will get fast busy. Even with AA, or call center queue the calls end up getting connected to internal phones, so the bottleneck would likely be the PRI capacity.

Some phone companies will sell you a fractional PRI, usually with 12 bearer channels, rather than the standard 23.


rob.huffman Sat, 07/14/2007 - 10:00

Hi Arvind,

These are always interesting type threads, so it's good to see them pop up. Like Dave so nicely noted the PRI can route multiple calls to the appropriate areas within your Company. Your internal configuration will really determine the number of simultaineous calls to any specific number. For example;

If 800-qout routes to 644-5010 and the Phone the has 5010 on it has a "Busy Trigger" of 2 then call number 3 will get a Fast Busy.

Hope this helps!


a.gooding Sat, 07/14/2007 - 12:14

guys i think i understand completely and here i spoke to the provider and here is what they said.

1. no multiple pilots on a single PRI becuase of only 1 D-CHANNEL

2. i can have 800 numbers and any kind of numbers in a PRI but it cannot be a pilot number (pilot meaning 800-quot is a pilot number that is also associated to say 623-4455,7623-4456 so in the even that someone calls 800-quot it routes to 623-4455 and if that is busy goes to 4456). therefore they say i can have EITHER 800-QUOT or 623-2201(which is associated with 16 pstn lines in a hunt).

3. based on this i also cannot have 800-serve and 800-care as well on the same PRI since again it is only 1 D- CHANNEL and all these are pilots that are separate trunks.

4. their recommendation is-------

so ---------------exactly hehehe...this thing is harder to understand that the ENTIRE CALL MANAGER SYSTEM..and i was soo proud when i understood CSS and know what too, its so hard to relate to these providers especially when they hold the monopoly. they rarely try to assist and the attitude is do you want it or NOT?.....its so lame

dgahm Sat, 07/14/2007 - 12:43

They don't seem to grasp that you want the old hunt group disconnected. All calls to 800-quot just need to go to a single number that will be routed to your PRI. There will be no overflow to any other numbers. This is not required on a PRI.

a.gooding Sat, 07/14/2007 - 16:22

ive called a meeting with the provider. will keep you guys up to date.

again thanks for everything, these answers (not onyl the pri) help out so much when you feel youre stumped.

thanks again and i hope that one day i can return the favour.


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