PRI provider questions

My provider has sent me a list of question about what I need for the provisioning of the circuit. Most of them I was able to answer but I have a few that Im just not 100% about…this is a copy and paste of the questions in question.

Number of digits you’d like us to send on inbound traffic

Do you want inbound calls to ascend or descend trunks

Framing (ESF/B8ZS I assume?)

Variant (NI2?)

I assume the number of digits I need would be 10 (npa-nxx-xxxx)its just seems to have been too simple of a a question I thought

The ascend or descend seems to be just preference because I don’t see anything about it anywhere. I was going to go for descending but is there a reason for ascending?

The other 2 seem to be fine for what they are suggesting my question is, is there a better reason to do it differently?

Thanks for your help.
I have tried to Google these things and search in the forum but I didnt find much if anything.

Everything you said is correct.

Some “Background” . . . .

The ascending/descending question is a legacy of traditional T1’s where if an inbound and outbound call collided on a channel in time there was a small chance of “glare” where the e&m signals (ear and mouth) where briefly in a non resolvable state as to who “owned” the channel, this is not a problem with ISDN PRI’s, the only use in a PRI is to see post-factum the trunk usage more easily as the indound go up and the outbound go down, but you will change that yourself by using trunk group g0 g1 to suit. NI2 signalling (National ISDN version 2) is generally a good compromise between ESS and DMS switches, if they can do QSIG that is better, the signalling and framing are probably also left over from Traditional T1 forms, there is no reason to use AMI or D4 line coding/framing as they are more error prone. As to the number of digits sent, if interfacing with a PBX , then we sometimes prefer 4 digits and assume the first six (or seven :wink: ), simply because it saves us typing stuff, and they are all normally coming from the same Central Office withe the same office code. I always try and keep my numbering within the last four unique when buying SIP DID’s for the same reason, as it allows unambiguous 4 digit dialing throughout the switch, avoid NNNN’s that start with 0, 1 or 9 , for reasons that are not that important until you run into them, then they can get to be a real PITA, (think Most Significant Digits here). (this last bit for those of us in NANP land) They are not in-coincidentally the first that will be offered you because of their unpopularity.

What you say,dicko, is true…except…what happens when the ultimate user decides to LNP legacy numbers. A little extra typing is trumped by the extra flexibility 7 or even 10 digit DIDS afford.


Of course if the last four collide with an existing DID there is a problem, with one LNP and one common block of 100, fully used, a one percent chance statistically I believe. If that happened then I agree, there would be a need to reprovision the PRI and lot more typing needed to accomodate such a change. So far I have not been that unlucky though. I wonder if the Vendor would have that incompatabilty flagged at their end? The bigger inelegence would be the inability to map 4 digit extensions to DID’s uniquely on the PBX. Being a pragmatist, I would probably arrange for an RCF on that LNP to an unused DID in the common block to avoid such a situation. As Clint might say "How lucky do you feel today, trunk? . . . "