PRI for RAS. Can it be used for IPT regular voice calls?

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Overall Rating: 5 (2 ratings)
shikamarunara Sat, 08/04/2007 - 15:13

It should work, but call the telco that proivisions the circuit first and get the relevant information on it (anything you need to configure it on the router). You might find out that it's a fractional T1, which will matter. Verify the switch type the circuit uses, etc.


Paolo Bevilacqua Sat, 08/04/2007 - 15:45

Hi Shikamaru, that circuit can't be a fractional T1, because FT1 doesn't do dial-up access for modem users, as has been indicated.

shikamarunara Sat, 08/04/2007 - 16:39

Why can't a Fractional T1 be used for RAS? I've seen fractional T1 PRI circuits before, they can't be used for dial-up access?


Paolo Bevilacqua Sun, 08/05/2007 - 00:18


A fractional t1 is a data circuit provisioned with a single set of timeslots,less than 24. AKA sub-T1 access.

A PRI ImeansPrimary rate interface) is a link to PSTN with a variable number of B-channels and a D-channel on TS 23. It can be used for voice and data, in both cases with switched calls.

The two things are very different, and a FT1 PRI doesn't really exists. One can say the only thing they have in common is the physical media, that is T1.

shikamarunara Sun, 08/05/2007 - 06:47

Well, it does in fact exist. It's also inconvenient. I did a cutover for a site where their PRI circuit was not full T1 and when I did the SRST testing I found that I could place calls but couldn't recieve calls. A q931 debug showed that I was trying to seize a channel on the top end that didn't exist on the circuit . . . because it was fractional. I had to add "isdn bchan-number-order ascending" to get it to seize a channel from the bottom end (which is bad because you can have glare issues.) The client upgraded the PRI to full.

So, yes, I think verifying the specifics of the circuit is warranted before he moves it.


Paolo Bevilacqua Sun, 08/05/2007 - 08:20


what you have met is correctly called a partially provisioned PRI. Still different from an FT1, especially in cisco parlance.

It would be like saying a that a CAS T1 with 12 TS if FT1. It is not.

shikamarunara Sun, 08/05/2007 - 08:24

Okay, well, whatever it is it's safe to say that the author of the original post should check for it.



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