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Walkthrough Wednesdays

Odd dialing behavior with Nortel 81c PBX

I'm wondering if anyone has ever experienced the following or has any idea what might be causing this.  I have a 2821 with 2 PRI trunks into a Nortel 81c pbx.  I'm using Q.sig as the switch type.  The ISDN layers are up and operational.  The 81c is connected to the PSTN with multiple PRIs.  Here is the configuration of the D channel:

interface Serial0/0/0:23
no ip address
encapsulation hdlc
isdn switch-type primary-qsig
isdn incoming-voice voice
isdn supp-service name calling profile Network-Extension operation-value-tag local
isdn outgoing ie facility
no isdn outgoing ie notify-indicator
isdn outgoing display-ie
isdn outgoing ie caller-number
isdn outgoing ie called-number
isdn incoming ie channel-id accept-qsig-variant
no cdp enable

The problem is that I am able to successfully place a call to some 1800 numbers, but not others, including 1877 and 1866.  Also, none of my 7 digit dialing is working - 9NXXXXXX.  When a non-working 800 number is dialed or 7 digit #, the phone just rings and the eventually I get a busy and it hangs up.  These non-working numbers are able to be dialed from non-Voip phones connected to the 81c.  It  seems very odd that one 800 number would work, and one wouldn't.

I've debugged isdn q.931 events but that hasn't led to any appears that the call is handed off to the 81c successfully, then a disconnect is eventually received after the ringing has stopped.

Any ideas?



Look at the traces on the PBX side.  You can see what the switch sees by looking at dchannel messages in LD 96.  You have to make sure your COS / FRLs on the Cicso trunks give you permission to get out on the PSTN trunks.  A PRI debug of the PSTN trunks, if the calls are trying to get out will show you if you have a digit manipulation / dial plan issue.  Can you dial internal / Nortel extensions?


Thanks for the reply.  At the end of last week the PBX folks turned on dchannel messaging which unfortunately didn't lead to any clues, at least that we could tell.  I asked them to check to the other items you mentioned so we'll see if that turns up anything.

Re: dialing internal/Nortel extensions, yes, I have no problem dialing Nortel extensions, both into and out of the router.  Is it just me or is it very odd that I can successfully dial a particular 800 number, but then a different (working) 800 number just rings and rings? I guess that is where debugging the PSTN PRI trunk might shed some light on it, if perhaps not all the digits are being passed for whatever reason.

Thanks again,


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