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ISDN PRI w/ incoming-only channels AND normal channels, noncontiguous

Unanswered Question
Mar 31st, 2003
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I am trying to setup a 3725 with 12.2.(8)T5 to use an ISDN PRI that our telco (Telecom Italia) provisioned with the following channels:

- 1-8 are normal channels, capable of incoming and outgoing calls

- 25-31 are incoming-only channels

16 is signalling as usual, and the other channels are unassigned and unusable.

I am now configured with pri-group timeslot 1-8,16,25-31, which means that I am accepting all incoming calls, but half of the outgoing calls must be retried, in some cases many times, before succeeding.

I am using DDR, with local user configuration (no aaa new-model). There are users enabled for callback.

Can anybody think of a dialer/pri/whatever configuration to correctly support this, or a better workaround, other than having the PRI reprovisioned (something I would prefer not to do, due to customer relationships).

Best regards and thanks in advance,


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tepatel Mon, 03/31/2003 - 09:55
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  • Cisco Employee,

Answer to tht question is NO..That is because of you just have one E1 line.

You can configure the router to use ds0's for dialout (or callback) in bottoms-up (default) or top-down order but that will not gurentee that timeslots configured for only dialout will be tired.

So let say the box is configured for dialout using top-down order of ds0's as 1-8 ds0's are for dialout (and dialin) and if all of them are busy with dialout or dialin, the next dialout call will fail as router can't be configured to use certain ds0's for dialin/out.

Better off will be some ds0's for dialin only and some for dialout only..that will make the setup little closure to work but again no gurentee..

Ideally, you need to have seperate E1 for both..That way you can use "modem dialout controller ..."command to reserve one E1 line to be used for dialout only. Visit


bergonz Mon, 03/31/2003 - 10:17
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The "modem dialout controller" appears to be available only on the AS5300, not in the 3725 IOS, but anyway I have just that single PRI.

As for calling top-down or bottom-up, this is a point I missed and seems very interesting: empirically the router is now always starting from channel 31, with no success, but I will try "isdn bchan-number-order ascending" and keep you and the group informed. I don't care if it tries 25-31 when 1-8 are busy: when 1-8 are busy it is in fact impossible to place any call, it will simply take longer time and more effort to fail.

bergonz Thu, 04/10/2003 - 23:42
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Changing the order to "ascending" in fact solved my problem. The 3725 is now calling from channel 1 going up, and calls are succeeding. Thank you for the insight.


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