ISDN channels 17-31 Unavailable

Unanswered Question
Apr 15th, 2011
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We installed a fractional PRI in a site using h323. Everything seems to be working correctly most of the time until some of the users began complaining that they were unable to receive calls inbound on their phones at random parts of the day...

When troubleshooting using 'debug ISDN q931' I found that the calls were being rejected when the controller tried to use the channels 17 - 31 on the serial interface (see output below):

Apr 15 10:46:21 UTC: ISDN Se1/1:15 Q931: Received SETUP  callref = 0x809C callID = 0x00F5 switch = primary-net5 interface = User
Apr 15 10:46:21 gmt: %ISDN-6-CHAN_UNAVAILABLE: Interface Se1/1:15 Requested Channel 17 is not available
Apr 15 10:46:21 UTC: ISDN Se1/1:15 **ERROR**: CCPMSG_InCall: ChannelID IE invalid 44(0x2C) rejecting call
Apr 15 10:46:21 UTC: ISDN Se1/1:15 Q931: TX -> RELEASE_COMP pd = 8  callref = 0x809C
        Cause i = 0x80AC18 - Requested circuit/channel not available
Apr 15 10:46:41 UTC: ISDN Se1/1:15 Q931: RX <- SETUP pd = 8  callref = 0x003E
        Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA98392
                Exclusive, Channel 18
        Calling Party Number i = 0x1083, '353879911644'
                Plan:Unknown, Type:International
        Called Party Number i = 0x81, '4495'
                Plan:ISDN, Type:Unknown
        Sending Complete

when I make another call the controller tries to use the next channel and will fail if it is between 17 and 31. As soon as it goes back down to channel 1 - 16, it works fine again. Can anyone help me out here. Is there a way to stop using the channels 17-31 and just use channels 1-16?

Would appreciate help on this as I dont want to open  a TAC case,


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barry@nettitude... Fri, 04/15/2011 - 04:22
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Hi Shane

How many timeslots have you got configured on your T1/E1 controller? I suspect you've got a fewer number of timeslots configured than your carrier has..?


shane.oconnell Fri, 04/15/2011 - 04:48
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Hi Barry,

We have 16 timeslots configured. We had a lot of trouble with this site recently and changed it to this as we were informed it was a fractional PRI and not a full PRI as we previously were informed.

Anyway, is it possible to turn off the channels 17-31 somehow?



barry@nettitude... Fri, 04/15/2011 - 04:59
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Hi Shane

Not for incoming calls, as it is your carrier that is selecting and allocating the inbound channel.

The router is rejecting the call as the carrier is selecting a channel number (in this case 17) which it hasn't got configured.

Two solutions for this problem:

1. Get the PRI carrier to change their equipment so that they only use channels 1-16 for calls.

2. Change your pri-group on the T1/E1 controller so that your channels match up with the number of timeslots that are in use.

option 2 is a disruptive change in that you have to shut the controller down and remove the old pri group. if you do this, also back up your voice-port, serial interface and dial-peers as well, as they will all be removed to some extent or other when you remove the old pri-group.


shane.oconnell Fri, 04/15/2011 - 06:34
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Thanks man, I'll go with option 1st before I try option 2.

When you say the dial-peers and voice-port and serial int will be removed what exactly do you mean? Will this be wiped out and I will need to configure it again?

barry@nettitude... Fri, 04/15/2011 - 06:42
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Hi Shane

You can't change the "pri-group timeslots" command on the fly; you need to do a "no pri-group timeslots" command and reconfigure it. When you do this, the serial0/x/0:15 interface will be removed. Anything that points to it (e.g. dial-peers) will have their references to it removed.

The dial-peers will still be there, however the "port" command that references the controller interface will be removed from each of them and you'll need to add them back manually.

Hope this helps.


Muthurani Lavan... Mon, 04/18/2011 - 03:57
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Try using the Trunkgroup option. There is a new feature in 12.4 code that allows you to define individual timeslots of the PRI and assign them to different trunk groups. These trunk groups can be used instead of a voice port in a POTS dial peer, so you can direct calls to very specific B channels on the PRI.

Since your other end has configured only 1-16 channels, you can also configure only 1-16 channel for the voice calls and your calls will land only to the specific trunkgroup and avoid landing on other channels which are not configured.

Following is a config that demonstrates this feature on E1 interfaces -


controller E1 1/0

pri-group timeslots 1-31

trunk-group Customer1 timeslots 1-10

trunk-group Customer2 timeslots 11-20

trunk-group Customer3 timeslots 21-30



dial-peer voice 1 pots

description - enable DID on group 1

incoming called-number .


trunkgroup Customer1




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