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How do I troubleshoot missing Caller ID over PRI?

  • October 31, 2014
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Some instructions for resolving problems of missing caller ID over PRI (T1/E1/J1) connections.


If inbound PRI calls are not displaying caller ID information, the first thing to verify is that the incoming SETUP messages contain caller ID. You will want to make sure that they contain caller ID info. Once you obtain a PRI debug capture from the PBX, you should check for the inbound SETUP message. Look for a line like the following:

< Message type: SETUP (5)

This indicates the beginning of a SETUP message that was received, which is what signals the start of an inbound call. The preceding '<' characters indicate that this message is incoming, rather than outgoing (which is depicted by a '>' character).

Within that message you should see lines like the following:

< Display (len=15) [ DIGIUM ]
< [6c 0c 21 81 34 30 38 33 31 34 36 35 35 36]
< Calling Number (len=14) [ Ext: 0  TON: National Number (2)  NPI: ISDN/Telephony Numbering Plan (E.164/E.163) (1)
<                           Presentation: Presentation permitted, user number passed network screening (1)  '2564286000' ]

The "Display" line is the caller ID name, and the "Calling Number" line is the caller ID number. As indicated by the above message, the telco is sending caller ID information inside the SETUP message. If you do not see any caller ID info in these messages, you will need to contact your telco to get them to enable it.

Some carriers use other methods of sending caller ID info. For example, it is not uncommon to find the caller ID name sent separately in what is called a "Facility" message. If this is the case, you will see a separate incoming message that begins with the following:

< Message type: FACILITY (98)

In the line beginning with < Facility you should see a string, which contains the caller ID name. If the telco is sending the CID name in this manner, you may need to configure your PBX to wait a few seconds before answering the call, so that it has enough time to receive the FACILITY message containing the CID name; otherwise the PBX will answer the call too early, and it will not receive or display the CID name. This can be configured in the Channel Group settings for Switchvox, and in the dialplan (extensions.conf) file on an Asterisk system.

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