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Transform PSTN Number to internal Number

Level 1
Level 1


We have implemented a SIP Trunk to PSTN recently for the first time. We have problem in our incoming calls that do not establish. How can I translate in PSTN number to internal directory number in cucm?

Thank You


2 Replies 2

Slavik Bialik
Level 7
Level 7

It is very simple, but give us more information like what is the full DID range and if the DID contains in its end the internal number in the CUCM? For example, if you have a DID +16465881500, does it mean that in your CUCM the internal number is 1500?

Given the example above, if that's the case, you can easily configure a "Translation Pattern" in your CUCM like in the attached screenshot.

In my example, I'm having a DID range of 10 numbers: +16465881500 - +16465881509

And I'm translating the above to internal numbers: 1500-1509.

Look at the red markers I've made in the screen shot:

  1. Partition - a partition that you have in your CUCM that is visible when an inbound calls goes into your CUCM. That means that in your SIP Trunk, in the Inbound CSS you need to choose a CSS that sees the chosen partition for this translation patter. It is mostly "Internal" by my convention (and others, heh).
  2. Calling Search Space - this is the CSS that after the translation pattern found, it'll go and look matches of internal DNs, patterns, and etc by the configured CSS in the translation pattern. So you must put a CSS that sees all your phones.
  3. Called Party Transformation - Discard Digits - In this example, I configued "PreDot", it means that it looks on the translation pattern which contains a dot character, and strips everything that is on the left of the dot. Means, it only leaves "150X".


You can do more tricks with the Discard Digit option, like if you a have DID range like in my example above, but it should be translated to internal numbers: 2500-2509 and not 1500-1509. So you can configure "PreDot" like in the example, but in a field named "Called Party Transform Mask" you can put 2XXX. The 3 X's will take the last 3 digits, and it'll concatenate the digit 2 in the start.


Hope it helped. Anyway, you can give us a specific case and we'll gladly show you how to configure the relevant translation pattern you need.

Thank you very much for your great comments.

Actually we don't have DID and just want to translate the incoming call to a specific directory number.

For example we want to translate 8135041440 to 4907.

We did all the tasks you mentioned before, but it didn't work. We also applied CSS for the inbound section of the SIP Trunk configuration too.

I should tell you something more. We have connected our SIP Trunk modem to the firewall (not voice gateway). Is this topology correct or not?