Translation Pattern For Overlapping Numbers

In this centralized deployment we have three sites, Paris, Madrid and Berlin, the phones are registered in the CUCM located at Paris.

The issue we have in this scenario is the overlapping extension between Madrid and Berlin that use the same extension range 2XXX.

To solve this issue from Cisco SRND:

Systems with many sites or overlapping site extension ranges can benefit from the use of a variable-length dial plan with the following:

  • Within a site, the system retains the use of abbreviated dialing for calls to on-net extensions (for example, four-digit dialing).
  • Between sites, users dial an access code followed by a site code and the destination’s on-net extension.
  • Off-net calls require an access code followed by a PSTN number.

Let’s deploy a dial plan to solve this issue.

To dial between site, we use: Access code + Site code + extension.

Access code 9 for dialing outside

Access code 8 for dialing internal

In this scenario we use 8 + seven-digit number for internal dialing.

For sites with 4-digit extensions, we use 3-digit site codes.

  • For Paris, we use 8-401-1XXX
  • For Madrid, we use 8-501-2XXX
  • For Berlin, we use 8-601-2XXX

Let’s implement this with Partitions, CSSs and Translation Patterns.

First we need a specific partition for each site.

  • Paris-PT
  • Madrid-PT
  • Berlin-PT

Second we need a partition to use for dialing between sites, the Inter-Site-PT partition.

Then we need for each site, a specific Calling Search Space CSS containing the specific site partition first and the Inter-Site-PT Partition second.

  • Paris-CSS
  • Madrid-CSS
  • Berlin-CSS

After defining the Partitions and the Calling Search Spaces, we need a Translation Pattern for each site.

Translation Patterns contains the following settings:

Pattern + Partition = Match this

Called Party + Calling Party = Perform Digit Manipulation

CSS = Look for number here

For example:

Pattern = 8401.1XXX in the Partition = Inter-Site-PT, then with the discard PreDot in the called number, the dialed number will be four digits, to call successfully the resulting of this translation pattern 1XXX, the CSS is set to Paris-CSS.

Now if anyone in Madrid site or Berlin site dials 8-401-1001, the translation pattern above belongs to the partition Inter-Site-PT, the user at Madrid site or at Berlin has a CSS that contains this partition (Inter-Site-PT), so it (the translation pattern) matches, we discard PreDot for the called number to get 1001, we will look for this number and we find the partition Paris-PT in the CSS Paris-CSS, finally we find the extension 1001. 1001 will ring.

Published by:

Redouane MEDDANE

Redouane MEDDANE is Cisco Instructor CCSI #35458, 3xCCNP Collaboration, Security and Enterprise and he a published author of some of the most important OSPF Protocol, Security and Collaboration books in the world titled OSPF Demystified With RFC, Network Security All-in-one, and Dial Plan and Call Routing Demystified on CUCM. He is also a blogger at and writes articles about collaboration and security to demystify the most complex topics. His books are known for their technical depth and accuracy especially the OSPF Demystified With RFC book, which is considered as the best OSPF book in the world and named "One of the best OSPF ebooks of all time" by BookAuthority It gives you a hint at the ability to explain complex topics with remarkable ease. He worked as a Cisco Instructor and consultant indifferent Cisco Learning Partner and awarded twice as Cisco Distinguished Instructor Award and Cisco Security Instructor Excellence Award on 2018 and 2019, and Cisco Collaboration Instructor Excellence Award on 2020. The Distinguished Instructor Award recognizes the top 5% of Cisco's most influential CCSI's who provide the highest quality training experience and demonstrate the best overall instructor performance across multiple Cisco technologie and Instructor Excellence Award recognizes the top 25% of elite CCSIs being recognized for delivering top quality training and maintaining high customer satisfaction in their field of expertise.

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