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.
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.
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
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.