Back to blog
Blog , How-To

Diagnosing the Dial Plan – Partitions & Calling Search Space

Ben Petroff
May 9, 2017

Diagnosing problems in your Cisco unified communications dial plan can be difficult as there are a large variety of ways in which it can be broken and generally, to identify these, a solid base understanding of the underlying features is required. With that said, let’s look at the base of your UC dial plan and a few problems that could arise at this level.

At its base, Cisco Unified Communications Manager (CUCM) is built upon Partitions and Calling Search Spaces. We need to understand how these interact before we can hope to solve any issues with our dial plan.



Partitions are used to logically segregate directory numbers in your system. Every Directory Number, Route Pattern, and Translation have an associated partition.

Partition Configuration.jpg


Calling Search Space

Calling Search Spaces (CSS) are used to determine which partitions a given device can dial. If a device is not configured with a Calling Search Space and/or its Calling Search Space does not contain any partitions, said device would not be able to make any calls.

Calling Search Space Information.jpg

When a new call is made, the line and device CSS are combined in that order, and a pattern is matched in the following order:

  • Most specific match with priority.
  • Most specific match without priority.
  • If equal, Partition order in the CSS.


You have a new user who complains they are not able to dial certain extensions.


  • Go to the device configuration of User A
  • Validate that the device is configured with a Calling Search Space
  • Check the Partition associated to User B’s directory number


  • Validate that the Partition of User B’s directory number is configured in Device A’s Calling Search Space
  • If the line appears with multiple entries in the Route Plan Report, that could be the source of our issue. Check to see if the Calling Search Space of User A’s device contains multiple of these partitions.


User complains that when they call a specific number, there is a significant delay before the phone starts ringing.


Validate if there is another pattern with equal or greater priority for which the pattern is longer than the user’s, but the initial digits are the same.

In this case, CUCM would then wait for more digits to see if it matches the longer extension — this delay is referred to as the “interdigit timeout”. Either set the user’s pattern to priority or delete the other pattern.


User: 4553

Problematic pattern: 45531

Tip: Dialed Number Analyzer is a good tool for diagnosing these types of issues.

Connecting to DNA: https://<<cucmipaddress>>/dna

This tool allows you to simulate the logical path which a call will take from a given device.

Should you require assistance with dial plan architecture or implementation, our Cisco UC experts are available to help!

Ready to take your unified communications from headache to hassle-free?

No throwing darts at proposals or contracts. No battling through the back-end. No nonsense, no run-around.