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Rolando Valenzuela

One Calling Search Space to rule them all?

Hi everybody!

I'm new in this whole CUCM configuration, and something the immense number of options, setting, elements and others CUCM has are overhelming!!

Today I noticed the many, many places where we can set a Calling Search Space (CSS) and I would like to know if CSS set somewhere prevails over


This is where I have found the option to set a CSS

  • Device Pool -> Device Mobility Related Information (Device Mobility Calling Search Space)
  • Device Pool -> Device Mobility Related Information (
  • End User (SUBSCRIBE Calling Search Space)
  • Phone (Calling Search Space)
  • Directory Number (Calling Search Space)
  • Directory Number -> "Call Fonuard and Call Pickup Settings" (Calling Search Space)

Most probably this field should be somewhere else, but this is when I got really confused.

Fore example a Phone can be related with a DN, with a Device Pool, with an End User.... each of this this four elements, can be assigned with a different CSS.

Now, if for example I want to allow or restrict a international call (based on the CSS) where be the best place to do it?

Do I need to change the CSS everywhere?

Thank you!!

Gergely Szabo


most of the parameters - including Calling Search Spaces - may be configured at multiple places.

There is one important thing to remember, though: if a parameter is not set for a certain entity, it might be still applied - using the parameter value at a lower level.

So if CSS is not set at the Line level, the CSS set at the Device level is applied (in other words, if no CSS is set on the Directory Number page, then the CSS set at the Phone Device level is applied).

That's the easy part.

Now, what happens if the CSS is set at both the Directory Number and the Device level: the lists of partitions are concatenated. First comes the partitions from the DN, then the partitions from the Device.

So if there's a CSS called "LineCSS" containing partitions A, B, C and a CSS called "DeviceCSS" with partitions X, Y, Z, then anyone calling from that DN would have access to partitions (and in this order): A, B, C, X, Y, Z.

Unless it's a CTI Port, because then the order is different, first comes Device, then the line, so it would be X, Y, Z, A, B, C.

A bit confusing, isn't it?

Now, back to the list you posted: not everything named CSS is related to calling restrictoins. Restrictions, yes.

Take the SUBSCRIBE CSS - it's related to who can see whose presence information.

I would recommend you to take a look at the "Help for this page" for each page - they might contain useful information for a beginner.

Have fun,



Thank you so much!!!

Just one more thing... if the phone doesn't have a CSS, it will take the one registed in the Device Pool for "Calling Search Space for  Auto-registration"??

Thanks again


if the phone does not have a CSS, well, then... it does. No kidding. It has an imaginary CSS that contains only the "None" Partition (or rather, Partition) meaning that the phone without any CSS will still be able to reach basically anything that resides in the partition. You might have noticed that Directory Numbers do not require a Partition.

The Calling Search Space for Auto-registration is applied to phones created with the auto-registration function of the CUCM. Basically, you plug in the phone, and CUCM creates and pushes its configuration, including the CSS set at the device pool level.


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