Block Calls to PSTN

Unanswered Question
Nov 3rd, 2008

Hi there !

I have some IP Phones that should not be able to reach the PSTN...

Those phones are calling to Secretary, and she is transfering they're calls to PSTN.. how can I block this ?



I have this problem too.
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Jaime Valencia Mon, 11/03/2008 - 09:04

change the CSS to something that cannot reach the route pattern to PSTN

there is no way to block that, you can block PSTN to PSTN transfers but no IP phone to ip phone then PSTN.

tell your secretary to not do that as that is a basic method of call fraud!



if this helps, please rate

andrei.goncalves Tue, 11/04/2008 - 02:10


thanks for your information...

I would say that talk to secretary would be easy if the company where I work was not a 15,000 people.. and lot's of them have access to PSTN and could transfer the call..

But ok, I'm gonna create some lab to test.


ahmed_maher Mon, 01/05/2009 - 05:52


I've the same issue, did you find a solution for this issue


ahmed_maher Mon, 01/05/2009 - 06:15


I've the same issue, did you find a solution for this issue


mshavrov Mon, 01/05/2009 - 06:28

As it was answered above, you have to create separate partitions for phones and PSTN route patterns, combine them as needed into multiple CSS, and then assign CSS to phones accordingly.

For example, you create partitions PT_Phones, PT_Emergency and PT_PSTN. All phone lines go to PT_Phones. Your emergency route pattern (911 or whatever you have in your country) goes into the partiton PT_Emergency, and your PSTN route pattern (for example, everything starting with 9) goes into the PT_PSTN. Then you create two CSS: CSS_Restricted and CSS_Unrestricted. CSS_Restricted has 2 partitions: PT_Phones and PT_Emergency, and CSS_Unrestricted has all 3 partitions. Then you assign CSS_Restricted to your secretary phone, and CSS_Unrestricted to your phone. As a result your secretary will be able to call all internal numbers (which reside in PT_Phones) and police in case of emergency. And your phone will be able to call all numbers including PSTN.

Good luck,


CCNP, CCDP, CCVP, CCSP, CCIE Voice (in progress)

ahmed_maher Mon, 01/12/2009 - 10:49

Thanks Mike for Reply,

But my case is that i need to block the transfer To PSTN from any IPPhone not only the Secretary.

something like transfer-pattern command in CallManager Express (for Ex. transfer-pattern 2...), this means that the IPPhones can transfer to any Extension of 4 digit starting with 2 and willn't be able to transfer to 9.!

Please advice


Jaime Valencia Mon, 01/12/2009 - 10:54

you can only block PSTN to PSTN transfers, there is no way to limit the transfer to only 4 digit extensions as transfers use the same CSS as any other call in CUCM.



if this helps, please rate

Ronald Spencer Mon, 01/12/2009 - 15:36


How about moving the guys who should not have PSTN Access to a new calling search space. In that calling search space you would create a translation that would convert the number they are used to dialing for the secretary to a new number (that she has access to). This new number, or line appearance, would show up on her phone and she will know that calls coming in on it cannot have access to PSTN.

To further ensure that this will happen, set the Line CSS of that new DN to a CSS that has no access to PSTN.

There are obvious gotcha's to this plan. To ensure that you do not endanger these people, please be sure to make emergency dialing available to this new CSS.


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