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CUCM/CUC Spam call mitigation (require caller input to connect call for external callers)






As I'm sure everyone with a PSTN connected phone is aware SPAM callers and spoofing are pandemic these days.

Within our org which has over 1000 DIDs we are getting an increasing number of complaints and feeling like our hands are tied.

CID and number spoofing is standard practice as is constant number rotation, so number blocking is a lost cause.

Blocking private/unknowns might take care of some of the calls but also catch plenty false positives.


In thinking about what we could offer to mitigate these calls the best I can come up with is a call handler that would require external callers to press a key to be connected to the called party.


The problem is I am not expert enough with all of the features in these systems to build this in an easily applicable way.

Ideally this would be a single drop-in setting for a user which when enabled would route external callers to a generic handler with a defined keypress that would simply transfer the call to the actual extension.


Can any of the experts out there see a quick way to this?


Off the top of my head I am thinking some routing in CUCM that looks at all destinations from external patterns and if the destination DN is in a list the call goes to the handler first. The handler would hopefully then be able to transfer to the original dialed number. This is where it seems like things are less possible. I'd hate to have to make a routing rule and a handler for each user, though this would be something offered on complaint rather than enabled for all by default (short of a high level policy decision).


Ext Caller -----> Routing Rule -----> Dest DN in list -----> xfer to handler -----> require press 1 -----> xfer to dest
                                               \____>Destination DN not in list -----> connect to dest

Any thoughts or corrections would be greatly appreciated. My google-fu turned up very little.



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Re: CUCM/CUC Spam call mitigation (require caller input to connect call for external callers)

No, you're correct, and that's why CUC is not usually used for this

A) You would need to create the specific call flow for EVERY SINGLE DN.

B) Due to the above, management becomes a nightmare.

C) You would end up using up resources and tying up ports for every single call and possibly exhausting the ports.


Might be a better idea to simply create an IVR for those specific DNs, catch them in CUCM, send to an IVR where you ask people to enter the extension.



if this helps, please rate

Re: CUCM/CUC Spam call mitigation (require caller input to connect call for external callers)

Hi Jason,


I feel your pain as i had faced this issue in the past. And just reject rule  on the gateway was not enough to fix.


Therefore, i had to use IVR in CUC to force the caller to make a choice before routing the call or drop the call if there is no choice within x seconds. In my case, i had to convert all the incoming call to 3 digits extension and send the calls to CUCM and CUCM tranfers to CUC. And voila. Never heard of these nasty calls again!


Good luck.


Re: CUCM/CUC Spam call mitigation (require caller input to connect call for external callers)

I found the attached documents some time ago which may help you. I haven't implemented the solutions outlined but it seems logical.

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