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New Member

Block hairpin calls


I have the following setup CCM---H.323 VG---PBX.

The H.323 gateway and PBX are connected via a PRI. I want to stop calls routing back to CCM once it orignates from CCM.

For example, if I dial 5xxx from a CCM phone and the call is routed to the PBX, which may in return send the call back to CCM. This can fill up the PRI real quick just sending calls back and forth.

I know H.323 gateway blocks h.323-to-h.323 calls by default.

Can someone confirm?



Re: Block hairpin calls

You need to specify in Route pattern more specific ranges, so once the call comes back to cucm it gets rejected.

In route pattern we have the block this pattern option.

From an architecture point of view when u place a call to PBX, for cucm we have 2 call ids, ip phone and gw call id.

When the call is route back to cucm via vg from pbx , for cucm thats a new call and we cannot keep track of that call since H.225 GUId changes, if you are having this problem you need to review carefully your dial plan, since this problem is normally related to a bad dial plan design.


New Member

Re: Block hairpin calls

I was looking for an easier way to take care of this, but after I posted my question I realized that H323 blocks hairpin by default but that is for VoIP dialpeers.

Thanks for the tip, my plan was to build route patterns to block, but for 15-20K phones it becomes hard especially knowing that it is temporary.



Re: Block hairpin calls

You could make use of Path Replacement and PINX number so that CCM and PABX knows where the call orginated from and drops the link if it is a tromboned call- or deny trunk to trunk - PABX will most certainly have this option if CCM does not.