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MGCP/QSIG Tromboning


We are running CCM 4.2 integrated with an Ericcson MD110.

The Gateway is a 2811 running QSIG into a Westell DPNSS Convertor then DPNSS to the MD110.

We have had problems with tromboning on the link, ie all channels filling up due to a single call being repeatedly transferred up and down the link.

Is their a setting within the CCM or the Gateway that we can use to prevent this.

Due to the way the legacy MD110 has been configured the only parameter we can change on there would have to be done on several thousand individual routes via RODDI.


Re: MGCP/QSIG Tromboning

You should be able to configure the gateway Calling Search Space to reject those calls that are now being looped back to the PBX. You may also be able to modify user CSS so those calls never go to the PBX.

Without knowing more about your dial plan and what calls are looping it is tough to be specific, but in general you need a gateway CSS with partitions containing route patterns only for those calls that the MD110 should be sending to the Call Manager. Or the route patterns that are sending calls to the PBX need to be modified to only send calls that the PBX can route normally.

When a call is routed to the PBX, and tromboned back to the Call Manager, the caller will get fast busy with only 2 channels used.

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Re: MGCP/QSIG Tromboning

We are running into something similar. To help us with this, I'm proposing that we create additional partitions with a suffix of ViaPBX. This will allow us to create calling search spaces accordingly. For example, we have a default business class partition, bus_def_pt, since there are lines on the PBX that fall into this category as well, I created bus_def_viaPBX_pt. I then make sure to exclude any viaPBX partition from the PBX trunk's calling search space.

It's not entirely scalable but it should do fine.

Basically put, the rule is (as described above) you should not allow a trunk's calling search space to access route patterns that send a call back to itself.

You won't be able to stop a PBX user from forwarding their phone to an IP phone that is forwarded back to a PBX phone, but I believe there is an enterprise or service parameter that you can use to limit forwarding hops.

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