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Fast Busy During Intercluster Call


Here is the breakdown:

  • We are running CallManager 4.3(2)
  • We have multiple clusters connected to a gatekeeper using H225 Gatekeeper controlled trunks.
  • Calls between clusters are working fine except for one group of phones
    • These phones are remote site to the cluster (Clsuter A) and are statically configured to point to the CallManager Cluster
    • Calls from any other cluster to the phones that are sitting locally with Clusuter A work fine
    • When calls are made to the phones that are at the remote site the phone will ring but will go to fast busy upon answering.
    • Calls from the remote site to phones on Cluster A  work fine
    • Calls from the remote site to phones in other clusters result in ringing then a fast busy upon answer=

Any ideas?



5 Replies 5


It seems MTP or Transcoding problem , troubleshoot the Media resources, media resources groups and region configuration.


It's codec issue. Codec is negotiated after the call is answered. And that is why call is getting disconnected.

You need to check the region setting

Check the Device Pool and Region of the GK Trunk

Check the Device Pool and Region of the Remore Phone

What codec is configured between them? Same thing needs to be done on the other cluster who  is making call.

If you make the remote phone same device as the Local Phone on Cluster A, it should work.


- Abu

I am still trying to gain access into the other Cluster A CUCM.  I was thinking Codec negotiation also.  I am set to use G.729 but blew it out to Swideband so it should negotiate any codec the other end is advertising but I still got a fast busy.  I will update as soon as I get access.

Thaks for the input!

There was a combination of issues with asynchronous routing and firewalls.  We are up and good now.  Thanks for the help!

i got the same problem! fast busy tone after the called part pickup the phone!

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