Intermittent fast busy when calling across ICT

[nelson.chu]

Symptom:

When calling from CUCM 7.1(3) IP phone to CCM 4.3(2) IP phone across the ICT trunk, the 1st call attempt is always a fast busy, but the 2nd call attempt completes sucessfully.

When I change the Device Pool and Callmanager Groups for the CUCM 7.1(3) IP phone, this issue seems to disappear.  However, the IP phone on the CUCM 7.1(3) must register to (1) of the (3) subscribers which is specified under CCM 4.3(2) ICT trunk configuration: Remote Callmanager Servers.

CCM 4.3(2) 8 nodes

CUCM 7.1(3) 8 nodes

Could incorrect CM group configuration in Device Pool for the ICT trunk cause this issue?

[Abu Hadee · Accepted solution]

How many CUCM is defined on the ICT trunk on 7.1(3)? Also, These 4.3(2) CUCM must match the call manager group on the device pool of that is defined on ICT of 4.3(2)

Lets say, on ICT Trunk on 7.1(3) has ccm423-sub1, ccm423-sub2, ccm423-sub3, then ccm423-sub1,ccm423-sub2,ccm423-sub3 should be in the ccm group of device pool that is on ICT trunk of 4.2(3)

Also, are you using the Route-list in the route pattern, or directly pointing the ICT Trunk? If you are using Route List, what device pool on the Route List?

If still fails, can you collect logs from cucm or wireshark trace of the fail call?

Thanks

- abu

[nelson.chu]

Hi,

I did check on Callmanager groups and Device Pools and it does match.  It is poiniting to ICT trunk and not using Route List.

Thanks,

Nelson

[Tracy Larson · Accepted solution]

I had this issue way back in the day connecting my new version 6 cluster to a 4.1 cluster. The problem for me turned out to be the ordering of my servers in the ICT setup. Make sure that the primary subscriber is the first in the ordered list of the settings. Primary subscriber being the server that the phones are registered with. Sometimes people have phones registering with the publisher instead of a subscriber, in any event - whichever server the phones are registered with make that the first server in the ICT settings.

[nelson.chu]

Hi,

What if I have phones registered to mulitple subscribers?  My phones are registered on (6) different subscribers.

Thanks,

Nelson

[Tracy Larson · Accepted solution]

Are the phones that are registered per subscriber in a decently ordered numbering scheme? If so, try creating a single ICT for each individual server, then in your route pattern point that specific pattern range to that specific ICT. Do this on each environment if needed, meaning each way from the version 4 to version 7 and vise versa. Try it with no backup servers in the ICT setup. If this solves your problem then you can slowly add in some backup subscribers to each ICT created.

Basically if you have 50 phones registered with subscriber A, create an ICT to subscriber A then create a route pattern for that block of extensions using that ICT.

Then do that for the phones registered to subscriber B and so on.

[nelson.chu]

Hi Tracy,

No, the servers don't follow any number schemes, but your suggestions gives me some another ways to configure the ICT trunks.

Thanks,

Nelson