i got a problem (ICT Non-Gatekeeper Controlled between CUCM 8.6 and CUCM 4.2)! fast busy tone after the called party pick up the phone.
I would start by checking "Enable Inbound FastStart" on both sides, maybe you are using FastStart. Are you using MTP by the way?
There are different older posts on this forum on similar issue, please also check them
This sounds like a codec issue, what type of devices are you using for the calls?
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