Call Transfer to external number fails.

[dipars1953om]

Dear Team,

Call Transfer to external number fails. We have tested with "Warm Transfer/Announced Transfer", "Blind Transfer" and "Direct Transfer to an External Number" fails. 

Only Call Transfer to an internal number is working. 

Call Flow:

PSTN > CUBE  (SIP) > CUCM > Extension A > Tries to Transfer to Extension B, which is forwarded to an external number > CUBE (SIP) > PSTN

Call Manager Version: 10.5.2.22900-12
CUBE IOS Version: IOS XE 17.03.04a

CUBE Model: 4451

Note: No Call Transfer restriction has been configured in CUCM Service Parameter. IOS MTP has been configured on CUBE and registered in CUCM and using the same MTP in MRGL for the SIP Trunk configured towards CUBE.

Any help on this would be much appreciated. Please assist me what could be the issue and where to start with. Thanks in advance. 

[Leonardo Santana]

Hi,

The reverse path is working? Transfer an incoming PSTN call to a internal extension?

Collect a debug ccsip messages from the CUBE to see whats going on.

[dipars1953om]

Hi Leonardo,

Transfer an incoming PSTN call to a internal extension is working. Any transfer to an internal extension is working. Only issue is with while transferring to an external number. 

Not sure if this is related but I am seeing a lot of below:

SIP/2.0 415 Temporarily Unavailable-Unsupported Media Type.

[Leonardo Santana]

Hi,

With the output of the debug ccsip messages you can check whats going on.

If its possible share the output of this command. You need to enable the debug and reproduce the error.

[Steven L]

Is the PSTN connection SIP or ISDN?

There is a CODEC mismatch somewhere. do you have debugs

debug ccsip messages

debug isdn q931 if the connection is ISDN