Analog phone->PABX1->VG1->WAN->VG2-CUCM2->Cisco 7821 phone ->transfer to another Cisco phone in same CUCM.

PABX1 - 3rd party telephony system in Site 1 (Aastra, ex-Ericsson MD110)
VG1 - old Cisco voice gateway router running as H323 gateway in Site 1(E1 to IP)
WAN - IPVPN link between PABX1 & VG1 in site 1 to CUCM2 &VG2 in site 2
CUCM2 - CUCM 10.5 controlling VG2 via  H323(Site 2)
VG2 - Cisco 2901 ISR

Hi all,

I have deployed CUCM 10.5 with 3 phone models, Cisco 7821, Cisco 8945 and DX 650. All are running SIP protocols.

As per scenario above, when the Cisco 7821 try to transfer the call from the analog phone to another cisco 7821/8945/DX 650 phone, the transfer will fail. From my observation as soon as the call is put on hold, the call is going to be disconnected once you try to resume. I have tried upgrading to the latest firmware sip78xx.10-2-1-12SR1-4 also not able to resolve the issue. However, if call is just between the analog phone and Cisco 7821 there is no problem in conversation.

If the call transfer is internal within the CUCM 10.5 , there is no issue with the 7821. Only when the call is coming from the 3rd party PABX and need to transfer, it fails. However, for Cisco 8945 and DX 650, they have no problem transferring call from the 3rd party PABX.

So, I am wondering if this a compatibility issue for the Cisco 7821 phone.

Also to add, there is also no issue on transfer using Jabber mobile on phone.