Alcatel Unleashed

I am facing a problem interconnecting 2 OXO over VOIP.My configuration seems to be OK.When i try dialling the number of the branch ofice from the head office.I can hear the ring at the extension .The problem is that even if someone picksup the extension at the other end,i still hear the ringback tome at my end.The voice channel is net getting setup.Please let me know what can be the problem.

I am using OXO release 4.0 in the head office with the VOIP daughter boards on the CPU and OXO release 2.1 on the branc office with CPU and CoCPU boards.

Are you using Class of service on your network

May be interconnection problem beetwen R2.1 and R4.
In our network was some 4400 and OXO R2 connected through IP.
When we connect OXO R4 - was connection problems like yours.
In our case problem was solved - 4400 release was updated.