GVP Error

In standalone GVP everything is working f9.But when I am activating a CTI link(Behind the switch) with the genesys framework(SIP) and afterwords putting the call directly on the GVP port i am getting this error

“Media controller failed to create media session: Unable to create connection”.

We have a single NIC card in our machine …Observed where handsheking between SIP server and IPCS are happeneing bt while generating an RTP packert is having an issue.

So having a single NIC card is the problem??Do we have to use two NIC card in our M/c. if any one has faced this issue then please help me to get read of
it.

Thanks