1. Don't think about making your UA asymmetric, make it symmetric 2. I t is possible to use Mediaproxy with your asymmetric client but you would still need to set port forwarding in your NAT device so stick to point 1 3. Symmetric means to use same port for sending and receiving data ----------- Hi Sorry if this is already answered, but i've search the archives and couldn't find what I'm looking for. Basically I would like to have the following scenario: UA1 asym --> NAT/Firewall --> Ser/mediaproxy --> PSTN Gateway PSTN Gateway is a Quintum box, we already have several of this, and it can only support asymmetric rtp, that's why we are looking at mediaproxy I develop the UA1 myself, and can support both symmetric or asymmetric rtp. My question, is this possible with Ser/mediaproxy? If it is, could somebody give me pointer on how to configure Ser with mediaproxy Currenty I have the call goes to the pstn gateway but no voice on each side. Another question, how do you know if the sip signalling is asymmetric or not? Thanks, Fikri