Direct SIP call to IP

Question

I am programming for my End Project an application that should have VoIP capabilities. I have started testing with the new SIP API that android 2.3 includes. The problem is that I am actually living in a student's dormitory, so I am connected to the internet through the building's proxy and it seems to have a strict firewall that doesn't let anything pass.

I have tried several free SIP servers and clients and the result is always the same: from my UAC I can see if other clients are online, I even can send text messages, but it is impossible to establish an actual call. I never get any response from the client called. Using a Linphone client I can't even connect to the SIP server to authenticate.

The thing is, that it seems I cannot make calls outside my building, but I have successfully contacted a Linphone client installed on my PC from another Linphone client installed on an emulator. Apparently I can make calls inside my local network without any SIP server, just by using the local address of the receiver instead of its SIP domain.

The question is: Can I do the same with the new android 2.3 SIP API? Can I make a call inside my local network just by calling the receiver's local address, without the necessity of authenticate with any SIP server outside my building?

As my application is for demonstration purposes, this will be enough for me. I have been looking for a solution to this problem during the past three days but I haven't come up with anything useful. :/

Thanks in advance.

Answer 1

Because audio and video data is sent via different port number than sip port number. Sip port is tcp and you can login your sip server on internet. But media port is udp and you are behind nat and you cant making a call. To do this, firewall needs to understand sip messages and then it should open port for udp media. Also you need stun server for nat traversal messages.

Answer 2

I don't see any reason why It should not be possible in Android 2.3. Peer to peer call is possible with other clients local address with port.

You can also install SIP server Brekeke server on your PC. and you can use full sip URI for making calls.