sip_r54, red5phones can't call each other, sound is not continuous

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What steps will reproduce the problem?
1. Install red5 server 1.0 RC1 
2. Compile and install sip_r54
3. Setup elastix/asterisk server on CentOS
4. Setup softphone Zoiper to call for testing
5. Call from red5phone to softphone
6. Call from red5phone to softphone

What is the expected output? What do you see instead?
1. When I call from red5phone to softphone, the sound out/in are good.
When I call from red5phone to another red5phone (different sips), sound out/in 
are not continuous and not clear. 

2. When I let red5phone successfully singed in for about 1,2 minutes, it can't 
receive incoming calls and seems can't call too. I need to refresh the browser 
and sign in red5phone again to use it.

Do you have any ideas or any experiences about these things?

Original issue reported on code.google.com by hnth...@gmail.com on 15 Nov 2011 at 2:23