[asterisk-dev] "cRTP, anyone?" and more crackpot ideas

[Steve Underwood]

John Todd wrote:
> Abdul -
>    I would disagree with you slightly on the statement that "Anything  
> other than RTP header compression is bound to fail using the public  
> internet."  This is already not the case - take a look at how IAX2  
> does multi-session trunking. (http://www.voip-info.org/wiki-Asterisk+bandwidth+iax2 
> )  There is always a risk of reordering in transit, but that is a risk  
> that is inherent in any RTP or RTP-like session.
>   
Packets reorder quite frequently, especially when the path has high 
jitter. RTP packets are sequenced, and a good receiver attempts to 
reorder them in its jitter buffer. So, any RTP like session has no 
problems, though many implementations of an RTP channel don't handle 
things well.

I didn't realise how often packets reorder in the real world until I 
started investigating T.38 failures. If you simply say "packets X and 
X+2 arrived, so X+1 must be a lost packet" you get significantly worse 
results than waiting a while to see if packet X+1 appears.

Steve