[xiph-rtp] Interesting post on AVT list

[David Barrett]

Tor-Einar Jarnbjo wrote:
> Luca Barbato wrote:
>> Which method would deliver the SDP unreliably?
>>
> RTSP and SIP, isn't that what we're talking about? Both methods usually 
> use UDP transport.

Well, TCP is only reliable because it layers retransmissions atop IP. 
SIP is likewise reliable because it layers retransmissions atop UDP.

So SDP is delivered reliably by SIP, because SIP has reliability built 
into it.

Regardless, sending any SIP packet using UDP bigger than the MTU will 
probably still fail despite SIP's reliability measures because SIP has 
no fragmentation ability (that I know of -- can anyone correct me 
here?), and fragmented UDP is sometimes blocked by 
NATs/routers/firewalls.  That's why SIP states anything over the MTU 
should be delivered using TCP.

-david