Please see inline...

-----Original Message-----
From: [email protected] 
[mailto:[email protected]] On Behalf Of Aaron 
Clauson
Sent: Monday, June 21, 2010 9:27 PM
To: [email protected]
Subject: Re: [Sip-implementors] Retransmits on reliable transports?

> -----Original Message-----
> From: Brett Tate [mailto:[email protected]]
> 
> If I recall correctly... requests and 3xx-6xx responses are not
> retried; however 1xx-2xx responses expecting ACK or PRACK are retried.

Ok understood. Next questions. 

What's the logic behind that? Why would some responses be retransmitted and
not others since getting an error response through is as important as
getting a 2xx response through not to mention requests? What mechanism
should be used to ensure reliability when a TCP UA knows its outbound proxy
is stateless and uses UDP for the next hop?

[MSW] In case of requests and non-2xx response retransmission is taken care at 
every hop. If next hop is UDP then the transaction layer in next hop would take 
care to retransmit request as it had responded with 100 response upstream for 
INV. Unlike requests and non-2xx response, 2xx of INV is retransmitted end to 
end and it is handled by TU layer. Hence retransmission of 2xx is required 
independent of underlying transport.

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