Subject: SIP over TCP question

From: Shail Bhatnagar <[email-masked]>
Date: Wed, 25 Aug 1999 14:01:41 -0400

When running SIP over TCP, what should the UAC do if he does not see
any response within 500 ms of sending the INVITE ?

1 Just terminate the session
2 Wait for another second ( Even UDP will not wait for more than 3 
seconds, since UDP client will get a ICMP error on the second
or third INVITE).

Thanks,
-- 
Best regards,
Shail

---

From: Sean Olson <[email-masked]>
Date: Tue, 31 Aug 1999 16:18:32 -0500 (CDT)

> I've always disliked all statements like "over UDP do this, but over TCP
> do that." It might be wasteful to retransmit over TCP, but then again,
> maybe not. Maybe the TCP got the bytes, but somehow the application never
> gets them, or makes a mistake putting the bytes back together into SIP
> requests....
> 
> Can't we just say that SIP is independent of the underlying transport, be
> it UDP, TCP or carrier-pigeon?

I second that. There is a small savings in bytes sent with TCP as currently
specified in the SIP draft but it is lost by the fact the even UDP 
implementations are supposed to stop re-transmitting the request once a 
provisional response is received (and since most implementations will
immediately send back a "100 Trying" response, this effectively means that
you don't gain any bandwidth savings by using TCP)

I would even go so far as to say that the reliability mechanism in SIP should
be independent of the request method, but I realize there are
reasons for doing so.

Finally, reliable provisional responses are handled completely differently
adding yet another twist. While I don't propose anything so radical as MDTP...
maybe there is a compromise that can be made here?

> Sorry for the rant.
> Scott

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Sean Olson            E-mail: [email-masked]
Ericsson Inc.         Voice: (972) 583-5472 
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