Subject: [Sip] TCP timeout

From: "James Ford" <[email-masked]>
Date: Wed, 21 May 2003 13:50:38 +0000

Hi,

I was wondering how to handle TCP timeouts with SIP.
If a connection is opened to a _non existing_ destination, the TCP stack 
(using non-blocking sockets and select) will only inform about an error 
after a TCP timeout (that can be considerably long on some systems).
(Existing destination with no listening port usually facilitates ICMP and 
"tells" that there is no listener).

My understanding is that SIP handles that by implementing invite timeout 
that is T1*64 (which is also quite long).

Here are the issues I'm struggling with:
1 - Does SIP has any other mechanism to handle such scenarios (H323 
facilitates a 4 seconds timeout on every outgoing call)?
2 - Doesn't this scenario compromises part of rfc3263 - locating sip 
servers, because the user is not likely to wait that long until a second 
server is reached.

Thanks,
James.

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From: Prabhas Ranjan Sinha <[email-masked]>
Date: Wed, 21 May 2003 10:44:58 -0400 (EDT)

Is there any draft on SIP usage in WLAN arena ?
Any help would be appreciated.

Prabhas

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From: "Dean Willis" <[email-masked]>
Date: Tue, 27 May 2003 11:08:36 -0500

> Any help would be appreciated.

I suppose "Just use it -- we don't really care whether the IP traffic is
over WLAN, ethernet, frame relay, barbed wired, or avian carrier" isn't the
answer you're looking for. But really, the IETF (outside of task specific
areas like the Performance Implications of Link Characteistics working
group) isn't generally concerned with specific lower-layer aspects.

The short answer is that SIP works just fine over 802.11b (I'm using it that
way right now) and should work over "a" and "g" just fine too.

3GPP (www.3gpp.org) is doing some work on extending IMS Release 6 (Internet
Multimedia Subsystem) which uses SIP onto WLAN. However, I'm not yet
completely certain that what they mean by WLAN and what you mean by WLAN are
the same thing -- they seem to be mostly worred about the sort of WLAN that
would be installed by mobile operators in hotspots and tied to one's mobile
phone account. Consequently, they're interested in things like using the
mobile's SIM card for authentication over WLAN, differential access pricing
by service, Q0S interworking with UMTS, and all of the usual 3G-mobile-phone
type things.

--
Dean