Subject: Advantage & disadvantage of static tcp/sctp link and dynamic tcp/sctp link

From: "Leslie, Qi Wang \(qiwa\)" <[email-masked]>
Date: Mon, 10 Oct 2005 17:10:11 +0800

Hi, all
 
If we want to setup SIP call over TCP transport, we can create a static
tcp link for all sip call, or dynamically create a tcp link per one sip
call and tear down it after each call.  What's the advantage and
disadvantage of them?
 
If we use SCTP as transport protocol, what's the advantage and
disadvantage? SCTP is more secure than TCP. Is it better to use first
static link for all sip call?
 
Regards 
Leslie

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From: Randall Stewart <[email-masked]>
Date: Thu, 13 Oct 2005 16:39:08 -0400

Leslie:

Some general comments...

> call and tear down it after each call.  What's the advantage and 
Well .. every connection TCP/SCTP requires overhead of the setup
packets... if you setup/tear down a lot.. you increase your
overhead...

SCTP does have a nifty feature in the socket api though.. its called
auto-close.. so you can setup a association and set a timer on it
to close automatically... if it goes idle... so say you
dynamically set one up.. set the auto-close timer to 2minutes..
Now forget about it.. if the connection goes idle for 2 minutes.. it
closes..

Of course I think you need to use the 1-2-many model for this.. which
also allows you to do an implicit setup by just sending to an address.

> static link for all sip call?

Don't know what you mean by "secure".. it does use a 4-way handshake
and is less subsceptible to spoofing because of the v-tag...

As to sip calls.. I would think if you need to communicate on multiple
calls the head of line blocking issue would be paramount. Belcore did
tests on this for TCP and SS7 call control (ISUP) and basically they
could project with any sort of loss the call timers may start to
blow since any one call would effect others..

With SCTP you can use the streams to get around this.. put different
calls in different streams.. each call's signalling data arrives in
order with respect to the call. but a lost message in one call will
not block another...

Also the multi-homing may be important for redundancy... depending
on how fault tolerant you need to be..

Hope that helps

R

-- 
Randall Stewart
ITD - Cisco Systems Inc.
803-345-0369 <or> 815-342-5222 (cell)