Subject: Call Leg in SIP

From: Steve Little <[email-masked]>
Date: Tue, 29 Feb 2000 20:40:52 -0800 (PST)

Hi, according to SIP, a call leg is defined as an
end-end relation b/w UAs and has nothing to do with
intermediate servers.

Now does that mean that a particular call can have
multiple call legs _only_ if some server in between
forked and not otherwise ?

And also then, the Tag field is the differentiator for
call legs within a call-id. Is this true ?

One more Q - H.323 (afaik) defines call legs as

A-P and P-B where P is the GK and A & B the EPs.

Any concrete reason why the call leg of SIP/H.323
differs in definiton ?

Thx

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 02 Mar 2000 03:00:05 -0500

> forked and not otherwise ?

For the base spec, yes. Call control allows call legs to be explicitly
added.

> call legs within a call-id. Is this true ?

Call leg is defined as local+remote participants plus Call-ID. The tag
is part of the local and remote participant.

> Any concrete reason why the call leg of SIP/H.323

They were developed independently. Call leg also has a different meaning
still in traditional circuit telephony.

-Jonathan R.

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