Vineet Gupta wrote:
> Hi,
>
> I have a small doubt related to use of Supported and Require header.
> While from RFC 3261 it is clear the Require header is used by the UAC
> and UAS to enforce the extension implemention for a particular session,
> while the Supported header is mostly used by UAC to express the
> extensions which can be enforced by UAS through the Require header.
>
> My doubt is that, is it *mandatary that every extension that is present
> in Require header must be present in Supported header *in the request?
> According to me, presence/absence of Required extensions in Supported
> header does not make any impact on UAS handling. *Even if it is not
> mandatory, what is the preferred approach?*
This is pretty loosely defined.
For one thing, Require doesn't necessarily apply to a "particular
session". The most that can be said with certainty is that is applies to
a transaction. Often it applies longer, but how long isn't well defined.
Second, there is some asymmetry in Supported/Require, but this varies
based on the option. Require from a UAC states what it requires of the
UAS, but doesn't necessarily imply that a Require for the same option,
coming the other way, would be supported.
Also, Supported and Require are often used together to do a negotiation:
Supported in a request is paired with Require of the same option in the
response to negotiate its use.
In most cases there is no requirement to include Supported in requests.
The main place it is essential is in a 420 response.
Thanks,
Paul
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