[SIPForum-discussion] Option tags in "Supported" Header

[XIAO Xiaohong]

Hello, the stentence you listed "This is to prevent servers from insisting that clients implement non-standard, vendor-defined features in order to receive service. "
should answer your question.
If all kinds of SIP entity add different privite extensions (although maybe nice), how to inter-operate?

-----Original Message-----
From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Raj Jain
Sent: 2008年6月27日 12:33
To: sreenivasulu.mavilla at wipro.com
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Option tags in "Supported" Header

On Thu, Jun 26, 2008 at 2:00 PM, <sreenivasulu.mavilla at wipro.com> wrote:
>
> Hi,
>
> Is it allowed to have an optional tag starting with "x-" (e.g., x-myOwn-param) in "Supported" header, here x- indicates experimental.
>
> I am trying to understand, how the other party from the public side of the network accepts it, read it and ignore if not required and continue processing the request. Or is it not allowed to have any option-tag other than published in RFC3261 (such as 100rel).

RFC 3261 section 8.1.1.9 contains the following language on this:

   The option tags listed MUST only refer to extensions defined in
   standards-track RFCs.  This is to prevent servers from insisting that
   clients implement non-standard, vendor-defined features in order to
   receive service.  Extensions defined by experimental and
   informational RFCs are explicitly excluded from usage with the
   Supported header field in a request, since they too are often used to
   document vendor-defined extensions.

That said, I'm not sure why the RFC text takes such a stringent stand on this, because this is a nice extension mechanism and is used in practice.

--
Raj Jain
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