Subject: Re: [SIP] How to detect interworking ?

From: [email-masked]
Date: Thu, 13 Jul 2000 18:12:17 +0530

Well,
we did do a similar thing in our SIP-323 GW - we added a proprietary token that
the signalling gateway would insert in one of the headers.
However, it would be nice if we all had one "well known" way of doing it.
Reason being that though the IWF box is a legit SIP UA on the SIP side, while
developing one, we often put in only basic features (we just did a call setup
and teardown) and dont want the end SIP UA to do more fancy stuff (like SIP call
transfer etc) assuming it was a SIP-SIP call .

Well, thats really an implementation ramble from this side, and our proprietary
extension worked fine since we had HSS UAs too...

So rafi, we faced the same issue (if thats what we would like to call it) -
maybe some time down the line, when more people jump into
implementing a  SIP-H.323 GW, putting some fixed token with a fixed value to
indicate a protcol X - SIP conversion would be nice.

Regds
Arjun

Jonathan Rosenberg <[email-masked]> on 07/13/2000 11:39:33 AM

To:   rafi <[email-masked]>
cc:   [email-masked]

Subject:  Re: [SIP] How to detect interworking ?

By its nature such an interworking box appears as a perfectly legitimate
SIP UA. So, from a pure protocol perspective, no.

However, I have been updating the caller preferences spec. One of things
I added is that you can use the new Contact parameters in the Contact in
INVITE and 200 OK to convey useful info about who/what was contacted.
One of the things that you can include is a textual description, so:

200 OK
Contact: sip:[email-masked];description="interworking with H.323"

This is not useful for automated processing, but could allow the user to
know.

-Jonathan R.

> rafi wrote:
>
> Hi,
>
>    Is it not useful for a UAC to know whenever
> there is an interworking taking place (For e.g.
> SIP-H323)? Is it possible for a "gateway" to
> indicate such information to UAC?
>
> Thank you
> Rafi Assadi H.M

--
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 17 Jul 2000 01:40:21 -0400

> transfer etc) assuming it was a SIP-SIP call .

This is very, VERY bad.

SIP already defines mechanisms that allow a UAC to determine what
extensions, methods, body types, etc. are supported by the UAS
(including whether it supports transfer). Defining another method to do
that which identifies a "profile" of SIP with a single new header seems
a slippery, dangerous road to take. Many people argued strongly about
this during the sip-h.323 bof.

> indicate a protcol X - SIP conversion would be nice.

No, I think this would be a dreadful mistake. It is *fundamental* to the
nature of this conversion that the SIP UA component be a true SIP UA.
Having some kind of special extensions in there required to support it
means its no longer interoperable with baseline SIP. IP phones,
gateways, etc. would now all need to know about this special thing
called a SIP-H.323 gateway, and adjust behavior accordingly. As we
define more and more of such conversion boxes, it becomes a nightmare to
manage this, and all interoperability will eventually go away.

I fail to understand why this device is so special that it cannot use
the normal SIP extensibility mechanisms.

-Jonathan R.