b2bua Supported: header

Hi,

draft-marjou-sipping-b2bua-00
    If a SIP INVITE message sent by Alice indicates some
supported
   extensions (e.g. 100rel), it is important that the B2BUA
forward
   these extensions in the SIP INVITE message sent to Bob.
Otherwise,
   the two users will never be able to use these SIP
extensions.

I can get from there that Supported must be forwarded, isn't
it illegal.
For example UA1 has some xxx feature what B2BUA won't
support, now B2BUA 
forwards it to UA2, UA2 requires to handle it but B2BUA
don't know how.

I think B2BUA must always generate it's own Supported: with
value what 
it supports  or i miss something ?

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I agree with this comment.

The trouble with defining "transparent B2BUA" is
defining "how 
transparent". If it were entirely transparent it would
be a proxy. If it 
is doing anything that a proxy can't do then it is
necessarily at least 
somewhat opaque. This means that it must assess whether the
things it 
does have some impact on each option. In many cases it may
indeed be 
proper to forward a "Supported" option. But each
one must be judged 
separately. If the B2BUA doesn't understand an option then
it can't make 
a judgment whether it is safe to forward it or not. If it
does forward 
it, then it may have made a promise it cannot keep. This is
one of the 
major weaknesses of B2BUAs.

	Paul

Ivar wrote:
> Hi,
> 
> draft-marjou-sipping-b2bua-00
>     If a SIP INVITE message sent by Alice indicates
some supported
>    extensions (e.g. 100rel), it is important that the
B2BUA forward
>    these extensions in the SIP INVITE message sent to
Bob. Otherwise,
>    the two users will never be able to use these SIP
extensions.
> 
> I can get from there that Supported must be forwarded,
isn't it illegal.
> For example UA1 has some xxx feature what B2BUA won't
support, now B2BUA 
> forwards it to UA2, UA2 requires to handle it but B2BUA
don't know how.
> 
> I think B2BUA must always generate it's own Supported:
with value what 
> it supports  or i miss something ?
> 
> _______________________________________________
> Sip-implementors mailing list
> Sip-implementorscs.columbia.edu
> https://lists.cs.columbia.edu/cucslists/listinf
o/sip-implementors
> 
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---------- Forwarded message ----------
From: Xavier Marjou <xavier.marjouorange-ftgroup.com>
Date: Jun 1, 2007 3:32 PM
Subject: Re: [Sip-implementors] b2bua Supported: header
To: Ivar <ivarlumisoft.ee>


This draft is in an early state and has not received much
feedback, so
consider it as an individual work-in-progress (ie: it's far
from being
an RFC). Of course, any feedback is very welcome, though I
would
prefer to do it on IETF sipping list.

Coming back to your point, the text you have extracted has
some
limitations. Let's consider the "100rel" option:
it does not make
sense that the B2BUA relay the "100rel" extension
if it does not
support the 100rel extension itself (e.g. what is B2BUA does
not
support PRACK of RFC3262). Another example is the 
"join" extension
received in a request on one side of a B2BUA. The B2BUA can
not simply
relay "Require" or "Supported" headers
as it needs to be able to
perform a correlation between 2 dialogs as indicated in
RFC3911.

I thus think that additional text is needed indicating that
the B2BUA
has to understand/implement any extension. If supported,
then the
B2BUA can forward the support for this extension, otherwise
no.


On 6/1/07, Ivar <ivarlumisoft.ee> wrote:
> Hi,
>
> draft-marjou-sipping-b2bua-00
>    If a SIP INVITE message sent by Alice indicates some
supported
>   extensions (e.g. 100rel), it is important that the
B2BUA forward
>   these extensions in the SIP INVITE message sent to
Bob. Otherwise,
>   the two users will never be able to use these SIP
extensions.
>
> I can get from there that Supported must be forwarded,
isn't it illegal.
> For example UA1 has some xxx feature what B2BUA won't
support, now B2BUA
> forwards it to UA2, UA2 requires to handle it but B2BUA
don't know how.
>
> I think B2BUA must always generate it's own Supported:
with value what
> it supports  or i miss something ?
>
> _______________________________________________
> Sip-implementors mailing list
> Sip-implementorscs.columbia.edu
> https://lists.cs.columbia.edu/cucslists/listinf
o/sip-implementors
>
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