I do agree with you that the proxy should forward all 2xx responses and
forward the best one of other final responses according to bis05.
But I didn't find the UAC should establish only one connection on receiving
multiple 2xx responses. Although I know the behaviour of proxy should have
nothing related to the configuration of UA (whether it enable multiple
dialogs or not), I still have the doubt.
Or it's wrong for me to think that the UAC could establish connections to
all answered parties? Although forking can help caller to reach callee
on multiple contact addresses, only one should be picked establish the
final communication channel?
"Arunachalam Venkatraman"
<[EMAIL PROTECTED]> To: Wei BJ
Lu/China/IBM@IBMCN
Sent by: cc:
<[EMAIL PROTECTED]>
[EMAIL PROTECTED] Subject: Re:
[Sip-implementors] How does forking proxy handle To Tag
lumbia.edu in errorresponse selection?
2001-11-16 12:11
Please respond to
"Arunachalam Venkatraman"
That depends on the UAC implementation.
The UAC may use a user interface to let the caller decide, if it is capable
of handling multiple appearances. Otherwise, it can set up the call after
the first 200 Ok and when a second 200 OK is received it can send BYE after
ACKing it.
I don't understand your reference to the proxy behavior based on UAC
enabling multiple dialogs. Where is this mentioned?
----- Original Message -----
From: "Wei BJ Lu" <[EMAIL PROTECTED]>
To: "A Venkatraman" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Thursday, November 15, 2001 8:37 PM
Subject: RE: [Sip-implementors] How does forking proxy handle To Tag in
errorresponse selection?
>
> I have noticed the bis says proxy only forwards 2xx responses. But I
still
> have the doubt: If the UAC does not enable multiple dialogs, then what
> should
> it do on the arrival of multiple 200 responses?
>
> -Lu Wei
>
>
>
>
> "A Venkatraman"
> <[EMAIL PROTECTED]> To: Wei BJ
Lu/China/IBM@IBMCN, "McMurry, Kathleen"
> Sent by:
<[EMAIL PROTECTED]>
> [EMAIL PROTECTED] cc:
<[EMAIL PROTECTED]>
> lumbia.edu Subject: RE:
[Sip-implementors] How does forking proxy handle To Tag
> in er
rorresponse
selection?
>
> 2001-11-16 09:20
> Please respond to "A
> Venkatraman"
>
>
>
>
>
> a. How does a UAC enable multiple dialogs?
> b. The proxy only forwards all 200 class final responses. See line 2345
of
> bis-05 pdf.
> Also, see line 2423 which specifies that a proxy should send CANCEL on
> all legs that sent a provisonal but no final response.
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Wei BJ Lu
> Sent: Thursday, November 15, 2001 6:58 PM
> To: McMurry, Kathleen
> Cc: [EMAIL PROTECTED]
> Subject: RE: [Sip-implementors] How does forking proxy handle To Tag in
> er rorresponse selection?
>
>
>
> I have some doubt on "the proxy should select the best response from the
> ones it has
> received and send it to the OUA". I think it it not always true. To my
> understanding,
> the behaviour of a forking proxy on receiving final responses should be
> different
> under two circumstances:
>
> a. If the UAC does not enable multiple dialogs(call-legs), the proxy
> should forward
> the best final response upstream and cancel all the unfinished forking
> branches.
>
> b. If the UAC enable multiple dialogs, the proxy should forward all the
> final
> responses to the UAC. Since on the UAC's side, different To tag means
> different dialog.
> When 180 with To tag u1 and u2 comes, the UAC will create two dialogs. If
> the proxy
> only forward 486(this tag u1) to the UAC, the UAC will only terminate one
> dialog and
> the other dialog will keep ringing.
>
> -Lu Wei
>
>
>
>
>
> "McMurry, Kathleen"
> <[EMAIL PROTECTED]> To: "'Bob
> Penfield'" <[EMAIL PROTECTED]>, A Venkatraman
> Sent by:
> <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
> [EMAIL PROTECTED] cc:
> lumbia.edu Subject: RE:
> [Sip-implementors] How does forking proxy handle To Tag
> in er ror
response
> selection?
>
> 2001-11-16 04:02
> Please respond to "McMurry,
> Kathleen"
>
>
>
>
>
>
>
> >-----Original Message-----
> >From: Bob Penfield [mailto:[EMAIL PROTECTED]]
> >Sent: Thursday, November 15, 2001 1:19 PM
> >To: McMurry, Kathleen; A Venkatraman; [EMAIL PROTECTED]
> >Subject: Re: [Sip-implementors] How does forking proxy handle To Tag in
> >er ror response selection?
>
>
> >>
> >> >> Suppose a proxy forks a request from UAC to uas1, uas2,
> >> >> and each returns a 18x, with tag u1 and u2 respectively, which are
> >> >> forwarded, as is, to UAC,
> >> >> and then uas1 returns a 486 with tag u1 and uas2 returns 500 with
tag
> u2
> >> >> Proxy picks best response 486 to return to UAC.
> >> >>
> >> >> Question:
> >> >> Will the TO tag in the 486 reponse be u1? Or, will there be no TO
> tag.
> >> >> Is this implementation specific or does the protocol specify this
> >> >anywhere?
> >> >>
> >> >Based on section 16.6 on bis-05, the tag received in the response is
> >> >preserved when the selected response is forwarded to the UAC.
> Therefore,
> it
> >> >would be u1 for your example. The proxy is not allowed to modify the
To
> >> >header in the forwarded response.
> >>
> >> A 2xx response is the only type of response that is truly "forwarded"
by
> >the
> >> proxy. Any non-2xx response is really hop by hop. Therefore, in your
> >> example, the proxy will add its own To tag when it responds to the
UAC.
> >> Niether u1 or u2 would be used.
>
> >Section 16.6 of bis-05 explicitly forbids the proxy from adding its own
> tag.
> >It is not a UAS in this case. The proxy is suppose to select the best
> >response from the ones it has received and forward that response to the
> UAC.
>
>
> I agree that the proxy should select the best response from the ones it
has
> received and send it to the OUA. I also agree that the spec. does not
> clarify the two different cases well.
>
> In the case of a 2xx response, the proxy forwards the response to the OUA
> leaving the To tag alone. For a non-2xx response however, the To tag is
> used to match the corresponding ACK for each hop. Therefore, when the
> non-2xx response is received by the proxy, it should ACK the UAS with the
> To
> tag that was added by the UAS. But when the proxy sends the response to
> the
> UAC, the proxy should use a To tag that it generates so that it can
> determine that the corresponding ACK is meant for the proxy and should
not
> be forwarded.
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