Subject: [Sip] Retransmission of INVITEs

From: "James Undery" <[email-masked]>
Date: Thu, 3 Oct 2002 12:57:25 +0100

Hi,

	Whilst refreshing my knowledge of retransmission I came across a problem I thought had been resolved, and yet can't find it in the SIP archives. Retransmission of INVITEs cease upon receipt of provisional responses (the reliability of final responses is left to the server transaction), however, this introduces a problem for 100 responses (not generic 1xxs). The problem is a UAC sends an INVITE, a proxy responds with 100 and then promptly dies. The UAC has ceased retransmission of the INVITE waiting for a response that'll never come. My favoured solution would be for 100s to INVITEs to step the retransmission to T2 and have non 100 provisional responses stop retransmission. Anyway is this a non problem / stupid solution?

James

P.S. I am far less concerned about proxy failure once the request has actually reached the UAS, so ignored that.
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---

From: "Medhavi Bhatia" <[email-masked]>
Date: Thu, 3 Oct 2002 12:57:29 -0400

James,

I dont understand why the retransmission will be necessary in this case
after the 100. Since it is a UA, the user is already
monitoring the call, so he will hangup when no response is received. If its
a B2BUA/proxy, timer C should take care of this.

-Medhavi.

----- Original Message -----
From: "James Undery" <[email-masked]>
To: "SIP (E-mail)" <[email-masked]>
Sent: Thursday, October 03, 2002 7:57 AM
Subject: [Sip] Retransmission of INVITEs

Hi,

Whilst refreshing my knowledge of retransmission I came across a problem I
thought had been resolved, and yet can't find it in the SIP archives.
Retransmission of INVITEs cease upon receipt of provisional responses (the
reliability of final responses is left to the server transaction), however,
this introduces a problem for 100 responses (not generic 1xxs). The problem
is a UAC sends an INVITE, a proxy responds with 100 and then promptly dies.
The UAC has ceased retransmission of the INVITE waiting for a response
that'll never come. My favoured solution would be for 100s to INVITEs to
step the retransmission to T2 and have non 100 provisional responses stop
retransmission. Anyway is this a non problem / stupid solution?

James

P.S. I am far less concerned about proxy failure once the request has
actually reached the UAS, so ignored that.
_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: "Arunachalam Venkatraman" <[email-masked]>
Date: Thu, 3 Oct 2002 13:08:17 -0500

James
What is the problem with this scenario that you are seeking to solve?

If the calling user does not get a response in a certain time the user will
hang up.

If the UAC is concerned about the calling user(possibly automata or truant
caller) not giving up on the call, then a timer can be run to CANCEL the
INVITE.

If the INVITE is expected to take a long time to elicit a response from the
called user, then it is recommended that an INVITE be re-sent before 3
minutes have elapsed (even thoug a 100 TRYING has been received), since
intervening proxies run a timer > 3minutes before CANCELing the INVITE.

Venkat

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of James
Undery
Sent: Thursday, October 03, 2002 6:57 AM
To: SIP (E-mail)
Subject: [Sip] Retransmission of INVITEs

Hi,

James

---

From: Jiri Kuthan <[email-masked]>
Date: Thu, 03 Oct 2002 23:29:20 +0200

I don't understand what you don't understand.

The problem is an INVITE gets lost, nobody learns that,
caller gets never a final reply and eventually hangs up
even if there is a callee willing to have a call and
restarted proxy willing to help set up the call.

I think James' T2 proposal is fair enough.

-Jiri

--
Jiri Kuthan            http://iptel.org/~jiri/

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From: "Medhavi Bhatia" <[email-masked]>
Date: Thu, 3 Oct 2002 18:04:30 -0400

I was talking from a protocol perspective (as to resources getting released
on proxies
and all). I agree with you guys that from the user perspective,
the choice is nothing versus a busy tone after a while (if T2 is
incorporated). Is that
right ?

In the latter case, the retransmission stops when a 180 is received. What
happens
if the same situation arises (proxy dies etc) ?

-Medhavi.

----- Original Message -----
From: "Jiri Kuthan" <[email-masked]>
To: "Medhavi Bhatia" <[email-masked]>; "James Undery"
<[email-masked]>; "SIP (E-mail)" <[email-masked]>
Sent: Thursday, October 03, 2002 5:29 PM
Subject: Re: [Sip] Retransmission of INVITEs

-Jiri