Subject: RE: [SIP] Detection of UAC failure

From: Kevin Summers <[email-masked]>
Date: Wed, 23 Aug 2000 17:41:09 -0500

Take a look at the following draft:

http://www.ietf.org/internet-drafts/draft-ietf-sip-session-timer-02.txt

Additionally, Henning's tasty faq-o-matic addresses keepalives:

http://www.cs.columbia.edu/~hgs/sip/faq.cgi?_highlightWords=keep&file=40
	
-----Original Message-----
From: Marc Petit-Huguenin [mailto:[email-masked]]
Sent: Wednesday, August 23, 2000 1:23 PM
To: IETF SIP
Subject: [SIP] Detection of UAC failure

Hi,

In the initial INVITE, how an UAS can know that the UAC is still alive?

The UAC can do this by retransmitting the INVITE periodically or by
bounding the duration of the INVITE with a Expires header, but how an
UAS can be sure that the UAC is alive (if the UAS send the 200 OK after
a very very long time), if the PRACK extension is not supported and the
UAC do not add an Expires header?

Thank you for your help,

-- 
Marc Petit-Huguenin
Home: mailto:[email-masked]
Work: mailto:[email-masked]
"So much to do and so little time" The Joker - Batman (The Movie)

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---

From: Marc Petit-Huguenin <[email-masked]>
Date: Wed, 23 Aug 2000 15:55:21 -0700

> http://www.cs.columbia.edu/~hgs/sip/faq.cgi?_highlightWords=keep&file=40

Session timers can only be used after the session is established (or am
I wrong?). My question is how to know if the client is alive, before
sending the 200 OK:

UAC        UAS
 | INVITE   |
 |--------->|
 | 100      |
 |<---------|
 | 180      |
 |<---------|
 |          |
Here there is a long long time and the user do not pickup the phone (if
its a telephony application). If the UAC is dead, the phone continue to
ring (the crash of the UAC will be detected when the 200 is send, but
that's not the point). How I can check that the UAC is alive without
using PRACK?

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 25 Aug 2000 01:03:50 -0400

> I wrong?). My question is how to know if the client is alive, before

You could poll it with an OPTIONS, but I think this not really worth it.
This is a corner case; the failure will be detected when the ACK never
shows up for the 200 OK.

-Jonathan R.

-- 
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

---

From: Henning Schulzrinne <[email-masked]>
Date: Fri, 25 Aug 2000 09:20:20 -0400

In a distributed system, it will always take O(time estimate of longest
likely sequence of packet loss) to detect outages of another end system.
In addition, there is no clear delineation between "long sequence of
packet loss" and "network dead", unless you have some direct way of
observing the physical infrastructure. 
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs