Subject: [Sip] Outbound and 410

From: Adam Roach <[email-masked]>
Date: Sat, 18 Mar 2006 14:20:58 -0600

I'm a slight bit concerned about the user experience that results from 
the interaction between sending of a 410 because of a loss of a flow and 
the way UAs interpret 410s.

Imagine that I have a UA that doesn't know anything about the outbound 
extension. It knows about 410s, though: 410s mean that the AOR they're 
trying to use is forever gone.

Cullen is using a UA that performs outbound to a proxy.

So, I use my client to call Cullen. A flow ID is established at call 
setup time, and written into our route.

Somewhere in the middle of the call, something goes wrong on Cullen's 
end, and his outbound connection to the proxy goes away.

Now, I hang up. Because the flow indicated in my route is no longer any 
good, I get a 410 response to my BYE.

Now, my client knows what 410 means: it means "The requested resource is 
no longer available at the server and no forwarding address is known.  
This condition is expected to be considered permanent."

Armed with this knowledge, it reacts to this error in a very reasonable 
way: it puts up a dialog box, "The address for Cullen Jennings 
<sip:[email-masked]> is no longer valid, and no forwarding address 
is known. This condition is expected to be permanent. Should I 
permanently remove this address from your address book?"

(Here I am thinking: "Oh. Of course. That's why the call was cut off: 
Cullen suddenly ceased to exist.")

If we want to avoid inventing another code for this situation, I would 
argue that either 480 or 481 would likely result in more correct system 
behavior than 410. In fact, the interaction between using 481 for this 
purpose and RFC 3265 procedures appears to be more appropriate than the 
other choices in this case.

/a

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From: "Jeroen van Bemmel" <[email-masked]>
Date: Sat, 18 Mar 2006 23:59:05 +0100

Adam,

> other choices in this case.

The proxy should be able to distinguish between flow failure and temporary 
failures / non-existing calls, to implement the logic in section 6.2. I 
agree with you that 410 cannot be used here, but IMHO neither can 480/481.

It looks like a new code is needed, something that says "Flow Gone"

Regards,

jeroen

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From: Paul Kyzivat <[email-masked]>
Date: Mon, 20 Mar 2006 10:50:08 -0500

I'm concerned about further overloading 481, which already has three 
overloads: (transaction doesn't exist for CANCEL, dialog doesn't exist, 
dialog usage doesn't exist.)

	Paul