Subject: [Sip] draft-ietf-sip-outbound-01, Service-Route and flows

From: Alex Fritze <[email-masked]>
Date: Thu, 01 Dec 2005 12:44:24 +0000

Hi,

draft-ietf-sip-outbound-01 isn't very explicit about when exactly a UA 
should monitor a particular flow for failures; in particular when a 
REGISTER request returns a Service-Route with an outbound proxy that is 
different from the configured outbound proxy. In this case, the 
Service-Route will replace the configured route, as per 
draft-rosenberg-sip-route-construct-00. (From the IETF64 sip-outbound 
minutes, I gather that this is also the current consensus).
In such a scenario, should the UA a) keep alive the original flow to the 
registrar or b) perform DNS resolution on the first proxy in the new 
route and start sending STUN requests to it?

Thanks,
Alex

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From: Cullen Jennings <[email-masked]>
Date: Mon, 19 Dec 2005 22:23:11 -0800

> route and start sending STUN requests to it?

It should do b. I need to update the draft to be clear on this. It would
only send the stun requests if the URI of the proxy had a ;sip-stun

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From: Alex Fritze <[email-masked]>
Date: Tue, 20 Dec 2005 10:12:11 +0000

>only send the stun requests if the URI of the proxy had a ;sip-stun

Given that the Service-Route might contain names that each resolve to 
several addresses, I still see a problem of pinning down the exact route 
and making sure that inbound requests traverse the flows that are 
actually being kept alive.
Maybe the UA should send a new REGISTER request over a service route 
returned by an initial REGISTER if its first hop differs from the hop 
over which the original REGISTER was sent? Or maybe there should be a 
restriction of only allowing ip addresses (or at least names that 
resolve to single addresses) in Service-Route?

- Alex

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From: [email-masked]
Date: Tue, 20 Dec 2005 16:22:18 +0200

Hi,

Is it so that the only way for a UA to know if the proxy supports STUN for keep-alive purposes is so that the UA needs to be configured to know it? Is the only reason for the existence of sip-stun URI parameter that it is a convenient way to represent the configuration information, i.e. it makes no difference if the parameter is present in the actual SIP requests sent by the UA?

Would there be any problem for the UA to test the support by sending a STUN request to proxy IP address and port? If it does not succeed, it can start using e.g. SIP OPTIONS as  a keep-alive mechanism. Perhaps this kind of thing could be mentioned in the draft.

Regards,
	Markus