Subject: [dispatch] Query on SIP 380 response for emergency service

From: Ranjit Avasarala <[email-masked]>
Date: Tue, 26 Jul 2016 14:21:01 -0500

Hi

There was an emergency outage sometime back and the emergency service
returned a 380 Alternate Service response.  But the wireshark call traces
do not capture 380, but always show 300 Multiple Choices response.

Though 380 is considered a success case along with 300, I am curious why
the call trace does not show 380 but shows 300.

any comments?

Thanks
Ranjit

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From: [email-masked] (Dale R. Worley)
Date: Wed, 27 Jul 2016 13:39:31 -0400

> the call trace does not show 380 but shows 300.

I suspect the reason is that 380 is being intercepted and acted upon by
a proxy that is downstream of the point that you are watching with
Wireshark, much as a 301 response would be.  By contrast, 300 cannot be
acted upon automatically.  RFC 3261 section 21.3.1:

   The address in the request resolved to several choices, each with its
   own specific location, and the user (or UA) can select a preferred
   communication end point and redirect its request to that location.

Dale

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From: Ranjit Avasarala <[email-masked]>
Date: Wed, 27 Jul 2016 12:48:19 -0500

True. so does this mean that all 380 responses would be intercepted as 300
responses?

Regards
Ranjit

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From: [email-masked] (Dale R. Worley)
Date: Thu, 28 Jul 2016 15:41:15 -0400

> True. so does this mean that all 380 responses would be intercepted as 300

A proxy may intercept and act on 3xx (RFC 3261 section 16.7 item 4), but
is not required to.

Dale