Re: [Insipid] Requirement for Intermediaries to Update Session ID for other parties

Brett Tate <brett@broadsoft.com> Tue, 07 June 2016 16:42 UTC

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From: Brett Tate <brett@broadsoft.com>
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Date: Tue, 7 Jun 2016 12:41:58 -0400
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To: insipid@ietf.org, Paul Giralt <pgiralt@cisco.com>
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Subject: Re: [Insipid] Requirement for Intermediaries to Update Session ID for other parties
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Hi,

> There are several references in the draft that indicate
> an Intermediary SHOULD update endpoints involved in a
> session if the session ID on one call leg changes, but
> it does not require it. Is there any reason why we should
> not change these to a MUST so that Intermediaries are
> required to update the Session ID for any participant it
> knows is out of sync?
>
> If there are good reasons for leaving as a SHOULD,
> I’d like to hear them.

The following are a few thoughts on the topic.

1) A proxy can't really do it.

2) I assume proxy B2BUA's that only initiate BYE's would not want to do it
except when sending BYE.

3) Because it causes extra traffic and potential for glare, the
administrator might not want the extra messaging to occur solely to update
the UUID.

4) The request might not reach the device that the intermediary is
attempting to update.  Thus, it could be completely useless extra traffic.

5) Methods that the intermediary is willing to use for the update might not
be within the received Allow header.

6) It can cause the intermediary to be part of an infinite change loop
unless use re-INVITE without offer.

7) The intermediary might not have auth credentials to allow the change to
be successful.

8) Because of race conditions and other things, the intermediary initiated
messaging intended to correct the UUID could cause other locations to switch
to an incorrect value.