Re: [straw] AD review of draft-ietf-straw-sip-traceroute-02

[Hadriel Kaplan <[e-mail]>]

On Apr 11, 2014, at 1:44 PM, Richard Barnes <[e-mail]> wrote:

> I have reviewed this document in preparation for IETF LC.  It is clearly written, but I have one technical concerns that I would like to address before IETF LC. 
> 
> I'm concerned that, as described, the mechanism will lead to confusion by UAs.  How does a UA that initiates a loopback call know if it got the real endpoint or just some intermediate B2BUA that happened to be the last one to handle the INVITE?

Section 3.2:
   ... When the ultimate target UAS answers a loopback-based INVITE
   with a Max-Forwards greater than or equal to 0, the Reason header
   would not be added to the response and the UAC will know the
   traceroute is complete.


> Even if there is some indicator, it seems better to have the B2BUAs only respond if there's some consent flag (e.g. Supported: middlebox-answer).  Otherwise, you're requiring every existing UA to check that it actually got all the way through. 

It's only requiring UAs that implement this doc to do so; and it's not a very hard thing for the UAC to check.

If a UAC just wants to do media-loopback to the final UAS, it would set Max-Forwars to 70 on its first attempt. Though it would still need to check the answer's Reason header field to verify some B2BUA hadn't answer it due to reaching the hop limit, but that's a good thing to check for. Ultimately the purpose of media-loopback is for testing+troubleshooting, so giving more info isn't a bad thing. :)

-hadriel