Subject: [tsvwg] Circuit Breaker draft - one final check

From: "Black, David" <[email-masked]>
Date: Tue, 29 Mar 2016 17:37:37 +0000

draft-ietf-tsvwg-circuit-breaker has been approved by the IESG and the
current -14 version responds to the IESG's comments; there were a lot
of changes to the text, mostly editorial, see the diff for details:

https://www.ietf.org/rfcdiff?url1=draft-ietf-tsvwg-circuit-breaker-13&url2=draft-ietf-tsvwg-circuit-breaker-14

There is one change that ought to be run by the WG before the final  approval
is announced - as proof that the ADs do actually read our drafts ;-), one of them
found a "MUST" statement that should've been removed last fall (and has now
been removed in the latest -14 version).

As the shepherd for this draft and a WG co-chair, I believe that removal of this
"MUST" statement is in accordance with  WG rough consensus, but the purpose
 of this message is to provide an opportunity for anyone who feels differently
to object.

The offending "MUST" statement was in requirement #1 of section 4 - the
following text was removed between the -13 and -14 versions:

        The CB MUST trigger if there is a failure of the
        communication path used for the control messages.  That is, the
        feedback indicating a congested period needs to be designed so
        that the CB is triggered when it fails to receive measurement
        reports that indicate an absence of congestion, rather than
        relying on the successful transmission of a "congested" signal
        back to the sender.  (The feedback signal could itself be lost
        under congestion).

WG list discussion back in October concluded that this was not the right thing to
do when the control path is different from the data path.  This topic is now
covered (extensively) by requirement #16 in section 4; the current -14 text
on this design topic is:

        The preferred
        CB design is one that triggers when it fails to receive
        measurement reports that indicate an absence of congestion, in
        contrast to relying on the successful transmission of a
        "congested" signal back to the sender.  (The feedback signal
        could itself be lost under congestion).

        in-Band:  An in-band control method SHOULD assume that loss of
           control messages is an indication of potential congestion on
           the path, and repeated loss ought to cause the CB to be
           triggered.

[... snip ...]

        Out-of-Band:  An out-of-band control method SHOULD NOT trigger
           CB reaction when there is loss of control messages (e.g., a
           loss of measurements).  This avoids failure amplification/
           propagation when the measurement and data paths fail
           independently.

Requirement #16 was requirement #18 in the -13 version. 

If anyone objects to removal of the above "MUST" statement from
requirement #1 in section 4, please comment on the list within the next week.

Thanks, --David
----------------------------------------------------
David L. Black, Distinguished Engineer
EMC, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953     Cell: +1 (978) 394-7754
[email-masked]        
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