Re: [sip-overload] Review of draft-ietf-soc-overload-rate-control-07.txt

"Vijay K. Gurbani" <vkg@bell-labs.com> Wed, 25 June 2014 15:26 UTC

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Date: Wed, 25 Jun 2014 10:28:44 -0500
From: "Vijay K. Gurbani" <vkg@bell-labs.com>
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Subject: Re: [sip-overload] Review of draft-ietf-soc-overload-rate-control-07.txt
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On 06/13/2014 09:08 AM, phil.m.williams@bt.com wrote:
> Vijay,
>
> Thanks for your comments. My responses embedded below. I think
> Eric may respond next week.
>
> I can suggest some more specific suggested wording/revisions for
> my first somewhat lengthy reply, but I was hoping to get some
> other views about this  first.

Phil: Please see inline.  Issues that we agreed on are removed
from inlining below.

>> Here are my comments, in document order.  Generally, the draft is well
>> written; some of the comments below may be helpful.
>>
>> - S1, fourth paragraph: The rate-control draft is not as much an
>>    extension to draft-ietf-soc-overload-control as much as it is
>>    a specification for an alternative overload control mechanism.
>>    As such, probably best to state that "This document proposes an
>>    alternative, rate-based overload control algorithm within the
>>    framework defined in [draft-ietf-soc-overload-control-15].  The
>>    rate-based control algorithm guarantees an upper bound ..."
 >
> [PhilW] Please excuse me for a bit of semantic ramble: I suspect that
> some readers may get confused about how the two specs relate to each
> other - I know that I have been. I suggest that we should be more
> explicit about how they differ, because the intention is that they
> are essentially the same (using the same framework) but with a few
> key differences.
[...]
> To summarise, if the intention is an 'alternative' set of
> requirements, which is the same as SIP Overload Control, but where
> the default(mandatory) restriction algorithm is rate-based rather
> than loss-based (the latter being optional), then it would be
> helpful to state this explicitly.

The intention of the WG was that the rate-control draft contain a
overload based scheme that is not loss-based, the tautological
impact of the first half of this sentence notwithstanding.

The only default and m-t-i algorithm that the WG decided to go with
is loss-based.  However, the framework makes provisions to plug in
other algorithms.  And rate-based is one of them.

Insofar as requirements are concerned, I don't see that the rate-control
draft imposes an "alternative set of requirements" as stated above.
The requirements of overload are satisfied by the overload-control
draft, so I am at a loss to see why rate-control is deriving new
requirements when we consider it as an alternative overload scheme.

Supporting rate-control implies supporting overload-control.  An
implementation cannot say it supports overload control if it only
implements the rate-control scheme and nothing else.

>> - S1, fourth paragraph, last sentence: s/loss approach./loss-based
>>    approach./
> [PhilW] Agreed.
>>
>> - S3.2: I am not sure what is the implication of the last paragraph.
>>    I suspect a value in the oc parameter that triggers overload control
>>    at the client informs the client of "overload state".  Why this
>>    overload state occurred (i.e., what resources are being exhausted by
>>    the server) is rather immaterial at the client, no?
 >
> [PhilW] I'm not sure of the intended meaning here either - furthermore it
> is not the desired rate, but the desired maximum rate. I would be happy
> to move it to the start of the section (or delete it altogether), i.e.
> 3.2. Via header field parameters for overload control
> The use of the via header oc parameter(s) inform clients of the
> desired maximum rate. They are defined in
> [draft-ietf-soc-overload-control-14] and summarized below...

Either of these actions is fine.  I have no preference.

>> - S3.4, sixth paragraph: "... at a rate below its target SIP request
>>    rate..."  Here, "its" refers to client? or server?  I think it is the
>>    client, but some clarification would be good.
> [PhilW] Yes it is a little ambiguous but I think this is because the grammar
> is incorrect - would this do  "...at a rate below their target (maximum)
> request rate..."?

Yes.

>> - S3.5.2: the fact that the client maintains two categories of requests,
>>    one subject to reduction and the other not, is an artifact of the
>>    loss-based algorithm in [draft-ietf-soc-overload-control-15].  Thus, I
>>    don't think that this is a requirement of [draft-ietf-soc-overload-
>>    control-15] as much as an artifact of how the loss-based algorithm
>>    works.
> [PhilW] I don't think that there is such a dependence upon the loss-based
> algorithm in 5.10.1 of draft-ietf-soc-overload-control-15, and my
> interpretation is that this section doesn't necessarily imply just
> two levels of priority (say normal and 'priority'). In fact since several
> types of 'high priority' requests are discussed in 5.10.1, one can
> envisage that they may be classed as different priority levels, although
> I am not necessarily implying that is necessarily a good approach from
> a performance perspective.

Sure ...

>>    That said, almost any client will automatically gravitate towards two
>>    similar categories.  Thus it is best to specify the opening sentence
>>    of S3.5.2 as follows:
>>
>>       As with the loss-based algorithm of [draft-ietf-soc-overload-
>>       control-15], a client implementing the rate-based algorithm also
>>       prioritizes messages into two categories of requests: ...
> [PhilW] I suggest that this should read 'two or more categories',
> or 'at least two categories'

... works for me.

Thanks,

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60563 (USA)
Email: vkg@{bell-labs.com,acm.org} / vijay.gurbani@alcatel-lucent.com
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