Re: [sip-overload] A modest (and new) proposal on multiple algorithms for overload control

[<[e-mail]>]

Volker,

I concur with Hadriel. It wasn't clear to me what was being proposed, but I don't see how what you are suggesting is workable.

I pointed out in [1] that the server needs to determine the algorithm to be used, otherwise it has to use an overload control method that will support a mix of restriction algorithms on the client, which would be significantly more complex for the server than the client having to support two restriction algorithms (which I view as relatively straightforward to specify and implement). Because the draft spec does not specify the server algorithm, it gives the illusion that most complexity is in the client, whereas in reality it is most likely to be on the server.

In [2] I gave an example modification of the draft whereby the client algorithms are mandatory, which removes the complexity of the negotiation as well.

Regards,

Phil

[1] http://www.ietf.org/mail-archive/web/sip-overload/current/msg00632.html
[2] http://www.ietf.org/mail-archive/web/sip-overload/current/msg00629.html

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Volker Hilt
Sent: 12 July 2011 15:00
To: [e-mail]
Subject: Re: [sip-overload] A modest (and new) proposal on multiple algorithms for overload control

Hadriel,

the idea is to have a mandatory algorithm in the base draft and, at the 
same time, to leave the draft open for extensions to other algorithms. 
The second draft will then specify such an algorithm.

That way RFC A is the common denominator supported by all devices and 
advanced devices can implement RFC A and B.

Thanks,

Volker (as individual)





On 7/12/2011 9:09 AM, Hadriel Kaplan wrote:
>
> So in summary you're proposing to resolve the issue that having two mechanisms is a bad idea, by specifying the two mechanisms in two separate docs??
>
> OK, well if we have to have two ways of doing the same thing, then I suggest we MANDATE BOTH, by putting them in the same document and a "MUST implement both" written right in it.
> Otherwise, if you have RFC A and RFC B, then some devices will do A and others B and there won't be interop.
>
> -hadriel
>
>
> On Jun 27, 2011, at 5:47 PM, Vijay K. Gurbani wrote:
>
>> Folks: I am trying to close the conversation on SIP overload
>> control algorithms.
>>
>> To recap, we had a decision on making loss-based as the default
>> mandatory-to-implement algorithm and had agreed to allow the
>> choice of rate- and windows-based algorithms.
>>
>> This is what's currently reflected in the protocol draft [1].
>>
>> During the Prague IETF, it was suggested that we revisit this
>> decision and use only one algorithm.  This suggestion lead to
>> a subsequent thread [2] about which algorithm should be
>> chosen --- loss-, rate- or windows-based one.
>>
>> I think we have to be realistic here in recognizing that
>> the relative performance of all the algorithms is about the same.
>> So therefore, if the relative performance is the same then there
>> may be certain network deployments where the choice of one algorithm
>> seems better than the other.
>>
>> Rate-based one will work well in managed networks where the set of
>> upstream clients sending requests is bounded and rather static; this
>> also makes it easier to apply capacity guarantees.  Loss-based one
>> works well where the set of upstream clients sending traffic is
>> unbounded and frequently changing.
>>
>> The loss-based algorithm is less complex than the rate-based one
>> or the windows-based one.
>>
>> Phil Williams has put out a proposal [3] to support all three
>> algorithms simultaneously, thereby eliminating the need for protocol
>> machinations to choose one.  However, issues still remain: first,
>> this will force implementations to implement all of the algorithms,
>> and this I believe is a heavy burden.
>>
>> Second, it does not eliminate the need or the desire to change
>> algorithms mid stream, and finally, this decision forces an overloaded
>> server to maintain considerable state as to which particular
>> algorithm has been chosen with the paired upstream client.
>>
>> It seems that we are at an impasse.
>>
>> So, let me suggest another concrete proposal, which will help move
>> the work forward expeditiously if all agree.
>>
>> I propose that draft-ietf-soc-overload-control continue as it
>> is now with the following exception:
>>
>>     1) Take window class out of the mix, leaving rate and
>>        loss.  No one is explicitly championing the windows-based
>>        one; it could be added later if desired.
>>
>>     2) Invite Phil Williams, Eric Noel, or Janet Gunn to start
>>        working on a rate-based draft that uses the agreement
>>        mechanisms defined in draft-ietf-soc-overload-control
>>        and fleshes out how rate-based mechanism will function.
>>
>>     3) Move draft-ietf-soc-overload-control and the new draft
>>        in (2) as a bundle so that no one algorithm gets an
>>        undue advantage of being specified first.
>>
>> Note that (2) and (3) effectively mitigate Phil's concern that
>> "proceeding with a single mandated algorithm would result in
>> non-adoption of the other algorithms by suppliers and in effect the
>> alternatives would become redundant."
>>
>> Personally I do not think that the market will favour a sub-optimal
>> algorithm and if loss-based does not work I am sure it will
>> be replaced in short order.  But I do empathize with the perceived
>> advantage that loss-based one seems to benefit from if it is made the
>> only mandatory-to-implement algorithm in [1].  Therefore, (2) and
>> (3) above should mitigate this particular concern.
>>
>> I suspect what will end up happening is that implementations geared
>> to managed network providers will end up supporting both loss-
>> and rate-based algorithms while other implementations can support
>> only the loss-based one.
>>
>> Do folks think that this is an agreeable compromise?  It is no
>> worse off than what we had agreed to before, and in fact it is
>> much better since we have eliminated windows-based one and are
>> moving loss-based and rate-based ahead at the same time.
>>
>> I do note that the chairs may have to re-negotiate the charter
>> deliverables with the ADs, but modifying the charter or deciding
>> to make the rate-based draft as an extension to the second
>> deliverable ("2. A specification for an SIP overload control
>> mechanism based on implicit/explicit feedback.") is a minor
>> detail once everyone agrees to this proposal.
>>
>> Please comment.  Thank you.
>>
>> [1] http://tools.ietf.org/html/draft-ietf-soc-overload-control-02
>> [2] http://www.ietf.org/mail-archive/web/sip-overload/current/msg00616.html
>> [3] http://www.ietf.org/mail-archive/web/sip-overload/current/msg00629.html
>>
>> - vijay
>> --
>> Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
>> 1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60566 (USA)
>> Email: vkg@{bell-labs.com,acm.org} / [e-mail]
>> Web:   http://ect.bell-labs.com/who/vkg/
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