Re: [Dime] Mirja Kühlewind's Discuss on draft-ietf-dime-drmp-05: (with DISCUSS and COMMENT)

Steve Donovan <srdonovan@usdonovans.com> Tue, 10 May 2016 21:04 UTC

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To: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>, Alexey Melnikov <aamelnikov@fastmail.fm>, "Gunn, Janet P" <Janet.Gunn@csra.com>
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From: Steve Donovan <srdonovan@usdonovans.com>
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Date: Tue, 10 May 2016 16:04:40 -0500
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Subject: Re: [Dime] =?utf-8?q?Mirja_K=C3=BChlewind=27s_Discuss_on_draft-ietf-d?= =?utf-8?q?ime-drmp-05=3A_=28with_DISCUSS_and_COMMENT=29?=
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Mirja,

Please see my comments inline.

Regards,

Steve

On 5/10/16 9:46 AM, Mirja Kuehlewind (IETF) wrote:
> Hi all,
>
> sorry for my late reply.
>
> I think the part with the two queues was a little confusing. Sorry for that as well. I originally meant to describe this to illustrate the problem rather than describing a solution. However, using two queues (which fully is an implementation detail) does not even match the problem correctly that I wanted to describe… the actually point would be about the scheduling that one would need to implement to serve the queues. Here my thinking was that, instead of implementing a strict priority scheduling, you could also implement a scheme that guarantees a certain minimum serving rate for the non-priority-defined requests to avoid full starvation. However, I don’t want to confuse you even more here. So let me try to phase my concern again (I’ve also edited my discuss text):
>
> I don’t think it is a good idea to assign a default priority to non-priority-defined requests at all. If you have high priority traffic that does not support this extension (yet) this traffic could be starved by lower priority traffic when assigning a middle range priority. I don’t think that is what you want to achieve.
SRD> Actually, this is what we want to achieve.  It is an requirement 
that messages explicitly marked as high priority get treated even if it 
results in starving lower priority messages.  The starving of lower 
priority messages is not an problem, it is a requirement.
>
> I think this point is even more true with respect to the discussion that went on with Alissa and Ben. There, you said, you’d need to define a priority scheme for a certain application before you could use it. Given that it does not make sense to define a default priority value to for all uses because depending of with priority range you select to use in your scheme, the default might be a low, high, or midrange value.
SRD> I don't understand the statement that it doesn't makes sense to 
define a default priority value.  When defining a priority 
scheme/profile to be used within a Diameter network, all applications 
will need to take the "universal" default value into consideration.  
That default value will then be used in the handling of requests where 
either the application does not yet have a defined priority scheme or 
when the node originating the messages does not yet support the 
applications priority scheme.
>
> To make it even more clear I would like to propose the following text change in the doc:
>
> OLD:
>     Diameter nodes MUST have a default priority to apply to transactions
>     that do not have an explicit priority set in the DRMP AVP.
>
>     Diameter nodes SHOULD use the PRIORITY_10 priority as this default
>     value.
>
> NEW:
>     Diameter nodes MAY set a default priority to apply to transactions
>     that do not have an explicit priority set in the DRMP AVP if it is
>     known that the transactions that define a higher priority than the default
>     are always higher priority than the transactions that do not define
>     a priority explicitly. The default value will depend on the used priority
>     range in a given deployment setup.
SRD> One of the goals of the default priority value is to keep nodes 
like Diameter relays from needing to understand application semantics.  
This requirement would break those Diameter relays as application level 
knowledge is required to know if a message without an explicit priority 
value is of a higher priority.

SRD> In addition, there is only one priority range, as defined in the 
document.  It is important that the range be the same across all 
applications for the mechanism to work, especially in nodes handling 
messages for multiple applications.
>
>     Diameter node SHOULD not assign
>     a default priority if no additional information about the transaction
>     that do not define an explicit priority is known. In this case the
>     diameter node SHOULD provide a minimum serving rate for transaction that do
>     not define an explicit priority to avoid full starvation of these
>     transactions the may or may not have a higher priority than other
>     transactions that provide information about their priority.
SRD> This is explicitly NOT a requirement.  It is acceptable to starve 
lower priority messages.
>
> I hope that makes sense to you. Please propose edits (if not)!
SRD> I don't yet see a reason to change the original wording.
>
> Mirja
>
>   
>> Am 05.05.2016 um 08:32 schrieb Alexey Melnikov <aamelnikov@fastmail.fm>fm>:
>>
>> Hi Mirja,
>>
>> On Wed, May 4, 2016, at 04:50 PM, Mirja Kuehlewind (IETF) wrote:
>>> Hi Janet,
>>>
>>> there are clearly more options than the two mention below.
>>>
>>> E.g. one option is the one explained in my initial comment: hhaving two
>>> queues, that are both served with a certain rate.
>>>
>>> I’m sure there are more (and potentially more complex) solutions to this
>>> problem as well.
>>>
>>> Assigning an arbitrary priority is not the right option from my point of
>>> view and can actually hurt the systems.
>> I hope this will help to clarify things:
>>
>> One point of assigning default priority is that as this is an extension,
>> there is a desire to avoid upgrading all clients on the network, as that
>> would be effectively trying to deploy a new protocol. Consider a network
>> where proxies and servers understand this extension and none of the
>> clients do. Then default priority would be assigned to all traffic and
>> the behaviour of the system is unchanged from the case when the
>> extension is not deployed. The default priority only makes a difference
>> if there is a mixture of clients implementing this extension and clients
>> that don't.
>>
>> Best Regards,
>> Alexey
>>
>>> Mirja
>>>
>>>
>>>> Am 04.05.2016 um 17:45 schrieb Gunn, Janet P <Janet.Gunn@csra.com>om>:
>>>>
>>>> My comment below.
>>>> Janet
>>>>
>>>> -----Original Message-----
>>>> From: DiME [mailto:dime-bounces@ietf.org] On Behalf Of Mirja Kuehlewind (IETF)
>>>> Sent: Wednesday, May 04, 2016 10:31 AM
>>>> To: Alexey Melnikov <aamelnikov@fastmail.fm>
>>>> Cc: draft-ietf-dime-drmp@ietf.org; dime-chairs@ietf.org; dime@ietf.org; The IESG <iesg@ietf.org>
>>>> Subject: Re: [Dime] Mirja Kühlewind's Discuss on draft-ietf-dime-drmp-05: (with DISCUSS and COMMENT)
>>>>
>>>> Hi Alexey,
>>>>
>>>> see below.
>>>>
>>>> The point is, if you explicitly indicate that you have a lower priority, you are okay to be starved. However, if you don’t indicate anything (maybe just because you have not been aware that it is possible to do so), you might have the same or even a higher priority, and in this case it’s not okay to be starved.
>>>>
>>>> Mirja
>>>> <JPG> If a message comes in without a priority, into a system which serves messages based on priority (regardless of the specific mechanisms)you have two options
>>>> 1- Discard the message (Not a good idea in most systems)
>>>> 2 - Assign the message an ARBITRARY priority (we call this arbitrary value the "default priority")
>>>>
>>>> You can (and probably will) argue 'til the cows come home on what that arbitrary/default value SHOULD BE.  And different sytems/applications might have different "default values".
>>>>
>>>> But I don't think there should be any argument that, if a message comes in without a priority, you need to assign it a priority.
>>>>
>>>> </JPG>
>>>>
>>>>
>>>>
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