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

"Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net> Wed, 04 May 2016 14:31 UTC

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From: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
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To: Alexey Melnikov <aamelnikov@fastmail.fm>
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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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Hi Alexey,

see below.

> Am 04.05.2016 um 14:03 schrieb Alexey Melnikov <aamelnikov@fastmail.fm>fm>:
> 
> Hi Mirja,
> 
> On Wed, May 4, 2016, at 12:45 PM, Mirja Kuehlewind (IETF) wrote:
>> Hi Alexey,
>> 
>> 
>>> Am 04.05.2016 um 13:37 schrieb Alexey Melnikov <aamelnikov@fastmail.fm>fm>:
>>> 
>>> Hi Mirja,
>>> 
>>>> On 4 May 2016, at 12:13, Mirja Kuehlewind <ietf@kuehlewind.net> wrote:
>>>> 
>>>> However, the one part that does actually concern me is:
>>>> "When using DRMP priority information, Diameter nodes MUST use the
>>>> default priority for transactions that do not have priority specified
>>>> in a DRMP AVP."
>>>> This part seems dangerous and I would proposed to instead basically have
>>>> to different queues: one if a priority is defined and another one for
>>>> requests without priority indication to make sure that requests out of
>>>> the second queue will be served at some point in time and cannot be
>>>> starved by other low priority requests completely.
>>> 
>>> I think I disagree with you: default priority handling is orthogonal to the number of queues used. Some implementations would use one queue per priority, so you are effectively suggesting that no priority is treated as its own priority. I think this is an implementation detail.
>>> 
>>> 
>> Yes, queues are implementation details. That was just meant as an
>> illustration. My point it, I don’t think all requests without priority
>> should get an default priority assigned
> 
> Why not? Why not assigning a priority any different than assigning a
> unique priority?
> 
> (SMTP Priority extension RFC which I edited made the same choice:
> https://tools.ietf.org/html/rfc6710)
> 
>> (and especially not a very low
>> priority).
> 
> True, but the default is mid range.
> 
>> Further it has to be ensured that requests that don’t assign a
>> priority do not get starved (as they might be important).
> 
> That I agree with. However the whole point of priorities is that higher
> priority messages can starve lower priority messages. Using emergency
> services as an example: during normal operations all messages will have
> default priority (no priority). During an emergency, some messages will
> have high priority which might starve no priority messages (regular
> traffic).

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