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

Stephen Farrell <> Wed, 01 June 2016 10:19 UTC

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To: Steve Donovan <>, Alexey Melnikov <>, "Mirja Kuehlewind (IETF)" <>
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From: Stephen Farrell <>
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Subject: Re: [Dime] Mirja Kühlewind's Discuss on draft-ietf-dime-drmp-05: (with DISCUSS and COMMENT)
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Great. And Alissa's discuss is cleared so if you want to
go ahead and shoot out a revision with these changes then
I can send the approval and get this shipped off to the
RFC editor. (If doing a revision is a problem, send me
the changes in OLD/NEW form and I can enter them as an
RFC editor note and they'll be done later on.)


On 01/06/16 11:16, Steve Donovan wrote:
> I'm okay with this suggestion.
> Regards,
> Steve
> On 5/29/16 7:28 AM, Alexey Melnikov wrote:
>> Hi,
>> Finally getting back to this.
>> I think authors did a good job in the latest version by adding sections
>> 1.1 (Applicability) and 10 (Considerations When Defining Application
>> Priorities).
>> I would like to suggest the following clarification:
>> In Section 8:
>> Unchanged:
>>     Diameter nodes MUST have a default priority to apply to transactions
>>     that do not have an explicit priority set in the DRMP AVP.
>> OLD:
>>     Diameter nodes SHOULD use the PRIORITY_10 priority as this default
>>     value.
>> NEW:
>>     In order to guaranty consistent handling of messages from nonupgraded
>>     Diameter clients,
>>     Diameter nodes SHOULD use the PRIORITY_10 priority as this default
>>     priority value. PRIORITY_10 is a mid range priority that corresponds
>>     to "normal" traffic and thus would be a suitable default for most
>>     deployments,
>>     while still allowing different Diameter applications to designate
>>     other
>>     priorities for lower and higher priority traffic.
>> Best Regards,
>> Alexey
>> On Wed, May 11, 2016, at 06:39 PM, Mirja Kuehlewind (IETF) wrote:
>>> Hi Alexey,
>>> yes, please provide some text and maybe a warning.
>>> I’ve cleared my discuss as no actual changes to the spec are needed
>>> based
>>> on the common understand we have now, however, I would still like to see
>>> further text in the doc about points that came up in this discussion.
>>> Thanks!
>>> Mirja
>>>> Am 11.05.2016 um 13:13 schrieb Alexe Melnikov <>:
>>>> Hi Mirja,
>>>>> On 11 May 2016, at 07:07, Mirja Kuehlewind (IETF)
>>>>> <> wrote:
>>>>> Okay let me go for an example here and see if that can be a use
>>>>> case that we are talking about.
>>>> Yes, this is helpful.
>>>>> You have a system where some clients run a communication service
>>>>> for emergency doctors as well as for firefighters and then there
>>>>> are also ‚normal‘ users that run some kind of communication service.
>>>>> Now you actually have an emergency: some part of the system is down
>>>>> and the number of request is high such that the system is overloaded.
>>>>> Both the emergency doctors have would have two different priority
>>>>> classes, one for important message about instruction (what and
>>>>> where people should do something) and one for communication between
>>>>> the doctors/firefighters which has still higher priority than any
>>>>> other communication of the other people (as you assume doctors and
>>>>> firefighters are more responsible to not misuse this communication
>>>>> channel).
>>>>> Now only the emergency doctors communication service was upgraded
>>>>> to use this extension, but the firefighter’s administrations is
>>>>> just too slow or they currently have not enough money because they
>>>>> have specialized expensive hardware and software that is not easy
>>>>> to change.
>>>> "Doctor, it hurts when I do that..." - "Don't do that!"
>>>> I don't think this would be a common deployment case.
>>>> I agree that there is an issue in the scenario you specified.
>>>> Default priority helps with a single application + normal
>>>> (unupgraded) traffic. I do think it helps with the most common case.
>>>> So instead of having lots of SHOULDs and MAYs, I suggest we add text
>>>> describing possible issues and when multiple DIAMETER applications
>>>> are deployed we either recommend that all clients are upgraded to
>>>> support this extension at the same time or at least deployments
>>>> specify compatible policies for different applications.
>>>> I can suggest some text.
>>>>> Is it okay in this situation that the private chat of two doctors
>>>>> about their last ski-holidays starves requests to access the
>>>>> network to send instructor message to the firefighters?
>>>> We can't prevent all problems like this, as the above is really a
>>>> social problem combined with misconfiguration. But we can warn about
>>>> it.
>>>>> (And how do i make sure that that all other other requests actually
>>>>> select a lower priority than 10…? But that’s a different question…)
>>>>> Mirja
>>>>>> Am 11.05.2016 um 06:59 schrieb Alexey Melnikov
>>>>>> <>:
>>>>>> Hi Mirja,
>>>>>> On 10 May 2016, at 17:59, Mirja Kuehlewind (IETF)
>>>>>> <> wrote:
>>>>>>>>> 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 we are still talking past each other.
>>>>>> Most definitely :-).
>>>>>>> If you explicitly assign a priority, starvation might be okay.
>>>>>>> However, if you don’t have a priority explicitly signaled, the
>>>>>>> transaction might have a very high priority
>>>>>> So some agent in the system needs to decide that a transaction is
>>>>>> important.
>>>>>>> but you just don’t know and by assigning a random mid-range
>>>>>>> priority this important request could get starved.
>>>>>> Here I disagree with you, because the way to know that a
>>>>>> transaction is important is to upgrade client to explicitly assign
>>>>>> high priority to it. So default priority is a backward
>>>>>> compatibility mechanism, that would work for most common cases.
>>>>>> You seem to be suggesting that when this extension is deployed all
>>>>>> clients need to be updated at the same time. This is not realistic.