From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Fri Jul 13 2007 - 16:29:53 ART
Mike,
Djerk was talking about different ways of PQ.
This is different ways of policing, which is what I was pointing out
in #4.
I thought this is actually the case on low level platforms too.
-Carlos
Mike Kraus (mikraus) @ 13/07/2007 16:19 -0300 dixit:
> On higher end platforms (> 7200), there can be two modes of operation
> for LLQ. (Depends on platform, IOS, modules...).
>
> Voice Traffic
> There are two configurations that are generally used for the low-latency
> ("realtime" or "priority") class, which are distinguished by the
> policing mode used. MQC supports two priority queue policing
> configurations:
>
> Congestion-aware policer
> class SP-VOIP
> priority [percent <%>|<kbps>] <burst>
> set ip dscp|prec <dscp|prec> or set mpls experimental <0 through 7>
> imposition
>
>
> In this mode, the priority queue traffic is only policed when the
> interface is congested. This mode is initiated by using the "rate"
> option on the priority command.
>
> Always On policer
> class SP-VOIP
> priority
> police <bps> bc <bytes> conform transmit exceed drop
> set ip dscp|prec <dscp|prec> or set mpls experimental <0 through 7>
> In this mode the priority queue traffic is permanently policed. This
> mode is initiated by using a discrete police statement within the
> priority queue class. This method is more favorable for service
> providers who wish to strictly enforce the VoIP contract
>
> http://www.cisco.com/en/US/netsol/ns341/ns396/ns172/ns103/networking_sol
> utions_white_paper09186a00801b1c5a.shtml
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Carlos G Mendioroz
> Sent: Friday, July 13, 2007 1:42 PM
> To: Djerk Geurts
> Cc: ccielab@groupstudy.com
> Subject: Re: Class-default contradiction
>
> Djerk,
> Djerk Geurts @ 13/07/2007 08:23 -0300 dixit:
>> Carlos,
>>
>>> Djerk,
>>> this is exactly what I was saying, so we agree.
>>> (Nobody remembers custom queueing ???)
>> Correct. Nobody _wants_ to remember custom queueing... ;)
>>
>>> I don't understand the PQ(LLQ) thing you are bringing up though.
>>> PQs have priority, which is a police statement. They get ALL the
>>> bandwidth, even first thing (PQ, right?) but up to this much.
>>> AFAIK, a queue becomes a PQ when you use the priority keyword, and
>>> this implies the policing of it, so there is no way you can have a PQ
>
>>> w/o policing.
>> Apparently this is not true, CCO doesn't help here as there are too
>> many conflicting docs on QoS there.
>>
>> One has to distingush here between software (up to 7200) and hardware
>> (7300 GSR CRS-1) based platforms. The priority key-word, like you say,
>
>> enables the priority queue. However the word strict has come to mean
>> (to me at least) a policed PQ. The confusion is that a priority
>> statement with bandwidth % isn't a policed PQ, resulting in
>> 'unpredictable' behaviour when shaping VoIP traffic. So does this mean
>
>> it is a strict PQ? I recall something from Networkers this year that
>> best practice is to use the priority keyword with a police statement
>> and not use the bandwidth option on the priority statement.
>>
>> So please correct me if I'm wrong Cannes was back in January after all
>
>> and I've not had the time since to look it up in my notes or
>> hand-outs. Btw, I don't trust CCO anymore on the subject of QoS...
>>
>> I understand that things may be different from what they said at
>> Networkers to what we study for the lab. Networkers referred to the
>> CRS-1 mostly (due to marketing?) while the lab uses only SW based
> routers.
>
> Well, this is possibly above my level of knowledge, and I usually agree
> with things being far more messier than it shows.
> But:
> 1) MQC is a syntax. If the implementation in a platform of a given
> config is different from another, I would call this a bug (or a
> feature:)
> 2) PQ is PQ is PQ. I don't really know what "strict" PQ is.
> If there is a strict, there should be a loose version of it ? :)
> 3) As far as I know, there is no way to make a queue a PQ without using
> the priority keyword. Percent only changes the meaning of the numbers,
> by scaling them.
> 4) priority implies policing. Allmost. The implied policer only works
> when queue management is engaged (i.e. interface congested).
> Configuring an explicit policer engages it (the policer) all the time.
>
>>> The whole thing I was trying to say is that the default queue works
>>> like a "low priority" queue, but without the grace of the policing of
>
>>> the rest, and thus the starving possibility.
>>> (when no bandwidth is assigned)
>> I agree totally
>>
>>> BTW, queues don't need to know their bit rates, just their "share"
>>> of available BW. In your examples, 3/4/3 or 1/5/4.
>> And again 100% correct
>>
>>> -Carlos
>> Djerk
>>
>
> BTW, do you have any pointer to NW presos ?
> Take care,
> -Carlos
>
> --
> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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