Re: [aqm] first WGLC on draft-ietf-bmwg-traffic

Hi Gorry,

We will add the scoping language that you requested and also incorporate your core document comments.

Thank you for taking the time to review this work.

Barry Constantine


-----Original Message-----
From: bmwg [mailto:[email protected]] On Behalf Of [email protected]
Sent: Friday, September 26, 2014 4:21 AM
To: ramki Krishnan
Cc: [email protected]; MORTON, ALFRED C (AL); [email protected]; [email protected]
Subject: Re: [bmwg] [aqm] first WGLC on draft-ietf-bmwg-traffic

I think that it is a good plan to expect a separate draft on more advanced techniques.

However,  AQM has been deployed in places (and likely more so), so what I was hoping was that this particular draft could scope itself carefully to state the constraints of the tests. I don't think it is wise simply to ignore the AQM-related issues, although this scoped could well be addressed in the start and end of the document.

I agree the details of AQM tests and QoS-based tests are likely to be more complicated and best declared out of scope.

Gorry

> Hi Gorry,
>
> Many thanks for your detailed comments.
>
> The goal of this draft is to describe the commonly used traffic 
> management techniques in switches and routers. AQM (RED, WRED etc.) is 
> an advanced traffic management technique which we plan on  addressing 
> in a separate draft. Tail drop is the commonly used technique in 
> switches and routers for addressing congestion control. Please see 
> references to Cisco and Brocade configuration guides - 
> (http://www.cisco.com/c/en/us/td/docs/routers/10000/10008/configuratio
> n/guides/qos/qoscf/10qqueue.html#wp1041728;
> http://www.brocade.com/downloads/documents/product_manuals/B_NetIron/NetIronUnified_05400a_ConfigGuide.pdf).
>
> BTW, David asked us at the last IETF meeting about AQM and the above 
> response was well received by the working group.
>
> We will address all your non AQM comments in the next version of the 
> draft.
>
> Thanks,
> Ramki
>
> -----Original Message-----
> From: bmwg [mailto:[email protected]] On Behalf Of 
> [email protected]
> Sent: Thursday, September 25, 2014 12:33 AM
> To: [email protected]; MORTON, ALFRED C (AL)
> Cc: [email protected]
> Subject: Re: [bmwg] [aqm] first WGLC on draft-ietf-bmwg-traffic
>
>
> I have a few comments from a quick pass through this document. I think 
> it is useful to define such tests, and I suspect those performing the 
> tests may understand the wider context of testing a specific 
> mechanism, but I have a concern that the tests would produce strange 
> results if deployed with sophisticated traffic management, and this is 
> not really discussed. I think this needs to be addressed, and if 
> necessary the cope of the tests clearly stated.
>
> I am worried that while the tests may help characterise a single 
> shaper/policer, there is a need to extend the document at least to 
> comment on more complex interactions that can occur.
>
> QoS Frameworks define policies (e.g. DS) that can map DSCPs (or MF 
> classified traffic) to treatments, possibly aggregating behaviours for 
> different traffic aggregates. Treatments are not independent - traffic 
> with one marking can and does traffic with a different marking (well 
> its intended to). Testing multiple DSCPs in DS at the same time is 
> more complex, it should not be assumed that each of these can be 
> characterised separately.
>
> AQM seeks to manage buffering, and this reaction is likely to be 
> triggered by test sequences. When triggered, the response (loss, 
> delay) can impact the flow's treatment long after the traffic burst 
> that triggered AQM in the first place.
>
> Many AQM methods are also used in combination with scheduling, again 
> this can be and often is non-trivial and depends on the number of 
> flows and sometimes the hashing of the flows to queues, etc within the 
> scheduling framework.
>
> Other specific comments follow.
>
> Gorry
>
> ---
>
> Section 1:
> Introduction needs to define terms when first used.
> - would be good to define VLAN and DSCP
>
>
> /sent onto to the next network/sent to the next network/
> - is it also possible to say "forwarded" rather than "sent"?
>
> Active Queue Management (AQM):
> - would be good to cite:
> https://datatracker.ietf.org/doc/draft-ietf-aqm-recommendation/
>
> Please define MEF
>
> /of it's egress ports/of its egress ports/
>
> /The Network Delay Emulator (NDE) is a requirement for the TCP
>    stateful tests/
> - probably true of any control-loop based congestion control (i.e. TCP 
> is an example, SCTP, DCCP and other congestion controls layered on UDP 
> would also need this (including some uses of RTP).
>
> Please define BDPs
>
> Section 3:
>
> /Another goal is to devise methods that utilize flows with
>    congestion-aware transport (TCP) /
> - I think TCP is an example here, and needs an e.g., to avoid it 
> seeming like this is the only test case. Note also this comment 
> applies later in the same para.
>
> When it comes to an active technique, the concept of Burst Size 
> Achieved
> (BSA)  and Lost packets (LP) is less clear, since won't this also 
> depend on the recent history of the flow traffic patterns and could be 
> significantly influenced by scheduling mechanisms between flows (i.e.
> whether the flow is hashed to a separate queue, whether the flow is 
> classified as "new" or "old" and the total number of flows being 
> serviced). Performance could be quite different for a single flow test.
>
> With Active management, Packet Delay (PD) also becomes a function of 
> traffic.
>
> Section 4.2 - I think the document should mention the need to test for 
> other non TCP congestion-controlled traffic, although I could see that 
> for simplicity the tests are defined only for TCP.
>
> 5.1.1 Burst Hunt with Stateless Traffic
> - A cautionary note here could be helpful, that advises that if AQM is 
> used, the bursts must be sufficiently separated in time that they do 
> not cumulatively trigger a response - since AQM algorithms can have 
> history, treatment of a subsequent burst can be influenced by an earlier burst.
>
> 5.2.1. and 6.4:
> - could note that multiple flows may also be queued and scheduled 
> separately within the device.
>
> Informative References
> -missing
>
>
>> BMWG (and AQM):
>>
>> A WG Last Call period for the Internet-Draft on Traffic Management
>> Benchmarking:
>>
>>    http://tools.ietf.org/html/draft-ietf-bmwg-traffic-management
>>
>> will be open from 23 September 2014 through October 21 2014.
>>
>> These drafts are beginning the BMWG Last Call Process. See 
>> http://www1.ietf.org/mail-archive/web/bmwg/current/msg00846.html
>>
>> which says:
>> ...
>> The primary change is a requirement that approximately four WG 
>> members complete a review template for the draft (or set of drafts), 
>> upon entry to the Last Call Process. The WG reviewers should be 
>> outside the body of active contributors (editors + authors).
>> The goal is to produce a quality review with valuable feedback on the 
>> draft(s), and not to set a minimum number of people willing to 
>> complete the review template. Directed feedback, regardless of 
>> quantity, is a better condition by which BMWG can more clearly assess 
>> a draft's readiness to advance.
>> (the template is appended to the archived message)
>>
>> Please read and express your opinion on whether or not these 
>> Internet-Drafts should be forwarded to the Area Directors for 
>> publication as Informational RFCs.  Send your comments to this list 
>> or [email protected] and [email protected]
>>
>> Al
>> bmwg co-chair
>>
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>>
>
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