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

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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 [e-mail] and [e-mail]
>
> Al
> bmwg co-chair
>
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