[Bloat] review: Deployment of RITE mechanisms, in use-case trial testbeds report part 1

Dave Täht dave at taht.net
Sat Feb 27 14:04:41 EST 2016

On 2/26/16 3:23 AM, De Schepper, Koen (Nokia - BE) wrote:
> Hi Wes,
> Just to let you know that we are still working on AQMs that support scalable (L4S) TCPs.
> We could present some of our latest results (if there will be a meeting in Buenos Aires, otherwise in Berlin?)
> * Performance of HTTP Adaptive Video Streaming (HAS) with different TCP's and AQMs
>    o HAS is currently ~30% of Internet traffic, but no AQM testing so far has included it

I am aware of several unpublished studies. There was also something that
compared 1-3 HAS flows from several years back from stanford that I've
longed to be repeated against these aqm technologies.


>    o the results are very poor with a particular popular AQM

Define "very poor". ?

> Presenter: Inton Tsang
> Duration: 10mins
> Draft: Comparative testing of draft-ietf-aqm-pie-01, draft-ietf-aqm-fq-codel-04, draft-briscoe-aqm-dualq-coupled

> For experiment write-up, see Section 3 of https://riteproject.files.wordpress.com/2015/12/rite-deliverable-3-3-public1.pdf

At the risk of sounding grumpy and pedantic, partially driven by trying
to read through 58 pages of text on a b/w kindle (before I switched to
something higher res)

No source, can't reproduce.

The diagrams of the topology, etc, were quite helpful. Insight into the
actual complexity of BT's network was quite useful. I would love to know
the actual usage of the various QoS queues in terms of real traffic...

Has DCTP's not responding to drop properly problem been fixed in linux
yet? (sec 3.3.2). That remains a scary bug....

More detailed comments:

The tests tested download traffic only and seem to have assumed that the
uplink would never have been a bottleneck. Home connections are
asymmetric and increasingly so - comcast, for example is now putting out
links with 75Mbit down, 5.5Mbit up. It is not clear what the uplink rate
of the emulated or real network is in this paper.

2) Section 2 - would have been tons more interesting had it evaluated
the effects of other workloads against actual "twitch" games such as any
of the quake series, call of duty, or starcraft. The game chosen was
quite uninteresting from "needing a low latency and jitter to win" on,

Applying interesting background network workloads while game bots
competed as in here http://sscaitournament.com/ would have been great
fun! - injecting random jitter and delay into the network stack has been
what Karl Auerbach has been doing to the competitors at the DARPA robot
competitions, and he's probably been the cause of quite a few of those
real-life robots falling over (I can hear his evil chuckles now).

Artificially applying a wifi loss rate of 1.5% is a far cry from what
actually happens on wifi, where what you see is more typically large
spikes in l2 delay, nowadays.

3) As for section 3 - it uses a "bottleneck of 20Mbps and RTT of 20ms,
ten TCP long file download flows as background traffic and one HAS
request, which launch two TCP flows." I will try to restrain myself, but:

A) In a cable modem scenario, the typical uplink varies from 2mbit to
4mbit on a 20mbit link. I am not aware of many 20mbit symmetric links,
aside from FIOS. I would love symmetry on home links, is BT deploying that??

B) this is a workload that has very little resemblance to any reality I
can think of and seems expressly designed to show the burst tolerance
and additional latency induced by pie and dualQ to an advantage, and
fq_codel at a local minimum.

For the sake of science, varying the number of long running downloads
from, say, 2,4,8 and 16, would have provided a more rounded picture.
Still I am really hard pressed to think of any case where home HAS
traffic will be competing with more than 2-3 long running full rate
downloads in your typical home. I HAVE seen 3 android devices attempt to
update themselves all at once, but that's it....

Using bittorrent to generate 5-15 flows down, perhaps? Even then, most
real world torrents are not running very fast, there's utp based
congestion control, and torrenters spend way more time in the upload
phase than the download.


Using web access bursts (10-100 flows lasting for 2-8 seconds), chock
full of dns accesses, seems to be a good test against HAS traffic. I see
there is a section doing that, but it is against 5 background flows,
also and I'm pretty sure there will be a pause between bursts, and
although the "The web requests followed an exponential arrival process,
while the size of the downloaded files were designed to represent actual
Internet web objects following a Pareto distribution with size between 1
Kbyte and 1 Mbyte" is documented...

I could do the math assuming that distribution * the number of files...
but I would prefer the total size of the web transfer be documented, and
it's time to complete a load presented... nor is it clear if dns lookups
are enabled or counted. Unless I missed it somewhere? If you are going
to measure two loads - one HAS, one web, presenting the results for both
for contrast, seems logical.

"Figure 3.22 shows that HAS-DCTCP can maintain its performance even with
the additional 100 web traffic request per second as background traffic.
It consistently delivered segments of 2056 Kbps encoding
bit rate. In contrast, under the same network condition, the additional
web traffic deteriorate further the performance of HAS-CTCP as the
delivered segment alternated qualities between 688 Kbps and
991 Kbps encoding rates. This had a lower overall quality when compared
with the previous experiment, which without the additional web traffic
could achieved a sustainable delivery of segment with 991 Kbps
encoding rates, as shown in Figure 3.18"

This kind of stuff really gets under my skin. What was the web page
completion time? Which matters more to the users of the household? a
slight decline in video quality, or a web page load?

Sacrificing all other network applications on the crucible of 4k video
is really not my goal in life, I would like to see videoconferencing,
gaming, web, in particular, work well in the presence of HAS.

Please, please, please, put web page completion times in this document?


Also that sort of web traffic would probably cycle on a 30-60 second
basis at most - people just can't read that fast! Secondly, a search
engine query often precedes an actual web page lookup.

 (I note that web page size growth has slowed dramatically since this wg
started, it is now well below the projections we had a few years ago
(7mbit by 20XX, more like 4 now, but I'd have to go redo the math -
growth went from exponential-looking in 2012 to linear now...). There's
also some data presented recently by some googlers at netconf 1.1 that
showed the impact and commonality of dns failures across their
subscriber base.....

I freely confess that maybe i'm out of touch, that maybe having perfect
television quality while waiting seconds for web pages to load, is what
most internet users want, and they deserve to get it, good and hard,
along with their supersized mcgreasy burgers and calming drugs delivered
to their door.

C) And no reverse traffic whatsoever in section three.

In your typical HAS video streaming home scenario, the worst behaviors I
can think of would be bittorrent generated *on the upload*, but the
simplest case of a single upload happening at all - tends towards
starving the ack streams and ramp up times on the video download flows.
Which was not tested. Sigh. How long have I banged on this drum?

D) It is unproven from a QOE perspective (I think) that having a video
stream change qualities on a "better average" basis is of benefit to the
user - seeing a stream never pause "for buffering", and consistent
quality, seems saner. I notice when the quality changes down, but rarely
up. "buffering" - that I seriously notice.

I would have liked reference data for drop tail vs the various
experiments in this paper. Typical amounts of head end buffering on
docsis 3.0 arris cmtss seem to be in the 800ms range at 20mbit.

E) A workload that I would like to see tested with some rigor is a
family of four - one doing a big upload (facebook/instagram), another
browsing the web, another doing a phone call or videoconference, and a
fourth attempting to watch a movie at the highest possible resolution.

The bar for the last has moved to SD or HD quality in the past few years
- 18mbits is a number I keep seeing more and more. Someone with a 20Mbit
link IS going to try for the highest quality, and showing the dynamic
range of that (1-18mbits) would be more interesting than 1mbit to 2, as
in in this paper.

I also would welcome 2-3 HAS testing on downloads against these AQMs,
attempting those rates, along the lines of the stanford thing I
mentioned first.

I petered out before reading sections 4 and 5. I will try to get to it
this week.

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