[Cerowrt-devel] [aqm] [Bloat] the side effects of 330ms lag in the real world

Tue Apr 29 13:02:08 EDT 2014

On Tue, Apr 29, 2014 at 9:44 AM, Jim Gettys <jg at freedesktop.org> wrote:
>
>
>
> On Tue, Apr 29, 2014 at 3:56 AM, Mikael Abrahamsson <swmike at swm.pp.se>
> wrote:
>>
>> On Tue, 29 Apr 2014, Fred Baker (fred) wrote:
>>
>>> Well, we could discuss international communications. I happen to be at
>>> Infocom in Toronto, VPN’d into Cisco San Jose, and did a ping to you:
>>
>>
>> Yes, but as soon as you hit the long distance network the latency is the
>> same regardless of access method. So while I agree that understanding the
>> effect of latency is important, it's no longer a meaningful way of selling
>> fiber access. If your last-mile is fiber instead of ADSL2+ won't improve
>> your long distance latency.
>
>
> FIOS bufferbloat is a problem too.
>
> Measured bufferbloat, symmetric 25/25 service in New Jersey at my inlaw's
> house is 200ms (on the ethernet port of the Actiontec router provided by
> Verizon).  So latency under load is the usual problem.

ESR's link, before and after the cerowrt SQM treatment:

https://www.bufferbloat.net/projects/codel/wiki/RRUL_Rogues_Gallery#Verizon-FIOS-Testing-at-25Mbit-up-and-25Mbit-down

> Why would you think the GPON guys are any better in principle than cable or
> DSL?  Cable and DSL may be somewhat worse, just because it is older and
> downward compatibility means that new modems on low bandwidth tiers are even
> more grossly over buffered.

Well, buffering on the DSLAM or CMTS needs to be more actively
managed. Fixed limits are much like conventional policing, always
either too large or too small to handle sustained or bursty traffic
respectively.

I have been fiddling with Tim Shepard's "udpburst" tool as a quick
means of measuring head end buffering, even with fq_codel present on
the inbound. (It's not suitable for open internet use as yet, but code
in progress can be had or enhanced at
https://github.com/dtaht/isochronous ). I just added ecn and tos
setting support to it.

server: ./udpburst -S -E -D 32 # Server mode, enable ECN marking, set
dscp to 0x20 (CS1)

client:

This is from a 22Mbit down CMTS

d at nuc:~/git/isochronous$ ./udpburst -f 149.20.63.30 -E -C -d -n 400 -s 1400
1400 bytes -- received 382 of 400 -- 365 consecutive 0 ooo 0 dups 2 ect

........................................................................
........................................................................
........................................................................
........................................................................
........................................................................
.... .. .   ... . ...  . ..    ..  .  .
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2   2 2   2       2 2 2   2   2 2 2     2   2 2         2 2     2

or roughly 512k of buffering.

A DSL link (6400 down)

d at puck:~/git/isochronous$ ./udpburst -f snapon.lab.bufferbloat.net -n
100 -C -d -s 1000
1000 bytes -- received 71 of 100 -- 71 consecutive 0 ooo 0 dups 0 ect

......................................................................

 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

or roughly 64k worth of buffering. Interestingly the bandwidth disparity between
the server (gigE in isc.org's co-lo), is so great that fq_codel can't
kick in before
the 64k dslam buffer is overrun.

> You can look at the netalyzr scatter plots in
> http://gettys.wordpress.com/2010/12/06/whose-house-is-of-glasse-must-not-throw-stones-at-another/
>
> Now, if someone gives me real fiber to the home, with a real switch fabric
> upstream, rather than gpon life might be somewhat better (if the switches
> aren't themselves overbuffered....  But so far, it isn't.
>                                       - Jim
>
>                                   - Jim
>
>                                                          - Jim
>
>>
>>
>> --
>> Mikael Abrahamsson    email: swmike at swm.pp.se
>>
>> _______________________________________________
>> Bloat mailing list
>> Bloat at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/bloat
>>
>
>
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-- 
Dave Täht

NSFW: https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_indecent.article