From: Alex Burr <ajb44.geo@yahoo.com>
To: Dan Siemon <dan@coverfire.com>,
bloat <bloat@lists.bufferbloat.net>,
"codel@lists.bufferbloat.net" <codel@lists.bufferbloat.net>,
"cerowrt-devel@lists.bufferbloat.net"
<cerowrt-devel@lists.bufferbloat.net>
Subject: Re: [Bloat] [Codel] [Cerowrt-devel] FQ_Codel lwn draft article review
Date: Tue, 4 Dec 2012 01:23:46 -0800 (PST) [thread overview]
Message-ID: <1354613026.72238.YahooMailNeo@web126202.mail.ne1.yahoo.com> (raw)
In-Reply-To: <1354590837.29387.9.camel@ganymede.home>
[Oops, intended to CC the list.]
An extra 15-20ms of latency, which is what you're seeing there,
shouldn't be caused by packet overhead in the actual VDSL modem part of
the device. Worst case the implementation of the PTM-TC layer (the
equivalent of ATM) might round the packet up to a multiple of 64 bytes
(although it's not supposed to), but unless your line rate is 25kbps,
that should not cause 20ms of latency.
VDSL2 operates at 4Khz or
8Khz symbol rate, and while it contains and interleaving or
retransmission layer which can add up to 64ms in its most high-latency
configuration, those layers do not operate at the level of packets and
I'm pretty sure that that latency cannot be affected by packet size in a
conformant implementation.
This latency is being caused by something else.
The
best way to figure out the per-packet overhead in your VDSL2 modem is
probably to count the number of packets that get through, not measure
latency.
Alex
----- Original Message -----
> From: Dan Siemon <dan@coverfire.com>
> To: bloat <bloat@lists.bufferbloat.net>; codel@lists.bufferbloat.net; cerowrt-devel@lists.bufferbloat.net
> Cc:
> Sent: Tuesday, December 4, 2012 3:13 AM
> Subject: Re: [Bloat] [Codel] [Cerowrt-devel] FQ_Codel lwn draft article review
>
> On Mon, 2012-12-03 at 15:58 +0000, David Woodhouse wrote:
>> ADSL is basically just ATM with a strange PHY. You have a bunch of
>> options for how you use this ATM link. Mostly it's RFC2364 PPP-over-ATM
>> or it's PPPoE on top of RFC2684 Ethernet-over-ATM.
>
> Speaking of xDSL, does anyone on the list happen to have a good
> understanding of how much per-packet overhead there is on VDSL2? I've
> been tweaking the buffering and shaping on my upstream link and noticed
> unexpected behavior with small packets.
>
> The link below (use wayback machine version) has a good description of
> per-packet overhead for various forms of ADSL but I haven't found
> something similar for more modern DSL variants.
> http://www.adsl-optimizer.dk/thesis/
> http://web.archive.org/web/20090422131547/http://www.adsl-optimizer.dk/thesis/
>
> I started a discussion on DSLReports
> http://www.dslreports.com/forum/r27565251-Internet-Per-packet-overhead-on-Bell-s-VDSL-ATM-based-
> but experimentally the overhead discussed there doesn't appear to be
> correct
> http://www.coverfire.com/archives/2012/11/29/per-packet-overhead-on-vdsl2/
>
>
>
> _______________________________________________
> Bloat mailing list
> Bloat@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat
>
next prev parent reply other threads:[~2012-12-04 9:23 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAA93jw5yFvrOyXu2s2DY3oK_0v3OaNfnL+1zTteJodfxtAAzcQ@mail.gmail.com>
2012-11-23 8:57 ` [Bloat] " Dave Taht
2012-11-23 22:18 ` Paul E. McKenney
2012-11-24 0:07 ` Toke Høiland-Jørgensen
2012-11-24 16:19 ` Dave Taht
2012-11-24 16:36 ` [Bloat] [Cerowrt-devel] " dpreed
2012-11-24 19:57 ` [Bloat] [Codel] " Andrew McGregor
2012-11-26 21:13 ` Rick Jones
2012-11-26 21:19 ` Dave Taht
2012-11-26 22:16 ` [Bloat] " Toke Høiland-Jørgensen
2012-11-26 23:21 ` Toke Høiland-Jørgensen
2012-11-26 23:39 ` [Bloat] [Cerowrt-devel] " dpreed
2012-11-26 23:58 ` Toke Høiland-Jørgensen
2012-11-27 16:41 ` Oliver Hohlfeld
2012-11-28 0:51 ` Toke Høiland-Jørgensen
2012-11-28 19:21 ` Greg White
2012-11-28 19:45 ` Simon Barber
2012-11-28 20:01 ` Oliver Hohlfeld
2012-11-28 21:40 ` Greg White
2012-11-28 20:09 ` Oliver Hohlfeld
2012-11-28 21:45 ` Greg White
2012-11-26 17:20 ` [Bloat] " Paul E. McKenney
2012-11-26 21:05 ` [Bloat] [Codel] " Rick Jones
2012-11-26 23:18 ` Rick Jones
2012-11-27 22:03 ` [Bloat] [Cerowrt-devel] " Jim Gettys
2012-11-27 22:31 ` David Lang
2012-11-27 22:54 ` Paul E. McKenney
2012-11-27 23:15 ` [Bloat] [Codel] " Andrew McGregor
2012-11-28 0:51 ` Paul E. McKenney
2012-11-28 17:36 ` Paul E. McKenney
2012-11-28 14:06 ` [Bloat] " Michael Richardson
2012-11-27 22:49 ` Paul E. McKenney
2012-11-27 23:53 ` [Bloat] [Codel] " Greg White
2012-11-28 0:27 ` Paul E. McKenney
2012-11-28 3:43 ` Kathleen Nichols
2012-11-28 4:38 ` Paul E. McKenney
2012-11-28 16:01 ` Paul E. McKenney
2012-11-28 16:16 ` Jonathan Morton
2012-11-28 17:44 ` Paul E. McKenney
2012-11-28 18:37 ` Michael Richardson
2012-11-28 18:51 ` Eric Dumazet
2012-11-28 21:44 ` Michael Richardson
2012-11-28 19:00 ` Eric Dumazet
[not found] ` <87vcckb0el.fsf@toke.dk>
2012-12-02 21:47 ` Andrew McGregor
2012-12-03 8:04 ` Dave Taht
2012-12-02 22:07 ` Eric Dumazet
[not found] ` <87lidgaynn.fsf@toke.dk>
2012-12-02 22:30 ` Eric Dumazet
2012-11-28 17:20 ` [Bloat] " Paul E. McKenney
[not found] ` <20121202230635.GA16359@linux.vnet.ibm.com>
[not found] ` <87obib5qf8.fsf@toke.dk>
2012-12-03 11:31 ` Dave Taht
[not found] ` <87fw3n5m9g.fsf@toke.dk>
2012-12-03 14:58 ` Paul E. McKenney
2012-12-03 15:49 ` [Bloat] [Codel] " Eric Dumazet
2012-12-03 15:03 ` [Bloat] " Paul E. McKenney
2012-12-03 15:58 ` David Woodhouse
2012-12-04 3:13 ` [Bloat] [Codel] " Dan Siemon
2012-12-04 9:23 ` Alex Burr [this message]
2012-12-05 3:41 ` Dan Siemon
2012-12-05 20:33 ` Alex Burr
2012-12-06 4:12 ` Dan Siemon
2012-12-06 23:41 ` Alex Burr
2012-12-05 0:01 ` Sebastian Moeller
2012-11-30 1:09 ` [Bloat] " Dan Siemon
2013-01-01 20:50 ` Dan Siemon
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