[Codel] [Cerowrt-devel] FQ_Codel lwn draft article review

Sebastian Moeller moeller0 at gmx.de
Tue Dec 4 19:01:33 EST 2012

Hi Dan,

silly question, are you sure your ISP actually delivers PTM-TC instead of ATM? (Should be easy to check, ATM carrier will show a "quantized" in crease in ping time, increasing only every 48byte, but I guess you know more about theses things than I do). Also what about simply empirically increasing the overhead in your shaper until the anomaly goes away to figure out whether this is simply a misjudged per packet overhead? And then maybe the exact overhead value will give a clue about what is happening thereā€¦


On Dec 3, 2012, at 19:13 , Dan Siemon wrote:

> 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/
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