On Tue, 21 Dec 2010, Jesper Dangaard Brouer wrote:
On Thu, 16 Dec 2010, Jan Engelhardt wrote:
On Thursday 2010-12-16 10:57, Jesper Dangaard Brouer wrote:
> [...] NetConf 2010, see:
>
> http://vger.kernel.org/netconf2010.html
I just went over a few slide sets, and noticed Dave's Netfilter summary
about your IPTV talk, enlisting the point
* Ethernet switches buffer too small
("too small".. "too few"?) Given the recent uproar about bufferbloat in
routing devices (see LWN coverage about Getty's articles), wanting
larger buffers seems to almost contradict what Getty would like.
Always wanting small buffers doesn't make sense. It seem that he is not
considering that network equipment can be used for other things than TCP/IP.
I have created a blogpost:
http://netoptimizer.blogspot.com/2010/12/buffer-bloat-calculations.html
Where I explain how it makes sense to have small buffers on links with a
small bandwidth.
- ISPs need to adjust the buffer size according to the bandwidth of the
link.
Wanting more buffers vs. wanting less buffering seems to be quite
contradictory. Jesper, what is your take on this?
Skimming through Getty's blog post, I think Getty has actually missed what is
happening. He should read my masters thesis[1]... The real problem is that
TCP/IP is clocked by the ACK packets, and on asymetric links (like ADSL and
DOCSIS), the ACK packets are simply comming downstream too fast on the larger
downstream link, resulting in bursts and high-latency on the upstream link.
Adjusting my statement; the asym ACK issue might be part the issue,
causing the packets to queue in the buffer.
The buffer-bloat issue is very true and a real-life issue. ISPs need to
adjust the buffers according to the bandwidth on the link!
Cheers,
Jesper Brouer
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MSc. Master of Computer Science
Dept. of Computer Science, University of Copenhagen
Author of http://www.adsl-optimizer.dk
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