[quagga-users 12557] Re: bgp - quagga-0.99.18

Peter J. Holzer hjp+quagga at wsr.ac.at
Tue Nov 8 16:52:35 GMT 2011


On 2011-11-08 14:19:02 +0100, Ingo Flaschberger wrote:
> >>>Be careful what you do with buffers. See
> >>>http://www.bufferbloat.net/ if you don't understand how big buffers
> >>>can be bad.  I have to admit, I am not yet satisfied with how we're
> >>>handling buffering, and I'd like a dynamic solution. However, in
> >>>practice, we seem to be doing OK.
> >>
> >>Sorry - but this guy has no idea about buffers.
> >
> >Um. Which guy would that be, and why do you think so?
> 
> as Nick Hilliard outlined the size and speed of a buffer makes the
> difference.
> bufferbloat does not tell which size / speed is bad -

Jim Gettys gives a back of the envelope formula for the optimal buffer
size in his "bufferbloat" talk[1]:

    delay x bandwidth x √#flows

The optimal buffer size for a single flow is delay x bandwidth (this is
well known). I'm not sure where he gets the sqrt from (intuitively it is
clear that the buffer size must not increase linearily with the number
of flows, but how much less it must be I don't know). 

Less is bad because you waste time waiting for ACKs.
More is bad because you get excessive lag on congested links and TCP
won't throttle back.


> they only say buffers are bad - which is not true.

Who is "they" and where do they say that? I can't find "official"
statements at the site - even the link to the talk above I found only in
the mailing list archive.

        hp

[1] http://mirrors.bufferbloat.net/Talks/BellLabs01192011/110126140926_BufferBloat12.pdf
    page 66

-- 
   _  | Peter J. Holzer    | Auf jedem Computer sollte der Satz Ludwigs II
|_|_) | Sysadmin WSR       | eingeprägt stehen: "Ein ewig Rätsel will ich
| |   | hjp at wsr.ac.at      | bleiben, mir und andern."
__/   | http://www.hjp.at/ |    -- Wolfram Heinrich in desd
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