Re: [Bloat] Requirements for bufferbloat to occur

[sahil grover <sahilgrover013@gmail.com>]

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Thanks a lot for replying.

can you please explain me  the concept of  delay-bandwidth product,window
size and buffer size(or something related with pipe size and packets in
flight).

 because i am unable to understand it from papers/articles etc.

And the way you explained to me everytime, was very effective.

So please help in making me understand this(BDP,window size) concept too .





On Sun, Mar 29, 2015 at 2:09 AM, Jonathan Morton <chromatix99@gmail.com>
wrote:

>
> > On 29 Mar, 2015, at 11:04, sahil grover <sahilgrover013@gmail.com>
> wrote:
> >
> > (1) All say bufferSize should be set very large for bufferbloat to occur.
> >
> > But how much large?? is there any condition?
>
> There’s a clue in the name: if the buffer is significantly larger than it
> needs to be (and is unmanaged), we call that bufferbloat.
>
> If the buffer is too small to absorb a typical burst of packets, the
> resulting increase in packet loss will cause a reduction in throughput.
> The correct size for an unmanaged buffer is typically the delay-bandwidth
> product, which enables it to absorb a transitory burst from a single TCP
> flow.
>
> However, determining the delay is difficult a priori, and frequently
> differs substantially between different flows on the same connection.  So
> we usually make some reasonable assumption about the delay component of
> that formula: 100ms is typical for a broadband connection to the public
> Internet, and VoIP can just-about cope with that in practice.
>
> Or, to put it another way - if the buffer *induces* significantly more
> than 100ms delay under load, that is bufferbloat.
>
> > (2) even after setting buffersize very  very large,  if packets get
> dropped due to buffer
> > overflow  when heavy traffic is there.
> >
> > is it bufferbloat?
>
> Yes.  Packet loss has nothing to do with it - it’s the induced delay that
> matters.
>
> > sholud we take care that maximum limit of buffersize is never reached
> and no
> > packet  drop is there due to queue overlow for bufferbloat condition?
>
> Extremely large buffers are usually the result of hardware engineers
> naively attempting to achieve zero packet loss, by providing buffers larger
> than the TCP receive window size.  (That is a futile goal - rwnd is
> unlimited in modern operating systems which support window scaling.)
> However, zero packet loss is not a necessary condition.
>
> AQMs often deliberately drop packets in order to signal congestion to the
> endpoints.  Under some circumstances, this can actually result in less
> overall packet loss than on an unmanaged buffer.  Even without ECN, the AQM
> rarely causes burst losses, whereas overflowing an unmanaged queue often
> does.  With ECN, an AQM can often signal congestion sufficiently well
> without dropping any packets at all.
>
>  - Jonathan Morton
>
>

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