[BBLISA] November meeting: Jim Gettys on Internet buffer bloat

[stephen wadlow]

ALL:

I've removed bblisa-announce from the recipients list.   Please stop sending mail to that list for this discussion thread.

			thanks,
			   -steve



On Nov 7, 2012, at 3:56 PM, Daniel Hagerty wrote:

> Edward Ned Harvey <bblisa4 at nedharvey.com> writes:
> 
>> Let's assume a fast LAN getting congested through a WAN link.  There exists
>> a router, which is buffering the traffic it receives from the LAN.  There
>> exists such a thing as flow control.  At the mac layer, when the receiver
>> buffer is getting sufficiently full, the receiver (router) sends the PAUSE
>> frame (or newer more powerful alternatives) to the sender, on the LAN.  So
>> the sender, in hardware, knows to back off a little bit.  The application,
>> and even IP layer don't need to know about it.  No dropped packets.  Perfect
>> efficiency and optimization.  The only thing that can go wrong is a router
> 
>    You are describing an open-loop controller.  This is actually how we
> got here, when the distributed open loop was routinely overwhelming the
> 56k internet core, getting us to the current TCP congestion control
> algorithm.  TCP's current algorithm is a closed loop in the face of some
> assumptions that break down in the face of excessive buffering.
> 
>    I'd suggest some reading on control theory for some understanding of
> the differences and engineering tradeoffs.  It's old, compared to
> computers, with 150 years of experience in exploding steam engines,
> crashing cars, rocket engines shaking their rocket apart, and yes,
> collapsing data networks.  It's full of subtle "the naive thing will
> work up to here, and then it destroys itself" cases.  People earn PhDs
> in it, and sometimes proceed to blow stuff up real good anyway.
> 
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