more on response from Google to yet another twist

[David Farber <dave () farber net>]

Begin forwarded message:

From: Karl Auerbach <karl () cavebear com>
Date: January 10, 2006 3:52:31 PM EST
To: David Farber <dave () farber net>
Subject: Re: [IP] response from Google to yet another twist
Reply-To: Karl Auerbach <karl () cavebear com>


On Tue, 10 Jan 2006, David Farber wrote:

> From: David Presotto via RT <support () planet-lab org>

> The idea is to use some number of reference points (planet lab  
> nodes, google datacenters, etc) and measure latencies from google  
> customers to them.  We then use those latencies to try to place the  
> nodes in the 6D space.

> What do you think?   Are we doing something bad?

Well, apart from the notion of doing experiments on unknowning  
subjects...

Latency is only one of several factors that one wants to know when  
determining "proximity" on the net when selecting a peer and path to  
that peer.

For example, if one is proposing to do a large video transfer then  
latency is not really important.  More important is the bandwidth of  
the path and its ability to handle that bandwidth without packet loss  
during a TCP flow.  So for big video you want a content source that  
you can reach with a fat clean pipe even if it has somewhat longer  
latency than a skinny or noisy pipe.

If one is proposing to do a VOIP call, then the desired path not only  
has latency must also have low variation in that latency (i.e. low  
jitter.) Thus for voip a low latency+jitter path that is skinny is  
preferred over a fatter path that has worse latency+jitter.

A while back I created a draft of a protocol to find the numbers that  
are needed - and yes, there are still gaps in the protocol.  But it  
would, I believe, blow the socks off path and peer selelection using  
simple latency.

See my blog entry "What Is The Internet Distance From Hither To Yon?"  
at http://www.cavebear.com/cbblog-archives/000151.html

At the end of that blog entry there's a pointer to the year 2000 note  
that describes what I called the Fast Path Characterization protocol.  
(FPCP).
(Shortcut - http://www.cavebear.com/fpcp/fpcp-sept-19-2000.html)

                --karl--







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