Global Lambda Integrated Facility
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Subject Re: [GLIF tec] Buffering discussion
From Victor Reijs <victor.reijs@xxxxxxxxx>
Date Mon, 21 Feb 2005 10:57:31 +0000

Hello Steve,

Sorry I was not at the GLIF meeting (personal issues), but I am
wondering what the outcome or progress of this buffering discussion was.

In some way I don't like to use bufferring, makes me remind me of the
ATm times;-). By the way the buffering needed is quiet small or not,
only some 10 MByte for a long 10 GE link, so in some way it is doable, I
assume this 10 MByte is independant of the number of active tcp flows
(or is it per ftp flow?).
{Sorry, perphas this all has been discussed at the meeting....)

Here at HEAnet we had some brainstorm stimulated by this buffering
e-mail, and we came up with a wild idea;-).
I will send this wild idea soon to this list (I already send it to
another list and some feedback has been goitten, so I will adjust the
text somewhat [wild ideas always need the corret wording;-)]).

Thanks for your summary.

All the best,


Erik-Jan Bos wrote:

Tech Members,

Upon request of Steve I hereby forward his message on the buffering discussion.



From: Steven Wallace <ssw@xxxxxxxxxxx>
Date: February 13, 2005 4:23:18 PM EST
To: tec@xxxxxxx
Subject: Fwd: Buffering discussion?

Here's the gist:

Thanks to Guy Almes for finding a small issue related to the correct
value of C for fiber and a big issue where I was converting to bytes

What this graph is supposed to show is the buffering requirements of
9,953,280,000 b/sec flow going over a mix of WAN-PHY and LAN-PHY
connectivity.  The speed difference between these two circuit types
over 300Mb/s, so buffering the difference in speed for the duration
a windows worth of data can be substantial.

An Example:

[Host A]----10GE LAN-PHY-------[15454]-----10GE WAN-PHY------[Host B]

So the fastest TCP can operate is limited to the slowest part of the
path: the 10GE WAN-PHY section (i.e. 9,953,280,000 b/sec).  The
size to support a WAN-PHY speed TCP transfer at 1000 miles is
10,472,727 bytes.  Assuming the data is moving from host A to B, then
host A will be sending 10,472,727 bytes  (a window's worth of data)
line-rate toward host B.  The speed discontinuity between the LAN-PHY
and WAN-PHY sections of the circuit is 359,220,000 b/s, so for the
duration of the window transfer the 15454s must buffer this
in speed.

The following graph shows the buffering requirements for various
circuit distances and rate changes: