On Friday, March 7, 2003, at 04:37 PM, David G. Andersen wrote:
On Fri, Mar 07, 2003 at 10:09:51PM +0100, Mikael Abrahamsson quacked:
On Fri, 7 Mar 2003, Richard A Steenbergen wrote:
Production commercial networks need not apply, 'lest someone realize that
they blow away these speed records on a regular basis.
What kind of production environment needs a single TCP stream of data at 1 gigabit/s over a 150ms latency link?
Just the fact that you need a ~20 megabyte TCP window size to achieve this
(feel free to correct me if I'm wrong here) seems kind of unusal to me.
It's unusual, but it's not completely unheard of. One of the biggest sources of such data is VLBI (interferometry to measure the movement of the earth's crust), in which signals from geographically distributed measurement sites have to be recorded and correlated at a central site:
http://web.haystack.edu/vlbi/vlbisystems.html
The signals are massive. Right now they use specially made tape drives that can record 1Gb/s:
ftp://web.haystack.edu/pub/mark4/memos/230.2.pdf
ftp://web.haystack.edu/pub/mark4/memos/HDR_concept.PDF
and they send the data around via airplanes. They'd love to be able to do real-time correlation of the data, but that involves collecting 6 of these feeds at a central site (more coming). The feeds must be capable of running unattended for up to 24 hours (86 terabytes each, or an aggregate of half a petabyte per day).
VLBI is moving to hard drive replacements for the expensive 1 inch tapes currently
used (known as Mark V). There are active projects for "e-VLBI" - at CRL in Japan
http://www.ntt.co.jp/news/news01e/0107/010706.html
and at Haystack Observatory in Massachusetts
http://web.haystack.edu/e-vlbi/meeting.html
In e-VLBI there is no need for reliable transmission and UDP is the way to go.
I am still involved with this peripherally, especially with the idea that the traffic be sent
"worse than best effort", so as not to collide with regular traffic.
BTW, when I did VLBI for the Navy, we used to move literally tons of tapes around the world
per month and achieved sustained bandwidths > 1 Gbps, albeit with FED-EX, not routers.
Yes, backbones push more than a gigabit across links, but not as for a single flow of data.
-Dave
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