Re: 923 Mbps across the Ocean ...

[Marshall Eubanks <tme () multicasttech com>]

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
>
> --
> work: dga () lcs mit edu                          me:  dga () pobox com
>       MIT Laboratory for Computer Science           
> http://www.angio.net/
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                                 Regards
                                 Marshall Eubanks

T.M. Eubanks
Multicast Technologies, Inc.
Phone : 703-293-9601       Fax     : 703-293-9609
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