[Mep-dev] TCP Performance Issues

[Phil Karn]

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On Mon, Nov 24, 2008 at 10:07 AM, Dave hartzell <hartzell@gmail.com> wrote:

>
> Actually, modern TCP implementations (BIC, CUBIC, FAST) can go several
> Gbps over international links....granted that is only sometimes half
> the GEO RTT, but it is possible...


This isn't necessarily true. Terrestrial fiber links are now so fast
compared to satellite links that the bandwidth*delay product of the fiber
route can exceed that of the satellite link. Many terrestrial backbone links
are now 10 Gb/s.

Round trip over the Internet from San Diego to the east coast usually runs
around 90 ms. Round trip through geostationary satellite (both ways) is
about 500 ms. So if the fiber link is only 5.5 times the speed of the
satellite link, they have equal bandwidth*delay products.

(SD and NYC are about 3900 km apart, so the direct speed of light delay
would be only 13 ms, or 26 ms round trip. However, fiber has a velocity
factor of about 0.66, the route isn't great circle, and there are multiple
multiplexing, buffering and store-and-forward delays in the path.)

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<br><br><div class="gmail_quote">On Mon, Nov 24, 2008 at 10:07 AM, Dave hartzell <span dir="ltr">&lt;<a href="mailto:hartzell@gmail.com">hartzell@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d"><br>
</div>Actually, modern TCP implementations (BIC, CUBIC, FAST) can go several<br>
Gbps over international links....granted that is only sometimes half<br>
the GEO RTT, but it is possible...</blockquote><div><br>This isn&#39;t necessarily true. Terrestrial fiber links are now so fast compared to satellite links that the bandwidth*delay product of the fiber route can exceed that of the satellite link. Many terrestrial backbone links are now 10 Gb/s.<br>
<br>Round trip over the Internet from San Diego to the east coast usually runs around 90 ms. Round trip through geostationary satellite (both ways) is about 500 ms. So if the fiber link is only 5.5 times the speed of the satellite link, they have equal bandwidth*delay products.<br>
</div><br>(SD and NYC are about 3900 km apart, so the direct speed of light delay would be only 13 ms, or 26 ms round trip. However, fiber has a velocity factor of about 0.66, the route isn&#39;t great circle, and there are multiple multiplexing, buffering and store-and-forward delays in the path.)<br>
<br><br></div><br>

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