Learning about the internet

William Herrin bill at herrin.us
Mon Nov 3 22:14:45 UTC 2014


On Mon, Nov 3, 2014 at 4:15 PM, Paige Thompson <paigeadele at gmail.com> wrote:
> I
> would be able to find an answer as to why the latency between here in
> greece and Los Angeles is roughly ~250ms.

> 10.|-- be2171.mpd22.dca01.atlas.cogentco.com  0.0%    10   62.6  62.7
>  62.4  63.3   0.0
> 11.|-- be2112.ccr41.iad02.atlas.cogentco.com  0.0%    10  155.5 155.8
> 155.5 156.1   0.0

^^ There's the largest part part of your answer. IAD and DCA are both
Northern VA airports; there should be perhaps 4ms of latency between these
locations.

A more smug answer is, "Cogent." Google "cogent congestion," "Cogent
peering," and similar search terms.


Other parts of the answer include:

1. The routers are mostly doing store and forward which means each must
receive your entire packet before it can forward it onward to the next
router. This will take more or less time depending on the link speed.

2. There are layer 2 devices doing the same thing in between some of the
routers. Layer 2 is invisible to the layer 3 traceroute. There may also be
MPLS systems in there with the same impact.

3. Greece and LA are more than 11,000 km apart as the crow flies. This
means round-trip packets travel something like 25,000 km. There is some
signal propagation delay involved. U.S. East Coast to Hawaii (about 80% of
that distance) is typically 120 ms.

Regards,
Bill Herrin


--
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
May I solve your unusual networking challenges?


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