Quote:
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Originally Posted by mr-b
Ping statistics for 216.168.3.20:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 175ms, Maximum = 269ms, Average = 203ms
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I don't think I've ever seen such a detailed, or useful fault report.
200ms RTT is far too high to get 3Mbit/s with the tcp window the netcaches are advertising.
Tracing a single download ( at the origin server )...
Inktomi
max win adv: 63712 bytes
min win adv: 1448 bytes
avg win adv: 25236 bytes
NetCache
max win adv: 17520 bytes
min win adv: 144 bytes
avg win adv: 9810 bytes
BDP for Dummies:
http://www.speedguide.net/bdp.php
And if you really need to get to sleep...
http://www.tcpipguide.com/free/index.htm
The Inktomi caches probably just use the ( possibly tweaked ) underlying OS TCP behaviour, and happily ramp up from a small initial window to ~64K, which is good for 375Kbyte/s upto 175ms (didn't advertise window scaling).
The NetCaches are a bit different and with the window advertised above, they'll only be good for 375Kbyte/s if the orgin servers are under ~40-50 ms (rtt) from the cache. It's tweakable, I guess that's what the techs are looking at (either that or they are going to move the entire internet within 50ms!), but larger windows = fewer connections.
On a cache hit none of this matters.