WAN Connections vs Window Size etc

[peterlyttle]

Hello,

I was wondering if someone can help shed some light on the following query.

I have the following test setup

ServerA -> RouterA -> NTE -> NTE -> RouterB -> ServerB

ServerA/B -> RouterA/B set to Auto/Auto, detecting at 1000 Full
RouterA/B -> NTE set to Auto/Auto, detecting at 100 Full (the WAN link is 100mbit)

NTE Auto/Auto is an ISP requirement

Latency between the NTE and NTE is approx 30ms.

This means that with the default window size (64KB)

64KB = 65536 Bytes (65536 * 8 = 524288 bits)
524288 bits / 0.030 seconds = 17476266 bits per second throughput = 17.4 Mbps maximum possible throughput.

Extract taken from -

http://bradhedlund.com/2008/12/19/how-to-calculate-tcp-throughput-for-long-distance-links/

Can someone please explain to me why when you have a 10mbit Internet connection do you manage to get your full link throughput even though there is latency involved which seems to contradict the above article?

Also if I am to try and increase throughput should I increase the window size at ServerA/B and RouterA/B to 256KB (2097152bit) max 61.44mbit throughput (I guess any higher and I will risk fragmentation?)

WAN optimizers are outside the scope of my testing.

Any help much appreciated!
Cheers,
Pete