Download speed and TCPIP window sizing

[Pang]

Hello,
  Recently, I have leased a rack in Asianetcom and some bandwidth. 
However, the speed for my curcuit is substantially slower than my 
provider's company site. The provider said my circuit and their one are 
treated exactly the same way.
  Below is the URL for the download:
My circuit*: http://203.192.137.194/test.rar
ANC curcuit: 
http://www.asianetcom.com/pub/communications/AsiaNetcomNews_2006Q2.pdf
*This server is using FreeBSD 6.2 patch 4 with Apache in the port tree. 
The kernel is custom built but I haven't made any modification in sysctl

  I have asked many techs in Asianetcom and they blamed on TCPIP window 
sizing. I am not sure what it is, so I do a search in Google and find 
the following:
http://www.vad1.com/tcp-throughput-limit.html

  After reading the article above, I feel the situation is very similar. 
But, from my understanding, the download speed should be proportional to 
the ping speed. However, test done on Canada is much higher (about 3 
times higher) than in US while the ping is very similar.

  Could anyone tell me whether my understanding on Window sizing 
correct? Also, is there any way to alter the window sizing in freebsd or 
apache?

Thanks
Pang