Internet Bandwidth problem

Question

I m using a Redhat linux AS 4 proxy
server in my office,in which I configure squid 2.5 for sharing the
internet(BSNL dataone leased line).the band width provided by the ISP
is 2 Mbps,but when I check the bandwidth in http://dataone.in from the
proxy server it shows around 400 kbps.

http://dataone.in is the official bandwidth testing web site of BSNL dataone (ISP)

Then I connect a dual
boot client pc ( windows XP sp2/fedora 6) to the same port I use for
the proxy server in NORTEL 8300 switch.Now I got the increased
bandwidth (around 1.77 mbps) in XP but again low bandwidh with fedora. plz tell me why linux operating system show me the low bandwidth ?