How the Azure VM bandwidth be calculated?

this topic listed the each size of VM's network bandwidth:

http://social.msdn.microsoft.com/Forums/windowsazure/en-US/775a7d55-4ad5-438c-be2b-1f10e2eaa0d6/network-capacity-within-cluster-datacenter-and-across-datacenter

For example, a Small Size VM have 100Mbps bendwidth, but I try to use series benchmark test softwares and try to download/upload files to different host, the bendwidth is far less than 100Mbps, just about 10~20Mbps. I'm use a Small VM Size by my MSDN Subscription, and OS is Win2008R2, Region is East Asia.

who can tell me that the how the Azure VM bandwidth be calculated, what way, what environment and the config profile.

Thanks a lot.

Zhongyan