In Windows Azure each VM size has its own Network IO capability defined as below:

Source:

http://player.microsoftpdc.com/Session/d77df625-90b5-4d6c-ad64-7f608f8900b9


VM Type

CPU

Memory

Peak Mbps

Extra Small

1

768MB

5

Small

1

1.75GB

100

Medium

2

3.50GB

200

Large

4

7.00GB

400

Extra Large

8

14.0GB

800