By default windows will reserve you bandwidth up to some extent
to disable that follow these instructions
Note : only for windows

1) Click Start
2) Select Run
3) enter gpedit.msc
4) Click enter
5) Compuer configuration termplates
6) Network
7) QoS Packet Sheduler
8 ) Choose Limit reservable bandwidth properties
9) Choose enabled and enter 0%

Done

Enjoy!!