confusing internet speed!?

[alireza Yousefi]

hi
my internet speed in speedtest.net is around 900kb/s but in internet dl manager it doesnt go more than 120kb/s!im sure that no one steals my internet and im sure that no application uses all of my speed!i called isp but they said that my internet connection is working properly but my guess is that isp is sharing my internet connection!what should i do?is there anyway that i can boost my internet speed?im in iran.....
i sometimes notice that even loading websites is very slow!
and i tried another urls ofcourse but my problem isnt that!
thanks
my internet connection is dsl and im using a dlink wireless adsl router!
and my internet speed must be 1mb/s
thnaks!