bandwidht restricted.

[debian]

I�m ask my self if there is an utility to resctrict the bandwidht consumed 
by services. The problem is that when someone use ftp service or smtp 
service with a important size of byte, others can�t use services on our 
little network. 

Is There any utility which allows me restrict the use of bandwidht? It�s 
possible restrict by service and or by IP, users etc... 

Could anyone help me to solve this problem? 

Thanks you in advance.