bandwidht restricted.

[debian]

Iīm 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 canīt use services on our 
little network. 

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

Could anyone help me to solve this problem? 

Thanks you in advance.