How to monitor internet bandwidth consumption

HI. I've this issue. From some weeks I've noted a general slowdown on my ADSL Internet Connection. In my network there are 6 servers and e few number of clients. The six server are: a VoIP server, a DC, a FreeNAS server, etc... The question is: may I use WireShark to monitor and identify how much ADLS bandwidth each server is consuming in real time? In other words: may I know (and monitor) during the day (and night) which type of upload and download connection every server is performing so may I isolate the source of the issue (general internet slowdown)? Thanks in advance.