Filtering Voice across the link

Hi

Our Office has a 4MBPS link to the Internet. The users use different chat software’s for their conversation. And now we are facing lot of link fluctuations and through net flow we found out that the problem is because of the voice chat done by the users. We use checkpoint as our firewall. So could any one tell me how we can filter the voice from consuming the bandwidth?

Regards
Benny

After a lot of search i got the solution for this poblem. The voice can be filtered by blocking H.323 and SIP ports.