TCP Port Usage Monitoring

I would like a way to capture the number of bytes or number of packets that are transmitted across a certain TCP port (ex. Capturing amount of traffic across port 22 --ssh--). I'm just
looking for a simple utility or method that captures the data to a file or dumps it to the console. I'm looking to use it on a unix or linux system. I plan to write a script that
uses this information to determine the health regarding activity on a port. Example, I might expect there to be at least some traffic on port 4444 at least once an hour, if not, my script
should notify an administrator that something may be wrong. Please let me know of any ideas.

Thanks!