Slow internet on t1

I would call out a specalist but don't take your ISP's word on 'all good at our end'. Get somebody to come out - demand it!

While you wait. Turn off all PC /MAC - Turn on one at a time to see where the slowdown starts - reinstall the PC. Sounds like a virus / malware...

It wouldn't hurt to run a Speed Test for the T1 line off the primary computer that it's connected to as well.

While the ISP may be perfectly correct in saying what they are there can be physical problems with the line as well a technical ones and the line could need maintenance. I would first try with just the primary computer connected with either all the rest shut down or disconnected from the T1 line as see what happens.

If that's fast you can look at your end for something hogging Bandwidth but if it's slow I would be jumping on the provider for a solution. A Bandwidth Sniffer would also not go astray at all as you need to know just what is happening on the line. If you are broadcasting a lot of data you could have an infection that needs addressing or Worst Case Scenario you could be hosting a Bot that has taken over your system and is doing illegal work for some other person. So you do need to know just how much upload/download is going on at any time.

Col

use a packet sniffer like Ethereal (free at ethereal.com) and find out what traffic is going across your network. It may not be a connection problem, but a traffic problem as your bandwidth could possibly have maxed out. Also check your port settings and switch/router/modem settings.