This is a gigabit LAN with a few dozen workstations and an SBS 2011 sever.
File transfers between any workstation and the server can be very fast or extremely slow, or fluctuate fast/slow during the same transfer.
The same happens with remote connections from outside the LAN, or with regular internet access from inside the LAN.
1. Workstations' connection to the internet goes directly to the router, does not depend on the server.
2. Workstations' connection to the server does not depend on the internet connection speed.
3. So the issue is not related to the server, nor to the internet connection speed.
How can one detect the source of such network congestion that comes and goes?
Are there any tools that can help?