The network rating has many people mystified. Some say it's based on speed, others say pings. This is what UD has to say in the UD Project FAQ
"The Agent determines what type of connection to the internet that you use and performs a benchmark speed test. This consists of timing the transmission of a fixed amount of data (a 100k file containing data that cannot be compressed) from the UD servers to your system. This time (speed) is then compared to a reference system that UD have calculated (a download speed of 1MB/s) and a rating is given. This benchmark is normally run before sending a completed result to the UD servers however, it may not be run every time a result is sent back."
"The network rating can change based on the quality or throughput of the last connection with UD. Unfortunately, you will be penalized for anything that slows up the process between you and UD. Just because you have a fast connection doesn't mean that the complete path between you and the UD servers will operate at top speed. Cable systems are shared by everyone in a particular area. As more people sign up for cable access to the net your bandwidth will go down during peak periods (7 p.m. to 10 p.m.) This is actually true of any system. As more people sign up with your ISP the bandwidth available to each person becomes less until the ISP adds more capacity. In many areas cable is the only reasonably priced high speed access so you will see more and more signing up and more and more complaints about the bandwidth slowing down."
"Note: A default value of 100 normally indicates the net benchmark could not be run. The net rating is also set to 100 after installation or upgrade and will show the correctly benchmarked value when the first result is returned."
"Note 2: The devices shown when viewing the network rating (below This Device:) is what Windows has told UD exist. UD does not use the first one listed for the network connection but the default that windows is configured with. If you hover your pointer over the devices listed you will see them all."