How do you know you are connected at 1GB on Actiontec Rev I router

Have Actiontec Rev I router and some PCs with 1000MBPS En adapters. How do I know that they are connected at 1GB and not a slower speed? Have seen posts on other forms where 1GB LAN adapters have connected at 10 or 100 Mb not 1000 Mb. How do you determine connection speed?