One way for a vendor to rack up a good score in quality-of-service tests is to "nail up" a fixed amount of bandwidth for the exclusive use of high-priority traffic. This is similar to the TDM method used in older data networks, where bandwidth is reserved and thus never available - even when there's no high-priority traffic present.As a check against this, we ran the test a second time while offering only medium- and low-priority traffic. Vendors weren't allowed to change configurations between the first and second tests. In this second test, the medium-priority traffic should have consumed any bandwidth previously used by the high-priority class.That's generally what happened (see 2-Class QoS chart below), Even though no switch delivered exactly the rates we desired for both traffic classes, all made use of bandwidth previously allocated to high-priority traffic. Better still, the switches generally did better with both classes this time than in the previous test with link aggregation. Back to main review: "Testing 10 Gig Ethernet switches"