1.3.3 QoS Diagnostics: Network Test

QoS diagnostics for network tests facilitates the determination of a network path's bottleneck bandwidth (or "capacity"), its available bandwidth, and the existence of a prioritization mechanism in a network equipment over a network path. Each of these is a form of network test operation that can be achieved by the use of two roles: a controller and a sink. The controller role is initiated by a local application. The sink role is implemented in a responder.

The controller's job is to manage a network test session by initializing and resetting the sink, sending test frames to the sink, and accepting test frames that the sink sends back.

For each network path (defined as the network link between a controller and a sink), a higher-layer application can use the time stamp and success code that is returned via the controller to compute the bandwidth. Applications can also learn about the existence of a prioritization mechanism by instructing controllers to have sinks manipulate the 802.1q tag header for returning test frames (see the T-bit and 802.1p value in the QosProbe frame defined in section 2.2.5.4). For more information on how the tag header influences Ethernet frame routing, see [IEEE802.1Q].