1.3.4 QoS Diagnostics: Cross-Traffic Analysis
QoS diagnostics for cross-traffic analysis facilitates the detection of network traffic congestion by means of analyzing network packet counters. An application can analyze these packet counters by invoking the role of the cross-traffic analysis initiator. The application explicitly identifies each responder from which it wants to obtain the counters. (The application might have previously learned the responders via quick discovery, or any other method. Hence, this service does not necessarily require that quick discovery be performed first.) The initiator's role is simply to make these counters available to the application, where possible.
Responders that support this feature maintain a history of the following counters:
Number of bytes received.
Number of bytes sent.
Number of frames received.
Number of frames sent.
Intermediate devices, such as access points (APs) and bridges, can make per-network interface counters and aggregate link counters available through this protocol. These counters allow cross-traffic detection even in the absence of responders on the segment. Examples of available network interfaces on a typical AP device are:
Basic service set identifier (BSSID) of a wireless band. Note that multiband APs use separate BSSIDs for each band that they support.
Wired Ethernet network interface that is usually connected to a built-in switch.
The aggregate (across all network interfaces on the same link) counters indicate the amount of traffic that is entering and leaving the link, which enables consideration of the capacity of the uplink in QoS wireless area network (WAN) admission decisions.
It is assumed that the bottleneck point for an AP is always the wireless link. As such, APs are not required to provide the wired local area network (LAN) counters.