1.3 Overview

This document specifies the Quality Windows Audio/Video Experience (qWave): Layer 3 Probing Protocol, which operates over the TCP/IP and UDP/IP protocols. qWave enables applications to evaluate the link bandwidth and quality by analyzing timestamps of probe packets transmitted between two devices.

In qWave, a device can take on the role of the initiator or the sink.<1> An application that is interested in enlisting the services of the qWave Protocol invokes the role of the initiator. The initiator needs to know the target device (the sink) that it wishes to probe against. The actual process of analyzing and interpreting the timestamp data obtained via probing is beyond the scope of the protocol and is left up to the application.

qWave supports three types of network probing experiments:

  • Packet pair

  • Probegap

  • Route check

Packet pair is a probing experiment that involves sending two or more consecutive probe packets of highly entropic data from the initiator to the sink. The probe packets are sent over UDP/IP but the sink will respond with the probe timestamp results via TCP/IP. This technique is used to estimate bottleneck bandwidth of the network path between the initiator and sink devices. For an example of how packet pair can be used by an application, see [PacketPair].

Probegap is a probing experiment that involves sending one or more probe packets from the initiator to the sink and then back to the initiator. The intention is to gather a series of one-way delay (OWD)  samples. The probe packets are sent over UDP/IP. This technique is used to estimate available bandwidth of the network path between the initiator and sink devices. Probegap is synergistic to packet pair in the sense that the available bandwidth calculation is computed relative to the bottleneck bandwidth; the former cannot be done without knowing the latter. For an example of how probegap can be used by an application, see [ProbeGap].

Route check is a probing experiment that involves sending a series of probe packets of varying sizes from the initiator to the sink. The probe packets are sent over UDP/IP. This technique is used to detect the presence of IEEE 802.1p prioritization support on the path between the initiator and sink devices. For more information about this technique, see [USPATENT7397801].

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