Users Guide

Audio Video Bridging 1685
IEEE 802.1AS
IEEE 802.1AS is a protocol designed to synchronize clocks in the nodes of a
distributed system that communicate in a bridged network. 802.1AS also
provides a mechanism to measure link delays, which may be used to calculate
end-to-end propagation delay.
The IEEE 802.1AS standard specifies the protocol and procedures for
ensuring that QoS requirements are met for time-sensitive applications such
as audio and video. The IEEE 1588 Precision Time Protocol (PTP) forms the
basis of the IEEE 802.1AS standard. PTP specifies a precise clock
synchronization protocol that relies on timestamped packets. The PTP
protocol is applicable to distributed systems that consist of one or more nodes
communicating over some set of communication media. The distribution of
synchronous time information is performed in hierarchical manner with a
grandmaster clock at the root of the hierarchy. The grandmaster provides a
common and precise time reference for one or more directly-attached slave
devices by periodically exchanging timing information. In other words, all
slave devices synchronize their clocks with grandmaster clock. The slave
devices can, in-turn, act as master devices for further hierarchical layers of
slave devices. These relationships are shown in Figure 47-1.