Users Guide

1690 Audio Video Bridging
conveyed using the follow up message. The delay requestor captures RX
timestamp of PDELAY_RESP_FOLLOWUP message (t4). This sequence is
shown in the below diagram:
Figure 47-3. Link Delay Measurement Sequence
After the completion of delay request/response exchange, the delay requestor
has all four time stamps (t1, t2, t3, t4). The link delay is computed using the
following equation:
Tmean_delay = ((t2 - t1) + (t4 - t3))/ 2
The mean time interval between successive PDELAY_REQ messages sent
over a link is defined by the 802.1AS standard. If the link delay between two
time-aware systems is greater than a “reasonable” cable delay (a few
microseconds), then the ports on those links are not enabled for 802.1AS. The
accuracy of this algorithm depends on symmetric link propagation delay
between the peers, meaning that the link delay from requestor to responder is