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PTP Operational Overview
Compensating for Causes of Asymmetric Delay
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PRISM MPI2-10-MPX2-10 User Manual
Setting the Diff Serve QoS on the switch and configuring the PTP messages with an
appropriate DSCP can also mitigate the effects of traffic delay.
Message Type Mismatch
Another cause of delay asymmetry is message type mismatch. For example, if the sync
message is Multicast and the delay request is Unicast, then some switches may process
the messages differently and cause a differential delay. Since the SMPTE profile allows a
mixed mode operation, switches should be evaluated to ensure they do not have this
effect. If transparent mode switches are used, then this effect should be corrected by
the slave.
Cable Delay Variation
The actual propagation delay through Cat 5 cable can be significantly different in one
direction versus the other direction. This can be due to the twist rate on the pairs,
routing inside the sheath, material differences, etc. The PTP system is incapable of
removing this effect, so the best way to prevent this is to use high-quality cable with a
minimum variation in the physical propagation delay.