Ravenna AES67 Practical Manual page 13

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Check if (PTP) multicast traffic is forwarded to all nodes (nodes need to receive the
ANNOUNCE messages from all other devices for proper BMCA execution). Although the PTP
multicast address (224.0.1.129) is a well-known multicast address which should be
forwarded by a switch by default, an IGMP request may need to be issued to activate
forwarding in certain switches.
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Check priority 1 values of devices which assume a GM role unexpectedly and compare with
the settings of the designated GM. You may have to lower the priority (increase the priority 1
value) of that particular device or assign "slave-only" operation. Alternatively, increase the
priority (lower the priority 1 value) of the designated GM.
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It may also help (even just for analysis) to select a different device to become GM by adjusting
the priority 1 fields accordingly, or by temporarily removing suspected devices from the
network.
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If you have PTP-aware switches in the network, it may help to switch PTP support off to
diagnose the situation. If the situation corrects after switching off PTP support, you need to
carefully check all PTP-related settings in the PTP-aware switches.
2.3.2 PTP accuracy
Check PTP accuracy on all nodes – slave devices generally inform about proper sync status. They
either have a sync indicator (traffic light or any other graphical means) or they indicate the current
offset from master numerically; in most cases single-digit microseconds are usually sufficient, sub-
microseconds are perfect.
If you don't have proper sync on all end nodes, you have to resolve this situation before proceeding
any further (i.e. configuring streams). You may want to check on these potential issues:
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SYNC message rate too low: some devices require a certain sync message rate in order to
reach a stable locking situation. Try to decrease the SYNC message interval at the chosen
Grandmaster (i.e. try a SYNC message interval of 2^-2 or 2^-3).
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QoS not properly configured: PTP traffic needs to receive the highest forwarding
prioritization. Check if PTP packets are marked with a proper DSCP value
participating switches in the network are configured to store packets with this DSCP value in
their highest priority queue.
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Removing traffic load: If you are unsure about properly configured QoS you can also try to
remove any foreign traffic on the network to reduce the bandwidth utilization (i.e. remove
potential network overload). The simplest approach would be to unlink devices or network
segments which are not relevant to AES67. You could also start building your network from
scratch by plugging in devices incrementally and checking each time for proper
synchronization.
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Mixed switch configuration (FE / GbE)
network link speeds may cause synchronization issues. In most cases, this will result only in a
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Some end devices offer individual configuration for DSCP markings; otherwise you may have to use tools
like Wireshark (https://www.wireshark.org/) to examine packets on the network.
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FE – Fast Ethernet (100 Mbit/s), GbE – Gigabit Ethernet (1000 Mbit/s)
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: In some cases the use of switches with different
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AES67 Practical Guide
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and if all