Historically when Audinate implemented an optional AES67 compliant mode to some of their products they decided to set the DSCP QoS values for AES67 PTP and Audio to match the DSCP QoS values that they had already used for their proprietary transport, and not the values provided by the AES67 standard.

Meaning if you mixed Dante and AES67 packets on the same switch - the Dante audio packets would have the same QOS que priority as the AES67 PTPv2 packets. This would cause PTP errors on your AES67 network.

There are two possible solutions:

1. Separate Dante traffic from other AES67 traffic with PTPv2 using physical separation like separate switches (recommended) or at least separate trunk lines (challenging with STP).

   Separating affected traffic into VLANs does not help since the DSCP markings are evaluated independent of the VLAN belonging - in the end the switch has only 8 hardware cues per switchport.

    

2. Configure the switch connected to the Dante equipment to re-stamp the Dante packets to have different DSCP values

Solution 2: Implementing this workaround with a Cisco SG350

A Cisco SG350 allows one to change values according to rules and to maintain best practice, we should change the RTP packets to have DSCP 34 & PTP to have 46 - this matches the AES67 standard.

There are a lot of steps…. And they must be done in order (enforced by the switch). There are actually several ways of arriving at the same place and other methods are detailed in this Cisco guide.

If no other device has packets with DSCP 56 (desirably), one can override (globally) this value on the switch to cover the PTP problem…

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Set QoS Advanced settings as above and open the DSCP Override table:

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Map 56 to 46. Now your Dante & AES67 PTPv2 packets have the same DSCP value. If 56 is required for something else, this method cannot be used so just create another ACL (see below) for PTP.

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Create an ACE for the ACL

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Above is an example RTP ACE (truncated screenshot). There is a source IP of "Any". The destination has wildcards in the 3rd and 4th byte so that any multicast beginning with 239.69 & DSCP 46 will be caught by the rule (Dante must use a fixed 2nd byte so make sure this matches your setup - 69 is default). The protocol is set to "Any" since RTP is not specifically available and we know that any address in the defined range will be RTP anyway.

Now add a class map (very simple - just map the ACL to a class map):

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Now add the class map to a policy:

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In the class map table, set the new DSCP value for the relevant packets:

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Now bind the policy to any port on the switch with a Dante device - set default action to Permit Any:

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