Ravenna AES67 Practical Manual page 7

Table of Contents

network, a device can be safely preconfigured offline. A spreadsheet or a device database is

essential to manage the network configuration.

2.1.3

Multicast

In order to avoid multicast packet flooding, your switches need to be configured for proper multicast

traffic registration and forwarding by activating IGMP. Three versions of the IGMP protocol exist

AES67 requires IGMPv2 to be supported by the network. You can also configure your switches to

support IGMPv3; they will, by definition, automatically revert to version 2 once any device is issuing

IGMPv2 messages.

Next, the IGMP snooping function

traffic needs to be disabled.

In order for IGMP snooping to work properly, an IGMP querier needs to be present on the network.

This function can usually be invoked on any managed switch. Although a network can accommodate

multiple IGMP queriers (and will automatically select one), it is safer to have only one IGMP querier

enabled, preferably on a switch sitting close to the root of your network topology.

On larger networks or when employing enterprise-class switches, further multicast traffic

management configuration may be required: some switches can be configured to forward any

incoming multicast to a so-called multicast router port; this may or may not be desirable, depending

on your network situation

2.1.4

QoS

Since clock and audio traffic require high forwarding priorities, AES67 end nodes support DiffServ

QoS and assign certain DSCP tags to those IP packets. The switches need to be configured to support

DiffServ QoS and prioritized forwarding. Most switches have layer 2 CoS QoS

this needs to be changed to layer 3 DiffServ QoS. Once enabled, check the priority assignments – a

managed switch usually has at least 4 priority queues per egress port and AES67 operating with the

recommended / default parameters requires this configuration:

•

DSCP EF (46) (clock traffic) à highest priority queue (4)

•

DSCP AF41 (34) (audio packets) à second-highest priority queue (3)

•

All other DSCP values (remaining traffic) à lowest priority queue (0)

Note: On some networks running other important / prioritized traffic other priority configuration may

be required; however, it is advised, that PTP traffic always receives highest priority treatment.

RAVENNA and Dante use other DSCP defaults (CS6 (48) for PTP, EF (46) for audio), but unlike Dante,

most RAVENNA implementations allow DSCP reconfiguration at the end nodes to match the AES67

defaults (or any other desired configuration). For guidelines on how to interoperate AES67 with

Dante devices in AES67 mode, refer to the respective chapter later in this guide.

https://en.wikipedia.org/wiki/Internet_Group_Management_Protocol

https://en.wikipedia.org/wiki/IGMP_snooping