Extron Electronics Dante Controller - Manual (Page 18)

Dante Controller User Guide
Copyright © 2013 Audinate Pty Ltd. All rights reserved. -18-
flows, multicast flows must be set up on the transmitting Dante device before receivers can subscribe to
these flows.
Advanced Routing: Using Multicast
Dante routing is unicast by default. This means that a separate flow is set up between each transmitter and
receiver. If several receivers are all subscribed to the same channels of a transmitter, it may sometimes be
more efficient to use
multicast.
Multicast sends the same set of channels to multiple receivers. In practice, this usually means that the
audio flow is flooded throughout the network. If many receivers want the same channels, using multicast
can reduce overall network use, especially on the transmitter, because only one copy of each audio
channel needs to be sent, rather than many.
Dante receivers will automatically prefer multicast to unicast if it is available. This means that if a new
multicast flow is created containing the channels that a receiver is currently receiving as unicast, the
receiver will switch over to receiving audio from the multicast flow and the unicast flow will be removed.
Clock Synchronization
All Dante-enabled devices use the IEEE 1588 Precision Time Protocol (PTP) across the network to
synchronize their local clocks to a master clock, providing sample-accurate time alignment throughout the
network.
One Dante device will be elected as the PTP Master Clock for the network; all other Dante devices act as
a PTP Slave Clocks to the elected master clock. Although many Dante devices may be capable of
becoming PTP Master Clock, only one device will win the election. Devices with clock inputs (e.g. word
clock or AES3) will be preferred in the election process. A gigabit connected device is preferred over a
device connected via 100Mbps. A tie-breaker rule of the lowest MAC address is used if several equivalent
candidate master clocks are available. The election process may be overridden by manually setting “PTP
Preferred” master on a device.
Dante Clock Types
Each Dante hardware device can derive its clock from either its high-quality onboard clock circuit, or an
externally connected word clock. In the case of Dante Virtual Soundcard, the computer’s clock will be
used.
Clock Settings
Slave to External Word Clock
A Dante device with "Slave to External Word Clock" set will use the external word clock from its host
equipment to tune its onboard VCXO. A Dante device with this attribute set will become the PTP Master
Clock, unless there is another Dante device present with "Preferred Master" set.
Preferred Master
Sometimes it may be necessary to force a particular device to provide the PTP Master Clock. A Dante
device with "Preferred Master" set will always be chosen as the PTP Master Clock. If more than one
device has "Preferred Master" set, the device with the lowest MAC address will be chosen.