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AEQ Audio Over IP
Routing System
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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.
1.4.5. 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 '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 Clock Word.
A Dante device set to "Slave to External Clock Word" 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.
Clocking and Synchronization in Redundant Networks.
In a redundant network, the clock synchronization protocol operates over both primary and
secondary networks. Each network will have a designated PTP master clock; usually this will be
the same device on both networks. If this is not the case (e.g. if a non-redundant device is
designated Preferred Master) then one device will bridge the clock synchronization information
from the primary to the secondary network, ensuring that all devices derive their clock from the
same source. Redundant PTP Slave clocks will synchronize their local clocks based on
information from one of the networks they are connected to. In event of a failure on one
network, a redundant device will continue to receive clock synchronization information over the
other network.