5700MSC-IP
IP Network Grand Master Clock & Video Master Clock System
Revision 0.2 Page - 55
3.6. AUTOMATIC CHANGEOVER OPERATION
For critical infrastructure requirements a 5700ACO automatic changeover unit can be used to connect
two 5700MSC-IP units in a dual redundant configuration. The automatic changeover unit monitors
signal health to decide which of the 5700MSC-IP units will be connected to the downstream outputs.
The automatic changeover unit allows for a dual-redundant installation of two 5700MSC-IP units.
Normally one of the 5700MSC-IP units is designated to the master, and its outputs are connected to
the automatic changeover unit. The second 5700MSC-IP unit is designated as the slave (or backup),
and its outputs are also connected to the automatic changeover unit. The automatic changeover unit
then provides relay-protected outputs to feed downstream equipment. The automatic changeover unit
can be switched manually (locally via front panel or remotely via SNMP), or can be put into automatic
mode where the outputs will be switched to the slave unit if a problem is detected with the master.
In order for a seamless switch to occur, redundant signals from both 5700MSC-IP units must be
running at the same frequency and phase and ideally locking both units to the same reference. It is
possible to lock the slave unit to the master but this reduces the protection offered by the automatic
changeover unit should a problem develop with the master unit. Additionally, it is required that both
5700MSC-IP units are configured identically so that their outputs settings match. For this to occur, an
IP syncro connection needs to be configured between one 5700MSC-IP acting as the IP Syncro
Master, and one or more other 5700MSC-IP units acting as slaves. This is done over the Ethernet
GigE-1 interfaces of all 5700MSC-IP Master Clocks that are intented to share the same settings.
The automatic changeover unit simplifies wiring by providing a single point of entry for an LTC
reference, and GPIs for both 5700MSC-IP units. The LTC input to the automatic changeover unit is
internally split to both Bank A and Bank B 5700MSC-IP units. Similarly, the GPI inputs are split to both
units, allowing any GPI trigger to affect both units simultaneously.
The automatic changeover unit uses latching relays to provide a fail-safe signal path. These relays will
maintain their last state should the automatic changeover unit experience a power supply failure or
main board failure. This ensures glitch-free failure events and glitch-free recovery from failure.
All inputs from both 5700MSC-IP units are passively monitored by the automatic changeover unit.
There are no active components in the signal path. This is accomplished by splitting a small portion of
the incoming signal to the control/monitoring circuitry of the automatic changeover unit.
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