User guide

N:M Hub Modem Redundancy
C-14 VMS User Guide
Figure C-8 N:M redundancy logic diagram
The switching control mechanism is completely monitored and controlled by
the host master processing VMS as shown in the logic diagram in figure C-8.
The VMS parameter backup and restore function is used to copy each primary
units configuration database information which are then stored in a lookup list.
The stored primary unit’s parameter files are used to put the image of a failed
primary unit’s parameters into a standby spare unit. The spare units should
always be in the parked configuration described in the section “Setting Unit to
Parked Configuration Mode” on page C-34, powered on, and listening and
responding to the local LAN network.
After the N:M redundancy has been installed, as described in the section
“Installing N:M Redundancy” on page C-15, the VMS starts listening for heart-
beat messages from each of the primary and backup spare units for health and
fault code response as shown in the logic diagram in figure C-8. If any primary
unit fails (has an alarm set or misses three consecutive heartbeats) the VMS will
invoke the backup procedure by sending a copy of the failed unit’s database to
the next available standby spare.
ETHERNET
Spares Backup
N Spares
Primary Units
SNMP IP
Network Controlled
AC Power Bus
RF Combiner/Splitter
Primary
Parameter
List
StatusWatchdog
Parameter
Copy
AC Power
Control
Poller
N to N Redundancy Process
OK
OK
Fault
V
M
S