Sierra Video Sequoia Family - Manual (Page 28)

SIERRA VIDEO SYSTEMS
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When it is necessary to remove a processor from the router, the master processor should not be
removed while the synchronization is in process, i.e. while Yellow LEDs are flashing. If it is
removed, the standby processor will take over with possibly out-of-date configuration information.
If the user knows that the two processors actually are in sync, this doesn’t matter and the master
processor can be pulled at any time. It can also be pulled if it doesn’t matter that the configuration
information changes when he does so.
The standby processor can be pulled at any time, even during synchronization, with no negative
impact on operation. When it is reinserted, the synchronization process will be restarted.
When the router is powered on with two processors that were not synced to one another, the
processor with the most recent configuration information should be the one with switch S1-1 on
(making it the Preferred Master). If the processor with the older configuration data were the one
with S1-1 on, it would become master processor and would send its older data to the standby
processor, wiping out its newer data.
For example, suppose the master processor is removed from the router for an extended period of
time. Later, it is reinserted. If it is inserted hot, without powering down the frame, then it will
become the standby processor and the master will synchronize it with the latest data. On the
other hand, if it is inserted with the frame powered down, with the S1-1 on and the processor that
has been running the frame has S1-1 off, then when the frame is powered on the processor that
has not been in the system for a long time becomes the master, and will operate the router with
obsolete configuration data. Furthermore, the other processor’s newer configuration data is wiped
out as it becomes synchronized with the other processor.
CAUTION!
Whenever it is necessary to remove a processor from the router, the master processor should not be removed while
synchronization is in process, i.e. while Yellow LEDs are flashing.
Synchronizing Host and Terminal Protocols
All three external serial ports can run either host or terminal protocol. If both processors are
powered on at the same time, they should both stay in sync with one another, and the ports on
the two processors should be running the same protocols. If the standby processor is inserted
after the master has been running for a while, the synchronization process described above
causes the standby processor to switch to running the same protocol as the master processor.
However, the standby processor may not be in sync with the master processor within that
protocol.
For example, suppose the master processor is running host protocol on the host port, and a
partial command has been sent to the port. Then, the standby processor starts up, and after that,
the rest of the command is sent to the host port.
The standby processor never sees the first part of the command, so it will ignore the whole
command. This situation is unlikely to cause problems, because usually host commands are sent
quickly, and any commands that the slave processor misses will have been sent before the
synchronization process even started. By the time the synchronization process finishes, the two
processors have their data in sync, and both are processing complete host commands.
The same situation could happen when terminal protocol is in effect, but in that case it has more
potential to cause problems. The user often stays in a submenu for a long time, when terminal
protocol is in effect, and the standby processor starts up in the main terminal menu, therefore
rendering it unable to sync itself to a submenu. To try to prevent out-of-sync problems from
occurring, every time the standby processor comes on line, the master processor’s terminal