CentreCOM 3600 Series Hub/Repeaters
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When a Backup takes over on behalf of a failed or removed Master, it already
has a current copy of all necessary configuration data. When you swap out the
failed Master and install a new module, the new Master will receive correct
and current configuration data from the Backup (previous Master). This
avoids the need to respecify all of the configuration preferences. The process
all happens transparently within seconds of the swapout.
Precedence
If you install a module from another network as the new Master in a
concentrator, it may (and probably will) contain some old configuration data
from its previous existence (it may have been installed in a different
department concentrator chassis at one time). When it begins operating, it
doesn’t know if its own configuration data is correct or not. The Backup has
some data, but its data may or may not be the correct data for this particular
chassis.
This issue between the two modules is resolved by an examination of their
respective elapsed time counters (each maintains a time-since-last-reboot). If
the Backup has been up and running longer than the Master, the conclusion is
that the Master must have just been inserted and contains “old” data. The
data from the Backup is more current and is therefore copied into the new
Master. But if both modules have just booted (presumably because you just
reset the entire department concentrator) then the clock alone cannot
determine whose data is correct (both clocks would read the same).
Voting
The Master attempts to resolve this through a process called “
voting
.” It polls
each installed module and examines the stored configuration data.
The configuration data that is stored on the greatest number of modules is
declared to be the correct data, i.e., the majority rules. For example, if a data
set we’ll call ‘A’ exists on modules 1, 3 and 4, and data set ‘B’ exists on module
5, it is concluded that data set A is probably correct. The management agent
adopts this set of configuration data for subsequent use.
However, a dilemma occurs when there are only two modules installed in the
chassis. In this case, there is no way to determine which data set is correct.
The system defaults to the Master data set, which might not be correct—you
may need to reconfigure when swapping a spare into the Master position of a
two-module department concentrator. Reconfiguration will not be necessary
if the recommended swapping procedure is followed.
Swapping Modules
Configuration data will always be retained if module swapping occurs with
power applied, i.e., as long as one module remains powered up throughout the
swapping procedure. This will cause the use of the proper data set based upon
clock comparison as described above.
If you must remove power for any reason, you should perform the swap by
either of the following methods (these steps are only necessary in a two-
module department concentrator):
❑
Pull out the old Master, then place the old Backup into the Master slot
position and install the spare module in the Backup position. The data
set of the old Backup will be used.
❑
Pull out the old Master, then place the spare module below the old
Backup, making the old Backup the new Master, and the spare module
becomes new Backup.
