User Manual

SGD-SB2025NT-TUM, Part 2
Jan 12 Page 71 DIAGNOSTICS
8 TM DUPLICATION
8.1 D UPLICATION O VERVIEW
The TM lies at the heart of a Solar network and loss of the TM whether due to a unit fault or
network failure will have a severe impact upon the operational capability of the system. To mitigate
the risk there is a “Facility Key” enabled option to have a second TM acting as a hot standby unit.
This additional or Secondary TM is able to automatically takeover operation of the Solar network
should the first or Primary TM become unavailable. Once the Primary TM becomes available
again, the Secondary TM will stand down and the Solar network will return to normal mode of
operation from the Primary TM.
Apart from a possible network traffic load change in parts of the network, there is no operational or
performance difference in operating the Solar network from a Secondary TM, since it is an identical
unit to the Primary TM. To maintain correct operation, it is very important that the same firmware
release is installed in both TM. Any firmware upgrade must be applied to both units (see Section
11.2.3 – Traffic Manager for more information).
Solar 2 has introduced an extension to the original 1+1 configuration option in that up to five
Primary TM can now be supported by a single Secondary TM. The duplication process involving
more than one Primary TM remains fundamentally the same as for a 1+1 configuration.
Knowledge of the network design is important when considering a duplicated configuration either at
the initial installation or if an existing Solar network is upgraded to duplicated TM operation. The
reasons for this are discussed briefly below.
8.1.1 TM Resilience
To obtain the maximum benefit from employing a duplicated TM configuration, the Primary and
Secondary TM equipment should be placed at different physical locations. This approach provides
better resilience compared to placing both TMs at the same location where single points of failure
can occur. However, diverse locations can produce unwanted effects when the change in traffic
flow through the network is taken into account. These effects are discussed in detail in Section 11
– Troubleshooting & Maintenance and in particular Section 11.1.3 – TM Duplication .
8.1.2 Duplication Operation
The Primary TM sends a summary of the system configuration file to the Secondary TM every
second, which the Secondary TM acknowledges. This serves to check if any configuration
changes have been made as well as confirming to each TM that the other is operating normally. If
configuration changes have been made in any of the Primary TMs, the Secondary TM will
recognise that situation and, in order to bring itself up to date, will request the full configuration file
from the Primary TM in question. The configuration update process is completed in a few seconds
as the file is very compact. Therefore, the Secondary TM will hold and maintain as many
configurations as there are Primary TMs on the network (to a maximum of five).
Other than entering the IP address information of the Secondary TM and those of the Primary TM
to be supported, no further configuration of a Secondary TM is necessary. If a change is made to
a setting on the Secondary TM that is online and acting for a Primary TM, i.e. a Primary TM has
become unavailable, that change will be overwritten by the Primary TM when it comes back online
since it has precedence.
As stated earlier, up to five Primary TM units can be supported by one Secondary TM but this
means that the Secondary TM can only take over from one Primary TM at a time. To cater for the
situation where more than one Primary TM becomes unavailable, rather than applying a “first
come, first served” rule, which could easily lead to an arbitrary result, the IP addresses for the
Primary TMs that are entered into the table in the Secondary TM also reflect the order of priority.