AudioCodes Mediant 500 E-SBC, User Manual

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User's Manual 524 Document #: LTRT-10437
Mediant 500 E-SBC
In the active device, all logical interfaces (i.e., Media, Control, OAMP, and Maintenance)
are active. In the redundant device, only the Maintenance interface is active, which is used
for connectivity to the active device. Therefore, management is done only through the
active device. Upon a failure in the active device, the redundant device becomes active
and activates all its logical interfaces exactly as was used on the active device.
31.2 Device Switchover upon Failure
When a failure occurs in the active device, a switchover occurs to the redundant device
making it the new active device. Whether a switchover is later done back to the repaired
failed device, depends on whether you have enabled the Revertive mode:

Revertive mode enabled: The Revertive mode specifies one of the device's as the
"preferred" device between the two devices. This is done by assigning a priority level
to each device (1 to 10, where 1 is the lowest). Whenever the device with higher
priority recovers from a failure, it first becomes the redundant device but then initiates
a switchover to become the active device once again; otherwise, after recovery, it
becomes the redundant device and remains as redundant. If you change the priority
level of the redundant device to one that is higher than the active device and then
reset the redundant device, a switchover occurs to the redundant device making it the
active device and the "preferred" device. If both devices are configured with the same
priority level, then Revertive mode is irrelevant.

Revertive mode disabled: A switchover is done only upon failure of the currently
active device.
As only the active device is cabled to the PSTN interfaces, you MUST enable the Revertive
mode and set the active device with the higher priority. When a switchover to the
redundant device occurs, only the IP calls are maintained; the PSTN calls are dropped (by
sending a SIP BYE message to the IP side). Thus, whenever the PSTN-connected device
recovers from failure, it becomes the active device again, providing connectivity to the
PSTN.
Note: When a switchover from active to redundant device occurs and the active failed
unit requires a return merchandise authorization (RMA), meaning that it will be out of
service for a long period, in order to maintain your PSTN calls, connect the same
PSTN equipment and in the same manner (same ports) to the redundant device. The
configuration between the devices is identical and thus, call routing process is
unaffected. When connected to the PSTN, new Gateway calls can be handled by the
newly active unit.
Failure detection by the devices is done by the constant keep-alive messages they send
between themselves to verify connectivity. Upon detection of a failure in one of the devices,
the following occurs:

Failure in active device: The redundant device initiates a switchover. The failed
device resets and the previously redundant device becomes the active device in
stand-alone mode. If at a later stage this newly active device detects that the failed
device has been repaired, the system returns to HA mode. If Revertive mode is
enabled and the originally active device was configured with a higher priority, a
switchover occurs to this device; otherwise, if it was configured with a lower priority (or
Revertive mode was disabled), the repaired device is initialized as the redundant
device.

Failure in redundant device: The active device moves itself into stand-alone mode
until the redundant device is returned to operation. If the failure in the redundant
device is repaired after reset, it's initialized as the redundant device once again and
the system returns to HA mode.