adept technology GadgetGateway User Manual page 106

Gadget Gateway Web-based Interface
5.9 Twin Mode Setup Page
Timeout Cushion: This sets the time period in milliseconds of latency cushion for the time
out for failure detection of the monitoring packets. In other words if after a time equal to
HeartBeat Time + Cushion, both monitoring packets are not detected by a router then a
monitoring failure has been deemed to have occurred. The routers then go to an active
diagnostic mode. The cushion should always be less than the HeartBeat Time but greater
than the expected latency due to propagation delays. The default is 200 ms.
AutoSync Time: This sets the time period in milliseconds between automatic synchroniza-
tion attempts from the twin to the inactive twin. The default is 5000 ms.
Diagnostic Retries: This sets the number of retries that the active diagnostic interrogation
request/response message will use. A diagnostic is sent out each interface (709 and IP)
whenever a monitoring failure occurs. If the interrogation packet fails after Diagnostic
Retries retries then a fault of the associated network interface will have been deemed to
have occurred. This will generate and alarm. The default is 2 retries. If spurious faults
occur it may be because the diagnostic retries is too low and the diagnostic responses are
getting lost due to collisions. The odds of lost packets due to collisions decreases signifi-
cantly for retry counts above 4.
Initial Arbitration Count: The Arbitration Count is a 64 bit number. The redundant twins
use an arbitration count encapsulated in the monitoring packets to determine which of the
pair should be active. The twin with the highest count wins the arbitration and goes active
while the one with the lower count will go inactive. If both have the same count then they
both pick random counts until one wins the arbitration.
On boot up both routers will default to active. The ensuing arbitration will result in one of
the routers going inactive. This menu option can be used to guarantee that a particular
router will win the boot up arbitration on the next reboot. The desired active one should
have the higher initial arbitration count. Use this menu option to set the initial arbitration
counts appropriately. The arbitration count is incremented twice per HeartBeat time. The
relative difference between initial arbitration counts should set big enough to account for
any variable latency in boot up time. The default is 0. If both nodes are set to zero, which
ever node boots up first will go active and start incrementing its arbitration count. The
other node will also go active but because it booted up later its arbitration count will be
lower and will go inactive. The arbitration count will eventually roll over to zero. Thus on
the next arbitration after roll over the active and inactive nodes will switch. Given that the
arbitration count is a 64 bit number, for a heartbeat time of 1 second and a initial arbitra-
tion count of 0, the rollover time is more than 292 billion years.
To reiterate, the initial arbitration count is only going to have an effect if there is an arbi-
tration on bootup. An arbitration only occurs when both nodes are in active forward state.
In order to force the inactive node to be active one must set the arbitration counts on both
nodes and then reboot both nodes.
Powerup in Forward Mode: Because on boot up both routers will default to active, they
could also both forward packets thereby resulting in a spike of duplicate traffic until arbi-
5-20