September 2011
60
V1.44
Copyright © 2011 Adept Systems, Inc. and Control Network Solutions Ltd All Rights Reserved.
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 synchronization
attempts from the twin to the inactive twin. The default is 5000 ms.
Diagnostic Retrie
s: This sets the number of retries that the active diagnostic interrogation
request/response message will use. A diagnostic is sent out from each interface (709 and IP)
whenever a monitoring failure occurs. If the interrogation packet fails after
Diagnostic Retries
number of retries then a fault of the associated network interface will have been deemed to
have occurred. This will generate an alarm. The default is two retries. If spurious faults occur it
may be because
Diagnostic Retries
is too low and the diagnostic responses are getting lost due
to collisions. The odds of lost packets due to collisions decrease significantly for retry counts
above Four.
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 member 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 Count
appropriately.
The arbitration count is incremented twice per
HeartBeat Time
. The relative difference
between initial arbitration counts should be set big enough to account for any variable latency
in boot up time. The default is zero. 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 lose the
arbitration and 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 an
Initial Arbitration
Count
of zero, 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 arbitration
on boot-up. 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
: On boot up both routers will default to active. As a result, they
could both forward packets thereby resulting in a spike of duplicate traffic until arbitration
completes. Setting this option to
Off
will disable forwarding of packets by both routers until
arbitration completes and only one router goes active. The default is
Off
.
