AROW Series
Data Diode
Installation and Operation
7-4
Loss of GBE link
It typically takes 1 second to detect that a Gigabit Ethernet link had been
lost.
High side
In the time period between the connection failure and the failure being
detected, data arriving from the optical connection will be stored in the 2
Gigabit internal RAM buffer on both Live and backup modules. As soon
as the failure is detected, the backup module will take over, send ARP
messages to resolve IP/MAC bindings and continue to send data from
the point at which the last acknowledge message was received.
At high data rates, the buffer will typically end up halfway full and will
take a long time to recover. If the buffer is already half full or more as the
error condition occurs, there is a high likelihood of the buffer over-running
and data being lost.
Additional manual throttling of the sending application may be required to
return the buffer to a "safe" level.
No data corruption is expected at lower data rates.
Low side
In the time period between the connection failure and the failure being
detected, TCP segments sent to AROW are lost and will require
(automatic) re-sending. When the sending socket has sent all the data it
can send without acknowledgement, it will pause and hold the sending
application until the backup module takes over.
The backup module takes over as soon as it has been notified of the
failure by sending out an ARP request and periodic keep alive messages
that will force the sending socket to acknowledge and resend lost data.
Once the lost data is resent, normal operation resumes.
To the end applications the switch over appear to be a network delay and
no data is lost or corrupted.
Module failure
A module failure such as power supply failure can be simulated by
removing the live module from its slot while an active TCP socket is
connected. Compared to a loss of Gigabit Ethernet connectivity,
detecting that the link between a live and backup module has been
severed is very quick (within 100uS).
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