YOKOGAWA Vnet/IP, Technical Information

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1. Overview of Vnet/IP
1-9
TI 30A10A05-01E
1.3.2 Achieving high reliability with Redundancy
Vnet/IP is a control network with dual-redundant buses. Statuses of both Vnet/IP stations and
communication paths are constantly monitored. The most suitable control communication path is
always selected to ensure stable plant operations.
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Status of Vnet/IP stations and communication paths
Vnet/IP stations can exchange their statuses and the statuses of communication paths with each
other. Therefore, the statuses of Vnet/IP stations and communication paths on Vnet/IP are stored
and updated periodically in Vnet/IP stations.
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Communication path selection
A Vnet/IP station comprehends the path status for a communication destination from its own
communication path information, and chooses a normal bus to transmit the control data required.
Vnet/IP usually uses bus 1 for the control communication path. It does not use bus 1 and bus
2 alternately. When a problem occurs in bus 1, the communication path switches to bus 2.
However, after bus 1 recovers, the communication path reverts to bus 1. The switching of buses
is performed on the respective communication paths that lead to the destination.
On the left side of the following figure, a communication error occurs in the cables between
station C and layer 2 switch for bus 1. In this case, bus 1 is used between stations A and B, while
bus 2 is used between stations A and C. On the right side of the same figure, the layer 2 switch
for bus 1 is not working. In this case, bus 2 is used between stations A and B, and between
stations A and C.
010301E.ai
L2SW
B A C
Bus 1 side
Bus 2 side
B A C
Bus 1 side
Bus 2 side
In cases where a failure occurs between
station C and L2SW cable on bus 1 side
In cases where L2SW
on bus 1 side is defective
L2SW
L2SW L2SW
Figure Selection of Transmission Path
Dec. 26, 2016-00