GE T1000, Technical Manual

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Chapter 4
– Functions
GE Reason Switches
80 REASON SWITCHES-TM-EN-3
Figure 42: addition of new hosts to the legacy VALN-unaware equipment
This demonstrates that changes and increases in a VLAN unaware network would
create problems, since it would be required to change all physical installations in the
network. The VLAN mechanism was created in this context.
In the modern power system communication, using only legacy equipment to
transmit IED communication through VLAN unaware equipment could create
problems at many points. One of them could be that traffic segregation of GOOSE,
Sampled Values and PTP messages would be done through different physical LAN
installation. This option would likely be unacceptable due to installation costs and
maintenance difficulties.
9.2 Virtual LAN Basics
Virtual LAN technology allows separating the network through logical and physical
networks. With VLAN information, it is possible to create logical networks based on its
usage instead of its physical installation, thus enabling much more flexibility on it.
In the example given, if VLAN technology is used to segregate traffic from the
different departments, the physical topology could be as demonstrated below. The
figure shows that installation issues would decrease, as hosts can be attached at any
VLAN-aware switch at the LAN.