
1.14
SEL-2701 Ethernet Processor Instruction Manual
Date Code 20020501
Introduction
Ethernet Networks
Switches
A switch acts as a hub, connecting nodes to form a network that operates
logically as a multidrop network. In addition to repeating data, however, the
switch decodes some parts of Ethernet messages and directs traffic on an
Ethernet network.
One method for avoiding message collisions on an Ethernet network is to limit
the number of network nodes. A group of nodes that share a common medium
is called a collision domain. When there are fewer nodes in a collision
domain, fewer collisions occur, and the Ethernet network operates more
deterministically and efficiently.
A switch reduces the collision domain of each node to the ultimate minimum–
two nodes. A switch decodes incoming traffic from each network node and
directs network traffic. The switch drastically reduces the number of message
collisions, greatly improving Ethernet network performance.
While switches are less reliable than hubs, the increased Ethernet network
performance offsets the decreased network reliability. Switches operate at the
lowest layers (Physical and Data Link Layers) of Ethernet networks and are
independent of the network stack or application protocol.
Routers
A router operates similarly to a switch. The difference is that routers keep
messages in a local network and send out only messages that need to leave the
local network. The router contains tables of how to route messages and
decodes some of the Layer 3 or stack information to direct messages. Because
routers operate at higher protocol layers than switches and hubs, you must
select routers that are compatible with the protocol stacks on your network.
Routers do not forward Ethernet broadcast messages, for example GOOSE
messages. Ethernet broadcast messages are not intended for nodes outside of
the local network. Some more advanced routers act as network bridges that
allow you to route non-routable protocols like GOOSE. You must be very
careful if you route broadcast messages because you may drastically increase
the traffic across low-bandwidth links between networks. High traffic can
significantly diminish the throughput of inter-network connections and
significantly increase the charges for metered network access services.
Routers may also act as firewalls. A firewall operates as a security barrier
between your local network and the outside world. Used properly, firewalls
and device password protection can prevent unauthorized access to critical
systems.
Содержание SEL-2701
Страница 8: ...This page intentionally left blank ...
Страница 10: ...This page intentionally left blank ...
Страница 14: ...This page intentionally left blank ...
Страница 32: ...This page intentionally left blank ...
Страница 40: ...This page intentionally left blank ...
Страница 56: ...This page intentionally left blank ...
Страница 68: ...This page intentionally left blank ...
Страница 76: ...This page intentionally left blank ...
Страница 88: ...This page intentionally left blank ...
Страница 126: ...This page intentionally left blank ...