|
A Guide to Ethernet Components and
Terminology
The power of an Ethernet LAN (Local Area Network) is tremendous
when applied to a factory floor or other industrial application.
However, to take full advantage of its features, it requires
more than simple wire connections from one device to another.
Following are descriptions and explanations of some of the
infrastructure devices that can make your Ethernet LAN come
alive.
Unmanaged Ethernet switches are a plug and
play installation. Switches increase the number of nodes and
the length of the LAN. They are designed to divide the network
into separate collision domains. This reduces overall traffic
on a LAN, improving communication speed and reducing errors.
Switches route communication to the desired end device instead
of broadcasting the communication to everyone connected to
the LAN. This is accomplished by the switch’s ability
to set up a table of device addresses connected to each leg
of the switch. With this information the switch knows where
to send each Ethernet packet once it is received. See
Unmanaged Ethernet Switches.
Managed Ethernet Switches allow advanced
control of your LAN. They usually include software to configure
your network and diagnostic ports to monitor LAN traffic.
If communications fail, most managed switches will alert the
manager via e-mail or by closing a relay to trigger an audible
signal or flash a light. Another feature available on managed
switches is QoS (Quality of Service) programming which prioritizes
messages ensuring important data receives the highest priority
on the LAN segment. See
Managed Ethernet Switches.
Ethernet Hubs are a simple way to increase
the number of nodes, extend network distances while introducing
the smallest amount of latency. Hubs don’t examine the
Ethernet packets for destination information so they deliver
the packets even more quickly than a switch. All messages
received by the hub are sent out on all legs to all the connected
devices. Installation is a plug and play operation. See
Ethernet Hubs.
Media Converters change Ethernet twisted
pair copper wires into fiber optic signals. Fiber optic is
often preferable because it is impervious to interference
that can disrupt the signals being carried by copper. Because
fiber can extend the distance of a network up to 2 km in each
segment, media converters can also increase the range of a
network. See Media
Converters.
10BASE-T - 10 Mbps Ethernet communications
over Category 3 or better cable.
100BASE-TX - 100 Mbps Fast Ethernet communications
over Category 5 or better cable.
10BASE-FL - 10 Mbps Ethernet transmitted
over fiber optic cable.
100BASE-FX - 100 Mbps Fast Ethernet transmitted
over fiber optic cable.
Auto-negotiation - A protocol defined in
the Ethernet standard that allows devices at either end of
a link segment to advertise and negotiate modes of operation
such as link speed (10 or 100 Mbps), half or full-duplex operation
and full-duplex flow control.
MDI - Medium Dependent Interface. The name
for the connector used to make a physical and electrical connection
between a transceiver and a media segment. For example, the
RJ45 style connector is the MDI for 10BASE-T and 100BASE-TX.
MDI-X - An MDI port on a hub or media converter
with an internal crossover function. A “straight-through”
cable can be used to connect a station to this port since
the signal crossover is performed inside the port.
Quality of Service (QoS) - Some switches
support QoS (per 802.1p and 802.1Q standards) wherein tagged
messages can be assigned one of eight levels of priority.
QoS can be important where time-critical applications can
be affected by data delays.
VLAN - Virtual Local Area Network. A LAN
that maps stations on a basis other than location —
such as by department, user type or application. Managing
traffic, workstations and bandwidth can be easier with a VLAN.
This improves network efficiency.
Structured Cabling — Nothing in Ethernet
is left to chance. A set of cabling standards for design,
installation, performance and testing provides a “structure”
for Ethernet. (Refer to EIA/TIA 568 and ISO11801)
|
Ethernet
Accessories