ACCESS &
HND Local Area Networks
HND
Computer Module tests: [OSI Model][Topologies][Media]
[WAN][Home] [Curriculum
2000]
[LAN
Topology diagrams]
LAN - Local Area Networks
Local Area Networks
Local area networks are mainly considerd local because of the practical
limitations of the media and the number of computers that can be connected
tog. The electrical characteristics of the cable also dictate LAN
limitations. Network designers work to recognised standards such
as the IEEE 10BaseT and 10Base2. These standards will define the
network topology, signalling speeds, the type of media, the maximum signalling
length of a segment, the number of nodes that can be connected in each
segment, the maximum number of segments that a LAN can be extended by.
Toplogies Basic topologies
are Bus, Ring and Star.
Media: Media can be
Unshielded Twisted Pair (UTP), Coaxial thick/thin, Fibre-optic or wireless
using infra-red, radio or micro-wave.
Hardware:
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Network interface cards (NICs)
To enable the physical connection of a media to a workstation connectors
are required. A NIC provides the connections along with the chips
needed to handle the communication signal.
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Repeaters as a signal
travels down a media it attenuates (weakens), a repeater can extend
the limitations of an ethernet cable by boosting the signal
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Bridges connect sytems
together of similar protocols, forwarding frames between them. They can
be used to sub divide networks to reduce congestion.
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Gateways connect systems
together that may require some form of conversion. It provides translation
between communication protocols.
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Routers routers are more
intelligent than bridges and also provide connection between between networks.
Routers are used on LANs and WANS. The internet and networks using
TCP/IP use routers to control traffic. They can provide alternative
rouuting facilities.
Software:
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Network operating system
In a peer-to-peer network where no controlling computer exists (server)
then the NOS needs to be on each workstation and each individual station
needs to excercise securioty control over its files. Priveleges for
other workstations to have access to files and directories can be given
by a work station but need to be applied workstation by workstation.
In a Client-server network the server is a file server. Workstations
are allocated a work area on the hard drive of the server computer.
The server then allocates priveleges of who can acces files and directories.
This type of network allows for gretaer security and management.
-
Drivers All peripheral
devices connected to computers need drivers to convert signals into a suitable
form for the processor. These include such devices as a mouse, a
printer or a network interface card (NIC)
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LAN Topologies
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Bus A single cable
connects each workstation. Signals are broadcast to all stations
but only the station that the packet is addressed to opens it. Traditional
ethernet uses this topology. A break in the cable affects the entire
LAN.
Star Workstations
are attached to a hub. Signals are passed from one workstation to
another in privacy. Messages can be broadcast to all stations if
required. This system is more secure as if a fault occurs in the
cable to one station it does not affect others on the network.
Star configured ring
An example of this topology is Token-ring. Signals are passed from
one station to another in a circle.
Star/bus configuration
A network that has groups of star-configured workstations connected with
bus trunks. Ethernet 10BaseT uses this topology.
