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Preview of A2 ICT - Unit 5 :NETWORKS

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LANs - Local Area Networks &
WAN - Wide Area Network
A local area network is connected by cable to allow a group of users in a small or limited area, usually
within one building or several buildings in close proximity. This is done in order to share data,
programs and hardware, users can then buy less hardware and share materials e.g. email, video
conferencing, graphics, printers etc
The way it is connected is called its topology. (Remember bus, ring, star)
Frequently LANs act as gateways hardware and software that gives all network users access
to other networks.
LANs generally have bus or ring topologies and a high bandwidth. (256kps to 100mps).
Consider Ethernet Cat5, fibreoptics and wireless networks.
There are LAN versions of many major pieces of software
A typical LAN Architecture will consist of LAN workstations, network cabling, Servers e.g.
File Server, Print Server, Communications Server.
No telecommunication lines are needed because computers on one site are linked together.
Files, printers, scanners and disk space can be shared
Users can communicate using software e.g. Lotus Notes
Software on the server can be used by anyone
All users can access the same database
Backup can be done automatically across the network
topology : The geometric arrangement of devices on the network. For example, devices can
be arranged in a ring or in a straight line.
protocols : The rules and encoding specifications for sending data. The protocols also
determine whether the network uses a peertopeer or client/server architecture.
media : Devices can be connected by twistedpair wire, coaxial cables, or fiber optic cables.
Some networks do without connecting media altogether, communicating instead via radio
LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted
over a telephone line but the distances are limited, and there is also a limit on the number of computers
that can be attached to a single LAN.
Describe TWO differences between a Local Area Network (LAN) and other networks such as a
Wide Area Network (WAN)
normally within same building maximum cable length 2km
connection is by local physical cable

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WAN Wide Area Network
A type of private network that uses a series of technologies including phone lines, modems,
microwave relaying stations, satellites to connect computers over a wide geographical area
Digital communication systems will greatly enhance the use of WANs.
WANs support distributed processing where computers are located throughout an organisation to
satisfy processing needs. e.g
Network Topology
Network Topology means the layout or shape of the network. The most common types of network
are Ring, Bus and Star.
The network cable links nodes.…read more

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Bus topology: All devices are connected to a central cable, called the bus or backbone. Bus
networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a
bus topology. Advantages are that less cable is needed than token ring, network can be easily
extended and that if one section of cable is faulty the network can be shortened and the remaining
section used while the fault is repaired.…read more

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Baseband transmission allows for very fast data transmission but it has one major disadvantage.
Electrical pulses flatten out when they travel through a long wire. This, together with other electrical
and factors impose a maximum length restriction on LAN's. The maximum length will depend on the
type of cable used but it is typically around 1 to 2 km and may be as low as several hundred metres.
Two strategies are used to overcome this length restriction.…read more

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In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also
associated with both a router, which use headers and forwarding tables to determine where packets
are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
Interactive Services e.g.
Electronic bulletin boards
EFT and Consumer Services
Information Utilities
Automatic Tellers (ATM's)
Computerised Booking
Online databases
(Remote databases) from modems e.g.…read more

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A company that provides Internet access to ISPs. Sometimes called backbone providers,
NSPs offer direct access to the Internet backbone and the Network Access Points
(NAPs). What does a browser do?
Web Browser
A software application used to locate and display Web pages. The two most popular
browsers are Netscape Navigator and Microsoft Internet Explorer. Both of these are
graphical browsers, which means that they can display graphics as well as text.…read more

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Distributed Databases
Distributed systems may contain a number of separate but connected processors, although
some centralised processing is possible. Read Heathcote and be able to explain the
difference between centralised and distributed computing.
Files and programs need not be held centrally in a distributed system functions can be
passed onto regional centres e.g. Police
Be aware of examples where data is distributed
Be aware of examples where control within the database (different functions) are distributed
Initially distributed systems still maintained a single central database.…read more

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System is dependent on high quality telecommunication lines, which may be vulnerable.
Need to maintain and enforce consistent standards and data definitions over a wide area.
Increased security problems need to enforce security procedures over wider area plus
increased problems over data transmission.
With a replicated database a central database is duplicated at all other locations. This is the most
appropriate for problems in which every location needs to access the same data.…read more

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A partitioned database is subdivided so that each location has only the portion that serves its local
needs. Partition. The database is partitioned with each node on the network containing that section of
the database that relates to it.
For example the section of the database that relates to customers served at that node. Other data is
held centrally and any changes to central data can be dealt with overnight by a batch update.…read more

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ClientServer networks
Networks with powerful servers in which different pieces of hardware work on the same
processing problem. The network tries to use the full processing power of each computer in the
network, including the fileserver and the user workstations or clients.
Servers are required to:
Manage the activities of the network
Can store application programs and data files
Can distribute programs or data files to other computers on the network as they request
It is less expensive and more flexible than mainframe.…read more


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