ICT networks for different geographical scales and uses
- ICT networks can be divided into two types:

Local Area Networks (LANs)
Wide Area Networks (WANs)

LANs
- The main features of LANs are:

confined to single building or site - the hardware and communications equipment is contained in one building or site.
ownership of the communications equipment - the organisation actually own all the communications equipment that links the terminals.

WANs
- The main features of WANs are:

Hardware is spread over a wide geographical area - devices are spread over a wide geographical are. The devices are spread over multiple buildings and sites.
Third party telecommunications equipment is used - hardware in a WAN is situated in many sites, which can be in different countries. Telephone, radio and satellite communications are needed, which are supplied by a third party.

Network topologies and types
Network topologies
- A network topology shows how the computers are connected when wires are used and if wireless issued, it shows how the devices in the network communicate with each other.

The ring topology
- All the computers are arranged in a circle
- Data sent by one computer passes around the ring until it reaches the correct computer

Advantages:

easy to add extra devices
each computer has the same access as the others so not one computer can 'hog' the network.

Disadvantages:

if there is a break in the connection, then whole network fails
faults are difficult to locate
impossible to keep the network running whilst equipment is added or removed because there is only one path for the data to follow.

The bus topology
- All the devices connected to the network are contact to a common shared cable called the backbone.
- Signals are passed in either direction along the backbone.

Advantages:

cost effective because of the small amount of cable needed
simple cable runs makes it easy to install
easy to add extra devices to the network

Disadvantages:

if more than about 12 devices are connect to network, then performance of network is degraded
if there is a break in the backbone cable, then the network cannot be used.

The star topology
- Uses a central connection point to connect all the devices on the network together. The central connection point can be a hub, a switch or a router.

Advantages:

faults tolerant - if one of the cables fails, then the other computers can still be used
load tolerant - extra computers can be added without much loss in performance because all the computers have their own path to the hub
easy to add extra computers - extra computers can be added without disturbing the network.

Disadvantages :

higher cost - the large amount of cabling needed makes it a more expensive topology
dependance on the central hub/switch/router - if the device at the centre of the network fails, then the whole network will fail.

The mesh topology
- Data sent using a mesh topology can take several different paths to its destination.

Advantages:

Fault tolerant - as there are many paths data can take to get to its destination, if one of the path fails, there is always another path that can be taken.
easy to locate faults.

Disadvantages:

higher cost - lots of cables
harder to maintain - lots of cables

Peer-to-peer or client-server
Networks can be divided into two main types:

peer-to-peer
client-server.

Peer-to-peer networks
- Networks where each computer has the same status and they are able to communicate with each other on an equal footing.
- This means that every computer can access all the resources of any of the other computers on the network.
- Used for home networks.
- P2P has become popular with internet users for sharing files between users. Each user is able to connect to another users computer over the network so there is no central management.
- P2P software systems such as Kazaa and Napsteer are one of the most popular software applications with users.

Advantages:

cost saving - no server is needed
no network manager is needed - all users take responsibility for the network
easy to set up - simplest of computer networks
lower operating costs - less setup and maintenance costs
peer responsibility - users decide what resources other users can use on their computer.

Disadvantages:

backups cannot be made centrally - places responsibility on all the users to back up their own data
users need more IT knowledge - as they will be responsible for the files on their own computers
poorer security - resources are shared, so users have to decide what resources of theirs other users on the network can use
some computers may run slowly - those computers that have resources on them that all the users use will run very slowly.

Client-server networks
- Preferred choice for large networks.
- All the computers are not the same status.
- A more powerful computer is used as the central computer, where all the files and programs are stored, and this computer is called a server. The other computers on the network are called clients.
- As the sever is such an important part of a client-server network, a network manager is usually appointed to be in charge of it.

Advantages:

security is better - because it is centralised and a person is given responsibility for it
centralised data - data is all held on the file server which means that all users have access to the same set of data
back ups are taken centrally - regular back ups are taken by network manager which means data is unlikely to get lost
faster access to programs and files - servers are used which are powerful computers, so the whole network runs faster
centralised administration - all the administration of the network is performed centrally so users do not have to worry about it.

Disadvantages:

more expensive - servers are expensive
need specialist knowledge - needs to have a person who understands the technicalities of a network in charge of the network
software is sophisticated and expensive

Characteristics of networks

The differences between the Internet and the World Wide Web
> Internet - a huge group of networks joined together. Each of these networks consists of lots of smaller networks. This means that the internet consists of hardware.
> World Wide Web - means of accessing information contained on the internet. It is an information-sharing model that is built on top of the internet. Uses HTTP, which is one of the languages used over the internet to transmit information. The WWW makes use of browser software to access documents called webpages.

	Criado por anyasan quase 10 anos atrás

Notas sobre iCT, criado por anyasan em 27-11-2014.