ICT2 - Information: Management and Manipulation
Network Environments
LAN - Local Area Network
WAN - Wide Area Network
Standalone - computer not on a network
Advantages of LAN Networks
Resources (e.g. printers, scanners, modems) can be shared
Information can be shared (e.g. transfer of files, an Intranet)
Applications can be installed on one computer and be made available across a network
E-mail can be sent between users
Easy to set up new users and equipment
Different types of computer can communicate with each other
Disadvantages of LAN Networks
Users are dependant on the server. If this fails, certain applications or hardware devices may not be available
A badly managed network is worse than a standalone machine. Much depends on the skill of the network manager.
Networks have more security issues than standalones (e.g. hackers)
Network traffic can degrade performance
Server Based v Peer-to-Peer Networks
Server Based Network - Different devices on the network are treated as clients or servers. The client devices send requests for service e.g. printing or retrieval of data. The server devices can be peripherals such as a printer, or it can be the file server itself.
On a server-based network (e.g. Novell Netware) software and the backing store are held separately. If the server goes down, everyone is affected. User IDs and passwords are held centrally. Some processing tasks are performed by the server and some by the desktop computer.
Peer-to-Peer Network - Each workstation communicates directly with every other workstation, without going through a server.
On a peer-to-peer network (e.g. Windows for Workgroups) storage facilities are distributed throughout the network. Software is held on individual machines. Security is not centrally controlled. Backup is the responsibility of individual users. This type of network is less expensive.
A peer-to-peer network is suitable for small offices where there are only 3-4 machines on the network. One disadvantage is that, if one workstation is switched off, the files on that station cannot be accessed from the rest of the network.
The Network Manager
Any network has to be managed. The network manager should ensure that:
Response time is adequate
Hardware is upgraded when necessary
The required software is loaded
Software is upgraded when necessary and users are informed of changes
A system of regular backups is adhered to
Network security is maintained
WANs - Wide Area Networks
Communication can be via microwave, satellite link or telephone line.
The use of "global networks" e.g. the Internet has grown because of the changeover from analogue to digital lines, improved file compression techniques (both of which make downloading files faster) and a reduction in the cost of computers.
Communication Links
Telephone lines may be public (a fee is paid to the telephone company for time spent using the service) or private/leased lines (where there can be unlimited usage in return for an annual fee).
Communication Media
Twisted Pair (copper cable) - e.g. telephone lines
Coaxial Cable - High quality insulated cable that transmits data at high speeds
Fibre Optic Cable - Pulses of light (instead of electricity) are sent in digital form
Microwave (e.g. mobile phone networks) - send signals in straight lines. Therefore, stations must be close together because of the earth's curvature.
Communications Satellite - Hundreds of satellites are in geosynchronous orbit about 22,000 miles above earth.
Bandwidth
Bandwidth is the range of frequencies that the line can carry. ISDN and ASDL lines provide greater bandwidth than a standard telephone line.
Bridges and Gateways
Bridges - connect two LANs
Gateways - computers that connect parts of a WAN
Modems
These convert from analogue signals to digital format.
Modem = MOdulator/DEModulator
Synchronous and Asynchronous Transmission
Asynchronous transmission is when one character at a time is sent, with each character being preceded by a start bit and followed by a stop bit. A parity bit is usually also included (this checks for errors).
Synchronous transmission - there is no need for the start and stop bits. Timing signals from the computer's internal clock control the rate of transmission. This is usually less error-prone.
Protocols
These are rules that allow different types of computers to communicate with each other on a network. Any equipment that uses the same protocol can be linked together.
Factors affecting the rate of data transmission
The speed of the modem can vary between 9kbps and 56kbps
The nature of the line (normal phone line, ISDN, ASDL etc.)
Type of cable used (e.g. fibre optic or twisted pair cable)
The type of transmission (synchronous or asynchronous)