Network Environments Communications Networks LAN – Local Area ...Presentation Transcript
LAN – Local Area Network
Collection of Computers and peripherals with a common connection in one building or site.
WAN – Wide Area Network
Groups of networks connected together over a larger geographical area.
Ultimate WAN ??
The topology of a network is its physical layout — the way in which the computers and other units (commonly referred to as nodes ) are connected.
LAN - Advantages
Disk storage, printers, modems, scanners etc.
Programs can be stored on one computer
Easier Setup procedures
Different types of computers can be connected
LAN - Disadvantages
Dependence on a single server machine.
Large systems will have a back-up server.
Hardware/software access depends on network
System Manager dependent
System must be properly organised for efficiency
Difficult to make system secure.
Vulnerable to hackers – particularly via modems
Performance degrades as use increases
Types of LAN
Server-based – Client-Server Architecture
Devices on networks are either clients or servers .
Workstations would be clients . They request a service from servers . For example, retrieve a file from the file server, or print a document on a printer which is a server device
Alternative architecture for small businesses (3 or 4 computers)
Each workstation can communicate directly with every other workstation with no central server.
Network Maintenance Tasks
Any network requires the management of:
Adequate response times
Necessary hardware upgrades
Provision of information for users
Comparison Individual computers must all have the same software loaded to control communication with other computers. Central node computer controls the communication protocol. Computers may be of a different type. No central server dependence If server goes down, all users affected. Back-up responsibility is devolved to individual users. Centralised back-up facilities. No central security User Ids, passwords and access levels are controlled centrally Copies of software held on individual machines. Basic network services to enable sharing of data, software and printers are provided. Generally easier to set up and maintain than servers. OK for small businesses. Software held centrally and shared. Server manages distribution of data and software to clients . Some processing may be handled locally but most done by file server. More speed and power but additional cost and complication. Distributed storage Centralised backing storage Peer-to-peer Server-based
Wide Area Networks
LAN is connected by cables.
WAN is spread over a wide geographical area
Mode of communication may be:
Telephone line, microwave, satellite link
Use of global networks has increased due to:
Telephone networks: analogue to digital
Reduced connection and network costs
Improved compression techniques
Communications links Possible Configuration Communications satellite Mainframe in Norwich Mainframe in London Mainframe in USA modem modem
Twisted pair (copper cable)
used in telephone network and LANs
high quality, well insulated cable
Fibre optic cable
sends pulses of light rather than electricity
almost line of sight (30 miles apart)
in geosynchronous orbit
Telephone Network Service
BANDWIDTH determines speed of data transfer and is defined as the range of frequencies that a line can carry. The following high bandwidth services are capable of sending voice, video and computer data.
Integrated Services Digital Network
Asymmetric Digital Subscriber Line
Other Linking Devices
A connection between 2 LANs
Connects LANs with WAN or mainframe
Modem ( Mo dulator/ Dem odulator)
Telephones designed for speech (analogue signal)
Modems at either end convert digital-analogue and then analogue-digital.
modem modem digital digital analogue
Sends 1 character at a time, with each character preceded by a start bit and followed by a stop bit. A parity bit is also usually included to combat incorrect transmission. Used by PCs, fast and economical for small amounts of data.
Transmission controlled by timing signals – no start and stop bits. Less error-prone than asynchronous.
In order that equipment from different suppliers can be linked or networked, standard sets of rules or PROTOCOLS have been devised to ensure compatibility. Any equipment using the same protocol can be linked together.
Where necessary, protocol converters can be used to overcome:
Different types of transmission – asynchronous(PC) or synchronous(mainframe).
Different character representations – ASCII(PC) or EBCDIC(mainframe).
Different error checking methods.
Factors affecting rate of data transmission
The speed of the modem
Different modems vary in data transmission rates, typically from 9K to 56K bps (bits per second).
The nature of the transmission line
A digital line such as an ISDN line has a much higher transmission speed than an analogue line.
The type of cable used
Twisted pair has a transfer rate of 10Mbps; fibre optic cable is about 10 times as fast.