Networks

Client-server model: Server provides services which may be requested by clients. At least one computer is used to "serve" while other computers are referred to as "clients."

Advantages

• Files and resources are centralised - centralised back-up and internet monitoring
• Manage security
• Save resources on server reduces the burden on the client

Disadvantages

• If too many clients try to access the server at once, the server may fail
• Response time will be slow if the client is too far from the server
• If server fails, there's no way clients can get the data

Uses

• Serving websites, file sharing, printer sharing

Internet: the global connection of interconnected computer networks that uses TCP/ IP protocol

WWW: Collection of interlinked, hypertext documents resources accessed via the internet. WWW uses HTTP protocols to transmit data, using URLs to specify the location of the web pages

Hardware

Router: Device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by most efficient way

• It joins multiple networks together using IP addresses

Gateway: Device or used between two dissimilar LANs, and is required to convert data packets from one protocol to another - can be hardware, software, or both.

Server: A device or software provides a specific function for computers using a network such as handling printing, file storage and the delivery of web pages (refer to the previous page)

PSTN (Public Service Telephone Network)

• Designed for two-way voice communication through a modem to allow data transfer and to create a dedicated line between two ends. 
• Over time, more users and end-points (ends) through a network of switches (circuit switching)
• All networks are connected together by circuit switching
• Data is transferred using existing telephone lines - allow any telephone to communicate
• While the data is being transmitted, the computer dials the network to set up a connection
• ISP pay the PSTN for access to this infrastructure and resell access to their customers
• It could provide access points for WiFi set up in individual rooms or buildings

Dedicated lines (leased lines - closely linked with PSTN)

• Telecommunications path between two points that allows to host and browse website
• Not shared in common among multiple users unlike PSTN - used in private businesses
• Allow users to maintain a continuous, uninterrupted presence on the Web

Advantages of using dedicated lines

• Consistent data transfer speeds
• High and consistent bandwidth - normally, this would drop at peak time when other customers of the same ISP are attempting to connect
• Fast upload speeds

Cell: Area where wirless network spreads over land

• Cell phones can be used as modems to connect computers to the Internet
• Each cell is served by at least one fixed-location transceiver known as a base stations
• Each cell uses a different frequencies to avoid interference
• When these are joined, cells provide radio coverage over a wide geographic area
• Portable transceiver (i.e. mobile phones) are able to communicate with each other and also access via base stations

Copper cable

Either in coaxial and twisted pair form (coaxial has one copper strand at the centre)

• Flexible - safe from breaking
• High resistance to heat - need little insulation unlike fibre optic cable
• Cheapest to install
• Easier to make terminations using copper

• Can be affected by EM and other effects unlike fibre optic cable
• Doesn't perform well with small electrical charge

Fibre optic cable

• Greater bandwidth than copper cable
• Have greater security - can't hack in easily
• Lighter in weight - easy to install
• Consume less power

Radio waves (for long-distance like broadcasting TV, communicating between satellites)

• Can travel over large distances as the wavelength is huge
• Experience less interference
• Can't transmit much data as the frequency is low (although it's more signals than wire)
• Can be affected radio stations with similar frequency

Microwaves (for networks within a building)

• Larger bandwidth
• Can point directly at the receiving antenna
• Have high info capacity due to the frequency being high
• Limited distance (to the sight propagation) - can't pass around hills unlike radio waves due to low wavelength
• Can be physically interfered like rainfalls that blocks the sight

BEING WIRELESS IS AN ADVANTAGE FOR ALL WIRELESS CONNECTION - CHEAP

Satellites (weather analysis, scientific application)

• High-quality communication available for remote areas without requiring massive investment in ground-based equipment - cheap for LONG DISTANCE
• Do not have limitations of ground-based wireless transmission - curvature of the Earth
• Easy to interfere
• Expensive to set up

Bit-streaming:  Sequence of digital signals over a communication path. Transfer of data at high speed requires fast broadband connection

On-demand bit streaming (streaming of an event): Digital videotape is converted to a bit-streaming format for broadcasting on the net which is known as encoding. These encoded streaming video files are then uploaded to a dedicated server.

• A link for the encoded video is placed on a website which a user clicks on the link to download. These can be paused, re-watch, fast-forward, etc.

Real-time bit-streaming (live-stream): An event is captured live with a video camera. Video signal is converted to streaming media files encoded on the computer. The encoded feed is then uploaded from the computer to a dedicated streaming server via a high-speed internet connection. 

• Cannot be paused

It is important to have high-speed broadband because data is streamed to a buffer and buffer stops video pausing as bits streamed. As the buffer empties, it fills up again so that viewing is continuous. (Need to display and download simultaneously)

Local Area Network (LAN): not over the large geographical area

Wide Area Network (WAN): formed by a number of LANs connected together; large geo area

• The Internet is a WAN therefore as more LANs are set up, it allows the Internet to expand and if they are maintained, they are in turn supporting the Internet