Communication systems p1

Communication system: a system that allows people and systems to transmit and receive data and information electronically. Communication occurs over a network, between hardware and software that transmit and receive.


Networks

LAN (local area network): network that connects devices over a small distance.

E.g. businesses and schools would use LAN.

WAN (wide area network): network that connects devices over a large distance.

E.g. The internet is a WAN. 


Hardware

Node: each device on a network is called a node.

NIC (network interface cards): a device must have a NIC to connect to a network. NICs slot into the motherboard and connect to a network using a cable. They can also be built into the motherboard and have an antenna to send data via radio waves using wireless networks.

Server: either specialised software on a general computer or a hardware device. Servers deliver special processing services to network users, such as file sharing, print services, database access and Internet access.

  • File server: a file server is a dedicated computer that stores files and application software.

  • Print server: a print server is a computer that manages all print tasks. All print requests are sent to the print server, which arranges them into a queue. The software that handles print jobs on a network is called a spooler.

  • Web server: a web server provides access to the Internet. 


Linking hardware

Hub: a non-intelligent device that connects nodes together into a network (hubs can be the centre of a LAN). Simple hubs just accept transmission through one cable and pass the transmission to every other device on the network.

Switch: switches are an intelligent device that connects nodes together into a network. They are like hubs, but signals are switched and only transmitted to the intended receiver. Switches set up a direct connection between the sender and receiver and are able to simultaneously receive and forward messages to and from multiple pairs of nodes. Most hubs have been phased out in favour of the more intelligent switch.

Bridge: Bridges connect two LANs that use the same protocol together. These two LANs are different. E.g. There are different LANs on each level of a school building. These LANs are connected by bridges.

Gateways: gateways connect two networks together – unlike a bridge, a gateway can connect networks that use different protocols. Usually used to connect a LAN to the internet.

Routers: routers direct messages between different networks with similar protocols. A router can translate one protocol into another, thereby overcoming software and hardware incompatibility. Specialises in directing messages on the most efficient path to their destination.

Modems: Modems are used to connect a network or individual computer to the internet. Modem is shorthand for modulator-demodulator. Modulation – digital computer signals are converted to analog signals that can be sent over a phone line. Demodulation – analog signals are converted back into digital data.


Transmission media, a.k.a. Communication links

Media: the medium through which messages are sent.

There is wired and wireless transmission media.


Wired transmission media

  1. Twisted pair cables use two insulated copper wires twisted together to reduce interference, but they're not completely protected, so some signals may get lost. (cheapest and slowest)

  2. A Coaxial cable consists of a thin core of copper wire surrounded by insulating material. More reliable data carrier, but is more expensive and less flexible. 

  3. A fibre optic cable is made up of very thin strands of glass fibre, surrounded by a layer of plastic. Able to support much faster and stronger transmission over long distances. (most expensive, fastest)


Wireless transmission media

Wireless transmission uses the atmosphere as a medium to carry electromagnetic waves between nodes. Wireless transmission can traverse rough terrain and allows nodes to move freely within the coverage area, like when you move your laptop from the couch to the desk.


Wireless transmission media:

  • Microwaves: direct line of sight required. Microwave towers have to be within around 40-50 km because they cannot bend. 

  • Satellites: microwave stations in the sky. If two microwave stations on earth want to communicate but are too far away, they can use the satellite.

  • Wireless LANs – WiFi

  • Bluetooth: communication system for short range transmission. Does not require line of sight.

  • Infrared: Infrared waves occur above microwaves, but before visible light. Requires “line of sight”. Think, remote controller. Used only over short distances.

  • Mobile phones: each mobile phone network is divided into a cell that has its own base station or mobile phone tower. Data is transmitted using radio and received using radio waves.

    • 3G, 4G and 5G refer to ‘Generations’ of mobile phone technology

    • Each generation of mobile phone technology has used different technologies and standards of transmission

    • 1G – 1980s: voice only, analog service, top speed 2.4 kbps 

    • 2G – 1991: allowed for call and text encryption as well as SMS, picture messaging and MMS, top speed 50 kbps

    • 3G – 1998: more data, video calling and mobile internet, top speed 2 mbps 

    • 4G:

    • released in the late 2000s, 500 times faster than 3G

    • Able to support high-definition mobile TV and video conferencing

    • Speeds are typically 10s of mbps for moving devices, up to 100s of mbps for stationary devices

    • 5G:

    • New technology currently being rolled out

    • Faster speeds and larger bandwidth size than 4G so able to support many more devices at any one time