Networking

1. Networking • Network Classification by there: • How they are linked together and • there hardware

2. Network Hardware • The main bits of network hardware are: • Network interface card (NIC) • Server (e.g. file, application, proxy, DHCP servers) • Switch and hub • Router, bridge

3. Network Hardware • Communications device • Hardware capable of transmitting data instructions or information between a sending device & a receiving device

4. The modem Modulator/demodulator Modulate = turn digital data into analogue sound for transmission over phone network. (when uploading) Demodulate (when downloading) = convert sound back to digital data. Transmission speed is measured in bits per second (not bytes per second!) 56Kbps modem downloads at a theoretical maximum of approx 56,000 bits per second (about 7KB/sec). Can only transmit (upload) at 33.6kbps. Digital modems ISDN, DSL and broadband cable modems)

5. Hardware - NIC The Network interface card (NIC) allows a stand-alone computer to connect to a network. There are be cabled or wireless (radio) cards. This ‘combo’ NIC accepts both BNC (coaxial) and RJ45 (UTP) connectors.

6. Hardware – NIC & WAP • NICs are rated by speed: 10, 100, or ‘Gigabit’ 1000Mbps. • For a NIC to work at its maximum speed, all the other network devices between it and the server must have the same – or greater – bandwidth (data-carrying capacity). • WAP, wireless access point, device allowing computers and devices to transmit data wirelessly among themselves.

7. Hardware – Hubs, Switches Hubs and switches are connection points where cables can join up or be split. Typically, a single incoming cable is split into multiple outgoing cables.

8. Hardware – Hubs, Switches Hubs and switches are the same except.. Hubs pass along all network traffic they receive. Switches (“switching hubs”) are clever enough to only pass on relevant network traffic. Switches greatly reduce network congestion.

9. Hardware – Routers Security device that guards the connection between a LAN and the outside world (another LAN or a WAN.) Can be programmed to only allow authorised incoming and outgoing traffic. E.g. it can block certain external sites or forbid MP3 music files to enter. Like an enthusiastic bouncer at the door of a club. Routers can protect one part of a network from another part of the same network, e.g. school admin LAN and curriculum LAN.

10. Hardware – Bridges Bridges connect different segments of a LAN. Nowadays, switches are used as bridges.

11. Communications channel • Bandwidth, used as a synonym for data transfer rate - the amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps). • Broadband, transmit multiple signals simultaneously, faster transmission • Transmission media; physical or wirless

12. Physical Media, Twisted pair cable • UTP (Unshielded Twisted Pair) e.g. CAT5 (‘Category 5’) • 10 mbps; 100 mbps or 1 Gbps,

13. Physical Media, Coaxial cable • Coaxial Cable • Single copper wire • 10 mbps • Not used today as other transmission media faster

14. Connections – Fibre optic • Made of glass • Optical, not electrical – little signal fade and no danger of sparks in hostile environments • Multiple signals on a single fibre • Resists EMI Fibre optic

15. Connections – Fibre Optic Fibre optic • Core is as thin as a human hair • Not very flexible – needs thick coat • VERY fast • VERY high bandwidth • Very secure (can’t be tapped or snooped) • VERY long distance (2km without repeaters) • Light weight, small size • Expensive adaptors to convert digital <> electrical signals

16. Connections – Wireless transmission media • Data is transmitted as radio signals between wireless NICs and base stations • relatively short distances (e.g. 80m-200m), reduced by obstacles • speeds are increasing – now about 54 Mbps • encrypted communications to prevent eavesdropping • many PCs can connect to a base station • PCs can “roam” and will automatically connect to the base station that has the strongest signal

17. Connections – Wireless • Good for temporary networks, or when PCs rarely needed in a location • Good for laptop-intensive places • Relatively expensive compared to cable, but a useful network add-on • Security concerns (warchalking, spying)

18. Connections – Wireless transmission media • Broadcast radio • Wireless medium distributing radio signals through air over long distances • Need a transmitter and a receiver • Bluetooth uses this technology • Bluetooth is a small chip enabling communication between devices; transfer rate, 1mbps – 2mbps • Devices must be within specified range, eg. 10 metres • Wi-Fi communications technology uses broadcast radio

19. Connections – Wireless transmission media • Cellular radio • Used for mobile communications, wireless modems & mobile phones • 1g, (first generation); transmitted analog data only • 2G, speed from 9.6 kbps to 19.2 kbps • 3G, speeds from 144kbps to 2.4 mbps

20. Connections – Microwaves • Microwaves, radio waves providing a high speed signal transmission • Microwaves use line-of-sight transmission, often placed on top of buildings, towers or mountains • Used where installing physical transmission media is difficult or impossible • Used by universities, hospitals, cable TV providers

21. Connections – Satellite • Communications satellite is a space station that receives microwave signals from an earth-based station • Earth-based stations are often microwave stations • Transmission from an earth-based station to a satellite is an uplink; reverse is a downlink • Air navigation, TV & radio broadcasts, VC, GPS systems use communication satellites • Equipment required is a satellite dish & satellite modem card

22. Connections – Infra-red • IrDA is a wireless transmission standard that sends signals using infra-red light waves • An IrDA port is included with mobile PCs and other devices, eg. printer and mouse • IrDA transmission requires a direct line of sight • Data transfer rates are between 115 Kbps and 4 Mpbs