Transmission media

Transmission media Wired Co-axial Twisted pair UTP/STP Optical fibre Telephone UTP STP UTP/STP Optical fibre Wireless Infrared Laser Microwave transmissions point to point & WiFi Cellular radio

Co-axial cable Single conductor Outside shield Good protection against interference Fiddly to install Used in bus-wired networks e.g. 10Base2 Used in Cable TV networks (see below)

Coaxial installation To correctly install coaxial cable, the individual layers need to be accurately trimmed to correct lengths to match the connector. Should use special crimp tool to attach the connector

Twisted pair cable UTP FTP STP Categories

UTP No outside shield Twists guard against interference Cheap & easy to install Standard in US & UK for data networks Cat 5e / Cat 6

Office 1 Office 2 PC with NIC PC with NIC UTP or STP cable (Up to 90m) Equipment Room Patch panel Switch Router

Up to 16Mbps e.g. Ethernet 10BaseT Cat 4 Up to 20MHz Cat 5 Cat No Recognised by TIA/EIA? Usage Cat 1 No POTS, ISDN, doorbells! Cat 2 Token Ring 4Mbps Cat 3 Yes Up to 16Mbps e.g. Ethernet 10BaseT Cat 4 Up to 20MHz Cat 5 Up to 100MHz Cat 5e Up to 100MHz e.g. 100BaseT & Gigabit Ethernet Cat 6 Up to 250Mhz Cat 6a ? Future spec for 10 Gbit/s Cat 7 Up to 600MHz using STP cable

STP / FTP True STP has shield round each pair + overall shield Difficult installation Very good against interference IF well installed FTP has standard UTP plus outside foil shield

Cable TV Cable TV companies use co-axial link to customer premises Many use siamese cable (1 co-ax and 2 or more pairs of telephony cable) Cable modem gives high speed connection Limited geographical availability

Fibre-optic Problems with copper cabling UTP limit is 90m Copper cabling not to be used outside buildings Copper can be subject to interference Fibre optic cable overcomes these problems Note US spelling is FIBER

Fibre optic cabling Reaches further (typically 285m in structured cabling network) Has high bandwidth Is immune to EMI Is safe to run outside buildings BUT is also More difficult to install More expensive Fragile

How fibre works Glass cable Two densities creates a barrier which reflects light. Multimode 62.5 /125 i.e. Core=62.5 microns / Cladding=125 microns A micron is 1/1,000,000 of a metre or 1/1,000 of a millimeter!

Multimode v. Single mode

Multimode v. Singlemode Easier to install Cheaper transmission equipment -> LED But shorter distance -> Up to 285m in LAN Singlemode More difficult to install More expensive transmission equipment -> Laser Longer distance -> 10s of km

Connecting fibre Ends of fibre core must be placed very close or touching Light jumps from one fibre to the other Alternative is fusion splicing – difficult & needs expensive equipment

Connecting fibre

Fibre connectors ST connector Bayonet locking SC connector

Infrared Uses invisible light beam to connect Requires line of sight e.g. remote controls Used to be commonly used on laptops Now being replaced by Bluetooth which doesn’t need line of sight

Laser Very high speed connection Requires line of sight Relatively short range i.e. up to 4km Susceptible to adverse weather (e.g. rain, snow, cloud, mist…)

Microwave Very high frequency radio beam Requires direct line of sight Can bridge long distances e.g. up to 100km Relatively resilient to adverse weather conditions

Radio Strictly speaking still microwave Line of sight NOT required WiFi (IEEE 802.11) for LAN use WiMAX (IEEE 802.16) Up to 50km (31 mile) range Suitable for MAN use

Fixed Wireless Networking Standards Institute of Electrical and Electronics Engineers (IEEE) 1997 802.11 2Mbps ** Obsolete ** 1999 802.11a 54Mbps in regulated 5GHz range 1999 802.11b 11Mbps in unregulated 2.4GHz range 2003 802.11g 54Mbps in unregulated 2.4GHz range (Backwards compatible with 802.11b) Many manufacturers offer products with a “Turbo” mode 2008? 802.11n 2nd draft issued Jan 2007 Testing to draft standard from early 2007. Ratification Nov 2008?

Benefits / Drawbacks of Wireless Aesthetics No unsightly wires Lower installation cost No faceplates No cable No labour Good for places where cable not possible Drawbacks Lower bandwidth Reliability issues Connectivity Interference Higher equipment cost Limited range Security -> WEP WEP Wired Equivalent Privacy (128bit encryption) Datalink (layer2) so all data sent gets encrypted

Satellite Line of sight (to satellite) required Good coverage Propagation delay Cost!!!

Cellular radio Historically only option for true mobile networking To date very low speed compared to other LAN / WAN technologies e.g. GSM 9600 bps (not Kbps or Mbps!!) GPRS up to 56Kbps i.e. PSTN dial-up speed New 3G networks offer much faster speeds e.g. Vodafone HSDPA service up to 1.8Mbps BUT Cost Coverage http://maps.vodafone.co.uk/coverageviewer/web/default.aspx