Transmission Media Wired Wireless Coaxial Twisted Pair (UTP / STP) Optical Fibres Wireless IR Microwave signals Radio Frequency

Wired LAN (Coaxial cable) high capacity communication cable using BNC Connector 2 concentric conductor one inner (inner core) one outer (metal mesh) nowadays mostly for cable TV transmission disadv : much thicker not flexible more expensive (c.f. UTP / STP)

Wired LAN (Twisted pair) Using ordinary copper wire the copper wires are twisted together to reduce crosstalk / electromagnetic interference by electrical appliances (motors, transformers) radio frequency interference if the twisted pair is enclosed inside a shield STP not enclosed inside a shield (unshield) UTP nowadays mostly for networking cabling

Wired LAN (Twisted pair) … cont’d Using RJ45 connector Adv : more flexible less expensive (c.f. coaxial cable) Categories Cat. 1 --- for analogue voice (old telephone system) Cat. 2 Cat. 3 --- 10baseT Ethernet (16Mbps) Cat. 4 Cat. 5 --- 100baseT Ethernet (100Mbps) Ref : http://www.siemon.com/us/standards/13-10_twisted-pair_balanced_cabling.asp

Wired LAN (Twisted pair) … cont’d Types of cables Straight through cable connecting PC to network devices (hub / switch) Crossover cable connection between PC & PC connection between network device with network device Rollover cable with connector RJ45 to DB-9 converter then to COM 1 or COM 2 of PC

Wired LAN (Optical fibres) made up of a bundle of thin tubes of glass thinner than a human hair do not conduct or transmit electrical signals not interfere by electromagnetic wave Transmission of info via light pulse Carry more info than copper wire at the same period of time signal can travel a very long distance because no / little attenuation But fragile … need more protection installation .. More labour intensive

Interference Original Signal

Noise

When signal and noise combined together

Resulting Signal detected

Wireless LAN use electromagnetic waves to transmit and receive data from one device to another suitable to env. where cabling is difficult / not practical / not economical construction site warehouse school campus hospitals usually as an extension or an alternative for a wired LAN transmitter : Access Point (AP)

Wireless LAN … cont’d Using IR / radio signals / microwaves Some of them require direct line of sight (e.g. : IR) Signal travels in straight line Stations using antenna & satellite To avoid the curvature of the Earth Mountains Tall buildings Other signal obstacles Advanced wireless technology Eliminate the limitation of direct line-of-sight More flexible

Wireless LAN … cont’d Problems faced by wireless transmission Signals can be weakened by bad weather and solar activity A satellite can be used for around 7-10 years Anyone can detect the signal (Security problem) Signal / data must be encrypted before sending

Advantages Wireless LAN … cont’d Easy installation Flexibility in usage Economical Expandability http://iclassroom.hkedcity.net/directory/index.phtml?iroom_id=1387&tool_id=853&folder_id=1520