Transmission Media

• Wired– 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 sam

e 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 r

eceive 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

• Wireless LAN … cont’d

–Advantages –Easy installation

–Flexibility in usage

–Economical

–Expandability

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