1 K. Salah Module 3.2: Transmission Media Electromagnetic Spectrum Guided Transmission Media –Twisted Pair –Coaxial cable –Optical fiber Unguided Transmission Media –Terrestrial Microwave –Satellite –Radio –IR –Cellular Telephony

2 K. Salah Electromagnetic Spectrum

3 K. Salah Guided Transmission Media Twisted Pair Coaxial cable Optical fiber

4 K. Salah Twisted Pair Most common medium Telephone network –Between house and local exchange (subscriber loop) Within buildings –To private branch exchange (PBX) For local area networks (LAN) –10Mbps or 100Mbps Pros and Cons: –Cheap –Easy to work with –Low data rate –Short range, about 100 meters.

5 K. Salah Unshielded and Shielded TP Unshielded Twisted Pair (UTP) –Ordinary telephone wire –Cheapest –Easiest to install –Suffers from external EM interference Shielded Twisted Pair (STP) –Metal braid or sheathing that reduces interference –More expensive –Harder to handle (thick, heavy) –Capacity Mbps UTP Categories Cat 3 –up to 16MHz –Voice grade found in most offices Cat 4 –up to 20 MHz Cat 5 –up to 100MHz –Commonly pre-installed in new office buildings RJ-11 vs. RJ-45 RJ-11 is a typical UTP phone connector. Has 2 pairs. RJ-45 is a UTP connector. Has 4 pairs.

6 K. Salah Coaxial Cable Most versatile medium Television distribution –Ariel to TV –Cable TV Long distance telephone transmission –Can carry 10,000 voice calls simultaneously –Being replaced by fiber optic Short distance computer systems links Local area networks Transmission Characteristics zAnalog yAmplifiers every few km yCloser if higher frequency yUp to 500MHz zDigital yRepeater every 1km yCloser for higher data rates

7 K. Salah Optical Fiber Greater capacity –Data rates of hundreds of Gbps Smaller size & weight Lower attenuation Electromagnetic isolation Greater repeater spacing –10s of km at least

8 K. Salah Transmission Characteristics zAct as wave guide for to Hz yPortions of infrared and visible spectrum zLight Emitting Diode (LED) used in MMF yCheaper yWider operating temp range yLast longer zInjection Laser Diode (ILD) used in SMF yMore efficient yGreater data rate zWavelength Division Multiplexing (WDM) using light prisms. MMF vs. SMF

9 K. Salah Comparison Cable TypeCost 1 = lowest 5 = highest Typical Capacity Installation 1 = easy 5 = hard Max Cable Length EMI Resistance 1 = low 5 = high Coaxial- Thinnet 210 Mbps2185 meters2 Coaxial- Thicknet 410 Mbps3500 meters2 UTP Mbps1100 meters1 STP Mbps2100 meters2 Fiber-optic5100+ Mbps5Multiple kilometers 5

10 K. Salah Wireless Transmission Unguided media Transmission and reception via antenna Directional –Focused beam –Careful alignment required Omnidirectional –Signal spreads in all directions –Can be received by many antennae Frequencies z2GHz to 40GHz yMicrowave yHighly directional yPoint to point ySatellite z30MHz to 1GHz yOmnidirectional yBroadcast radio z3 x to 2 x yInfrared yLocal pt-pt confined area

11 K. Salah Types of Radio Propagation

12 K. Salah Microwave Terrestrial Microwave Parabolic dish Focused beam Line of sight Long haul telecommunications Higher frequencies give higher data rates Satellite Microwave  Satellite is relay station  Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency  Requires geo-stationary orbit  Height of 35,784km  GEO vs. LEO  Frequency Bands: C, Ku, and Ka  Television  Long distance telephone  Private business networks

13 K. Salah WLAN Benefits of Ethernet WLAN –Cheap –Faster to deploy –Mobility –Watch for security  Need for authentication  Need for encryption during transmission What is an Access Point? A typical diameter is a room for one AP about 40 meters Frequencies used and data rate –IEEE b operates at 2.4 GHz range and gives 11Mbps –IEEE a operates at 5 GHz range and gives 54Mbps –IEEE g operates at 2.4 GHz range and gives 54Mbps Bluetooth gives 1Mbps. Bluetooth networks PDAs or cell phones with PCs. Operates in a short diameter (10 meters). –Operates at GHz –May have interference with Ethernet WLAN APs

14 K. Salah Others Broadcast Radio Omnidirectional FM radio UHF and VHF television Line of sight Suffers from multipath interference –Reflections IR (Infrared)  Modulate noncoherent infrared light  Line of sight (or reflection)  Blocked by walls  e.g. TV remote control, IRD port

15 K. Salah Cellular System Cellular Bands