06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 1 Transmission Media Electromagnetic signals representing data propagates in the transmission medium Wavelength (m)Frequency (Hz) Radio> 1 x < 3 x 10 9 Microwave1 x x x x Infrared7 x x x x Optical4 x x x x UV1 x x x x X-ray1 x x x x Gamma-ray< 1 x > 3 x 10 19

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 2 Twisted-Pair Cable Unshielded Twisted-Pair (UTP): Two conductors, each wrapped in an insulator, then twisted Suitable for both voice and data (100Hz-5MHz), very easy to use, cheap Category (by EIA) Properties Used for voice and low rate data Used for voice and data up to 4Mbps 3 twists/foot Up to 10Mbps Current standard for telephone systems Up to 20 Mbps (16Mbps for token ring) Up to 100Mbps

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 3 Twisted-Pair Cable Shielded Twisted-Pair (STP) A UTP cable covered in a metal sheath which is grounded Used in environments with high EMI/RFI STP has the same quality considerations More expensive and bulky

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 4 Coaxial Cable A central conductor enclosed in an insulating sheath, encased in an outer conductor Outer conductor: –Shield against noise –Completes the circuit Frequency range: 100kHz-500MHz Signal is FIELD between conductors

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 5 Optical Fiber Guiding light in a solid core  Light carries information Speed of light –In vacuum, c = 3x10 8 m/s –In other media, v ≤ c  v = λf  λ ≤ λ 0 –Index of refraction n = λ 0 / λ Critical angle and reflection θ1θ1 θ2θ2 n1n1 n2n2 θ1θ1 θ2θ2 n1n1 n2n2 n 1 sin θ 1 = n 2 sin θ 2

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 6 Optical Fiber Modes of optical fiber –Multimode Step-index vs. Graded index –Single mode Multimode Step-index –Multiple beams travel in the optical fiber Core Cladding n2n2 n1n1

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 7 Optical Fiber Multimode Graded-index Single mode –Step-index fiber and highly focused light source –Very low density (small n), small diameter  Critical angle close to 90º Core Cladding

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 8 Optical Fiber Light sources: –Light-Emitting Diode (LED) –Injection Laser Diode (ILD) Advantages –Noise resistant –Less signal attenuation –High bandwidth Disadvantages –Cost –Installation/maintenance –Fragility

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 9 Unguided Media: Wireless Unguided media transport EM waves without using a physical conductor  Wireless communication Three types of propagation

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 10 Bands BandRangePropagationApplication VLF3–30 KHzGroundLong-range radio navigation LF30–300 KHzGround Radio beacons and navigational locators MF300 KHz–3 MHzSkyAM radio HF3–30 MHzSky Citizens band (CB), ship/aircraft communication VHF30–300 MHz Sky and line-of-sight VHF TV, FM radio UHF300 MHz–3 GHzLine-of-sight UHF TV, cellular phones, paging, satellite SHF3–30 GHzLine-of-sightSatellite communication EHF30–300 GHzLine-of-sightLong-range radio navigation

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 11 Cellular Telephony Fixed-wireless communication  Wireless last hop Frequency reuse MSC BS PSTN

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 12 Satellite Communication Line-of-sight communication between satellites (and earth stations) Depending on the type of constellation, single or multiple hops Number of satellites needed for global coverage

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 13 Transmission Impairment Attenuation –Loss of energy –Restored via amplifiers –How about digital signals? Distortion Noise What can we do about distortion and noise?

06 - Winter 2006 ECE ECE 766 Computer Interfacing and Protocols 14 Comparison of Transmission Media MediumCostSpeedAttenuationEMISecurity UTPLow1-100MbpsHigh Low STPModerate1-150MbpsHighModerateLow CoaxialModerate 1Mbps- 1Gbps Moderate Low OpticalHigh Limited by devices Low High SatelliteHigh1-10GbpsVariableHighModerate CellularHigh KbpsLowModerateLow