2IC10 Computer Networks Physical layer Igor Radovanović Thanks to B. A. Forouzan A. Tanenbaum Igor Radovanovic, i.radovanovic@tue.nl 18/12/2019 18/12/2019 18/12/2019 1 1 TU/e Computer Science, System Architecture and Networking

Physical layer 18/12/2019

Analog versus digital signals 18/12/2019

Fourier Coefficients 18/12/2019

Fourier transformation 18/12/2019

Fourier transformation (cnt’d) 18/12/2019

Bandwidth 18/12/2019

Signal impairments 18/12/2019

Signal distortion attenuation distortion noise 18/12/2019

What is the bandwidth of this signal? Digital signal QUESTION: What is the bandwidth of this signal? 18/12/2019

Throughput 18/12/2019

Propagation time 18/12/2019

Wavelength 18/12/2019

Transmission media Magnetic tapes? 18/12/2019

Twisted pair 18/12/2019

Twisted pair (cnt’d) - bandwidth issue - (a) Category 3 UTP (b) Category 5 UTP 18/12/2019

Using twisted pair cables in a network Cat 3 Cat 3 or Cat 5 18/12/2019

Using twisted pair cables in a network (cnt’d) 18/12/2019

Twisted pair networks -example - ADSL Ethernet networks - 10BASE-T - 100BASE-TX - 1000BASE-T - 1000BASE-TX (Cat5e (enhanced)) 18/12/2019

Twisted pair - pros and cons - Pros: easy to understand mass production - low cost most widely used medium Cons: prone to electromagnetic interference in power plants, airport buildings, military facilities, cars… Note: In-building networks at our university are almost all twisted pair 18/12/2019

Transmission media 18/12/2019

Coax cable Category Impedance Use RG-59 75 W Cable TV RG-58 50 W Longer distances, higher bit-rates Category Impedance Use RG-59 75 W Cable TV RG-58 50 W Thin Ethernet RG-11 Thick Ethernet 18/12/2019

Coax cable network - example - 10Base2 Ethernet Note: Almost obsolete 18/12/2019

Coax cable network - example 2- cable modem 18/12/2019

Transmission media 18/12/2019

Optical fiber fundamentals Banding the light ray 18/12/2019

Optical fiber fundamentals 18/12/2019

Optical fiber fundamentals (cnt’d) 50 microns 5-10 microns 18/12/2019

Optical fiber fundamentals (cnt’d) 18/12/2019

Optical fiber network - example 1- 18/12/2019

Optical fiber network -example 2- 18/12/2019

Optical fiber - pros and cons - Pros: Low attenuation Large bandwidth Relatively “new” technology “Expensive” 18/12/2019

Comparing optical fiber to UTP Pros: Immune to electro-magnetic interference no crosstalk Reduced need for error detection and correction Enables longer link distances Attenuation unaffected by transmission rate Easier network upgrade Can combine different services: telephony, TV, internet… Cons: Optical components have higher cost Expensive deploying protocols 18/12/2019

Comparing optical fiber to UTP Unrepeated signal can travel larger distances 18/12/2019

Comparing coax to UTP coax cable performance UTP performance 18/12/2019

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Wireless Modern wireless digital communication began in the Hawaiian Islands What is “the best” frequency to use for communication? 18/12/2019

Politics of the electromagnetic spectrum IEEE 802.11b (11Mb), (22Mb) IEEE 802.11g (54 Mb) Bluetooth IEEE 802.11a (100 Mbps) Industrial Scientific and Medical band (ISM) Government regulated Transmission power is limited so as to limit interference 18/12/2019

Bandwidth delivery capability by technology http://www.pafiber.net/ftth/comm-benefits 18/12/2019

Multiplexing 18/12/2019

Frequency Division Multiplexing 18/12/2019

Wavelength Division Multiplexing 18/12/2019

Time Division Multiplexing 18/12/2019

Inverse Time Division Multiplexing Example: High-speed Ethernet networks 18/12/2019

TDM network -example- T1 high-speed digital network (1.544 Mbps) developed by AT&T in 1957 and implemented in the early 1960's supports long-haul voice transmission digitally representing analog telephone system 18/12/2019

TDM/FDM network -example- GSM phones uplink downlink 890MHz 915MHz 935MHz 960MHz 124 124 18/12/2019

Code Division Multiplexing Direct Sequence Spread Spectrum Frequency Hopping Spread Spectrum 18/12/2019

Comparing different techniques frequency time time time frequency frequency TDM CDM FDM TDM: 802.11 CSMA/CA TDM/FDM: GSM CDM: UMTS 18/12/2019

Internet @ home Dial-up ADLS Cable modem Fiber-to-the-Home? 18/12/2019

Modems (a) A binary signal (c) Frequency modulation (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation 18/12/2019

Asynchronous data transmission Bit encoding (1) Asynchronous data transmission Used for character oriented devices large indeterminate intervals between characters receiver resynchronizes with sender on start and stop bits polarity of stop bit different from polarity of start bit 1 0 0 1 0 0 1 0 Start bit Stop bit(s) 18/12/2019

Bit encoding (2) (a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding. 18/12/2019

Modems (2) (a) QPSK. (b) QAM-16. (c) QAM-64. 18/12/2019

ADSL TDM/FDM Asymmetric – higher bit-rate for downloading Use local loops (1.1 Mbps) Adapted data rate based on the conditions on the line 18/12/2019

ADSL (cnt’d) 18/12/2019

Cable modem Hybrid Coax-Fiber system 18/12/2019

Cable modem (cnt’d) Theoretical downstream data rate 30 Mbps, upstream - 12 Mbps 18/12/2019

Cable modem (cnt’d) 18/12/2019

TDM in combination with WDM Fiber-to-the-Home TDM in combination with WDM 18/12/2019

Fiber-to-the-Home (cnt’d) Passive fiber networks Easy to upgrade No electrical powering Immune to lightening, EMI What will happen to FTTH? Cost? Lifetime of telephone lines? 18/12/2019

Conclusions Physical layer is the basis of all networks limitations: attenuation, dispersion, noise, interference. aims: provide as much bandwidth and as larger span as possible, security, upgradeability @ low cost & protect investments, and facilitate reconstruction of the transmitted signal. Transmission media: guided & unguided Multiplexing techniques introduced to increase bandwidth TDM; FDM; (WDM); CDM Broadband access: ADSL; Cable modem; FTTH 18/12/2019