1 chapter 2 the physical layer. 2 it defines the mechanical, electrical, and timing interfaces to...

1 Chapter 2 The Physical Layer

2 It defines the mechanical, electrical, and timing interfaces to the network. Purpose: To transport a raw bit stream Each one has its own function in terms of bandwidth, delay, cost, ease of installation and maintenance

Max Data Rate of a Channel Nyquist Theorem noiseless channel Max Data Rate = 2Hlog 2 V bits/sec H : Bandwidth V : V discrete levels of a signal For binary = 2 levels Ex: for 3KHz channel, Max data rate 6000 bps Signal to Noise Ratio (SNR) SNR = Signal Power / Noise Power Measured in decibels (db) 10log 10 S/N For Noisy channel Shanon theorem Maximum number of bits/sec = Hlog 2 (1+S/N)

4 Physical Media Groups Roughly grouped into Guided media, copper wire and fiber optics, Unguided media, radio and lasers

5 Guided Transmission Media Magnetic Media Twisted Pair Co-axial cable Fiber optics

6 Guided Transmission Media Magnetic media It is the most common way of transferring data Transmission time is measured in minutes or hours Used Where very less frequent transportation is needed Where amount of data is very high Cost effective, especially for applications in which high bandwidth or cost per bit transported is the key factor. Ex.Ultrium Tape-200 Gigabytes.

7 Twisted Pair Transmission time is measured in milliseconds. Consisting of two insulated copper wires. Thickness = 1 mm Wires are twisted together in a helical form like DNA molecule. To remove electro-magnetic effect on data

8 Twisted-Pair Cable

9 Twisted Pair The most common application is telephone system Can transfer data for several kilometers without amplification But for very long distances amplification is needed Repeaters are used Many TP cables grouped together and covered by protected material. They can be used for digital as well as analog transmission. The bandwidth depends on the thickens of the wire and the distance traversed. It is the cheapest solution

10 Twisted Pair - Types Two types Category 3,4 pairs 16 MHz Gently twisted Category 5,4 pairs 100 MHz More twists Less crosstalk, better signal quality Category 6 (250 MHz) and 7 (600 MHz) are also coming It is also called UTP (Unshielded Twisted pair) cable.

11 Twisted-Pair Cable Figure 7-8

12 A Coaxial Cable

13 Coaxial cable Construction stiff copper wire as the core surrounded by an insulating material The insulator is encased by a cylindrical conductor a closely-woven braided mesh The outer conductor is covered in a protective plastic sheath

14 Coaxial Cable Advantages Better shielding than twisted pairs High bandwidth (1 GHz) [600 MHz] Excellent noise immunity Use Within the telephone system for long-distance lines For cable television For metropolitan area networks

15 Coaxial cable Two kinds of coaxial cable 50-ohm cable used for digital transmission 75-ohm cable used for analog transmission and cable television

16 Fiber Optics It transmit data by pulses of light A pulse of light indicates a 1 bit and the absence of light indicates a 0 bit Optical transmission system has three components The light source The transmission medium The detector

17 Working of Fiber Optics Light source is either LED or a laser diode. The transmission medium is ultra thin fiber of glass The detector is a Photodiode which emits electric pulse when light falls on it. Attaching a light source to one end of an optical fiber and a detector to the other, we have a unidirectional data transmission system that accepts an electrical signal, converts and transmits it by light pulses, and then reconverts the output to an electrical signal at the receiving end. Data rate = 10 Gbps

18 Example a) Three examples of light rays from inside a silica fiber impinging on the air/silica boundary at different angles b) light trapped by total internal reflection

19 The Single Mode Fiber Fiber with core diameter less than about ten times the wavelength of light then it is known as single mode fiber Single mode fiber acts like a wave guide, and the light propagates in a straight line They require expensive laser diodes but are more efficient and run for longer distances It can transmit data at 50 Gbps for 100 km without amplification The most common type of single-mode fiber has a core diameter of 8 to 10 m

20 Single-mode fibers are more expensive but are widely used for longer distances. Fiber with large (greater than 10 m ) core diameter called multimode fiber. A fiber can pass more than one rays at a time, at different angles then it is known as multimode fiber. The Single Mode Fiber

(a) Multimode fiber: multiple rays follow different paths (b) Single mode: only direct path propagates in fiber direct path reflected path

22 Transmission of Light Through Fiber Glass used is Very transparent! Attenuation of light passing thru glass depends on the wavelength of it Attenuation = reduction in power

23 Attenuation of Light Thru Fiber in the Infrared Region

24 The Spectrum Used Three wavelengths are used for optical communication. 0.85 micron, 1.30, 1.55 microns are centers Later two have less then 5% loss per km

25 Dispersion and Solution Light pulses spread out in length as they propagate, This spreading is known as chromatic dispersion The amount of dispersion is Wavelength dependent. Dispersion results in overlapping of light waves in multimode fiber To stop spread out pulses overlapping, is to increase the distance between them. This can be done only by reducing the signaling rate.

26 The Fiber Cable At the center is the glass core through which the light propagates. In multimode fiber, the core is about 50 microns thick,( thickness of human hair) In single mode fiber, the core is 8 to 10 microns wide

27 The Fiber Cable The core is surrounded by a glass cladding with a lower index of refraction Next comes a thin plastic jacket to protect the cladding Fibers are typically grouped together in bundles, protected by an outer sheath

28 Fiber Cables a) Side view of a single fibre b) End view of a sheath with three fibres

29 Light Sources A Comparison of LED and Semiconductor diodes as Light sources

30 Interfaces (With Computers) The connector is very difficult to make and substantial light is lost Two type of interfaces are used first one is called the Passive Interface second one is called Active repeater Both of them, at each computer, serves as a T junction to allow the computer to send and accept messages, and pass data through

31 A Fiber optic Ring With Active repeaters

32 The Active Repeater In the Active repeater the incoming light is converted to an electric signal It is regenerated to the full strength and retransmitted as light connector is a simple copper wire If an active repeater fails, the ring gets broken and the network goes down There is no virtual limit on the size of ring

33 Passive Interfaces: Passive interface consists of two tapes fused onto main fiber One tap has LED or Laser diode at the end of it and the other has the Photodiode It is extremely reliable because a broken LED or photodiode does not break the ring. It just takes one computer off-line.

34 A Passive Star Connection

35 Comparing Fiber and Copper High bandwidth with min loss of power Not affected by power line surges, Electromagnetic interference Repeaters are needed every 50km compared to 5 km in copper wire They are very thin and light weight

36 Comparing Fiber and Copper One thousand twisted pairs 1 km long weigh 8000 kg. Two fibers have more capacity and weigh is only 100 kg. Fibers do not leak light and are quite difficult to tap Since optical transmission is inherently unidirectional, two-way communication requires either two fibers or two frequency bands on one fiber It is an less familiar technology for most Engineers. Can be damaged easily by being bent too much Fiber interfaces cost more than electrical interfaces

37 Wireless Transmission For people who need to be on-line all the time For mobile users. Running a fiber to a building is difficult due to the terrain (mountains, jungles, etc.)

38 The Electromagnetic Waves When electrons move, they create EM waves that can propagate thru free space Frequency( f ) The number of oscillations per second of wave measured in Hz Wavelength () The distance between consecutive maxima or minima By attaching an antenna to an Electric Circuit, the EM Wave can be broadcasted and can be received by receiver some distance away.

39 The Properties of EMWs In Vacuum all EMWs travel at the same speed even though different frequency- 3 * 10 8 m/sec or 30 cm/nano sec In copper or fiber, it slows about 2/3 rd of above value and become slightly freq dependent.

40 The EM Spectrum

41 The EM Spectrum The Radio, microwave, infrared and visible light, all can be used for transmission Transmission can be done by modulating either amplitude, frequency or phase UV, X-rays, and gamma rays are hard to produce, do not propagate well thru buildings and are dangerous to living things

42 The Capacity of Transmission The amount of info an EMW can carry is related to its bandwidth It is possible to encode few bits per Hz at lower freqs but nearly 8 at high freqs

43 Transmission Methods Direct Sequence spread spectrum & Frequency hopping spread spectrum The transmitter and receiver hops from frequency to frequency hundreds of times per second makes transmissions hard to detect which spreads the signal over a wide frequency band good efficiency high noise immunity Used in military and commercial world

44 Radio Waves They are easy to generate, can travel long distances, penetrate buildings easily They are omni directional ( can travel in all directions) so transmitter and receiver are not needed to be aligned Radio waves are frequency dependent At low freq, power falls off sharply with distance from the source. At higher freq, they tend to travel in straight lines and bounce of obstacles

45 Continue In VLF, LF and MF bands radio waves follow the ground Easily pass through buildings These bands offer relative low bandwidth for data communication

46 Continue In HF and VHF bands, the ground waves tends to be absorbed by earth The waves that reach ionosphere, are refracted by it and sent back to earth military operates on these bands for long distance talks

47 Transmission of Radio Waves In the VLF, LF and MF bands, radio waves follow the Curvature of the earth In the HF, and VHF they bounce of The ionosphere

48 Microwave Transmission Microwave = Wave above 100 MHz Travel in Straight line Transmitting and receiving antennas must be accurately aligned with each other Repeaters are needed If towers are too far, the earth will get in the way Height : distance Ratio = r:r 2 Higher the tower, farther apart they can be.

49 Terrestrial Microwave

50 Microwave Transmission To achieve high data rate -10GHz, microwave is in routine use but At about 4 GHz, MW absorbed by water and generate hit These waves are only a few centimeters long and are absorbed by rain Sol n :- Shut off links where rain is falling & take another route

51 MW use microwave communication is so widely used for long-distance telephone communication, mobile phones, television distribution

52 Comparison with Fiber optics Inexpensive Putting up two simple towers may be far cheaper than buying 50 km of fiber through a congested urban area or up over a mountain

53 Infrared and Millimeter Waves Used for short range communication Remote control of electronic products Can not pass through solid objects due to high freq infrared system in one room will not interfere with a similar system in adjacent rooms No need of government license

54 Light Wave Transmission Lasers can connect two LANs Coherent optical signaling using lasers is inherently unidirectional Each one need its own laser and photo detector It offers very high bandwidth at very low cost

55 Continue Advantage : It is relatively easy to install, and no licensing is needed Disadvantage : It can not penetrate even a rain or thick fog Heat generated by sun can defocus the beam

56 A Bi-directional System With Two Lasers

Communication satellites Contains several transponders which listens to some portion of the spectrum, amplifies the incoming signal, rebroadcasts it at another frequency to avoid interference with the incoming signal.

Communication Satellites GEO (Geostationary Satellite) Orbit slots allocation is done by the ITU Min 2 degrees distance between satellites 360/2 = 180 satellites The effects of solar, lunar, and planetary gravity tend to move them away from their assigned orbit slots and orientations, an effect countered by on-board rocket motors. This fine-tuning activity is called station keeping.

Satellite Bands Ku = commercial telecommunication carriers Ka = commercial Many government and military bands also exists

Communication satellites A modern satellite has around 40 transponders, each with an 80-MHz bandwidth. Spot Beams - Each downward beam can be focused on a small geographical area elliptically shaped, and can be as small as a few hundred km in diameter. VSATs (Very Small Aperture Terminals) 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power. uplink -19.2 kbps, downlink - 512 kbps. Microstations do not have enough power to communicate directly with one another (via the satellite). Instead, a special ground station, the hub, with a large, high-gain antenna is needed to relay traffic between VSATs,

VSAT VSATs have great potential in rural areas.

Communication satellites - Properties Broadcast media Propagation delay 3 sec (fibre optic 5 sec) Because electromagnetic waves travel faster in air than in solid materials Satellites are a complete disaster: everybody can hear everything. Encryption is essential when security is required. High error rates Cost to any place is same

Satellites versus Fiber High bandwidth via satellite than Fiber Communication on move (mobile) Broadcasting A message sent by satellite can be received by thousands of ground stations at once. Launching one satellite was cheaper than stringing thousands of undersea cables Satellites is to cover areas where laying fiber is difficult or unduly expensive. Military communication systems in time of war, satellites win easily.

The Public Switched Telephone Network Structure of the Telephone System 64

8/30/201565 How TN is used for data communication.

Transmission line suffers from 3 problems Attenuation-it is loss of energy as signal propagates outward (db/km) Distortion- speed difference leads to distortion of received signal Noise-unwanted energy from sources other than transmitter. 66

8/30/201567 MODEM Aim = To transfer digital data in existing analog twisted pair cable Achieved through modulation of one or more properties of analog signal such as Amplitude Frequency Phase

Modulation (b) AM (c) FM (d) PM 68

AM, FM, PM AM PM FM

8/30/201570 Speed Modem can sample 2400 times per second Each sample is called baud During each baud one symbol is transmitted Symbol may carry one or more bits If the symbol consists of 0 volts for a logical 0 and 1 volt for a logical 1(or one bit per symbol), than bit rate is 2400 bps (2.4kbps)

8/30/201571 Baud Rate / Bit Rate voltages 0, 1, 2, and 3 volts are used, every symbol consists of 2 bits, so a 2400-baud line can transmit 2400 symbols/sec at a data rate of 4800 bps. Similarly, with four possible phase shifts, there are also 2 bits/symbol, so again here the bit rate is twice the baud rate. The latter technique is widely used and called QPSK (Quadrature Phase Shift Keying).

8/30/201572 Continue To improve the speed from one bit, we can use modulation techniques Using 4 voltage level (2 bit per symbol) Using 4 phase shifts (2 bit per symbol) Combination of both (4 bit per symbol)

8/30/201573 QPSK All advanced modems use a combination of modulation techniques to transmit multiple bits per baud. Often multiple amplitudes and multiple phase shifts are combined to transmit several bits/symbol. Fig- (a) has four valid combinations and can be used to transmit 2 bits per symbol. It is QPSK (Quadrature Phase Shift Keying).

8/30/201574 (a) QPSK. (b) QAM-16. (c) QAM-64. Constellation Diagrams

8/30/201575 QAM-16 In Fig-(b) we see a different modulation scheme, in which four amplitudes and four phases are used, for a total of 16 different combinations. This modulation scheme can be used to transmit 4 bits per symbol. It is called QAM-16 (Quadrature Amplitude Modulation). Sometimes the term 16-QAM is used instead. QAM-16 can be used, for example, to transmit 9600 (2400*4) bps over a 2400-baud line.

8/30/201576 QAM-64 Fig- (c) is yet another modulation scheme involving amplitude and phase. It allows 64 different combinations, so 6 bits can be transmitted per symbol. It is called QAM-64. Higher-order QAMs also are used. Each high-speed modem standard has its own constellation pattern and can talk only to other modems that use the same one

Modems types Extra bit for error detection V.32 => 4+1 = 5 v.90 => 33.6 kbps V.32 bis => 6+1 = 7 V.92 => 48 kbps V.34 => 28800 bps V.32 bis => 33600 bps

8/30/201578 Asymmetric Digital Subscriber Lines The maximum speed possible by modems is 56 kbps To start Services with more bandwidth than standard telephone service

8/30/201579 ADSL - Two Approaches Dividing the spectrum of 1.1 MHz into three frequency bands: POTS (Plain Old Telephone Service) Upstream (user to end office) and Downstream (end office to user). The alternative approach, called DMT (Discrete MultiTone )

8/30/201580 DMT Divide the available 1.1 MHz spectrum on the local loop into 256 independent channels of 4312.5 Hz each Channel 0 is used for POTS. Channels 15 are not used Of the remaining 250 channels, one is used for upstream control and one is used for downstream control. So rest(248) are available for user data.

8/30/201581 Operation of ADSL using discrete multitone modulation. 80%90% of the bandwidth is allocated to the downstream channel since most users download more data than they upload

8/30/201582 ADSL Arrangement DSLAM DSL Access Multiplexer Consists of DSP

8/30/201583 ADSL Arrangement NID (Network Interface Device) To interface with Telephone Network At customer premises Splitter(Analog filter) separates the 0-4000 Hz band (voice from the data) POTS signal routed to telephone network Data signal routed to ADSL modem Disadvantage: presence of the NID and splitter on customer premises required ADSL is physical layer standard.

8/30/201584 Wireless Local Loops What is the need of WLL ? Any company wishing to get into the local phone business in some city must do the following things First it must buy or lease a building for its first end office Second it must fill the end office with telephone switches and other equipment

8/30/201585 Continue Third, it must run a fiber between the end office and its nearest toll office so the new local customers will have access to its national network. Fourth it must acquire customers, typically by advertising better service or lower prices than those of the Existing companies. Fifth and hardest path is installing local loop So WLL, a cheaper solution was discovered

8/30/201586 Expectation of customer Fixed Wireless Gives high-speed Internet connectivity New customer should not have an objection with a large directional antenna on his roof Customer can not be mobile

8/30/201587 Freq Spectrum Allocation The 198 MHz of new spectrum was allocated for the use of WLL This service called MMDS (Multichannel Multipoint Distribution Service). Low bandwidth of MMDS limits the no of users because Allocated spectrum is shared by many users gave birth to LMDS (high BW service)

8/30/201588 LMDS ( Local Multipoint Distribution Service ) 1.3 GHz BW At frequencies of 2831 GHz in the U.S. and 40 GHz in Europe

8/30/201589 Architecture of an LMDS system

8/30/201590 Architecture of an LMDS system Tower is shown with multiple antennas on it, each pointing in a different direction. Each antenna defines a sector, independent of the other ones. Range is 25 km, which means that many towers are needed to cover a city. 36 Gbps downstream and 1 Mbps upstream, shared among all the users in that sector A single tower with four antennas could serve 100,000 people within a 5-km radius of the tower.

8/30/201591 Few problems with LMDS Waves propagate in straight lines Leaves absorb these waves well Rain also absorbs these waves

Circuit Switching and Packet Switching 92

Comparison 94

8/30/201595 The Mobile Telephone System Wireless telephones come in two basic varieties: Cordless phones consisting of a base station and a handset sold as a set for use within the home. Mobile phones (sometimes called cell phones).

8/30/201596 Three Generations Mobile phones Generations: 1. Analog voice. 2. Digital voice. 3. Digital voice and data (Internet, e-mail, etc.).

8/30/201597 Analog Voice (First-Generation Mobile Phones ) Mobile radio telephones used for maritime and military communication In 1946, the first system for car-based telephones was set up in St. Louis Single large transmitter on top of a tall building and had a single channel, used for both sending and receiving. To talk, the user had to push a button that enabled the transmitter and disabled the receiver Known as push-to-talk systems

8/30/201598 IMTS Improved Mobile Telephone System Was installed in the 1960s two frequencies, one for sending and one for receiving IMTS supported 23 channels spread out from 150 MHz to 450 MHz

8/30/201599 Disadvantages Small number of channels, users often had to wait a long time before getting a dial tone. The large power of the transmitter adjacent systems had to be several hundred kilometers apart to avoid interference The limited capacity made the system impractical

8/30/2015100 Advanced Mobile Phone System Invented by Bell Labs first installed in the United States in 1982 & was also used in England called TACS in Japan called MCS-L1

8/30/2015101 Implementation Geographic region is divided up into cells Area = 10 to 20 Km Each cell uses some set of frequencies not used by any of its neighbours

8/30/2015102 Same group of Freqs

8/30/2015103 Cells are divided in micro cells

8/30/2015104 Continue At the center of each cell is a base station to which all the telephones in the cell transmit The base station consists of a computer and transmitter/receiver connected to an antenna base stations are connected to an MTSO (Mobile Telephone Switching Office) or MSC (Mobile Switching Center) The MTSOs are connected to at least one telephone system end office

8/30/2015105 Handoff When phone moves from one cell to another cell, base station changes, It takes about 300 ms Two types of Handoff Soft Handoff :- Telephone is acquired by the new base station before the previous one signs off. In this way there is no loss of continuity. Telephone needs to be able to tune to two frequencies at the same time (the old one and the new one). Neither first nor second generation devices can do this

8/30/2015106 Continue Hard Handoff With breaking continuity Old base station drops the telephone before the new one acquires it. If the new one is unable to acquire it (e.g., because there is no available frequency), the call is disconnected abruptly. Users tend to notice this

8/30/2015107 Communication Channels Freq Spectrum divided in 832 full- duplex channels 832 simplex transmission channels from 824 to 849 MHz 832 simplex receive channels from 869 to 894 MHz

8/30/2015108 Channels The 832 channels are divided into four categories: 1. Control (base to mobile) to manage the system. 2. Paging (base to mobile) to alert mobile users to calls for them. 3. Access (bidirectional) for call setup and channel assignment. 4. Data (bidirectional) for voice, fax, or data.

8/30/2015109 Call Management Each mobile has a 32-bit serial number and a 10-digit(34-bit) telephone number. When a phone is switched on, it scans a preprogrammed list of 21 control channels to find the most powerful signal. The phone then broadcasts its 32-bit serial number and 34-bit telephone number base station hears the announcement, informs the MTSO, and customer's home MTSO

8/30/2015110 Call Management To make a call User dial a no and press send button No. is sent (on access channel) to base station On getting request base station informs MTSO MTSO allot free channel Channel no is sent back (on control channel) to mobile Mobile switches to that voice channel

8/30/2015111 Call Management Incoming calls all idle phones continuously listen to the paging channel When a call is placed to a mobile phone a packet is sent to the callee's home MTSO to find out where it is Packet sent to callees current base station Base station broadcast are you there Callees phone responses Base station send channel no Callees phone switches to that channel and ringing starts

8/30/2015112 Second-Generation Mobile Phones: Digital Voice Due to the lack of world wide standardization Four systems are in use now D-AMPS, (used in US) GSM, (Everywhere) CDMA, PDC (used in Japan) (almost same as first)

8/30/2015113 D-AMPS The Digital Advanced Mobile Phone System Frequency Allocation Upstream: 18501910 MHz Downstream: 19301990 MHz Wavelength=16 cm Antenna requirement 4 cm long

8/30/2015114 D-AMPS Voice signal picked up by microphone is digitized and compressed Compression is done through circuit called vocoder Advantage of digitization & compression: More than one users can use same frequency channel

8/30/2015115 D-AMPS Each frequency pair supports 25 frames/sec of 40 msec each Each frame is divided into six time slots of 6.67 msec each Each frame holds three users who take turns using the upstream and downstream links Using better compression algorithms, in which case six users can be stuffed into a frame

8/30/2015116 TDM Frame of D-AMPS User 1 sending User 3 receiving

8/30/2015117 Hand off In D-AMPS, 1/3 of the time a mobile is neither sending nor receiving. It uses these idle slots to measure the line quality. When it discovers that the signal is waning, it complains to the MTSO, The mobile tuned to a stronger signal from another base station. Takes about 300 msec to do the handoff. This technique is called MAHO (Mobile Assisted Hand Off).

8/30/2015118 GSM The Global System for Mobile Communication 124 pairs of simplex channels Each simplex channel is 200 kHz wide and supports eight separate connections on it

8/30/2015119 GSM uses 124 frequency channels, each of which uses an eight-slot TDM system

8/30/2015120 A portion of the GSM framing structure

8/30/2015121 A portion of the GSM framing structure Eight data slots make up a TDM frame 26 TDM frames = 120msec multiframe. Of the 26 TDM frames in a multiframe, slot 12 is used for control and slot 25 is reserved for future use, only 24 are available for user traffic. 51-slot multiframe is also used

8/30/2015122 A portion of the GSM framing structure TDM slot consists of a 148-bit data frame that occupies the channel for 577 sec Each data frame starts and ends with three 0 bits It also contains two 57-bit Information fields, each one having a control bit that indicates whether the following Information field is for voice or data. Between the Information fields is a 26-bit Sync (training) field that is used by the receiver to synchronize to the sender's frame boundaries

8/30/2015123 CDMA Code Division Multiple Access D-AMPS and GSM are fairly conventional systems. They use both FDM and TDM to divide the spectrum into channels and the channels into time slots. CDMA allows each station to transmit over the entire frequency spectrum all the time. If we have a 1-MHz band available for 100 stations, with FDM each one would have 10 kHz and could send at 10 kbps (assuming 1 bit per Hz). With CDMA, each station uses the full 1 MHz, so the chip rate is 1 megachip per second. Each bit time is subdivided into m short intervals called chips. Typically, there are 64 or 128 chips per bit, but in the example given we will use 8 chips/bit for simplicity.

8/30/2015124 Example Each station is assigned a unique m-bit code called a chip sequence. To transmit a 1 bit To transmit a 0 bit, it sends the one's complement of its chip sequence.

8/30/2015125 Continue Orthogonal property of chip sequences A. A = 1 A. A = -1 A. B = 0 A. B = 0

8/30/2015126 Continue When two or more stations transmit simultaneously, their bipolar signals add linearly

8/30/2015127 (a) Binary chip sequences for four stations. (b) Bipolar chip sequences. (c) Six examples of transmissio ns. (d) Recovery of station C's signal.

8/30/2015128 Continue

8/30/2015129 Third-Generation Mobile Phones: Digital Voice and Data Expectation of Industry Experts a lightweight, portable device that acts as a telephone, CD player, DVD player, e-mail terminal, Web interface, gaming machine, word processor, and more, All with worldwide wireless connectivity to the Internet at high bandwidth.

8/30/2015130 To Achieve this dream The single world wide technology was envisioned (IMT-2000) Basic services High-quality voice transmission. Messaging Multimedia Internet access

8/30/2015131 Several proposals came W-CDMA (Wideband CDMA), was proposed by Ericsson. Not backward compatibility was there with GSM UMTS (Universal Mobile Telecommunications System). Proposed by European Union CDMA2000, proposed by Qualcomm Handoff was problem

2.5G EDGE (Enhanced Data rates for GSM Evolution) GSM with more bits per baud GPRS (General Packet Radio Service) Packet network on top of D-AMPS and GSM Using unused TDMA channels of GSM If SMS over GPRS is used, an SMS transmission speed of about 30 SMS messages per minute may be achieved. This is much faster than using the ordinary SMS over GSM, whose SMS transmission speed is about 6 to 10 SMS messages per minute.

8/30/2015133 Cable television was conceived in the late 1940s Consisted of a big antenna on top of a hill to pluck the television signal out of the air, An amplifier, called the head end, to strengthen it, A coaxial cable to deliver it to people's houses, Cable Television - Community Antenna TV

8/30/2015134 HFC Hybrid fiber coax system (Electro optical converter)

Fixed Telephone System Internet on Cable a) A single cable is shared by many houses, whereas in the telephone system, every house has its own private local loop One-way amplifiers have to be replaced by 2 way amplifiers b) On the other hand, the bandwidth of coax is much higher than that of twisted pairs, but the cable is shared.

8/30/2015136 Internet over Cable

8/30/2015137 Cable Modems Two interfaces on it: one to the computer and one to the cable network. The headend assigns upstream and downstream channels for that modem Modem scans the downstream channel for system parameters

8/30/2015138 Cable Modems Ranging: modem determines its distance from the headend Typical details of the upstream and downstream channels

8/30/2015139 ADSL versus Cable ADSL providers can give specific statements about the bandwidth Increasing no of users do not affect speed Availability : You must be near the end office if you want ADSL More secure due to p to p connection More reliable: work even during a power outage

1 chapter 2 the physical layer. 2 it defines the mechanical, electrical, and timing interfaces to...

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