Analog and Digital Transmission PDF

Analog and Digital Transmission and Transmission Media What is Physical Layer in OSI Model? Physical layer in the OSI model plays the role of interacting with actual hardware and signaling mechanism. Physical layer is the only layer of OSI network model which actually deals with the physical connect...

Analog and Digital Transmission and Transmission Media What is Physical Layer in OSI Model? Physical layer in the OSI model plays the role of interacting with actual hardware and signaling mechanism. Physical layer is the only layer of OSI network model which actually deals with the physical connectivity of two different stations. This layer defines the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc. Physical layer provides its services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts them to electrical pulses, which represent binary data. The binary data is then sent over the wired or wireless media. Signals When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk. Both analog and digital data can be represented in digital or analog signals.  Digital Signals Digital signals are discrete in nature and represent sequence of voltage pulses. Digital signals are used within the circuitry of a computer system.  Analog Signals Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves. Transmission Impairment Transmission impairment occurs when the received signal is different from the transmitted signal. As we know, a signal can be transmitted as Analog signal or it can be transmitted as a digital signal. In Analog signals due to transmission impairment the resulting received signal gets different amplitude or the shape. In the case of digitally transmitted signals at the receiver side we get changes in bits (0's or 1's). When signals travel through the medium they tend to deteriorate. This may have many reasons as given:  Attenuation For the receiver to interpret the data accurately, the signal must be sufficiently strong. When the signal passes through the medium, it tends to get weaker. As it covers distance, it loses strength. Here are some examples of attenuation: 1. Signal Attenuation in Fiber Optic Cables: Light signals transmitted through fiber optic cables weaken over long distances due to scattering and absorption by the glass fibers. 2. Radio Signal Attenuation: When radio waves travel through the atmosphere, obstacles like buildings, trees, and mountains can cause signal loss, reducing the strength of the received signal. 3. Sound Attenuation in Air: Sound waves weaken as they travel through the air because of the absorption of sound energy by air molecules. Higher frequencies tend to attenuate more than lower frequencies. 4. Electrical Signal Attenuation in Copper Cables: Electrical signals in copper wires lose strength over long distances due to resistance, inductance, and capacitance in the cables. 5. Attenuation in Seismic Waves: Seismic waves generated by earthquakes lose energy as they propagate through different layers of the Earth, especially through soft soils or fractured rock. 6. Wi-Fi Signal Attenuation: Wi-Fi signals diminish in strength as they pass through walls, floors, and other obstructions, especially in materials like concrete or metal. 7. Attenuation in Ultrasound: In medical imaging, ultrasound waves weaken as they pass through tissues in the body. Denser tissues, such as bone, cause more attenuation compared to softer tissues. Analog and Digital Transmission Page 1 of 14   Dispersion As signal travels through the media, it tends to spread and overlaps. The amount of dispersion depends upon the frequency used. 1. Chromatic Dispersion in Fiber Optic Internet Cables  Example: Imagine sending light through a long fiber optic cable to deliver high-speed internet. Different colors of light (wavelengths) travel at slightly different speeds in the cable. As a result, parts of the light signal can arrive at the receiver at different times, causing the signal to spread out and blur. This makes it harder for the receiver to distinguish the data.  Simplified Explanation: It’s like shining a rainbow of colors through a tube, but when the rainbow reaches the other side, the colors are out of order and overlapping. 2. Modal Dispersion in Home Network Cables  Example: In some types of home internet cables (multimode fiber), light can take multiple paths through the cable. Some paths are shorter, and others are longer. This means parts of the signal arrive at different times, causing data distortion.  Simplified Explanation: It’s like sending several runners through different roads to the same destination. The ones on the short road get there first, and the ones on the long road arrive later, making it hard to know who should be counted first. 3. Group Velocity Dispersion in High-Speed Data Networks  Example: In high-speed data networks, different parts of a signal (like high and low frequencies) travel at slightly different speeds, causing the signal to spread and overlap with others. This can create interference between signals, making the data harder to read.  Simplified Explanation: It’s like having people talking at different speeds in a race. Over time, the fast talkers finish their conversation quickly, but the slow talkers drag behind, mixing up the conversation. 4. Dispersion in Radio Broadcasts  Example: When you listen to a radio broadcast, the signal travels through the atmosphere. If the signal has multiple frequency components, they may travel at slightly different speeds due to atmospheric conditions. This can cause parts of the signal to arrive at different times, distorting the sound.  Simplified Explanation: It’s like sending a message in a bottle, but the wind carries some bottles faster than others. When they arrive, some parts of the message are mixed up or jumbled. 5. Dispersion in Wi-Fi Signals Through Walls  Example: When Wi-Fi signals pass through walls, different frequencies of the signal may slow down or weaken at different rates. This causes parts of the Wi-Fi signal to spread out and lose strength, leading to slower internet speeds or dropped connections. 6. Dispersion in Sound Waves (Echo Effect)  Example: When you shout in a canyon, your voice reflects off different parts of the canyon walls. Because sound waves take different paths, you hear your echo at different times. This is a form of dispersion in sound waves.  Simplified Explanation: It’s like shouting into a room with lots of walls. Some of your voice hits close walls and bounces back fast, while other parts bounce off far walls and take longer to return. 7. Dispersion in Ocean Waves  Example: In the ocean, large waves and small waves travel at different speeds. As they move, the waves can spread out, causing them to lose energy and making it harder to predict where they will end up.  Simplified Explanation: It’s like dropping different-sized pebbles into a pond. The ripples they make start together but move at different speeds, eventually spreading apart. These examples simplify the idea of dispersion, showing how different parts of a signal or wave travel at different speeds, leading to distortion, loss, or spreading of the signal. Analog and Digital Transmission Page 2 of 14   Delay distortion Signals are sent over media with pre-defined speed and frequency. If the signal speed and frequency do not match, there are possibilities that signal reaches destination in arbitrary fashion. In digital media, this is very critical that some bits reach earlier than the previously sent ones. 1. Telephone Call with Poor Sound Quality  Example: During a phone call, if one person’s voice sounds jumbled or out of sync, this can be due to delay distortion. Different frequency components of the voice signal are delayed by different amounts as they travel through telephone lines, causing some parts of the conversation to arrive late, making the voice sound distorted.  Simplified Explanation: It’s like sending a sentence word by word, but some words get stuck in traffic and arrive later than others, making the conversation confusing. 2. Old TV Signal Distortion  Example: On older analog TVs, when receiving a broadcast, parts of the video signal (like colors or brightness) can be delayed differently. This causes the picture to appear fuzzy or have "ghosts," where parts of the image appear slightly after the main image.  Simplified Explanation: It’s like watching a video where the colors show up a little after the shapes, making everything look out of sync. 3. Internet Video Lagging  Example: When streaming a video, if parts of the video or audio are delayed while others play normally, it’s likely due to delay distortion. Different pieces of data (like sound and images) arrive at the computer at different times, causing the audio to lag behind the video or vice versa.  Simplified Explanation: It’s like watching a movie where the sound and picture don’t match, because the sound arrives later than the picture. 4. Data Transmission in Copper Cables  Example: In older copper telephone wires, delay distortion can occur because different frequencies in the signal (used for carrying data) travel at slightly different speeds. This results in parts of the data arriving out of sync, which can lead to errors or slower data transfer rates.  Simplified Explanation: It’s like mailing a package with several parts, but some parts get delayed and arrive out of order, making it hard to put everything together. 5. Wireless Communication Delay (Wi-Fi or Cellular)  Example: When using Wi-Fi or cellular data to send a message or file, delay distortion can cause certain bits of data to arrive at different times. This can result in data errors or make it seem like the internet is slow, even though the connection strength is good.  Simplified Explanation: It’s like sending pieces of a puzzle through the mail, but some pieces arrive later than others, making it hard to see the complete picture until everything is there. 6. Satellite TV or Radio Signal Distortion  Example: When watching satellite TV, delay distortion can happen when signals from different parts of the frequency spectrum travel through the atmosphere at different speeds. This causes portions of the TV signal to be delayed, resulting in poor picture quality or sound that’s out of sync.  Simplified Explanation: It’s like seeing a thunderstorm on TV but hearing the thunder several seconds after the lightning, because the signal got delayed along the way. 7. Musical Instrument Delay in an Online Jam Session  Example: In an online jam session, if one musician’s notes arrive late compared to the others, it could be due to delay distortion. Different frequencies of the musical notes are delayed by different amounts as they travel over the internet, causing the music to sound offbeat.  Simplified Explanation: It’s like playing music together, but some players are a little late because their sound is stuck in a slow-moving line, making the song sound uneven. Analog and Digital Transmission Page 3 of 14  These simple examples show how delay distortion affects the timing of different parts of a signal, making it harder for receivers to interpret or synchronize the information correctly.  Noise Random disturbance or fluctuation in analog or digital signal is said to be Noise in signal, which may distort the actual information being carried. Noise can be characterized in one of the following class: 1. Static on a Radio Station  Example: When you’re listening to a radio station and you hear static or hissing sounds along with the music, this is noise. It happens when unwanted signals from other radio sources or atmospheric conditions mix with the broadcast signal, making the music harder to hear.  Simplified Explanation: It’s like trying to listen to your favorite song while someone crumples paper right next to your ear. 2. Crackling on a Phone Line  Example: During a phone call, if you hear crackling or buzzing sounds, that’s noise. It can be caused by interference from other electronic devices or poor-quality wires in the telephone system, making it difficult to hear the other person clearly.  Simplified Explanation: It’s like having a conversation while there’s loud rustling or banging noises in the background, making it hard to understand what the other person is saying. 3. Grainy Picture on an Old TV  Example: When watching an old analog TV, you might see "snow" or a grainy picture caused by noise. This happens when the TV signal gets mixed with unwanted electrical interference from other devices or environmental factors.  Simplified Explanation: It’s like trying to watch a movie through a shower of confetti, where the picture keeps getting blocked by tiny dots. 4. Wi-Fi Interference from Other Devices  Example: When using Wi-Fi, you might experience slower speeds or dropped connections due to noise from other devices like microwaves, baby monitors, or neighboring Wi-Fi networks. These devices can interfere with your Wi-Fi signal, creating noise that disrupts the connection.  Simplified Explanation: It’s like trying to have a conversation at a party where multiple people are talking at once, and you can’t hear your friend because of the surrounding noise. 5. Buzzing in Audio Recordings  Example: If you’re recording audio and hear a low buzzing or humming sound in the background, that’s noise. It’s often caused by electrical interference from nearby equipment or faulty cables, making the recording sound less clear.  Simplified Explanation: It’s like recording someone’s voice while there’s a constant hum from a refrigerator, making the voice hard to hear. 6. Interference on Walkie-Talkies  Example: When using walkie-talkies, sometimes you’ll hear a high-pitched squeal or static noise along with the voice transmission. This happens due to interference from nearby electronics or because the signal is weak, making communication difficult.  Simplified Explanation: It’s like talking through a walkie-talkie while someone nearby is playing loud screeching noises, making the conversation jumbled. 7. Noise on a Digital Video Call  Example: On a video call, if the picture becomes pixelated and the sound cuts in and out, noise could be affecting the data transmission. This noise may come from poor internet connections or interference from other devices, causing parts of the video and audio to be lost or distorted.  Simplified Explanation: It’s like having a video call while someone throws sand over the camera and interrupts the audio, making the picture blurry and the sound hard to understand. Analog and Digital Transmission Page 4 of 14  8. Hiss in Headphones While Listening to Music  Example: If you hear a constant hiss or background noise when listening to music through headphones, that’s noise. This could be caused by electrical interference in the audio system or poor-quality wiring in the headphones.  Simplified Explanation: It’s like listening to your favorite song, but there’s a low hissing sound, like air escaping, constantly in the background, making it less enjoyable. These examples of noise show how unwanted interference can distort, block, or reduce the clarity of signals in communication systems, making it harder to transmit or receive information accurately. Crosstalk in communication refers to the unwanted interference that occurs when a signal transmitted on one communication channel or circuit leaks into another adjacent channel. This interference can result in the mixing of signals, causing distortion or noise in the affected channels. Crosstalk commonly occurs in communication systems that use cables with closely positioned wires, such as twisted pair cables, where electromagnetic coupling between the wires allows signals to cross over. Common Causes of Crosstalk:  Proximity of wires: Wires placed too closely together can cause electromagnetic interference.  Poor shielding: Insufficient insulation around cables can allow signals to bleed into adjacent cables.  High signal power: Strong signals can more easily induce interference in neighboring wires. Effects of Crosstalk:  Degradation of signal quality  Loss of data integrity in digital communication systems  Interference in voice calls (e.g., hearing parts of another conversation) Crosstalk can be minimized using proper cable shielding, twisted pair designs, and ensuring adequate separation between wires. Transmission Media The media over which the information between two computer systems is sent, called transmission media. Transmission media comes in two forms.  Guided Media All communication wires/cables are guided media, such as UTP, coaxial cables, and fiber Optics. In this media, the sender and receiver are directly connected and the information is send (guided) through it.  Unguided Media Wireless or open air space is said to be unguided media, because there is no connectivity between the sender and receiver. Information is spread over the air, and anyone including the actual recipient may collect the information. Channel Capacity Is the maximum amount of data that can be transmitted over a communication channel (like the internet or a phone line) without errors. It’s the limit on how much information you can send reliably. It depends on numerous factors such as:  Bandwidth is the amount of data that can be transmitted over a network or communication system in a specific amount of time. It’s usually measured in bits per second (bps), like megabits per second (Mbps) or gigabits per second (Gbps). Analog and Digital Transmission Page 5 of 14  Easy Explanation: Think of bandwidth like a highway. The more lanes (higher bandwidth) the highway has, the more cars (data) can travel at the same time. If the highway has only one lane (low bandwidth), traffic (data) will move slowly, but if there are many lanes, more cars can move at once, making the traffic flow faster. So, higher bandwidth means you can send or receive more data faster, which is why a faster internet connection allows you to download files or stream videos more smoothly.  Error Rate is the number of errors that occur when data is transmitted. This happens when bits of data (0s and 1s) get changed or lost due to noise, interference, or weak signals. It’s often measured as bit error rate (BER), which means the number of incorrect bits out of the total bits sent. Easy Explanation: Imagine you’re shouting instructions across a noisy room (the communication channel). The channel capacity is like how much you can shout clearly before the noise drowns you out. If you speak too fast or too much, some instructions (data) might get messed up—that’s the error rate. The noisier the room, the higher the error rate, and the fewer instructions you can send correctly. A lower error rate means more data can get through accurately, while a higher error rate means more mistakes are made.  Encoding: is the process of converting information into a specific format so it can be transmitted efficiently over the channel. Different encoding methods can pack more data into the same amount of space, helping get closer to the channel's capacity. Easy Explanation: Imagine you’re trying to send a message through a pipe (the channel). The channel capacity is the size of the pipe, which limits how much you can send at once. Encoding is like packing your message into smaller, more efficient packages (like folding paper or compressing a file) so you can send more through the pipe without exceeding its limit. Good encoding helps fit more data into the available channel space, allowing you to send information faster and with fewer errors. Data or information can be stored in two ways, analog and digital. For a computer to use the data, it must be in discrete digital form. Similar to data, signals can also be in analog and digital form. To transmit data digitally, it needs to be first converted to digital form. Digital-to-Digital Conversion This section explains how to convert digital data into digital signals. It can be done in two ways, line coding and block coding. For all communications, line coding is necessary whereas block coding is optional. Line Coding The process for converting digital data into digital signal is said to be Line Coding. Digital data is found in binary format. It is represented (stored) internally as series of 1s and 0s. Analog and Digital Transmission Page 6 of 14 Digital signal is denoted by discreet signal, which represents digital data. There are three types of line coding schemes available: Uni-polar Encoding Unipolar encoding schemes use single voltage level to represent data. In this case, to represent binary 1, high voltage is transmitted and to represent 0, no voltage is transmitted. It is also called Unipolar-Non-return-to- zero, because there is no rest condition i.e. it either represents 1 or 0. Polar Encoding Polar encoding scheme uses multiple voltage levels to represent binary values. Polar encodings is available in four types:  Polar Non-Return to Zero (Polar NRZ) It uses two different voltage levels to represent binary values. Generally, positive voltage represents 1 and negative value represents 0. It is also NRZ because there is no rest condition. NRZ scheme has two variants: NRZ-L and NRZ-I. NRZ-L changes voltage level at when a different bit is encountered whereas NRZ-I changes voltage when a 1 is encountered. Analog and Digital Transmission Page 7 of 14   Return to Zero (RZ) Problem with NRZ is that the receiver cannot conclude when a bit ended and when the next bit is started, in case when sender and receiver’s clock are not synchronized. RZ uses three voltage levels, positive voltage to represent 1, negative voltage to represent 0 and zero voltage for none. Signals change during bits not between bits.  Manchester This encoding scheme is a combination of RZ and NRZ-L. Bit time is divided into two halves. It transits in the middle of the bit and changes phase when a different bit is encountered.  Differential Manchester This encoding scheme is a combination of RZ and NRZ-I. It also transit at the middle of the bit but changes phase only when 1 is encountered. Bipolar Encoding Bipolar encoding uses three voltage levels, positive, negative and zero. Zero voltage represents binary 0 and bit 1 is represented by altering positive and negative voltages. Analog and Digital Transmission Page 8 of 14 Block Coding To ensure accuracy of the received data frame redundant bits are used. For example, in even-parity, one parity bit is added to make the count of 1s in the frame even. This way the original number of bits is increased. It is called Block Coding. Block coding is represented by slash notation, mB/nB.Means, m-bit block is substituted with n-bit block where n > m. Block coding involves three steps:  Division,  Substitution  Combination. After block coding is done, it is line coded for transmission. Analog-to-Digital Conversion Microphones create analog voice and camera creates analog videos, which are treated is analog data. To transmit this analog data over digital signals, we need analog to digital conversion. Analog data is a continuous stream of data in the wave form whereas digital data is discrete. To convert analog wave into digital data, we use Pulse Code Modulation (PCM). PCM is one of the most commonly used method to convert analog data into digital form. It involves three steps:  Sampling  Quantization  Encoding. Sampling The analog signal is sampled every T interval. Most important factor in sampling is the rate at which analog signal is sampled. According to Nyquist Theorem, the sampling rate must be at least two times of the highest frequency of the signal. Quantization Sampling yields discrete form of continuous analog signal. Every discrete pattern shows the amplitude of the analog signal at that instance. The quantization is done between the maximum amplitude value and the minimum amplitude value. Quantization is approximation of the instantaneous analog value. Encoding Analog and Digital Transmission Page 9 of 14 In encoding, each approximated value is then converted into binary format. Transmission Modes The transmission mode decides how data is transmitted between two computers.The binary data in the form of 1s and 0s can be sent in two different modes: Parallel and Serial. Parallel Transmission The binary bits are organized in-to groups of fixed length. Both sender and receiver are connected in parallel with the equal number of data lines. Both computers distinguish between high order and low order data lines. The sender sends all the bits at once on all lines.Because the data lines are equal to the number of bits in a group or data frame, a complete group of bits (data frame) is sent in one go. Advantage of Parallel transmission is high speed and disadvantage is the cost of wires, as it is equal to the number of bits sent in parallel. Serial Transmission In serial transmission, bits are sent one after another in a queue manner. Serial transmission requires only one communication channel. Serial transmission can be either asynchronous or synchronous. Asynchronous Serial Transmission It is named so because there’is no importance of timing. Data-bits have specific pattern and they help receiver recognize the start and end data bits.For example, a 0 is prefixed on every data byte and one or more 1s are added at the end. Two continuous data-frames (bytes) may have a gap between them. Analog and Digital Transmission Page 10 of 14 Synchronous Serial Transmission Timing in synchronous transmission has importance as there is no mechanism followed to recognize start and end data bits.There is no pattern or prefix/suffix method. Data bits are sent in burst mode without maintaining gap between bytes (8-bits). Single burst of data bits may contain a number of bytes. Therefore, timing becomes very important. It is up to the receiver to recognize and separate bits into bytes.The advantage of synchronous transmission is high speed, and it has no overhead of extra header and footer bits as in asynchronous transmission. To send the digital data over an analog media, it needs to be converted into analog signal.There can be two cases according to data formatting. Bandpass:The filters are used to filter and pass frequencies of interest. A bandpass is a band of frequencies which can pass the filter. Low-pass: Low-pass is a filter that passes low frequencies signals. When digital data is converted into a bandpass analog signal, it is called digital-to-analog conversion. When low-pass analog signal is converted into bandpass analog signal, it is called analog-to-analog conversion. Digital-to-Analog Conversion When data from one computer is sent to another via some analog carrier, it is first converted into analog signals. Analog signals are modified to reflect digital data. An analog signal is characterized by its amplitude, frequency, and phase. There are three kinds of digital-to- analog conversions:  Amplitude Shift Keying In this conversion technique, the amplitude of analog carrier signal is modified to reflect binary data. When binary data represents digit 1, the amplitude is held; otherwise it is set to 0. Both frequency and phase remain same as in the original carrier signal.  Frequency Shift Keying In this conversion technique, the frequency of the analog carrier signal is modified to reflect binary data. Analog and Digital Transmission Page 11 of 14  This technique uses two frequencies, f1 and f2. One of them, for example f1, is chosen to represent binary digit 1 and the other one is used to represent binary digit 0. Both amplitude and phase of the carrier wave are kept intact.  Phase Shift Keying In this conversion scheme, the phase of the original carrier signal is altered to reflect the binary data. When a new binary symbol is encountered, the phase of the signal is altered. Amplitude and frequency of the original carrier signal is kept intact.  Quadrature Phase Shift Keying QPSK alters the phase to reflect two binary digits at once. This is done in two different phases. The main stream of binary data is divided equally into two sub-streams. The serial data is converted in to parallel in both sub-streams and then each stream is converted to digital signal using NRZ technique. Later, both the digital signals are merged together. Analog-to-Analog Conversion Analog signals are modified to represent analog data. This conversion is also known as Analog Modulation. Analog modulation is required when bandpass is used. Analog to analog conversion can be done in three ways: Analog and Digital Transmission Page 12 of 14   Amplitude Modulation In this modulation, the amplitude of the carrier signal is modified to reflect the analog data. Amplitude modulation is implemented by means of a multiplier. The amplitude of modulating signal (analog data) is multiplied by the amplitude of carrier frequency, which then reflects analog data. The frequency and phase of carrier signal remain unchanged.  Frequency Modulation In this modulation technique, the frequency of the carrier signal is modified to reflect the change in the voltage levels of the modulating signal (analog data). The amplitude and phase of the carrier signal are not altered.  Phase Modulation In the modulation technique, the phase of carrier signal is modulated in order to reflect the change in voltage (amplitude) of analog data signal. Analog and Digital Transmission Page 13 of 14  Phase modulation is practically similar to Frequency Modulation, but in Phase modulation frequency of the carrier signal is not increased. Frequency of carrier is signal is changed (made dense and sparse) to reflect voltage change in the amplitude of modulating signal. References https://www.tutorialspoint.com/data_communication_computer_network/physical_layer_introduction.htm https://www.tutorialspoint.com/data_communication_computer_network/digital_transmission.htm https://www.tutorialspoint.com/data_communication_computer_network/analog_transmission.htm Analog and Digital Transmission Page 14 of 14