History of Data Communication PDF

**HISTORY OF DATA COMMUNICATION** - **1940: Small Step for Man, Great Leap for Communications** **George Stibitz** took networking technology a great leap forward when he sent computing commands over a teletype machine from his model - **1943: Teletype Computation** Stibitz\'...

**HISTORY OF DATA COMMUNICATION** - **1940: Small Step for Man, Great Leap for Communications** **George Stibitz** took networking technology a great leap forward when he sent computing commands over a teletype machine from his model - **1943: Teletype Computation** Stibitz\'s successful telegraph prompted a new method of computation, an **IBM adaptation** of this technology was able to transmit punched cards at a whopping 25 bits per second (bps). - **1948: Teletype Modems to Sage** Teletype communication modems were used to transmit multiple images across the United States to **Semi-automatic Ground Environment (SAGE)** computers. - **1958: American Telephone and Telegraph Bring the Digital Subset** Speed was boosted by over 4 times, sending a new record of 110 bits per second through **American Telephone and Telegraph (AT&T)** computer modems, called **Digital Subsets.** - **1962: AT&T Releases Bell 103 Data Phone** The **first civilian commercial computer modem**, the Bell 103 Data Phone, allowed digital data to be transmitted over regular unconditional telephone lines. - **1962: Intergalactic Computer Network** **J.C.R. Licklider leads the Advanced Research Projects Agency (ARPA**) to create and link a network of computers across the world, effectively known as the **Intergalactic Computer Network.** - **1965: Wide Area Network** The first wide-area computer network is created by **Thomas Marill and Lawrence G. Roberts,** linking PCs across multiple systems. This served as the precursor to the **ARPANET**, a project which **Roberts** would manage. - **1977: The Hayes 80-130A** The first personal computer modem, was designed by **Dennis Hayes and Dale Heatherington.** - **1981: The Hayes Smartmodem** An improved iteration, device offered 300 bits per second speed in an affordable body. It also **enabled users to perform new functions like initializing, hanging up, and auto dialing.** - **Mid 80s: Modems Hit the Fast Lane** **IBM PC clones** dominated the PC market, leading to a new ear of internal **Industry Standard Architecture (ISA).** **Peripheral Component Interconnect (PCI)** modem cards were designed for additional PC compatibility, extending WAN reach. This marked the era of **Broadband Services.** - **1989: The World Wide Web** Consumer demand for more visual imagery, a better web-browsing interface, and more online content prompted **Sir Tim Berners-Lee** to create an **Information Management proposal.** - **Mid 90s: Lower Costs and Faster Speeds** Home broadband entered the market in **1991**, and people all over the world began accessing the Internet using **Berners-Lee\'s World Wide Web.** - **1996: The 56K** **Brent Townshend** created the technology for the first 56K modem, a model which used a bitrate of 56.0/33.06 kilobytes per second. **Local Area Networks (LANs)** started becoming popular in commercial businesses. - **Early 2000s: Analog Out, ISDN, ADSL, and Cable In** **All digital phone lines (ISDN)** surfaced as an alternative to analog. Cable TV modems gathered a great amount of attention. Phone companies soon figured out how to deliver digital data more economically through **Asymmetric Digital Subscriber Lines (ADSL),** boosting speeds over existing telephone copper deployments. - **2002: 3G Arrives** **Commerical third-generation wireless connection (3G)** was launched, offering application services like wide-area wireless voice, mobile Internet (a fascinating feature), video calling, and on-the-go TV. - **Mid 2000s: The Wireless Age Matures** **Broadband Internet** services and wireless access networks quickly became mainstream technology due to the convenience and ease of access. Users no longer required two phone lines to connect to the Internet. File sizes for videos, video games, music, and pictures increased. - **2009: Enter 4G/LTE** **4G and LTE** represented the new generation of cellular standards, satisfying the speeds required by heavy file sizes. The **4G standard set peak speeds at 100 megabits** per second for high-mobility communication and 1 gigabit per second for low mobility.  - **Providing a Better Quality of Experience** Major markets across the world **became saturated with Internet-enabled devices**. Internet penetration rates quickly approached 100%, meaning **everyone had access to the web in various ways**. Speed was still important, but quality of experience, including service activation speeds, was now critical to success. - **2011-2014: How Fast can we Go?** **4G is ubiquitous. Fiber** **optic communications** gained popularity. **10 gigabits per second** was tested while 1 gigabit lines were made available in the United Kingdom and United States. - **2015: Network Function Virtualization -- The Next Evolution** **Fiber becomes commonplace.** Bitrate speeds are at an all-time high. Virtualization enables operators to manipulate modem functions through software, instead of relying on built-on hardware. Speed of service increased steadily.  - **2017 and Beyond** The **fulcrum pivots from human triggered communications to AI triggered communications.** Ultra-low latency high bandwidth applications such as **smart car with collision avoidance or robotic medical procedures.** The fifth generation (5G) opens new opportunities for humans and machines to communicate. **Digital Communication - Analog to Digital** The **communication that occurs in our day-to-day life is in the form of signals**. These signals, such as **sound signals, generally, are analog in nature**. When the communication needs to be established over a distance, then the **analog signals are sent through wire**, **The Necessity of Digitization** The **conventional methods of communication** used analog signals for long distance communications, which suffer from many losses such as **distortion, interference, and other losses including security breach.** The following figure indicates the difference between analog and digital signals. The digital signals consist of **1s** and **0s** which indicate High and Low values respectively. Necessity of Digitization **Advantages of Digital Communication** - The effect of distortion, noise, and interference is much less in digital signals as they are less affected. - Digital circuits are more reliable. - Digital circuits are easy to design and cheaper than analog circuits. - The hardware implementation in digital circuits, is more flexible than analog. - The occurrence of cross-talk is very rare in digital communication. - The signal is un-altered as the pulse needs a high disturbance to alter its properties, which is very difficult. - Signal processing functions such as encryption and compression are employed in digital circuits to maintain the secrecy of the information. - The probability of error occurrence is reduced by employing error detecting and error correcting codes. - Spread spectrum technique is used to avoid signal jamming. - Combining digital signals using Time Division Multiplexing (TDM) is easier than combining analog signals using Frequency Division Multiplexing (FDM). - The configuring process of digital signals is easier than analog signals. - Digital signals can be saved and retrieved more conveniently than analog signals. - Many of the digital circuits have almost common encoding techniques and hence similar devices can be used for a number of purposes. - The capacity of the channel is effectively utilized by digital signals. **Elements of Digital Communication**  1. **Source** The source can be an **analog** signal. **Example**: A Sound signal 2. **Input Transducer** Takes a **physical input and converts it to an electrical signal**. Consists of an **analog to digital** converter where a **digital signal** is needed for further processes, represented by a binary sequence. **Example**: microphone). 3. **Source Encoder** **Compresses** the data into **minimum number of bits**. It removes redundant bits (unnecessary excess bits, i.e., zeroes). 4. **Channel Encoder** Does the **coding for error correction**. During the **transmission** due to the **noise in the channel,** the signal may get altered to avoid this, channel encoder **adds some redundant bits** to the transmitted data. These are the **error correcting bits.** 5. **Digital Modulator** The signal to be transmitted by a carrier. The signal is also **converted to analog from the digital sequence,** in order to make it travel through the **channel or medium.** 6. **Channel** **Allows the analog signal** to transmit from the transmitter **end to the receiver end**. 7. **Digital Demodulator** This is the **first step at the receiver end**. The received signal is **demodulated** as well as converted again from **analog to digital.** 8. **Channel Decoder** After **detecting the sequence, does some error corrections**. distortions which might occur during the transmission, are corrected by adding some redundant bits. This **addition of bits helps in the complete recovery of the original signal**. 9. **Source Decoder** **Recreates the source output.** The **resultant signal is once again digitized** by sampling and quantizing so that the pure digital output is obtained without the loss of information. 10. **Output Transducer** **The last block which converts the signal into the original physical form, which** was at the input of the transmitter. Converts the **electrical signal into physical output** (**Example**: loud speaker). 11. **Output Signal** This is the **output which is produced after the whole process.**  **Example** − The sound signal received. **Pulse Code Modulation** **Modulation** is the process of varying one or more parameters of a carrier signal in accordance with the instantaneous values of the message signal. There are **many modulation techniques,** which are classified according to the type of modulation employed. The digital modulation technique used is **Pulse Code Modulation (PCM)**. A **signal is pulse code** modulated to convert its **analog information into a binary sequence,** i.e., **1s** and **0s**. The output of a **PCM** will resemble a binary sequence. Pulse Code Modulation Instead of a pulse train, PCM produces a series of numbers or digits, and hence this process is called as **digital**. **In Pulse Code Modulation,** the message signal is represented by a **sequence of coded pulses.** This message signal is achieved by representing the signal in discrete form in both **time and amplitude.** **Basic Elements of PCM** The **transmitter section** of a Pulse Code Modulator circuit consists of **Sampling, Quantizing** and **Encoding**, which are performed in the analog-to-digital converter section. The basic operations in the receiver section are **regeneration of impaired signals, decoding,** and **reconstruction** of the quantized pulse train. Following is the **block diagram of PCM which represents the basic elements of both the transmitter and the receiver sections.** 1. **Low Pass Filter** This filter **eliminates the high frequency** components present in the input analog signal which is greater than the highest frequency of the message signal. 2. **Sampler** This is the **technique which helps to collect the sample data at instantaneous values of message signal**. The **sampling rate must be greater than twice the highest frequency** component **W** of the message signal, in accordance with the sampling theorem. 3. **Quantizer** A **process of reducing the excessive bits and confining the data.** The sampled output reduces the redundant bits and compresses the value. 4. **Encoder** The digitization of analog signal is done by the encoder. It designates each quantized level by a binary code. The sampling done here is the sample-and-hold process. These three sections (LPF, Sampler, and Quantizer) will act as an analog to digital converter. Encoding minimizes the bandwidth used. 5. **Regenerative Repeater** This section increases the signal strength. The output of the channel also has one regenerative repeater circuit, to compensate the signal loss and reconstruct the signal, and also to increase its strength. 6. **Decoder** The decoder circuit decodes the pulse coded waveform to reproduce the original signal. This circuit acts as the demodulator. 7. **Reconstruction Filter** After the digital-to-analog conversion is done by the regenerative circuit and the decoder, a low-pass filter is employed, called as the reconstruction filter to get back the original signal. Hence, the Pulse Code Modulator circuit digitizes the given analog signal, codes it and samples it, and then transmits it in an analog form. This whole process is repeated in a reverse pattern to obtain the original signal. **What are Digital Modulation Techniques ?** There are mainly three types in Analog Modulation which are Amplitude Modulation, Frequency Modulation and Phase Modulation. Here the amplitude, frequency and phase of carrier wave changes with respect to amplitude of message signal. Whereas in Digital Modulation a process called as Shift Keying is used. **How do we transmit a bit stream?** Shift Keying means that the amplitude, frequency or phase of the carrier wave is shifted between two or more discrete values rather than varying continuously like Analog Modulation. Binary data requires two discrete levels of amplitude, frequency or phase for modulation called as Binary Shift Keying. A group of bits can be clubbed together to form M-ary Shift Keying. Pause Unmute Pause Unmute There are mainly three types of Digital Modulation techniques. They are : - Amplitude Shift Keying - Frequency Shift Keying - Phase Shift Keying **Amplitude Shift Keying** In [Amplitude Shift Keying (ASK)](https://www.geeksforgeeks.org/amplitude-shift-keying/), each symbol in the message signal gives a unique amplitude to the carrier wave. There are two types of ASK, Binary and M-ary. In Binary ASK, logic 1 is associated with certain amplitude of carrier wave e.g. 12V and logic 0 is associated with different amplitude other than 12V e.g. 0V. In M-ary ASK, a group of log2M bits are considered together rather than 1 bit at a time and the amplitude level is associated with this group of bits. For example, in 16-ary ASK, a group of 4 bits are considered and are given a respective amplitude. Since there are 16 possible 4 bit binary numbers (24), 16 different amplitude levels are required for modulation. If all such amplitudes are created using a single carrier wave, then it is called as coherent ASK. If multiple carrier wave each with different amplitudes are used for modulation then it is called as non-coherent ASK. Amplitude Shift Keying Waveform **Block Diagram of Amplitude Shift Keying** Given Below is the Block Diagram of Amplitude Shift Keying Block Diagram of Amplitude Shift Keying The analog message signal is converted to digital signal using Analog to Digital Converter. This digital signal is then passed to a multiplier which takes two inputs. A sine wave with high frequency is considered as carrier signal and is multiplied with the digital signal. When symbol present in the digital signal m(t) gets multiplied with the carrier Asin(2πft+p) it results in m(t)Asin(2πft+p). When m(t) is high, the carrier wave is passed as it is. But when m(t) is logic 0, then the result of multiplication is 0. Hence ASK wave is generated. However this ASK wave contains abrupt changes in amplitude which causes unnecessary high bandwidth usage. Hence this signal is passed through Band Pass Filter which limits the bandwidth usage. For demodulating, the ASK wave is passed through a multiplier again where the carrier wave is multiplied again which results in m(t)Asin2(2πft+p). This signal is passed through Low Pass Filter where the original digital message is received. This digital signal is converted to analog wave using Digital to Analog Converter. **Frequency Shift Keying** In Frequency Shift Keying (FSK), each symbol in the message signal gives a unique frequency to the carrier wave. There are two types of FSK, Binary and M-ary. In Binary FSK, logic 1 is associated with certain frequency of carrier wave e.g. 50MHz and logic 0 is associated with different frequency other than 50MHz e.g. 25MHz. In M-ary FSK, a group of log2M bits are considered together rather than 1 bit at a time and the frequency is associated with this group of bits. For example, in 16-ary FSK, a group of 4 bits are considered and are given a respective frequency. Since there are 16 possible 4 bit binary numbers (24), 16 different frequencies are required for [modulation](https://www.geeksforgeeks.org/what-is-modulation/). If all such frequencies are created using a single carrier wave, then it is called as coherent FSK. If multiple carrier wave each with different frequencies are used for modulation then it is called as non-coherent FSK. Frequency Shift Keying Waveform **Block Diagram of Frequency Shift Keying** Given Below is the Block Diagram of Frequency Shift Keying Block Diagram of Frequency Shift Keying The analog message signal is converted to digital signal using [Analog to Digital Converter](https://www.geeksforgeeks.org/analog-to-digital-conversion/). This digital signal is then passed to two multipliers which takes two inputs each. A sine wave with frequency f1 is considered as carrier signal for logic 1 and a sine wave with frequency f2 is considered as carrier signal for logic 0. These carrier waves are multiplied with the digital message signal. When logic 1 present in the digital signal gets multiplied with the carrier Asin(2πf1t+p) it results in Asin(2πf1t+p) only since the other multiplier gets logic 0 as input since it is passed through a [NOT gate](https://www.geeksforgeeks.org/not-gate/). When logic 0 present in the digital signal gets multiplied with the carrier Asin(2πf2t+p) it results in Asin(2πf2t+p) only since the multiplier gets logic 1 as input since it is passed through a NOT gate. Both this signals are added to form FSK wave A\[sin(2πf1t+p)+sin(2πf2t+p)\]. However this FSK wave contains abrupt changes in frequency which causes unnecessary high bandwidth usage. Hence this signal is passed through Band Pass Filter which limits the bandwidth usage. For demodulating, the FSK wave is passed through two multipliers again where their respective carrier waves are multiplied again. This signal is passed through two Band Pass Filters out of which the top BPF allows f1 frequency to pass if logic is 1 and the bottom allows f2 frequency to pass if logic is 0. The output of both BPF is compared with each other where the output of the comparator is high if output of BPF1 is greater than output of BPF2 and is low if output of BPF2 is greater than output of BPF1. Hence a digital signal is received at the output of the comparator. This digital signal is converted to analog wave using [Digital to Analog Converter](https://www.geeksforgeeks.org/digital-to-analog-conversion/). **Phase Shift Keying** In Phase Shift Keying (PSK), each symbol in the message signal gives a unique phase shift to the carrier wave. There are two types of PSK, Binary and M-ary. In Binary PSK, logic 1 is associated with certain phase shift of carrier wave e.g. 90° and logic 0 is associated with different phase shift other than 90° e.g. 0°. In M-ary PSK, a group of log2M bits are considered together rather than 1 bit at a time and the phase shift is associated with this group of bits. For example, in 16-ary PSK, a group of 4 bits are considered and are given a respective phase shift. Since there are 16 possible 4 bit binary numbers (24), 16 different phase shifts are required for modulation. If all such phase shifts are created using a single carrier wave, then it is called as coherent PSK. If multiple carrier wave each with different phase shifts are used for modulation then it is called as non-coherent PSK. Phase Shift Keying Waveform **Block Diagram of Phase Shift Keying** Given Below is the Block Diagram of Phase Shift Keying Block Diagram of Phase Shift Keying The analog message signal is converted to digital signal using Analog to Digital Converter. This digital signal is then passed to two multipliers which takes two inputs each. A sine wave with phase shift p1 is considered as carrier signal for logic 1 and a sine wave with phase shift p2 is considered as carrier signal for logic 0. These carrier waves are multiplied with the digital message signal. When logic 1 present in the digital signal gets multiplied with the carrier Asin(2πft+p1) it results in Asin(2πft+p1) only since the other multiplier gets logic 0 as input since it is passed through a NOT gate. When logic 0 present in the digital signal gets multiplied with the carrier Asin(2πft+p2) it results in Asin(2πft+p2) only since the multiplier gets logic 1 as input since it is passed through a NOT gate. Both this signals are added to form PSK wave A\[sin(2πft+p1)+sin(2πft+p2)\]. However this PSK wave contains abrupt changes in phases which causes unnecessary high[ bandwidth](https://www.geeksforgeeks.org/what-is-bandwidth-definition-working-importance-uses/) usage. Hence this signal is passed through Band Pass Filter which limits the bandwidth usage. For demodulating, the PSK wave is passed through two multipliers again where their respective carrier waves are multiplied again. This signal is passed through two Band Pass Filters out of which the top BPF allows the signal with phase shift p1 to pass if logic is 1 and the bottom allows the signal with phase shift p2 to pass if logic is 0. The output of both BPF is compared with each other where the output of the comparator is high if output of BPF1 is greater than output of BPF2 and is low if output of BPF2 is greater than output of BPF1. Hence a digital signal is received at the output of the comparator. This digital signal is converted to analog wave using Digital to Analog Converter. **M-ary Encoding** It Involves transmitting of more than two bits simultaneously on the same signal that can help to save bandwidth by efficiently utilizing the available frequency spectrum. - **M-ary ASK (Amplitude Shift Keying)**:It is also known as M-ASK or M-FSK,In this multiple amplitude levels are used to represent several different combinations of bits.Each amplitude level represents a specific pattern of bits which allows transmission of multiple bits in each signaling interval. - **M-ary FSK (Frequency Shift Keying)**:In this the carrier frequency is shifted to represent different symbols.It is Similar to M-ary ASK as it allows transmission of multiple bits per symbol by using multiple frequency shifts. - **M-ary PSK (Phase Shift Keying)**:It involves shifting the phase of the carrier wave to represent different symbols.By changing the phase of the carrier wave multiple symbols can be represented each corresponding to a unique bit pattern. **Applications of Digital Modulation Techniques** - Military Communication Systems, where security and accuracy of the signal plays a crucial role. Digital Modulation can provide confidential and error free communication. - Mobile Communication Systems, where the number of users are daily increasing and Digital Modulation can provide high capacity and less interference. Long distance communication can be easily done with the help of Digital Modulation. - Digital Broadcasting, Digital modulation techniques are used in digital broadcasting standards such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Terrestrial Digital Multimedia Broadcasting (T-DMB) for transmitting audio, video, and data content efficiently. - Radar Systems, In radar systems, digital modulation techniques like phase modulation (PM) and frequency modulation (FM) are used for transmitting radar pulses and modulating radar signals to detect and track objects accurately in various applications such as air traffic control, weather monitoring, and military surveillance. **Advantages of Digital Modulation Techniques** - **High Immunity to noise:** Since the modulated wave consist of finite collection of amplitude/frequency or phase shifts, changes occurred in above parameters due to noise, distortion and dispersion is less as compared to difference in amplitude/frequency or phase shift between two distinct symbols. For e.g. An Amplitude Shift Keyed wave will have higher noise tolerance since the interference cannot bring 0V i.e. logic 0 to 12V which is representing logic 1. Hence the demodulated wave at the receiver highly represents the input message signal applied at the transmitter. - **High Security: **Since the message signal is digital in Digital Modulation, encryption techniques can be employed to improve authenticity, confidentiality and integrity of data. After encrypting the digital message we can proceed with modulation process for transmitting the message. Such features are not available in Analog Modulation as message signal is of analog type. - **Efficient Usage of Bandwidth: **By using compression techniques we can reduce the number of bits of the message signal without affecting the data content in it. Hence if we compress the message signal and modulate it then it will take less bandwidth as compared to modulating the original message signal. - **High Accuracy of Data: **With the help of error detection and error correction techniques we can find the presence of errors in the demodulated wave at the receiver side and correct it accordingly to get the original message signal. - **High Capacity: **We can use Time Division Multiple Access (TDMA) instead of Frequency Division Multiple Access (FDMA) in case of Digital Modulation as frequency or spectrum is limited and it is not possible to assign certain frequency per user as number of users is quite high compared to available channels. Hence capacity can be increased by letting the users access the channel for certain time period one after the other. **Disadvantages of Digital Modulation Techniques** - **Additional Circuitry: **Analog to Digital Converter (ADC) must be connected before modulating the signal to convert analog message signal to digital signal at the transmitter side and Digital to Analog Converter (DAC) must be connected after demodulating the signal to convert digital signal back to analog wave. This can increase the cost of communication system. - **Synchronization:** For proper detection and demodulation of received signal synchronization is required. This requires oscillator circuitry which must be present at both transmitter and receiver. - **High Power Consumption:** While Shift Keying Modulation may consume less power than Analog Modulation, it still consumes more power as compared to Pulse Modulation techniques such as PAM, PWM and PPM where the message signal is analog but the carrier is rectangular wave. **Information theory** is a mathematical approach to the study of coding of information along with the quantification, storage, and communication of information. Conditions of Occurrence of Events If we consider an event, there are three conditions of occurrence. - If the event has not occurred, there is a condition of **uncertainty**. - If the event has just occurred, there is a condition of **surprise**. - If the event has occurred, a time back, there is a condition of having some **information**. These three events occur at different times. The difference in these conditions help us gain knowledge on the probabilities of the occurrence of events. Entropy When we observe the possibilities of the occurrence of an event, how surprising or uncertain it would be, it means that we are trying to have an idea on the average content of the information from the source of the event. **Entropy** can be defined as a measure of the average information content per source symbol. **Claude Shannon**, the "father of the Information Theory", provided a formula for it as − H=−∑ipilogbpiH=−∑ipilogb⁡pi Where **p~i~** is the probability of the occurrence of character number **i** from a given stream of characters and **b** is the base of the algorithm used. Hence, this is also called as **Shannon's Entropy**. The amount of uncertainty remaining about the channel input after observing the channel output, is called as **Conditional Entropy**. It is denoted by H(x∣y)H(x∣y) Ezoic Mutual Information Let us consider a channel whose output is **Y** and input is **X** Let the entropy for prior uncertainty be **X = H(x)** (This is assumed before the input is applied) To know about the uncertainty of the output, after the input is applied, let us consider Conditional Entropy, given that **Y = y~k~** H(x∣yk)=∑j=0j−1p(xj∣yk)log2\[1p(xj∣yk)\]H(x∣yk)=∑j=0j−1p(xj∣yk)log2⁡\[1p(xj∣yk)\] This is a random variable for H(X∣y=y0)\...\...\...\...\...H(X∣y=yk)H(X∣y=y0)\...\...\...\...\...H(X∣y=yk) with probabilities p(y0)\...\...\...\...p(yk−1)p(y0)\...\...\...\...p(yk−1) respectively. The mean value of H(X∣y=yk)H(X∣y=yk) for output alphabet **y** is − H(X∣Y)=∑k=0k−1H(X∣y=yk)p(yk)H(X∣Y)=∑k=0k−1H(X∣y=yk)p(yk) =∑k=0k−1∑j=0j−1p(xj∣yk)p(yk)log2\[1p(xj∣yk)\]=∑k=0k−1∑j=0j−1p(xj∣yk)p(yk)log2⁡\[1p(xj∣yk)\] =∑k=0k−1∑j=0j−1p(xj,yk)log2\[1p(xj∣yk)\]=∑k=0k−1∑j=0j−1p(xj,yk)log2⁡\[1p(xj∣yk)\] Now, considering both the uncertainty conditions (before and after applying the inputs), we come to know that the difference, i.e. H(x)−H(x∣y)H(x)−H(x∣y) must represent the uncertainty about the channel input that is resolved by observing the channel output. This is called as the **Mutual Information** of the channel. Denoting the Mutual Information as I(x;y)I(x;y), we can write the whole thing in an equation, as follows I(x;y)=H(x)−H(x∣y)I(x;y)=H(x)−H(x∣y) Hence, this is the equational representation of Mutual Information. Explore our **latest online courses** and learn new skills at your own pace. Enroll and become a certified expert to boost your career. Properties of Mutual information These are the properties of Mutual information. - Mutual information of a channel is symmetric. I(x;y)=I(y;x)I(x;y)=I(y;x) - Mutual information is non-negative. I(x;y)≥0I(x;y)≥0 - Mutual information can be expressed in terms of entropy of the channel output. I(x;y)=H(y)−H(y∣x)I(x;y)=H(y)−H(y∣x) Where H(y∣x)H(y∣x) is a conditional entropy - Mutual information of a channel is related to the joint entropy of the channel input and the channel output. I(x;y)=H(x)+H(y)−H(x,y)I(x;y)=H(x)+H(y)−H(x,y) Where the joint entropy H(x,y)H(x,y) is defined by H(x,y)=∑j=0j−1∑k=0k−1p(xj,yk)log2(1p(xi,yk))H(x,y)=∑j=0j−1∑k=0k−1p(xj,yk)log2⁡(1p(xi,yk)) Channel Capacity We have so far discussed mutual information. The maximum average mutual information, in an instant of a signaling interval, when transmitted by a discrete memoryless channel, the probabilities of the rate of maximum reliable transmission of data, can be understood as the **channel capacity**. It is denoted by **C** and is measured in **bits per channel** use. Discrete Memoryless Source A source from which the data is being emitted at successive intervals, which is independent of previous values, can be termed as **discrete memoryless source**. This source is discrete as it is not considered for a continuous time interval, but at discrete time intervals. This source is memoryless as it is fresh at each instant of time, without considering the previous values. **Types of Transmission Media** Last Updated : 23 Oct, 2024 - - - Transmission media refers to the physical medium through which data is transmitted from one device to another within a network. These medium can be wired or wireless. The choice of medium depends on factors like distance, speed, and interference. In this article, we will discuss the transmission media. In this article we will see types of transmission media in detail. **What is Transmission Media in Computer Networks?** A transmission medium is a physical path between the transmitter and the receiver i.e. it is the channel through which data is sent from one device to another. Transmission Media is broadly classified into the following types:  *Types of Transmission Media* **1. Guided Media** [Guided Media ](https://www.geeksforgeeks.org/wired-communication-media/)is also referred to as Wired or Bounded transmission media. Signals being transmitted are directed and confined in a narrow pathway by using physical links.\ Features: - High Speed - Secure - Used for comparatively shorter distances There are 3 major types of Guided Media: **Twisted Pair Cable** It consists of 2 separately insulated conductor wires wound about each other. Generally, several such pairs are bundled together in a protective sheath. They are the most widely used Transmission Media. [Twisted Pair ](https://www.geeksforgeeks.org/twisted-pair-cable/)is of two types: - **Unshielded Twisted Pair (UTP): **[UTP](https://www.geeksforgeeks.org/what-is-utpunshielded-twisted-pair/) consists of two insulated copper wires twisted around one another. This type of cable has the ability to block interference and does not depend on a physical shield for this purpose. It is used for telephonic applications. Unshielded Twisted Pair *Unshielded Twisted Pair* **Advantages of Unshielded Twisted Pair** - Least expensive - Easy to install - High-speed capacity **Disadvantages of Unshielded Twisted Pair** - Lower capacity and performance in comparison to STP - Short distance transmission due to attenuation  *Shielded Twisted Pair* **Shielded Twisted Pair (STP): **[Shielded Twisted Pair (STP)](https://www.geeksforgeeks.org/what-is-stpshielded-twisted-pair/) cable consists of a special jacket (a copper braid covering or a foil shield) to block external interference. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines. **Advantages of Shielded Twisted Pair** - Better performance at a higher data rate in comparison to UTP - Eliminates crosstalk - Comparatively faster **Disadvantages of Shielded Twisted Pair** - Comparatively difficult to install and manufacture - More expensive - Bulky **Coaxial Cable** Coaxial cable has an outer plastic covering containing an insulation layer made of PVC or Teflon and 2 parallel conductors each having a separate insulated protection cover. The [coaxial cable ](https://www.geeksforgeeks.org/what-is-coaxial-cable/)transmits information in two modes: Baseband mode(dedicated cable bandwidth) and Broadband mode(cable bandwidth is split into separate ranges). Cable TVs and analog television networks widely use Coaxial cables. Coaxial Cable **Advantages of Coaxial Cable** - Coaxial cables has high [bandwidth](https://www.geeksforgeeks.org/what-is-bandwidth-definition-working-importance-uses/). - It is easy to install. - Coaxial cables are more reliable and durable. - Less affected by noise or cross-talk or electromagnetic inference. - Coaxial cables support multiple channels **Disadvantages of Coaxial Cable** - Coaxial cables are expensive. - The coaxial cable must be grounded in order to prevent any crosstalk. - As a Coaxial cable has multiple layers it is very bulky. - There is a chance of breaking the coaxial cable and attaching a "t-joint" by hackers, this compromises the security of the data. **Optical Fiber Cable** [Optical Fibre Cable ](https://www.geeksforgeeks.org/optical-fibre-cable/)uses the concept of refraction of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the coating. It is used for the transmission of large volumes of data. The cable can be unidirectional or bidirectional. The [WDM (Wavelength Division Multiplexer) ](https://www.geeksforgeeks.org/difference-between-wdm-and-dwdm/)supports two modes, namely unidirectional and bidirectional mode.  **Advantages of Optical Fibre Cable** - Increased capacity and bandwidth - Lightweight - Less signal attenuation - Immunity to electromagnetic interference - Resistance to corrosive materials **Disadvantages of Optical Fibre Cable** - Difficult to install and maintain - High cost **Applications of Optical Fibre Cable** - **Medical Purpose: **Used in several types of medical instruments. - **Defence Purpose: **Used in transmission of data in aerospace. - **For Communication: **This is largely used in formation of internet cables. - **Industrial Purpose: **Used for lighting purposes and safety measures in designing the interior and exterior of automobiles. **Stripline** [Stripline ](https://www.geeksforgeeks.org/symmetric-stripline/)is a transverse electromagnetic (TEM) transmission line medium invented by Robert M. Barrett of the Air Force Cambridge Research Centre in the 1950s. Stripline is the earliest form of the planar transmission line. It uses a conducting material to transmit high-frequency waves it is also called a waveguide. This conducting material is sandwiched between two layers of the ground plane which are usually shorted to provide EMI immunity. **Microstripline** A **microstripline** is a type of transmission media used to carry high-frequency signals, commonly found in microwave and radio frequency circuits. It consists of a flat, narrow conducting strip (usually made of metal) placed on top of a dielectric material (an insulating layer), with a metal ground plane on the other side. **2. Unguided Media** It is also referred to as Wireless or [Unbounded transmission media ](https://www.geeksforgeeks.org/unguided-media/). No physical medium is required for the transmission of electromagnetic signals. **Features of Unguided Media** - The signal is broadcasted through air - Less Secure - Used for larger distances There are 3 types of Signals transmitted through unguided media: **Radio Waves** [Radio waves ](https://www.geeksforgeeks.org/radio-waves/)are easy to generate and can penetrate through buildings. The sending and receiving antennas need not be aligned. Frequency Range:3KHz -- 1GHz. AM and FM radios and cordless phones use Radio waves for transmission. radiowave *Radiowave* **Microwaves** It is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna. Frequency Range:1GHz -- 300GHz. [**Micro waves **](https://www.geeksforgeeks.org/applications-of-microwaves/)are majorly used for mobile phone communication and television distribution.  **Infrared** [Infrared waves ](https://www.geeksforgeeks.org/infrared-light-for-transmission/)are used for very short distance communication. They cannot penetrate through obstacles. This prevents interference between systems. Frequency Range:300GHz -- 400THz. It is used in TV remotes, wireless mouse, keyboard, printer, etc. Infrared **Difference Between Radio Waves, Micro Waves, and Infrared Waves** **Basis** **Radiowave** **Microwave** **Infrared wave** ------------------------ ----------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------ **Direction** These are omni-directional in nature. These are unidirectional in nature. These are unidirectional in nature. **Penetration** At low frequency, they can penetrate through solid objects and walls but high frequency they bounce off the obstacle. At low frequency, they can penetrate through solid objects and walls. at high frequency, they cannot penetrate. They cannot penetrate through any solid object and walls. **Frequency range** Frequency range: 3 KHz to 1GHz. Frequency range: 1 GHz to 300 GHz. Frequency range: 300 GHz to 400 GHz. **Security** These offers poor security. These offers medium security. These offers high security. **Attenuation** Attenuation is high. Attenuation is variable. Attenuation is low. **Government License** Some frequencies in the radio-waves require government license to use these. Some frequencies in the microwaves require government license to use these. There is no need of government license to use these waves. **Usage Cost** Setup and usage Cost is moderate. Setup and usage Cost is high. Usage Cost is very less. **Communication** These are used in long distance communication. These are used in long distance communication. These are not used in long distance communication. **Causes of Transmission Impairment** Transmission impairment refers to the loss or distortion of signals during data transmission, leading to errors or reduced quality in communication. Common causes include signal distortion, attenuation, and noise all of which can affect the clarity and reliability of transmitted data.  *Transmission Impairment* - **Attenuation: **It means loss of energy. The strength of signal decreases with increasing distance which causes loss of energy in overcoming resistance of medium. This is also known as attenuated signal. [Amplifiers ](https://www.geeksforgeeks.org/power-amplifier/)are used to amplify the attenuated signal which gives the original signal back and compensate for this loss. - **Distortion: **It means changes in the form or shape of the signal. This is generally seen in composite signals made up with different frequencies. Each frequency component has its own propagation speed travelling through a medium. And thats why it delay in arriving at the final destination Every component arrive at different time which leads to distortion. Therefore, they have different phases at receiver end from what they had at senders end. - **Noise: **The random or unwanted signal that mixes up with the original signal is called noise. There are several types of noise such as induced noise, crosstalk noise, thermal noise and impulse noise which may corrupt the signal. **Factors Considered for Designing the Transmission Media** - **Bandwidth: **Assuming all other conditions remain constant, the greater a medium's bandwidth, the faster a signal's data transmission rate. - **Transmission Impairment **: [Transmission Impairment ](https://www.geeksforgeeks.org/transmission-impairment-in-data-communication/)occurs when the received signal differs from the transmitted signal. Signal quality will be impacted as a result of transmission impairment. - **Interference: **Interference is defined as the process of disturbing a signal as it travels over a communication medium with the addition of an undesired signal. **Applications of Transmission Media in Computer Networks** Transmission media in computer networks are used to connect devices and transfer data. Here are some common applications: **Transmission Media** **Application** ----------------------------------- ---------------------------------------------------------- **Unshielded Twisted Pair (UTP)** Local Area Networks (LAN), telephones **Shielded Twisted Pair (STP)** Industrial networks, environments with high interference **Optical Fiber Cable** Long-distance communication, internet backbones **Coaxial Cable** Cable TV, broadband internet, CCTV **Stripline** Printed Circuit Boards (PCBs), microwave circuits **Microstripline** Antennas, satellite communication, RF circuits **Radio** Wireless communication, AM/FM radio, mobile phones **Infrared** Remote controls, short-range communication **Microwave** Satellite communication, radar, long-distance links