Computer Network Media (PDF)

the computer network is the connection of two or more computers or communication devices connected by transmission **media** and guided by a set of rules for communication purposes that allow users to communicate with each other and share applications and data. The fundamental components of a networ...

the computer network is the connection of two or more computers or communication devices connected by transmission **media** and guided by a set of rules for communication purposes that allow users to communicate with each other and share applications and data. The fundamental components of a network are devices, media, messages and protocols. **Network Media (Transmission Media)** For data to be transmitted from one location to another, a physical pathway or medium must be used. These pathways are called transmissions media and can be either physical or wireless. The physical transmission use wire, cable, and other tangible materials; wireless transmission media send communications signals through the air or space. The physical transmission media are generally referred to as cable media (example, twisted pair wire, coaxial cable, and fiber optic cable). Wireless media include cellular radio, microwave transmission, satellite transmission, radio and infrared media. Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are: ƒ Copper cables ƒ Glass or plastic fibers (fiber optic cable) ƒ Wireless transmission The signal encoding that must occur for the message to be transmitted is different for each media type. On metallic wires, the data is encoded into electrical impulses that match specific patterns. Fiber optic transmissions rely on pulses of light, within either infrared or visible light ranges or in wireless transmission, and patterns of electromagnetic waves depict the various bit values. Different types of network media have different features and benefits. All network media do not have the same characteristics and are appropriate for the same purpose Signal is an electric or electromagnetic form of data that passes over transmission media. A wire is a long thin piece of metal that is used to fasten things or to carry electric current. **Guided (Wired) Media** **Guided media** are those that provide a conduit from one device to another. These include **twisted-pair cable, coaxial cable and fiber-optic cable**. A signal traveling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cables use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light. **Twisted-pair Cable** A twisted pair consists of two conductors (normally copper), each with its plastic insulation, twisted together.One of the wires is used to carry signals to the receiver and the other is used only as a ground reference. In addition to the signal sent by the sender on one of the wires, interference (noise) and crosstalk may affect both wires and create unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the same on both wires because they are at different locations relative to the noise or crosstalk sources (for example, one is closer and the other is farther). This results in a difference at the receiver. By twisting the pairs, a balance is maintained. For example, suppose in one twist, one wire is closer to the noise source and the other is farther; in the next twist, the reverse is true. The twisting makes it probable that both wires are equally affected by external influences (noise or crosstalk). Fundamentally, twisted pairs are classified as **unshielded twisted-pair (UTP)** and **shielded twisted-pair (STP).** **Unshielded Twisted-Pair (UTP)** Unshielded twisted-pair **(UTP)** is the most common form of network cable. This cable format is used for the Ethernet wiring standards which are managed by the **Institute of Electrical and Electronics Engineers (IEEE).** These wiring standards are referred by **code 802.3**. The Ethernet standards include specifications of cable configurations and the types of connectors used to plug cables into devices. What we conventionally know as a network cable is an **802.3** specified cable for Ethernet networks. This type of cable, which is shown in Figure 2.5, can block interference and does not depend on a physical shield for this purpose. In modern networks, UTP cables are considered in different categories starting from cat1 to cat7 and so on. **UTP Cable Connectors** The most common UTP connector is **RJ45.** RJ stands for registered jack, implying that the connector follows a standard borrowed from the telephone industry, as shown in Figure 2.6. The RJ45 is a keyed connector, meaning the connector can be inserted in only one way. UTP cabling, terminated with **RJ45** connectors, is a common copper-based medium for interconnecting network devices such as computers with intermediate devices like routers and network switches. UTP cables are wired according to different wiring conventions. The individual wires in the cable have to be connected in different orders to different sets of pins in the RJ45 connectors. Ethernet straight-through and Ethernet crossover are the main cable types that are obtained by using specific wiring conventions. The straight-through is the most common type and is used to connect computers to hubs or switches (connect different network devices). They are most likely what you will find when you go to your local computer laboratory. Crossover Ethernet cable is more commonly used to connect a computer to a computer (connect similar network devices) and may be a little harder to find since they are not used nearly as much as a straight-through Ethernet cable. When electromagnetic signals are conducted on copper wires that are nearby (such as inside a cable), some electromagnetic interference occurs. This interference is called **crosstalk**. Twisting two wires together as a pair minimizes such interference and also provides some protection against interference from outside sources. Unshielded twisted pair is subject to external electromagnetic interference, including interference from nearby twisted pairs and noise generated in the environment. In an environment with several sources of potential interference (for example, electric motors, wireless devices and radio frequency (RF) transmitters), a ***shielded twisted-pair (STP***) may be a preferred solution. **Shielded Twisted-Pair (STP)** This type of cable, consists of a special jacket to block external interference. It is used in fast-data-rate Ethernet and voice and data channels of telephone lines. Shielded twisted-pair (STP) cable combines the techniques of cancellation and twisting of wires with shielding. Each pair of wires is wrapped in metallic foil to further shield the wires from noise. The four pairs of wires are then wrapped in an overall metallic braid or foil. STP reduces electrical noise from the cable (crosstalk) and outside the cable (EMI and RFI). RJ45 stands for Registered Jack 45. Electromagnetic (EM) waves are waves that are created as a result of vibrations between electric and magnetic fields. In other words, EM waves are composed of oscillating magnetic and electric fields. RF is short for radiofrequency. RF is any frequency within the electromagnetic spectrum which is associated with radio wave propagation. When an RF current is supplied to an antenna, an electromagnetic field is created and then able to travel or propagate through space. **Coaxial Cable** Coaxial cable (or coax), carries signals of higher frequency ranges than those in twisted pair cable in part because the two media are constructed quite differently. Instead of having two wires, coax has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath which is, in turn, encased in an outer conductor of metal foil, a combination of the two. The outer metallic wrapping serves both as a shield against noise and the second conductor which completes the circuit. This outer conductor is also enclosed in an insulating sheath and the whole cable is protected by a plastic cover. Coaxial cables are available in a variety of thicknesses, with two primary physical types: thick coaxial cable and thin coaxial cable, Thick coaxial cable ranges in size from approximately 6 to 18 mm (1/4 to 3/4 inch) in diameter. The thin coaxial cable is approximately 4 mm (less than 1/4 inch) in diameter. Compared to a thick coaxial cable which typically carries broadband signals, a thin coaxial cable has limited noise isolation and typically carries baseband signals. Thick coaxial cable has better noise immunity and is generally used for the transmission of analog data such as single or multiple video channels. **Coaxial Cable Connectors** To connect coaxial cables to devices, we need coaxial connectors. The most common type of connector used today is the **Bayonet Neill-Concelman** (**BNC**) connector. Figure 2.11 shows three popular types of these connectors: the BNC connector, the BNC T connector, and the BNC terminator. **Ethernet** is the traditional technology for connecting devices in a wired local area network (LAN) or wide area network (WAN). **Unshielded twisted-pair (UTP)** is a ubiquitous type of copper cabling used in telephone wiring and local area networks (LANs). There are different types of UTP cables - identified with the prefix CAT, as in category - each supporting a different amount of bandwidth. Coax, short for coaxial, is a type of cable used to **transmit data**, **the internet, video and voice communications.** **Electromagnetic** is used to describe the **electrical and magnetic** forces or effects produced by an electric current. **Fiber-optic Cable** Fiber-optic cabling uses either glass or plastic fibers to guide light impulses, Figure 2.12, from source to destination. The bits are encoded on the fiber as **light impulses**. Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings due to its immunity to the effects of moisture and lighting. Fiber optic cable can transmit signals over much longer distances than coaxial and twisted pairs. It can also carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. There are two common types of fiber cable: single mode and multimode cables. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. The single mode cable can provide more distance, but it is more expensive. **Fiber-optic Cable Connectors** There are three types of connectors for fiber-optic cables, as shown in Figure 2.13. These are subscriber channel (SC), straight-tip (ST) and Mechanical Transfer Registered Jack (MT-RJ) connectors. The **subscriber channel** (**SC) connector** is used for cable TV. It uses a push/pull locking system. The **straight-tip (ST**) connector is used for connecting cables to networking devices. It uses a bayonet locking system and is more reliable than SC**. MT-RJ** is a connector that is the same size as **RJ45.** **Unguided (Wireless) Media** Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as **wireless communication**. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. Unguided signals can travel from a given source to its destination in several ways: ground propagation, sky propagation and line-of-sight propagation. In-ground **propagation**, radio waves travel through the lowest portion of the atmosphere, hugging the earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. Distance depends on the amount of power in the signal. The greater the power, the greater the distance will be. In **sky propagation**, higher-frequency radio waves radiate upward into the ionosphere (the layer of the atmosphere where particles exist as ions) where they are reflected on earth. This type of transmission allows for greater distances with lower output power. In **line-of-sight propagation**, very high-frequency signals are transmitted in straight lines directly from antenna to antenna. Antennas must be directional, facing each other and either tall enough or close enough together not to be affected by the curvature of the earth. Line-of-sight propagation is tricky because radio transmissions cannot be completely focused. **a. Radio Waves** Although there is no clear-cut demarcation between radio waves and microwaves, electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves; waves ranging in frequencies between 1 and 300 GHz are called microwaves. However, the behavior of the waves, rather than the frequencies, is a better criterion for classification. Radio waves, for most parts, are omnidirectional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna sends waves that can be received by any receiving antenna. The omnidirectional property has a disadvantage too. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signals using the same frequency or band. Radio waves, particularly those that propagate in **the sky mode**, can travel long distances. This makes radio waves a good candidate for long-distance broadcasting such as **AM radio**. **Omnidirectional Antenna** Radio waves use omnidirectional antennas that send out signals in all directions. Based on the wavelength, strength and purpose of transmission, we can have several types of antennas. The omnidirectional characteristics of radio waves make them useful for multicasting, in which there is one sender but many receivers. **AM and FM radio, television, maritime radio, cordless phones** and **paging** are examples of multicasting. **b. Microwaves** **A microwave** is a line-of-sight wireless communication technology that uses high-frequency beams of radio waves to provide high-speed wireless connections that can send and receive voice, video and data information. Microwaves are unidirectional. When an antenna transmits microwaves, it can be narrowly focused. This means that the sending and the receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas. **Unidirectional Antenna** Microwaves need unidirectional antennas that send out signals in one direction. Two types of antennas are used for microwave communications: parabolic dish and horn. A **parabolic dish antenna** is based on the geometry of the parabola where every line is parallel to the line of symmetry (line of sight). the curve at angles such that all the lines intersect in a common point called the focus. The parabolic dish works as a funnel, catching a wide range of waves and directing them to a common point. More of the signal is recovered in this way than a single-point receiver. In microwave communications, line-of-sight devices must be placed in relatively high locations. Information is converted to a microwave signal, sent through the air to a receiver, and recovered. A **horn antenna** looks like a gigantic scoop. Outgoing transmissions are broadcast up a stem (resembling a handle) and deflected outward in a series of narrow parallel beams by the curved head. Received transmissions are collected by the scooped shape of the horn, like the parabolic dish, and are deflected down into the stem. **Applications of Microwave Technologies** Microwaves, due to their unidirectional properties, are very useful when unicast (one-to-one) communication is needed between the sender and the receiver. They are used in **cellular phones, satellite networks** and **wireless LANs** **c. Infrared Waves** Infrared, which is sometimes called infrared light, is electromagnetic radiation with wavelengths longer than those of visible lights. It is therefore invisible to the human eye. For example, you use infrared light waves to change channels on your TV. **Electromagnetic (EM)** waves are waves that are created as a result of vibrations between an electric field and a magnetic field. Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are, hence, known as electromagnetic waves. **Omnidirectional** means being in or involving all directions, especially receiving or sending radio waves equally well in all directions. **Omnidirectional antenna** is a wireless transmitting or receiving antenna that radiates or intercepts radio-frequency (RF) electromagnetic fields equally well in all horizontal directions in a flat, two-dimensional (2D) geometric plane. **Radio waves** are types of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of less or equal to 300 gigahertz (GHz). They are used in standard broadcast radio and television, shortwave radio, navigation and air-traffic control, cellular telephony and even remote-controlled toys. **Telecommunications Network** **Telecommunications Concepts** The term telecommunications generally refer to all types of long-distance communication that use common carriers, telephone, radio, and television. It is the exchange of information in any form (voice, data, text, images, audio, and video) over networks. Data communications is a subset of telecommunications and is achieved through the use of telecommunication technologies. In modern organizations, communications technologies are integrated. Businesses are finding electronic communications essential for minimizing time and distance limitations. Telecommunications plays a special role when customers, suppliers, vendors, and regulators are part of a multinational organization in a world that is continuously awake and doing business somewhere 24 hours a day, 7 days a week ("24/7 **Telecommunications system** A telecommunications system is a collection of compatible hardware and software arranged to communicate information from one location to another. These systems can transmit text, data, graphics, voice, documents, or video information. Such systems havetwo sides: the transmitter and the receiver. The major components are: **1. Hardware**--- all types of computers and communications processors (such as a modems or small computers dedicated solely to communications). **2. Communications media**--- the physical media through which electronic signals are transferred; includes both wireline and wireless media. **3. Communications networks**--- the linkages among computers and communications devices. **4. Communications processors**--- devices that perform specialized data communication functions; includes front-end processors, controllers, multiplexors and modems. **5. Communications software**---software that controls the telecommunications system and the entire transmission process. **6. Data communications providers**--- regulated utilities or private firms that provide data communications services. **7. Communications protocols**---the rules for transferring information across the system. **8. Communications applications**--- electronic data interchange (EDI), teleconferencing, videoconferencing, e-mail, facsimile, electronic funds transfer, and others. To transmit and receive information, a telecommunications system must perform the following separate functions that are transparent to the user: ƒ Transmit information. ƒ Establish the interface between the sender and the receiver. ƒ Route messages along the most efficient paths. ƒ Process the information to ensure that the right message gets to the right receiver. ƒ Check the message for errors and rearrange the format if necessary. ƒ Convert messages from one speed to that of another communications line or from one format to another. ƒ Control the flow of information by routing messages, polling receivers, and maintaining information about the network. ƒ Secure the information at all times. **Electronic Signals** Telecommunications media can carry two basic types of signals, analog and digital. Analog signals are continuous waves that "carry" information by altering the amplitude and frequency of the waves. For example, sound is analog and travels to our ears in the form of waves--- the greater the height (amplitude) of the waves, the louder the sound; the more closely packed the waves (higher frequency), the higher the pitch. Radio, telephones, and recording equipment historically transmitted and received analog signals, but they are rapidly changing to digital signals. Digital signals are discrete on-off pulses that convey information in terms of 1's and 0's, just like the central processing unit in computers. Digital signals have several advantages over analog signals. First, digital signals tend to be less affected by interference or "noise." Noise (e.g., "static") can seriously alter the information carrying characteristics of analog signals, whereas it is generally easier, in spite of noise, to distinguish between an "on" and an "off." Consequently, digital signals can be repeatedly strengthened over long distances, minimizing the effect of any noise. Second, because computer-based systems process digitally, digital communications among computers require no conversion from digital to analog to digital. **Communications processors** are hardware devices that support data transmission and reception across a telecommunications system. These devices include modems, multiplexers, front-end processors, and concentrators. **Modem**- a modem is a communications device that converts a computer's digital signals to analog signals before they are transmitted over standard telephone lines. The public telephone system (called POTS for "Plain Old Telephone Service") was designed as an analog network to carry voice signals or sounds in an analog wave format. In order for this type of circuit to carry digital information, that information must be converted into an analog wave pattern. The conversion from digital to analog is called modulation, and the reverse is demodulation. The device that performs these two processes is called a modem; a contraction of the terms modulate/ demodulate (see Figure 2.22). Modems are always used in pairs. **2.3.2 The Importance of Telecommunications** Advances in telecommunications technology allow us to communicate rapidly and learn at distance. Education sectors can take advantage of this technology and communicate almost anywhere in the world. In the business sector, telecommunications also reduce the amount of time needed to transmit information that can drive and conclude business actions. The range of telecommunications applications is broad and includes telephony and video conferencing, facsimile, broadcast and interactive television, instant messaging, e-mail, distributed collaboration, a host of Web- and Internet-based communication, and data transmission. In general, telecommunications create an impact on the everyday activities of people all over the world. Through telecommunications, people can develop solutions and provide support to causes and problems across the world, hence, making it a closer and safer place to live in. For example, to take advantage of telecommunications, Ethio-telecom is installing 4G LTE advanced across all regions The term **telecommunications** refers to all types of long-distance communication that use common carriers, **telephone, radio and television** for the exchange of information in any form (voice, data, text, images audio and video) over networks. **Telecommunications system** is a collection of compatible hardware and software arranged to communicate information from one location to another. **Telecommunications network components** are terminals (inputs used to transmit and receive data), telecom processors (devices that perform control and provide support function), telecom channels (media for transmission of information), various computer and telecom control software (programs that control telecom activities). **Mobile Communications** **Mobile communication** is the use of technology that allows us to communicate with others in different locations without the use of any physical connection (wires or cables). Mobile communication saves time and effort and makes our life easier. The following sections discuss basic mobile communications technologies. **2.4.1 A Bluetooth Network** **Bluetooth technology** is a short-range wireless communications technology to replace the cables connecting electronic devices, allowing a person to have a phone conversation via a headset. The Bluetooth Radio Frequency transceiver operates in the unlicensed Industrial, Scientific, and Medical (**ISM**) band centered at 2.4 gigahertz (the same range of frequencies used by microwaves and Wi-Fi). Every Bluetooth-enabled device in the system can establish a connection via pairing and can communicate with each other. **Wireless Local Area Network (WLAN)** With the success of wired local area networks (LANs), the local computing market is moving toward wireless LAN (WLAN) with the same speed as the current wired LAN. It is a communication system established through the use of radio frequency (RF) technology that can function either as an extension to an existing LAN or as an alternative for a wired LAN. There is a need for an access point (AP) that bridges wireless LAN traffic into the wired LAN. Wireless local area networks are flexible data communication systems that can be used for applications in which **mobility** is required. This gives users the ability to move around within a local coverage area and still be connected to the network. Currently, WLANs can provide data rates up to 11 Mbps, but the industry is making a move toward high-speed WLANs. The high speed makes WLANs a promising technology for the future data communications market. The International Enterprise for Electronics Engineering (IEEE) 802.11 committee is responsible for WLAN standards. Most modern WLANs are based on IEEE 802.11 standards and marketed under the Wi-Fi brand name. The access point (AP), can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes. To service larger areas, multiple APs may be installed with a 10-15% overlap. Figure 2.28 above shows the access points overlap. Mobility is the ability to move freely. Bluetooth is a wireless technology that uses a radio frequency to share data over a short distance, eliminating the need for wires. You can use Bluetooth on your mobile device to share documents or to connect with other Bluetoothenabled devices. Electromagnetic fields, radio waves, microwaves and wireless signals are referred to as radio frequency (RF) energy. **Wireless local area networking,** also known as WLAN or wireless LAN, is a term used to refer to wireless digital signals to connect computers and other devices. **Cellular Networks** A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, which is known as a cell site or base station. A cellular network is designed to provide communications between two moving units (called mobile stations (MSs)), or between one mobile unit and one stationary unit (often called a land unit). A service provider must be able to locate and track a caller, assign a channel to the call and transfer the channel from the base station to the base station as the caller moves out of range. To make this tracking possible, each cellular service area is divided into **small regions** called **cells.** Each cell contains an antenna and is controlled by a solar- or AC-powered network station called the base station (BS). Each base station is controlled by a switching office called a mobile switching center (MSC). The MSC coordinates communication between all the base stations and the telephone central office. It is a computerized center that is responsible for connecting calls, recording call information and billing. **Cellular** refers to a **network technology that facilitates mobile device communication over areas comprised of cells and transceivers**, which are also known as base stations or cell sites. In a cellular network, the most widely used mobile transceivers are mobile phones, or cell phones. **Base station** is a fixed transceiver that is the main communication point for one or more wireless mobile client devices. A base station serves as a central connection point for a wireless device to communicate. **Cell** is a small geographic unit in a cellular system. **Generation of Cellular System** The cellular communication networks are known by their numeric generation such as **1G, 2G, 3G** and **4G** designations**.** We are currently in the fourth generation with 5G emerging. **a. Fourth Generation (4G)** The fourth generation of cellular telephony is expected to be a complete evolution in wireless communications. Some of the objectives defined by the 4G working group are: ƒ High network capacity. ƒ Data rate of 100 Mbit/s for access in a moving car and 1 Gbit/s for stationary users. ƒ Data rate of at least 100 Mbit/s between any two points in the world. ƒ Smooth handoff across heterogeneous networks. ƒ Seamless connectivity and global roaming across multiple networks. ƒ High quality of service for next-generation multimedia support. ƒ Interoperability with existing wireless standards. 4G is also known as mobile broadband everywhere. **4G LTE** 4G LTE (long term evolution) is a type of 4G technology. It is a mobile broadband technology that promises data transfer rates of 100 Mbps. **b. 5G** 5G is the 5th generation mobile network and it is the latest in the evolution of mobile wireless technologies. 5G goes beyond 4G LTE and is expected to bring not just faster downloads, but a much more flexible and responsive network that can adapt to enable different uses. 5G enables a new kind of network that is designed to connect everyone and everything virtually including machines, objects and devices. 5G wireless technology is meant to deliver higher multi-Gbps peak data speeds, ultra-low latency, more reliability, massive network capacity, increased availability and a more uniform user experience to more users. Higher performance and improved efficiency empower new user experiences and connect new industries. **Satellite Networks** A satellite network is a combination of nodes, some of which are satellites that provide communication from one point on the earth to another point. A node in the network can be a satellite, an earth station, an end-user terminal or a telephone. The fundamental components of a satellite system are earth stations, uplink, downlink and transponder. Satellites communicate with antennas on earth by using radio waves. Satellite networks are like cellular networks in that they divide the **planet into cells**. Satellites can provide transmission capability to and from any location on Earth, no matter how remote they are. This advantage makes high-quality communication available to **undeveloped parts** of the world without requiring a huge investment in ground-based infrastructure. **Orbits of Satellite** An artificial satellite needs to have an orbit, the path in which it travels around the Earth. The orbit can be equatorial, inclined or polar. **Categories of Satellites** Based on the location of the orbit, satellites can be divided into three categories: **geostationary Earth orbit (GEO), low-Earth-orbit (LEO) and medium-Earthorbit (MEO).** Figure 2.34 shows the satellite altitudes concerning the surface of the Earth. There is only one orbit, at an altitude of 35,786 km, for the GEO satellite. MEO satellites are located at altitudes between 5000 and 15,000 km. LEO satellites are normally below an altitude of 2000 km. One reason for having different orbits is the existence of two Van Allen belts. A Van Allen belt is a layer that contains charged particles. A satellite orbiting in one of these two belts would be destroyed by the energetic charged particles. The **MEO** orbits are located between these two belts. A **satellite** is basically a self-contained communication system with the ability to receive signals from Earth and to retransmit those signals back with the use of a transponder - an integrated receiver and transmitter of radio signals. **Satellite networks** are defined as the orientation of various elements that establish communication through various nodes from one point of the earth to another. Any satellite network can provide both types of transmission technologies, i.e. point to point as well as broadcasting connections. **An orbit** is a regular, repeating path that one object in space takes around another one. An object in an orbit is called a satellite. A satellite can be natural like Earth and the moon. Many planets have moons that orbit them. A satellite can also be man-made like International Space Station. **Data Communications** **Data communication** is a specialized subset of telecommunications that refers to the electronic collection, processing, and distribution of data, typically between computer system hardware devices. The effectiveness of a data communication system depends on **four fundamental** characteristics: **delivery, accuracy, timeliness and jitter** **Components of Data Communication** A data communications system has five components They are protocol, message, transmission medium, sender and receiver **Data Transmission Mode/Flow** Data transmission mode refers to the direction of signal flow between two linked devices. Communication between two devices can be simplex, half-duplex or full-duplex. **Simplex** **In simplex mode**, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. Example of simplex transmission include remote control and television. Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction. **Half-Duplex** In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive and vice versa. The half-duplex mode is like a one-lane road with traffic allowed in both directions. When cars are traveling in one direction, other cars going the other way must wait. In half-duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time. Example of half duplex mode include walkie-talkie. The half-duplex mode is used in cases where there is no need for communication in both directions at the same time; the entire capacity of the channel can be utilized for each direction. **Full-duplex** In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time. In full-duplex mode, signals going in one direction share the capacity of the link with signals going in the other direction. This sharing can occur in two ways: either the link must contain two physically separate transmission paths, one for sending and the other for receiving, or the capacity of the channel is divided between signals traveling in both directions. For example computer and mobile communication network are full duplex One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions **Internet Protocol** The Internet Protocol (IP) is the principal communications protocol in internetworking; it would not be an exaggeration to say that you cannot comprehend modern networking without a good understanding of IP. **P Address** An IP address is a unique address that identifies a device on the internet or a local network. As it is described earlier, IP stands for Internet Protocol, which is the set of rules governing the format of data sent via the internet or local network. In essence, IP addresses are the identifier that allows information to be sent between devices on a network; they contain location information and make devices accessible for communication. The internet needs a way to differentiate among different computers, routers and websites. IP addresses provide a way of doing so and form an essential part of how the Internet works. The IP address has two fundamental versions: IPv4 and IPv6. IPv4 is a common version that can be used in current networks. IP v4 (version 4) addresses are 32-bit integers that can be expressed in hexadecimal notation. The most common format, known as dotted quad or dotted decimal, is x.x.x.x, where each x can be any value between 0 and 255. For example, 192.0. 2.146 is a valid IPv4 address **Classes of IP Address** When Internet addresses were standardized (the early 1980s), the Internet address space was divided into classes. TCP/IP defines five classes of IP addresses: Class A, B, C, D and E. Each class has a range of valid IP addresses. The value of the first octet determines the class. IP addresses from the first three classes (A, B and C) can be used for host addresses. The other two classes are used for other purposes. Class D is used for multicast and Class E for experimental purposes. The system of IP address classes was developed for Internet IP addresses assignment. The classes created were based on the network size. For example, Class A was created for the small number of networks with a very large number of hosts. Class C was created for numerous networks with a small number of hosts. ƒ **Class A:** The first octet is the network portion. Octets 2, 3 and 4 are for subnets/hosts. Class A starts with 0. ƒ **Class B:** The first two octets are the network portion. Octets 3 and 4 are for subnets/hosts. Class B starts with 10. ƒ **Class C:** The first three octets are the network portion. Octet 4 is for subnets/hosts. It starts with 110 **Network Masks** A network mask distinguishes which portion of the address identifies the network and which portion identifies the node. **Default Masks** ƒ **Class A**: 255.0.0.0 ƒ **Class B:** 255.255.0.0 ƒ **Class C:** 255.255.255.0 An IP address is **a unique address that identifies a device on the internet or a local network**. IP (Internet Protocol) is the set of rules governing the format of data sent via the internet or local network. **Netmasks** (or network masks) are shorthand for referring to ranges of consecutive IP addresses in the Internet Protocol. They are used for defining networking rules. Every entity (server or client) communicating on the internet will have a unique IP address. **Unit Summary** A transmission medium can be broadly defined as anything that can carry information from a source to a destination. For example, the transmission medium for two people having a dinner conversation is the air. The air can also be used to convey the message in a smoke signal or semaphore. The transmission medium for a written message might be a mail carrier, a truck, or an airplane. A guided medium provides a physical conduit from one device to another. Twisted-pair cable consists of two insulated copper wires twisted together. Twisted-pair cable is used for voice and data communications. Coaxial cable consists of a central conductor and a shield. Coaxial cable is used in cable TV networks and traditional Ethernet LANs. Fiber-optic cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket. Fiber-optic transmission is becoming increasingly popular due to its noise resistance, low attenuation and high bandwidth capabilities. Fiber-optic cable is used in backbone networks, cable TV networks and fast Ethernet networks. Unguided media (free space) transport electromagnetic waves without the use of a physical conductor. Wireless data are transmitted through ground propagation, sky propagation and line-of-sight propagation. Wireless waves can be classified as radio waves, microwaves or infrared waves. Radio waves are omnidirectional; microwaves are unidirectional. Microwaves are used for cellular phone, satellite and wireless LAN communications. Infrared waves are used for short-range communications such as those between a PC and a peripheral device. They can also be used for indoor LANs. The nature and characteristics of a wireless network are different from those of a wired network. There are some issues in a wireless network that are negligible in a wired network. Wireless communication is one of the fastest-growing technologies and the demand for connecting devices without the use of cables is increasing everywhere. Wireless networks, as the name implies, interconnect devices without using wires; instead they use air, radio frequency **(RF**) as the main transmission medium. Bluetooth technology is a short-range wireless communications technology to replace the cables connecting electronic devices, allowing a person to have a phone conversation via a headset, use a wireless mouse and synchronize information from a mobile phone to a PC, all using the same core system. Telecommunications are the means of electronic transmission of information over distances. The information may be in the form of voice telephone calls, data, text, images or video. Telecommunications link form a channel through which information is transmitted from a sending device to a receiving device. In data communication terminology, a transmission medium is a physical path between the transmitter and the receiver; that is, it is the channel through which data is sent from one place to another. Transmission media is broadly classified into the following types: guided and unguided. WLANs are flexible data communication systems that can be used for applications in which mobility is required. In the indoor business environment, although mobility is not an absolute requirement, WLANs provide more flexibility than that achieved by the wired LAN. Cellular network provides communication between two devices. One or both may be mobile. A cellular service area is divided into cells. Advanced mobile phone system (AMPS) is a first-generation cellular phone system. Digital AMPS (D-AMPS) is a second-generation cellular phone system that is a digital version of AMPS. Global System for mobile communication (GSM) is a second-generation cellular phone system used in Europe. The third-generation cellular phone system provides universal personal communication. The fourth generation is the new generation of cellular phones that are becoming popular. Satellite networks are defined as the orientation of various elements that establish communication through various nodes from one point of the earth to another. Any satellite network can provide both types of transmission technologies, i.e. point to point as well as broadcasting connections. A satellite network uses satellites to provide communication between any points on Earth. An IP address is a unique address that identifies a device on the internet or a local network. IP (Internet Protocol) is the set of rules governing the format of data sent via the internet or local network.