1. Chapter 6: Telecommunications and Networks

2. Agenda - I  What Is Telecommunications?  What Is Data Communications?  What are the Electromagnetic Waves?  What is Electromagnetic Signal Frequency?  What is a Communication Line Bandwidth?  Digital Versus Analog Data  Components of Communication Networks  Contacted and Radiated Media –Twisted Pair Wire –Coaxial Cable –Fiber-Optic Cable –Broadcast Radio –Microwave –Satellite Microwave

3. Agenda - II –Cellular Radio –Infrared Transmission  Selection of Media  Transmission Modes  Telecommunications Devices  Telecommunications Carriers and Services  Networks: LANs and WANS  Terminal-to-Host, File Server, and Client/Server Systems  Network Topologies –Star Topology –Bus Topology –Ring Topology  Coordinating Data Communications  Popular Communication Protocols  Home and Small Business Networks

4. What Is Telecommunications? Telecommunications is the electronic transmission of signals for communications between a sender and a receiver. The methods include telephone, radio, and television, etc.

5. What Is Data Communications?  Data communications is a specialized subset of telecommunications that refers to electronic collecting, processing, and distributing of data between computer system devices. This definition excludes the transmission of data to local peripherals such as disk, tape, and printers.  Data communications is sometimes called networking because it involves the transmission of data over a network.

6. What are the Electromagnetic Waves?  The motion of electrically charged particles produces electromagnetic waves. These waves are also called "electromagnetic radiation" because they radiate from the electrically charged particles.  Radio waves, microwaves, visible light, and x rays are all examples of electromagnetic waves that differ from each other in wave length.  Electromagnetic waves need no material medium for transmission. Light and radio waves can travel through interplanetary and interstellar space from the sun and stars to the earth. Regardless of their frequency and wavelength, electromagnetic waves travel at a speed of 299,792 km (186,282 mi) per second in a vacuum.

7. What is Electromagnetic Signal Frequency?  Frequency refers to the number of times a current (electromagnetic wave) passes through a complete cycle. The measure of frequency is a Hertz (Hz), which represents one cycle per second.  Frequencies are represented from a number from 0 Hertz to 300 GHz (called the electromagnetic spectrum). K=Kilo=1,000, M=Mega=1,000,000, G=Giga=1,000,000,000

8. What is a Communication Line Bandwidth?  Communication line bandwidth is the difference between the minimum and maximum range of frequencies allowed by the communication line.  Bandwidth = higher frequency - lower frequency. For example: A wire transmits in a frequency range from 100 Hz to 2,500 Hz. Its bandwidth is 2,400 Hz.  Bandwidth is important because it indicates how much data can be transmitted over a specific channel. A wider bandwidth allows more data to be transmitted at a given time.

9. Digital Versus Analog Data  Analog signals are represented by rising and falling voltages (waves) such as light, voice, video signals that are in a continuous form.  Digital signals are represented pulse of fixed voltages such as binary signals (o or 1) that are in a discrete form and can be used by computer.

10. Components of Communication Networks  In order for communication to occur, there must be a source, a medium, a receiver and a message.  The source (sender) is the device that sends the message (transmitter) and is any device that can be connected to the network like a PC or a telephone.  The medium connects the source with the receiver and can be a copper cable, a fiber-optic cable, airwaves or another physical path.  The receiver is the device that accepts the message.  The message can be a file, a request, a response, a status message, a control message or correspondence. The message must be understandable.

11. Contacted and Radiated Media  A Communication network cannot exist without a medium to connect the source and receiver. If this medium can be seen physically, it is considered a contacted medium.  Radiated media, or wireless media, do not use physical wires to transmit data. With radiated media, the signal is radiated through the air, water and vacuum of space.

12. Twisted Pair Wire  Twisted pair wire consists of two wires twisted together a specific number of times to create a magnetic field that reduces the amount of interference in the line.  In shielded twisted pair (STP), the twisted core is placed into a cladding shield, which is wrapped with wires to absorb any interference. Used when you have to pack many wires together in a small space or in an environment with a lot of electrical equipment. STP wires are reliable in high-speed areas.  In unshielded twisted pair (UTP), the twisted core is just covered with the plastic material without the use of cladding material. Often used in telephone systems. UTP lines are grouped into categories based on their quality and use.

13. Coaxial Cable  Coaxial cable is composed of a single copper wire (the inner conductor), surrounded by a insulating cladding material called a shell. The shell is then surrounded by a second conductor (usually a braided copper shield), which gives the cable the ability to transmit much more data than a twisted pair wire. Finally, the entire cable is enclosed in a rubber outer cladding called the jacket.  Coaxial cables allow the use of broadband and baseband transmission. In broadband transmission, a single cable is divided into many channels, each of which can carry a different transmission. The carrier wave is divided into bandwidths and separated by guardbands to prevent interference between the signals. In baseband transmission, only a single signal is transmitted over the cable.  A single coaxial cable can carry 1,000 simultaneous voice and data transmissions.

14. Fiber-Optic Cable  Fiber-optic cable uses light to transmit data signals. The core of the fiber-optic cable is composed of one or more thin tubes of glass or plastic. Each tube is called the optical fiber and is as thin as the human hair. A light-emitting diode (LED) or a laser is used to send light through the fibers.

15. Broadcast Radio  Broadcast radio involves sending signals through the air between transmitters, at frequencies from 30 to 300 MHz.  Amplitude modulation (AM) radio uses a low frequency and allows it to broadcast its signal far (530-1605 KHz).  Frequency modulation (FM) radio uses a higher frequency and the signal travels shorter distances (87.6-108 MHz).  Short wave radios transmit signals over long distances and utilize specific restricted frequency ranges.  Television stations use the ultra-high frequency (UHF) channels and very-high frequency (VHF) channels to transmit TV programs in the ranges 400-900 MHz and 50- 225 MHz respectively.

16. Microwave  Microwave transmission uses very-high frequency signals (3,000 MHz to 30 GHz) to transmit signals between stations. The high frequency permits large amounts of data to be transmitted. Unlike broadcast radio signals, which are omnidirectional, microwave transmission is focused and unidirectional. That means means that microwave stations use line-of-sight transmission and signals travel in straight line. The two types of microwave transmission are terrestrial and satellite:  Terrestrial microwave transmissions are sent between two microwave stations on the earth (earth station). It is the most common form of long- distance communication.  Satellite microwave transmissions involve sending microwave transmissions between two or more earth-based microwave stations and a satellite.

17. Satellite Microwave  Most communications satellites are placed into orbit 22,300 miles above the earth's surface. The earth's gravity keeps the satellite in orbit at the same rate as the earth (geosynchronous orbit). Such satellites are called geosynchronous orbiting satellites (GEOS).  Low earth orbiting satellites (LEOS) orbit the earth at a height of 325- 1,000 miles and they orbit around the poles (not in a fixed position relative to the earth).  Medium earth orbiting satellites (MEOS) are similar to LEOS but are positioned at 6,000-10,000 miles above the earth.  Because microwaves use line-of-sight, the satellite signal can only reach a part of the earth. This area is called a footprint.

18. Cellular Radio  Cellular telephones actually are radio devices that use cellular radio (form of broadcast radio with restrictions on how far the signal is transmitted) to transmit voice and data. The broadcast area of a cellular radio system is divided into cells. Here is how it works:  1. Using a cellular phone, the caller dials a number. The signal is sent from the cell phone's antenna to the cellular antenna located in cell 1.  2. The signal is sent to the regional cellular phone switching office.  3. The signal is switched to the local Telephone Company switching station.  4. The signal is now in the regular phone system and the call is switched to the number dialed.

19. Infrared Transmission  Infrareds (IR) transmission involves sending light signals at a frequency between visible light and radio waves. Commonly used in TV remote controls, now is used to provide LAN connections.  It is a line-of-sight transmission and has a maximum coverage of 30 to 80 feet.  Increasingly, computers and devices such as printers come with IrDA ports, which enable the transfer of data without the use of cables.

20. Selection of Media  In developing any network, the designer must take into account:  The cost of the medium  The speed at which it can transmit  The error rate that should be expected using the medium  The security of the data transmitted over the medium  The transmission distance  The availability of the medium  The environmental constraints

21. Transmission Modes Signals can be transmitted though telecommunications media in a number of different ways:  In simplex transmission, data can flow only in one direction  In half-duplex transmission, data can flow in both directions but it can only flow in one direction at any point in time  In full-duplex transmission, data can flow in both directions at the same time

22. Telecommunications Devices Telecommunication devices are hardware devices that allow electronic communication to occur.  Modems translate data from digital to analog and vice versa  Fax devices allow the transmission of text, graphs and other digital files via telephone lines  Multiplexers allow several signals to be sent over one channel  Communication processors are computers devoted to communications management  Bridges, Routers, Gateways, and Switches

23. Telecommunications Carriers and Services Several companies provide telecommunications media, devices and services called telecommunications carriers  Switched lines are standard telephone lines provided by telephone companies  Dedicated lines provide a constant connection between two points  Private Branch Exchange (PBX) is a communications system that can manage both voice and data transfer within a building and an outside line  Wide-area Telecommunications Service (WATS) is a billing method for heavy users of voiceband media (the 1-800 lines)  Integrated Serviced Digital Network (ISDN) is a technology that uses existing common-carrier lines to simultaneously transmit voice, video and image data in digital form  Digital Subscriber Line (DSL) uses existing phone wires to provide transmission speeds exceeding 500 Kbps.  T1 carrier increases the number of voice calls through the existing cables

24. Networks: LANs and WANS  A Computer Network is a collection of computers and peripherals linked together so that they can share applications, data, and resources such as printers, modems, and CD-ROMs.  A Local Area Network (LAN) enables computer users to transfer files, manipulate data, and share resources within the same office or building.  A Wide Area Network (WAN) ties together large geographic regions using microwave, satellite, or telephone lines.

25. Home and Small Business Networks

26. Terminal-to-Host, File Server, and Client/Server Systems  In a Terminal-to-Host network, the application and database reside on one host computer and the user interacts with the application and data using a “dump” terminal.  In the File and Client/Server model, certain machines and devices on the network are dedicated to providing services to the network. (cost, performance, security, privacy, virus, multi-vendor)  A Peer-to-peer network allows personal computers to be linked together to share their resources. In such an arrangement, a single peripheral as a printer connected to a workstation can be used by other network users. Users can also share programs and data.

27. Network Topologies The Topology of the Network is the network’s physical layout. This is what defines the path that information must take to move from one place to another on the network. The 3 basic topologies are: Star, Bus, and Ring

28. Star Topology  In a Star topology, all of the workstations and servers are connected to a centrally located device called a hub. The hub controls and directs messages.

29. Bus Topology  In a Bus or linear network topology, all workstations and servers are connected to a single cable called the bus. At the ends of the network circuit, a device called terminator is installed to complete the network circuit.

30. Ring Topology  In a Ring topology, all workstations and servers are chained together in much the same way as they are in a bus network. The exception is that the cables at the ends of the network are connected together rather than terminated.

31. Coordinating Data Communications  Polling is a procedure in which the main computer checks each device one at a time to see if there are any messages waiting to be communicated to other network devices.  Token passing is a technique in which an electronic "token" is passed from one device to another. If a device has the token and a message, the message can be transmitted.  Contention is a procedure in which a device checks to see if a message is currently being transmitted. If there are no messages being transmitted, the device starts the message- sending sequence.

32. Popular Communications Protocols  Ethernet is the most widely used networking protocol in use today, mainly because of the low cost of implementing the network and the lack of need for centralized control. Ethernet can be used to link many different types of computers together. Ethernet can run on coax, twisted pair, and fiber optic cabling. All cabling schemes support 10 Mbps speeds but the latest (10baseF) can also support 100 Mbps.  The Transmission Control Protocol/Internet Protocol (TCP/IP) was developed in 1973 for use in the APRANet network. Over time, TCP/IP has developed to be a suite network protocols that will support remote log-in capabilities, file transfer, e-mail, and routing. It is most commonly associated with the Internet since in 1983 TCP/IP was adopted as the Internet standard.  Bluetooth is a communications standard using short-range radio wave that defined by Ericsson for wireless communications

33. Communications Software  Network operating system (NOS)  Network management software –Simple Network Management Protocol (SNMP) –Fault detection –Performance management

34. Points to Remember - I  What Is Telecommunications?  What Is Data Communications?  What are the Electromagnetic Waves?  What is Electromagnetic Signal Frequency?  What is a Communication Line Bandwidth?  Digital Versus Analog Data  Components of Communication Networks  Contacted and Radiated Media –Twisted Pair Wire –Coaxial Cable –Fiber-Optic Cable –Broadcast Radio –Microwave –Satellite Microwave

35. Points to Remember - II –Cellular Radio –Infrared Transmission  Selection of Media  Transmission Modes  Telecommunications Devices  Telecommunications Carriers and Services  Networks: LANs and WANS  Terminal-to-Host, File Server, and Client/Server Systems  Network Topologies –Star Topology –Bus Topology –Ring Topology  Coordinating Data Communications  Popular Communication Protocols  Home and Small Business Networks