Chapter 6 Telecommunications and Networks

Chapter 6 Telecommunications and Networks Chapter 6 Telecommunications and Networks

Presentation Overview • The Evolution of Networking • Data Transmission Characteristics • Communications Media • Network Classifications • Network Topologies • Network Hardware • Network Software • Communications Software and Protocols

The Evolution of Networking Telecommunications, combined use of computer hardware and communications software for sending and receiving information, enables computer users throughout the world to communicate.

Data Transmission Characteristics The transmission of data over computer networks is characterized by the • Rate of transmission (bandwidth) • Type of signal (analog or digital) • Order of bits (parallel or serial)

Data Transmission Characteristics Bandwidth • Bandwidth is the number of bits that can be transferred per second over a given medium. • Terms for measuring bandwidth:

Data Transmission Characteristics Analog and Digital Transmission • An analog signal is composed of continuous waves transmitted over a medium at a certain frequency range. • A modem converts digital signals to analog signals so they can be sent over telephone lines. • Modulation – changing a digital signal into an analog signal • Demodulation – changing an analog signal into a digital signal

Data Transmission Characteristics Translating digital signals to analog signals

Data Transmission Characteristics • An internal modem is an electronic card inserted into an expansion slot on a computer’s motherboard. • An external modem is a stand-alone device connected to the motherboard by cable.

Data Transmission Characteristics Parallel and Serial Transmission • A parity bit is an extra bit added to a byte to ensure there is an accurate transmission. • In serial transmission, the byte plus the parity bit are transmitted one bit after another in a continuous line. • In parallel transmission, 8 bits (a byte) plus a parity bit are transmitted at the same time over nine separate paths.

Data Transmission Characteristics • In serial transmission, the bits are transmitted one after the other in a line. • In parallel transmission, the bits are transmitted at the same time, which is faster.

Communications Media • A communications medium is a link that connects computers in different locations. • Communications media are broadly classified as either wired or wireless. • Wired communications use three main types of communications media: • Twisted-pair cable • Coaxial cable • Fiber-optic cable

Communications Media Twisted-Pair Cable • One of the older types of communications media • Used to connect computers in networks for transmitting data over relatively short distances

Communications Media Coaxial Cable • Used for connecting computers in a local computer network, such as a network located on a college campus • Used for cable television connections and in telephone networks

Communications Media Fiber-Optic Cable • Transmits beams of light through a glass or plastic core • Is expensive and difficult to work with • Has very high bandwidth

Communications Media Other Wired Communications Media • Integrated Services Digital Network (ISDN)lines are used to dial into the Internet and receive information at high speeds. • Digital Subscriber Lines (DSL) use existing phone lines and new switched connections to achieve faster speeds than traditional dial-up. • T lines are digital, high-speed, long-distance lines capable of carrying signals across the line.

Communications Media Wireless Communications Media • Wireless communications media transmit information as electromagnetic signals through the air. • Many people are embracing wireless technologies as mobile and wireless devices become more powerful.

Communications Media Microwave systems transmit data through the atmosphere from one microwave station to another.

Communications Media A communications satellite is a solar-powered, electronic device that receives signals from ground transmission stations. The satellite then amplifies the signals and retransmits them to the appropriate ground location.

Communications Media Infrared technology allows data in the form of light waves to be transmitted from a special port in a computer to an infrared sensor in a printer.

Communications Media With cellular technology, signals sent by cell phones are transmitted and received from cell to cell until they reach their destination.

Communications Media • Wi-Fi is a wireless local area network technology. • Wi-Fi-enabled devices use a broadband Internet connection through a wireless access point.

Communications Media Bluetooth Wireless Connectivity • Built in to most PDAs, cell phones, and notebook computers. • Offers short-range connectivity with other Bluetooth devices, forming small, temporary networks.

Network Classifications • Networks can be classified by their architecture, by the relative distances they cover, and by the users they are designed to support. • Network architecture refers to the way a network is designed and built. Client/server and peer-to-peer are the two major architectural designs for networks.

Network Classifications In client/server architecture, networked client computers can send information to a server, which relays information back to that computer or to another on the network. • Fax machines and printers are shared resources. • The file server provides access to a shared hard disk.

Network Classifications Client/Server Architecture

Network Classifications In peer-to-peer architecture, computers comprising a network have equivalent capabilities and responsibilities—each acts as both client and server.

Network Classifications A local area network (LAN)is a private network that serves an organization with computers located in the same building or area. LANs use a file server that houses all network resources.

Network Classifications A wide area network (WAN) spans a large geographical area, connecting two or more LANs.

Network Classifications An intranet is a network that is housed within an organization to serve internal users.

Network Classifications An extranet is an extension of an intranet that allows specified external users access to internal applications and data via the Internet.

Network Topologies • Network topology is the pattern by which the network is organized. • Each network component is called a node. • The most common network topologies are bus, star, and ring.

Network Topologies In a bus topology, all computers are linked by a single cable (bus) with two endpoints. • All communications travel the length of the bus. • A terminator is a device that absorbs signals so they do not reflect back down the line.

Network Topologies In a star topology, multiple computers and peripheral devices are linked to a central hub. The hub acts as a switching station, sending and routing messages accordingly.

Network Topologies In a ring topology there is no hub, and each computer is connected to two or more other devices in a circular path. A single electronic signal, or token, is used to pass information between computers.

Network Hardware • A hub is an electronic device used in older LAN topologies to link computers and allow them to communicate with one another. Most manufacturers have ceased production of hubs to focus on more powerful networking hardware. • A switch is a hardware device that joins multiple computers together within one LAN.

Network Hardware A repeater is a specially designed electronic device that receives signals along a network, amplifies them, and then sends them along the network’s communication path.

Network Hardware A router is an electronic device, usually found in large networks (including the Internet), that joins two or more networks.

Network Hardware • A gateway is hardware and/or software that allows communication between dissimilar networks. • Here, the gateway is a server connecting a star network to a ring network.

Network Hardware • A bridge consists of hardware and/or software allowing communication between two similar networks. • This bridge connects two star networks.

Network Hardware • In order for a client computer to communicate with a server or another computer it must be connected to a network. • Each networked client computer must contain a network interface card (NIC).

Network Software • A network operating system (NOS) controls the flow of messages from client computers and provides services such as file access and printing. • Some systems, such as UNIX and the Mac OS, have networking functions built in. • Popular NOSs for Windows systems include Windows Server 2003 and Windows Server 2008.

Communications Software and Protocols • Communications software programs can be used to • Access and use the services of an Internet service provider (ISP), such as email and use of Web browsers • Send and receive information to and from other computers through LAN and WAN networks • Send and receive faxes

Communications Software and Protocols • A protocol is a set of rules and procedures for exchanging information among computers on a network. • To avoid transmission errors, the computers involved must have the same settings and follow the same standards.

Communications Software and Protocols Examples of Communication Protocol

Communications Software and Protocols Almost all communications use directional protocols to determine the flow of transmissions among devices. There are three possible directions: • Simplex – data flows in only one direction • Half-duplex – data flows in both directions, but only in one direction at a time • Full-duplex – data flows in both directions at the same time

Communications Software and Protocols Simplex, Half-Duplex, and Full-Duplex Directional Protocols

Communications Software and Protocols When communications are sent by asynchronous transmission, each byte of data is surrounded by control bits. • The start bit signals the beginning of a character. • The stop bit signals the end of a character. • The parity bit checks for errors.

Communications Software and Protocols With synchronous transmission, blocks of bytes are wrapped in start and stop bytes called synch bytes.

Communications Software and Protocols Local Area Network (LAN) Protocols • Ethernet protocols specify how these networks are set up, how devices communicate, how problems are identified and corrected, and how components are connected. • Token ring protocols send an electronic signal that can carry both a message and an address around the ring quickly.

Communications Software and Protocols Wide Area Network (WAN) Protocols • Systems Network Architecture (SNA) uses a polling protocol for transmitting data: workstations are asked individually if they have a message to transmit. • Fiber Distributed Data Interface (FDDI) is used for ring networks dispersed over a large area and connected with fiber-optic cables.

Chapter 6 Telecommunications and Networks