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Communications and Networks Chapter 8 Introduction • We live in a truly connected society. • Increased connectivity potentially means increased productivity, especially in business. • You will learn more about the concept of connectivity and the impact of the wireless revolution in this chapter. 2 Communications • Computer communications is the process of sharing data, programs, and information between two or more computers • Numerous applications depend on communication systems, including – E-mail – Instant messaging – Internet telephone – Electronic commerce 3 Communications Today • Connectivity uses computer networks to link people and resources • The Wireless Revolution – Single most dramatic change in connectivity and communications has been widespread use of mobile devices like smartphones and table PCs with wireless Internet connectivity 4 Communication Systems • Four basic elements – Sending and receiving devices – Communication channel – Connection devices – Data transmission specifications 5 Communication Channels Summary 6 Connection Device Signals • Types of signals – Analog – Digital • Transfer rate 7 Connection Devices • Modem – modulatordemodulator – Modulation – Demodulation • Transfer rate – Mbps • Types of Modems – – – – Telephone modem DSL Cable Wireless 8 Connection Services • Leased lines – T1 combined to form T3 and DS3 – Replaced by optical carrier (OC) lines • Digital subscriber line (DSL) – Uses phone lines – ADSL is most widely used type of DSL • Cable – Uses existing TV cable – Faster than DSL • Satellite connection services – Use almost anywhere – Slower than DSL and cable modem • Cellular Services – 3G and 4G cellular network connectivity 9 Bandwidth • Measurement of the width or capacity of the communication channel • Categories – Voiceband (or low bandwidth) – Medium band – Broadband: widely used by DSL, cable, and satellite connections for high-capacity transmissions – Baseband 10 Protocols • Communication rules for exchanging data between computers • Internet standard: TCP/IP (Transmission control protocol/Internet protocol) – Identification – unique IP address – Packetization – information broken down into small parts (packets) and then reassembled 11 Networks • A communication system that connects two or more computers • Allows exchange of information and resources 12 – Node—any device that is connected to a network. – Client —a node that requests and uses resources available from other nodes. – Server—a node that shares resources with other nodes. – Directory server—specialized server that manages resources such as user accounts for an entire network. – Host—any computer system that can be accessed over a network. – Router —a node that forwards or routes data packets from one network to their destination in another network – Switch—central node that coordinates the flow of data by sending messages directly between sender and receiver nodes. A hub previously filled this purpose; older, less efficient type of switch. • Network interface cards (NIC)— expansion cards located within the system unit that connect the computer to a network. • Network operating systems (NOS)—control and coordinate the activities of all computers and other devices on a network. • Network administrator—a computer specialist responsible for efficient network operations and implementation of new networks. Network Types • • • • Local area network (LAN) Home network Wireless LAN (WLAN) Personal area network (PAN) • Metropolitan area network (MAN) • Wide area network (WAN) 17 Topologies • • • • • Bus network Ring network Star Tree Mesh • Topology – Describes the physical arrangement of a network and how resources are coordinated and shared – Bus network • Each device is connected to a common cable called a bus or backbone and all communications travel along this bus. – Ring network • Each device is connected to two other devices, forming a ring. When a message is sent, it is passed around the right until it reaches the intended destination. – Star • Each device is connected directly to a central network switch. • Whenever a node sends a message, it is routed to the switch, which then passes the message along to the intended recipient. • Most widely used network topology today. • Range of applications includes small networks in the home to very large networks in major corporations. – Tree • Each device is connected to a central node, either directly or through one or more other devices. • Central node is connected to two or more subordinate nodes that in turn are connected to other subordinate nodes, and so forth, forming a treelike structure. • Also known as a hierarchical network – Mesh • Newest type of topology and does not use a specific physical layout. • Requires that each node have more than one connection to the other nodes. The resulting pattern forms the appearance of a mesh. • If a path between two nodes is somehow disrupted, data can be automatically rerouted. • Wireless technologies are frequently used to build mesh networks. Organizational Networks • Intranet – Private network within an organization – Works like the Internet, where employees use browsers to access Web sites and Web pages • Extranet – Private network that connects organizations – Works like the Internet, but provides suppliers and other trusted partners with limited access to the organization’s networks 25 Network Security • Firewall – Hardware and software controls access to network – Proxy server provides pass-through access – Protects against external threats • Intrusion detection system (IDS) – Works with firewall to protect organization's network – Analyzes all incoming and outgoing network traffic • Virtual private network (VPN) – Creates a secure private network connection between your computer and the organization 26 Intranet, Extranet, Firewall, Proxy Server 27