Chapter 8 Communications and Networks

Chapter 8: Communications and Networks Computer Concepts 8.1— Communications • Computer Communications— the process of sharing data, programs, and information between two or more computers • E-mail—provides a fast, efficient alternative to traditional mail by sending and receiving electronic documents. • Texting—provides very efficient direct text communication between individuals using short electronic messages. • Videoconferencing—provides a very-low-cost alternative to long-distance telephone calls using electronic voice and video delivery. • Electronic commerce—buying and selling goods electronically • Connectivity— a concept related to using computer networks to link people and resources; you can connect your personal computer to other computers and information sources almost anywhere - The single most dramatic change in connectivity and communications in the past decade has been the widespread use of mobile devices like smartphones and tablets with wireless Internet connectivity - Wireless communications allows you to share a high-speed printer, share data files, and collaborate on working documents with a nearby co-worker without having your computers connected by cables or telephone • Communication Systems— electronic systems that transmit data from one location to another ~ Basic Elements of a Communication System 1. Sending and receiving devices: These are often a computer or specialized communication device. They originate (send) as well as accept (receive) messages in the form of data, information, and/or instructions. 2. Connection devices: These devices act as an interface between the sending and receiving devices and the communication channel. They convert outgoing messages into packets that can travel across the communication channel. They also reverse the process for incoming messages. 3. Data transmission specifications: These are rules and procedures that coordinate the sending and receiving devices by precisely defining how the message will be sent across the communication channel. 1 4. Communication channel: This is the actual connecting or transmission medium that carries the message. This medium can be a physical wire or cable, or it can be wireless 8.2— Communication Channels • Communication Channels— are an essential element of every communication system; These channels actually carry the data from one computer to another ~ Physical Connections 1. Twisted-Pair Cable: consists of pairs of copper wire that are twisted together 2. Coaxial Cable: a high-frequency transmission cable, replaces the multiple wires of telephone lines with a single solid-copper core; used to deliver television signals as well as to connect computers in a network 3. Fiber-Optic Cables: transmits data as pulses of light through tiny tubes of glass ~ Wireless Connections - These devices move data through air by using radio waves to communicate 1. Bluetooth: a short-range radio communication standard that transmits data over short distances of up to approximately 33 feet 2. Wi-Fi: uses high-frequency radio signals to transmit data. A number of standards for Wi-Fi exist, and each can send and receive data at a different speed 3. Microwave: communication uses high-frequency radio waves. It is sometimes referred to as line-of-sight communication because microwaves can only travel in a straight line; a good medium for sending data between buildings in a city or on a large college campus 4. WiMax: is a new standard that extends the range of Wi-Fi networks using microwave connections 5. Cellular: communication uses multiple antennae (cell towers) to send and receive data within relatively small geographic regions (cells) 6. Satellite Connections: uses satellites orbiting about 22,000 miles above the earth as microwave relay stations; satellites orbit at a precise point and speed above the earth. They can amplify and relay microwave signals from one transmitter on the ground to another. Satellites can be used to send and receive large volumes of data • Uplink— relating to sending data to a satellite • Downlink— receiving data from a satellite • Global Positioning System (GPS)— use that information to uniquely determine the geographic location of the device • Infrared— uses infrared light waves to communicate over short distances. Like microwave transmissions, infrared is a line-of-sight communication 8.3— Connection Devices • Analog Signals— continuous electronic waves • Digital Signals— represent the presence or absence of an electronic pulse • Modem— modulator-demodulator; enables digital personal computers to communicate across different media, including telephone wires, cable lines, and radio waves • Modulation— the name of the process of converting from digital to analog 2 • Demodulation— the process of converting from analog to digital • Transfer Rate— the speed with which modems transmit data • Megabits Per Second (Mbps)— what the transfer rate is measured in ~ Common Modems 1. Digital Subscriber Line (DSL): modem uses standard phone lines to create a highspeed connection directly to your phone company’s offices. These devices are usually external and connect to the system unit using either a USB or an Ethernet port 2. Cable Modem: uses the same coaxial cable as your television. Like a DSL modem, a cable modem creates high-speed connections using the system unit’s USB or Ethernet port 3. Wireless Modem: also known as a WWAN (wireless wide area network) modem. Almost all computers today have built-in wireless modems. For those that do not, wireless adapter cards are available that plug into USB or special card ports • T1— copper, special high-speed lines from telephone companies • Optical Carrier (OC)— replaced T1 lines • Dial-Up Service— a type of service has been replaced by higher-speed connection services including DSL, cable, satellite, and cellular services 8.4— Data Transmission • Bandwidth— a measurement of the width or capacity of the communication channel ~ Categories of Bandwidth 1. Voiceband: also known as low bandwidth; is used for standard telephone communication. Personal computers with telephone modems and dial-up service use this bandwidth. While effective for transmitting text documents, it is too slow for many types of transmission, including high-quality audio and video 2. Medium Band: used in special leased lines to connect midrange computers and mainframes as well as to transmit data over long distances. This bandwidth is capable of very-high-speed data transfer 3. Broadband: is widely used for DSL, cable, and satellite connections to the Internet. Several users can simultaneously use a single broadband connection for high speed data transfer 4. Baseband: is widely used to connect individual computers that are located close to one another. Like broadband, it is able to support high-speed transmission, but it can only carry a single signal at a time • Protocols— rules for exchanging data between computers • TCP/IP (transmission control protocol/Internet protocol)— an essential features of this protocol involve (1) identifying sending and receiving devices and (2) breaking information into small parts, or packets, for transmission across the Internet • IP Address— every computer on the Internet has a unique numeric address • Domain Name Server (DNS)— a system that converts text-based addresses to IP addresses • Packets— when a message is reformatted or broken down into smaller parts 3 • Computer Network— a communication system that connects two or more computers so that they can exchange information and share resources ~ Terms • Node—any device that is connected to a network. It could be a computer, printer, or data storage device. • Client—a node that requests and uses resources available from other nodes. Typically, a client is a user’s personal computer. • Server—a node that shares resources with other nodes. Dedicated servers specialize in performing specific tasks. Depending on the specific task, they may be called an application server, communication server, database server, file server, printer server, or web server. • Directory server—a specialized server that manages resources, such as user accounts, for an entire network. • Host—any computer system connected to a network that provides access to its resources. • 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 by sending a received message to all connected nodes, rather than just the intended node. • Network interface cards (NIC)—as discussed in Chapter 5, these are expansion cards located within the system unit that connect the computer to a network. Sometimes referred to as a LAN adapter. • Network operating systems (NOS)—control and coordinate the activities of all computers and other devices on a network. These activities include electronic communication and the sharing of information and resources. • Network administrator—a computer specialist responsible for efficient network operations and implementation of new networks 8.5— Network Types • Local Area Networks (LANs)— networks with nodes that are in close physical proximity —within the same building; benefits by being flexible and economical • Network Gateway— a device that allows one LAN to be linked to other LANs or to larger networks • Home Networks— allow different computers to share resources, including a common Internet connection • Wireless LAN (WLAN)— wireless local area network; uses radio frequencies to connect computers and other devices • Wireless Access Point/Base Station— an access point interprets incoming radio frequencies and routes communications to the appropriate devices • Hotspots— access points that provide Internet access • Personal Area Network— a type of wireless network that works within a very small area —your immediate surroundings. PANs connect cell phones to headsets, keyboards to cell 4 phones, and so on. These networks make it possible for wireless devices to interact with each other Example: Bluetooth • Metropolitan Area Networks (MAN)— networks that are frequently used as links between office buildings that are located throughout a city • Wide Area Networks (WANs)— countrywide and worldwide networks. These networks provide access to regional service (MAN) providers and typically span distances greater than 100 miles. They use microwave relays and satellites to reach users over long distances 8.6— Network Architecture • Network Architecture— describes how a network is arranged and how resources are coordinated and shared. It encompasses a variety of different network specifics, including network topologies and strategies • Topology— describes the physical arrangement of the network ~ Common Topologies • 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 ring until it reaches the intended destination. • Star network—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. The star network is the most widely used network topology today. It is applied to a broad range of applications from small networks in the home to very large networks in major corporations. • Tree network—each device is connected to a central node, either directly or through one or more other devices. The 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. This network, also known as a hierarchical network, is often used to share corporate-wide data. • Mesh network—this topology is the newest type and does not use a specific physical layout (such as a star or a tree). Rather, the mesh network 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 around the failure using another path. Wireless technologies are frequently used to build mesh networks. • Strategy— a way of coordinating the sharing of information and resources • Client/Server Networks— use central servers to coordinate and supply services to other nodes on the network. The server provides access to resources such as web pages, databases, application software, and hardware; based on specialization and are widely used on the Internet • Peer-to-Peer Network (P2P)— have equal authority and can act as both clients and servers. The most common way to share games, movies, and music over the Internet is to use a P2P network 5 8.7— Organizational Networks • Intranet— a private network within an organization that resembles the Internet; uses browsers, websites, and web pages. Typical applications include electronic telephone directories, e-mail addresses, employee benefit information, internal job openings, and much more • Extranet—a private network that connects more than one organization. Many organizations use Internet technologies to allow suppliers and others limited access to their networks. The purpose is to increase efficiency and reduce costs ~ Network Security 1. Firewall: consists of hardware and software that control access to a company’s intranet and other internal networks. Most use software or a special computer called a proxy server. All communications between the company’s internal networks and the outside world pass through this server. By evaluating the source and the content of each communication, the proxy server decides whether it is safe to let a particular message or file pass into or out of the organization’s network. 2. Intrusion detection systems (IDS): work with firewalls to protect an organization’s network. These systems use sophisticated statistical techniques to analyze all incoming and outgoing network traffic. Using advanced pattern matching and heuristics, an IDS can recognize signs of a network attack and disable access before an intruder can do damage. 3. Virtual private networks (VPN): create a secure private connection between a remote user and an organization’s internal network. Special VPN protocols create the equivalent of a dedicated line between a user’s home or laptop computer and a company server. The connection is heavily encrypted, and, from the perspective of the user, it appears that the workstation is actually located on the corporate network. 6