CHAPTER 8 NETWORKS: COMMUNICATING AND SHARING RESOURCES

Size: px

Start display at page:

Download "CHAPTER 8 NETWORKS: COMMUNICATING AND SHARING RESOURCES"

Arthur Tate
6 years ago
Views:

1 CHAPTER 8 NETWORKS: COMMUNICATING AND SHARING RESOURCES This chapter focuses on the fundamentals of computer networking. As students continue on their journey toward computer fluency, they will need to be informed and literate about networking and know about its benefits and possibilities. This chapter explains the essential concepts of computer networking and teaches the basic networking terms students will need to discuss the subject intelligently. The major sections in this chapter are: 1. Network Fundamentals. The basic components of a network are defined, as are the standards for communicating over a network. The types of networks are identified, and the benefits of networking are explained. This section also covers how modems transform digital computer signals into the analog tones suited for the telephone system. 2. Advantages and Disadvantages of Networking. This section discusses that when you connect two or more computers, you see gains in every aspect of computing, especially with regards to efficiency and costs reduced hardware costs, application sharing, sharing information resources, centralizing data management, and connecting people. This section also discusses the disadvantages of networking, which include loss of autonomy, lack of privacy, security threats, and loss of productivity. 3. Local Area Networks (LANs). The basic components of a local area network are identified, including special hardware and software. Various networking models for LANs are explained. LAN topologies and protocols are also introduced. 4. Wide Area Networks (WANs). Identifies the basic components of a wide area network. This section discusses POPs, backbones, WAN protocols, and WAN technologies. The concepts of packet switching and circuit switching are also discussed in this section. KEY TERMS backbone In a wide area network (WAN), such as the Internet, a high-speed, high-capacity medium that transfers data over hundreds or thousands of miles. A variety of physical media are used for backbone services, including microwave relay, satellites, and dedicated telephone lines. bus topology The physical layout of a local area network that does not use a central or host computer. Instead, each node manages part of the network, and information is transmitted directly from one computer to another. circuit switching A type of telecommunications network in which high-speed electronic switches create a direct connection between two communicating devices. The telephone system is a circuit-switching network. client In a client/server network, a program that runs on users computers and enables them to access a certain type of data. client/server network A computer network in which some computers are dedicated to function as servers, making information available to client programs running on users computers. collision In local area networks (LANs), a garbled transmission that results when two or more workstations transmit to the same network cable at exactly the same time. Networks have means of preventing collisions. 1

2 communications device Any hardware device that is capable of moving data into or out of the computer. congestion In a packet-switching network, a performance interruption that occurs when a segment of the network experiences an overload. contention In a computer network, a problem that arises when two or more computers try to access the network at the same time. Contention can result in collisions, which can destroy data. contention management In a computer network, the use of one of several techniques for managing contention and preventing collisions. Ethernet A set of standards that defines local area networks (LANs) capable of operating at data transfer rates of 10 Mbps to 1 Gbps. About 80 percent of all LANs use one of several Ethernet standards. file server In client/server computing, a computer that has been set aside (dedicated) to make program and data files available to client programs on the network. hub In a local area network (LAN), a device that connects several workstations and enables them to exchange data. Internet address (IP address) The unique, 32-bit address assigned to a computer that is connected to the Internet, represented in dotted decimal notation (for example, ). Internet Protocol (IP) One of the two core Internet standards (the other is the Transmission Control Protocol, TCP). IP defines the standard that describes how an Internet-connected computer should break data down into packets for transmission across the network, and how those packets should be addressed so that they arrive at their destination. IP is the connectionless part of the TCP/IP protocols. latency In a packet-switching network, a signal delay that is introduced by the time network routers consume as they route packets to their destination. local area network (LAN) A computer network that connects computers in a limited geographic area. LocalTalk A protocol developed by Apple Computer that provides peer-to-peer networking among Macintosh computers and Macintosh-compatible peripherals such as laser printers. LocalTalk is a low-level protocol that works with twisted-pair phone cables. modulation protocol In modems, the communications standard that governs how the modem translates between the computer s digital signals and the analog tones used to convey computer data over the Internet. Modulation protocols are defined by ITU standards. The V.90 protocol defines communication at 56 Kbps. network A group of two or more computer systems linked together to enable communications by exchanging data and sharing resources. network administrator (sometimes called network engineers) Computer professionals who install, maintain, and support computer networks, interact with users, handle security, and troubleshoot problems. network architecture The overall design of a computer network that specifies its functionality at every level by means of protocols. network interface card (NIC) An adapter that enables a user to connect a network cable to a computer. 2

3 network layers Separate divisions within a network architecture with specific functions and protocols, allowing engineers to make changes within a layer without having to redesign the entire network. network operating system (NOS) The software needed to enable data transfer and application usage over a local area network (LAN). network topology The physical layout of a local area network (LAN), such as a bus, star, or ring topology, that determines what happens when, for example, two workstations try to access the LAN or transmit data simultaneously. node In a LAN, a connection point that can create, receive, or repeat a message. packet switching One of two fundamental architectures for a wide area network (WAN); the other is a circuitswitching network. In a packet-switching network, such as the Internet, no effort is made to establish a single electrical circuit between two computing devices; for this reason, packet-switching networks are often called connectionless. Instead, the sending computer divides a message into packets, each of which contains the address of the destination computer, and dumps them onto the network. They are intercepted by devices called routers, which send the packets in the appropriate direction. The receiving computer assembles the packets, puts them in order, and delivers the received message to the appropriate application. Packet-switching networks are highly reliable and efficient, but they are not suited to the delivery of real-time voice and video. packet In a packet-switching network, a unit of data of a fixed size not exceeding the network s maximum transmission unit (MTU) size that has been prepared for network transmission. Each packet contains a header that indicates its origin and its destination. See also packet switching. peer-to-peer network (P2PN) A computer network design in which all the computers can access the public files located on other computers in a network. point of presence (POP) A locality in which it is possible to obtain dial-up access to the network by means of a local telephone call. Internet service providers (ISPs) provide POPs in towns and cities, but many rural areas are without local POPs. protocol stack In a computer network, a means of conceptualizing network architecture in which the various layers of network functionality are viewed as a vertical stack, like the layers of a layer cake, in computers linked to the network. When one computer sends a message to the network, the message goes down the stack and then traverses the network; on the receiving computer, the message goes up the stack. protocol suite In a computer network, the collection of network protocols that defines the network s functionality. protocols In data communications and networking, a standard specifying the format of data and the rules to be followed. Networks could not be easily or efficiently designed or maintained without protocols; a protocol specifies how a program should prepare data so that it can be sent to the next stage in the communication process. For example, programs prepare messages so that they conform to prevailing Internet mail standards, which are recognized by every program involved in the transmission of over the network. ring topology The physical layout of a local network in which all nodes are attached in a circle, without a central host computer. router In a packet-switching network such as the Internet, one of two basic devices (the other is a host). A router is an electronic device that examines each packet of data it receives and then decides which way to send it toward its destination. 3

4 star topology The physical layout of a local network in which a host computer manages the network. TCP/IP The two most important Internet protocols. See Transmission Control Protocol and Internet Protocol. token A handheld device used to gain access to a computer system, such as an automated teller machine (ATM). Transmission Control Protocol (TCP) One of two basic Internet protocols (the other is Internet Protocol, IP). TCP is the protocol (standard) that permits two Internet-connected computers to establish a reliable connection. TCP ensures reliable data delivery with a method known as Positive Acknowledgment with Re-transmission (PAR). The computer that sends the data continues to do so until it receives a confirmation from the receiving computer that the data has been received intact. wide area network (WAN) A commercial data network that provides data communications services for businesses and government agencies. Most WANs use the X.25 protocols, which overcome problems related to noisy analog telephone lines. Wi-Fi A collection of wireless transmission standards for wireless networks. wireless LANs (WLANs) Local area networks that use a radio signal spread over a seemingly random series of frequencies for greater security. workstation A powerful desktop computer that meets the computing needs of engineers, architects, and other professionals who require detailed graphic displays. In a LAN, a workstation runs application programs and serves as an access point to the network. X.25 A packet-switching network protocol optimized for use on noisy analog telephone lines. 4

5 Computer networks link two or more computers so that they can exchange data and share resources. Networks enable communications (electronically sending and receiving data) through the establishment of communications channels. Computer networks can reduce hardware costs, enable users to share applications, create the means to pool all of an organization s mission-critical data, and foster teamwork and collaboration. Reducing hardware costs. Networks enable users to share expensive equipment and reduce costs. For example, dozens of users can share a single high-capacity printer or share a common connection to the Internet. Enabling shared applications. Networks enable users to share software. Network versions of applications are designed to be installed on a high-powered computer, called a file server. The file server makes these applications available to more than one user at a time. For example, at Platt Electric Supply, an Oregon-based industrial electric supply firm, sales representatives upload orders from notebook computers to an order-tracking program installed on the company s file server. After installing the network, employees found that they had up to 20 percent more time to focus on their customers needs. Building massive information resources. Networks enable users to create common pools of data, which employees can access to obtain the data they need. At publisher Prentice Hall, for example, a companywide network makes a vast archive of illustrations available to book designers that greatly reduces the amount of time spent tracking down appropriate photographs for textbooks and other publishing projects. Centralized data management. Storing data on a network allows multiple users to access the data, and at the same time it provides data security and integrity assurance through the use of firewalls and password protection. Centralized storage also makes it easier to maintain consistent backup procedures. Connecting people. Computers create powerful new ways for people to work together. For example, groupware applications enable workers to create a shared calendar for scheduling purposes. Team members can see instantly who s available at a given day and time. What s more, these people don t have to work together in the same building. They could be located at various places around the world and still function effectively as a team. The advantages of networks are balanced out by some disadvantages as well: Loss of autonomy. When you become a part of a network, you become a part of a community of users. Sometimes this means that you have to give up personal freedoms for the good of the group. For example, a network administrator may impose restrictions on what software you can load onto network computers. Lack of privacy. Network membership can threaten your privacy. Network administrators can access your files and may monitor your network and Internet activities. Security threats. Because some personal information is inevitably stored on network servers, it is possible that others may gain unauthorized access to your files, user names, and even your passwords. Loss of productivity. As powerful as networks are, they still fail. Access to resources is sometimes restricted or unavailable due to viruses, hacking, sabotage, or a simple breakdown. Data loss can be minimized by good backup practices, but waiting for your data to be restored is an inconvenience, or worse yet, a direct threat to your ability to produce work on time. In a peer-to-peer network (P2PN), all the computers on the network are equals that s where the term peer-to-peer comes from and there s no file server. In file sharing, each computer user decides which, if 5

6 any, files will be accessible to other users on the network. Users may also choose to share entire directories, or even entire disks. They can also choose to share peripherals, such as printers and scanners. Peer-to-peer networks are easy to set up; people who aren t networking experts do it all the time, generally to share an expensive laser printer or provide Internet access to all the workstations on the LAN. Peer-to-peer networks tend to slow down with heavy use, however, and keeping track of all the shared files and peripherals quickly becomes confusing. For this reason, peer-to-peer LANs aren t suitable for networks that connect more than one to two dozen computers. The typical corporate LAN is a client/server network, which includes one or more file servers as well as networked workstations, called clients. The file server on a client/server network is a high-capacity, highspeed computer with a large hard disk capacity. It contains the network operating system (NOS), the software required to run the network. The server also contains network versions of programs and large data files. Clients all the computers that can access the server send requests to the server. The client/server model works with any size or physical layout of LAN and doesn t tend to slow down with heavy use. The physical layout of a LAN is called its network topology. A topology isn't just the arrangement of computers in a particular space; a topology provides a solution to the problem of contention, which occurs when two workstations try to access the LAN at the same time. Contention sometimes results in collisions, the corruption of network data caused when two workstations transmit simultaneously. A bus is a network configuration in which the network cable is a single bus or backbone to which each workstation is connected. The two ends of the bus have special connectors called terminators. A star is a network where all other devices are connected to a central device, typically a computer. This configuration easily allows new users to be added to the network. A ring is a network design where all devices are connected in a closed loop or ring. In this network, data only travels in one direction around the ring. Computer networks require physical media, but their most important component consists of the protocols that define how network devices can communicate with each other. A network requires many protocols to function smoothly. When a computer sends a message over the network, the application hands the message down the protocol stack, where a series of protocols prepares the message for transmission through the network. At the other end, the message goes up a similar stack. By far the most widely used LAN protocol is Ethernet. The various versions of Ethernet are used by approximately 80 percent of all LANs. Although early versions of Ethernet (called 10base2 and 10base5) used coaxial cable in bus networks, the most popular versions today are Ethernet star networks that use hubs and twisted-pair wire. Two versions are available: 10baseT (10 Mbps) and Fast Ethernet (100 Mbps, also called 100baseT). The hardware to create a 10baseT Ethernet for five PCs can cost as little as $200. The newest LAN technology, Gigabit Ethernet, can transfer data at speeds as high as 1,000 Mbps. The special components that distinguish a WAN from a LAN are a point of presence and backbones. A point of presence (POP) is a WAN network connection point that enables users to access the WAN by a local analog telephone call (using a modem) or a direct digital hookup that enables a continuous, direct connection. Backbones are the high-capacity transmission lines that carry WAN traffic. WAN Protocols X.25 is the oldest packet-switching protocol; it is used by automated teller machines and credit card authorization devices; New protocols designed for digital lines and faster 6

7 data transfer rates are: Switched Multimegabit Data Service (SMDS); Asynchronous Transfer Mode (ATM). In circuit switching, the network creates a physical, end-to-end circuit between the sending and receiving computers. Circuit switching works best when it is essential to avoid delivery delays. In a circuitswitching network, high-speed electronic switches handle the job of establishing and maintaining the connection. In packet switching, an outgoing message is divided into data units of a fixed size, called packets. Each packet is numbered and addressed to the destination computer. The sending computer pushes the packets onto the network, where routers examine the packets. Routers are devices that examine each packet they detect. After reading the packet s address, the router consults a table of possible pathways to the packet s destination. If more than one path exists, the router sends the packet along the path that is most free of congestion. There s no guarantee that the packets will arrive in the same order that they were sent, but that s not a problem; on the receiving computer, protocols come into play that put the packets in the correct order and decode the message they contain. If any packets are missing, the receiving computer sends a message requesting retransmission. Circuit switching creates a permanent, end-to-end circuit that is optimal for voice and real-time data. Packet switching does not require a permanent switched circuit and can funnel more data through a medium with a given data transfer capacity. But packet switching introduces slight delays that make the technology less than optimal for voice or real-time data. END-OF-CHAPTER QUESTIONS Multiple Choice 1. Which of the following is not a computer network? a. local area network (LAN) b. leased-line area network (L2AN) c. wide area network (WAN) d. peer-to-peer network (P2PN) 2. Which technology enables networks to funnel messages to their correct destination? a. circuit switching b. packet switching c. both a and b d. none of the above 3. Which term describes a computer that is connected to a network? 7

8 a. unit b. mode c. workstation d. terminal unit 4. To connect to a LAN, a computer must be equipped with which of the following? a. network interface card (NIC) b. backbone c. both a and b d. none of the above 5. Which type of network topology is centered on a hub? a. star b. ring c. bus d. LAN 6. Which of the following is not a LAN topology? a. ring b. star c. hub d. bus 7. Which term describes the phenomenon of more than one computer trying to use the network at the same time? a. contention b. competition c. communication d. congestion 8. Which of the following is a WAN network connection point that enables users to access the WAN through a local phone call? 8

9 a. point of presence (POP) b. leased line c. permanent virtual circuit (PVC) d. frame relay 9. Which of the following is the most popular LAN standard? a. ISDN b. LocalTalk c. Ethernet d. Synchronous Optical Network (SONET) 10. Which of the following is the oldest and most widely used packet-switching protocol for WAN usage? a. 10BaseT b. category 5 (cat-5) c. X.25 d. T1 Fill in the Blank 1. A(n) links two or more computers together to enable data and resource exchange. 2. A(n) uses direct cables, radio waves, or infrared signals to link computers within a small geographic area. 3. When a PC is connected to a LAN, the PC is called a(n). 4. A(n) is a PC expansion board needed to connect a computer to a LAN. 5. With, an outgoing message is divided into data units of a fixed size called packets. 6. is a set of standards that offers Ethernet speed without wires. 7. install, maintain, and support computer networks, interact with users, handle security, and troubleshoot problems. 8. In a(n), the network cable forms a single bus to which every workstation is attached. 9. A network uses (standards) that enable network-connected devices to communicate with each other. 9

10 10. The high-capacity transmission lines that carry WAN traffic are called. 11. defines how one Internet-connected computer can contact another to exchange control and confirmation messages. 12. With a(n), file sharing allows users to decide which computer files, if any, are accessible to other users on the network. 13. is the networking system built into every Macintosh computer. 14. A(n) uses long-distance transmission media to link computers separated by a few miles or even thousands of miles. 15. With, the network creates a physical end-to-end circuit between the sending and receiving computers. 10

Computers Are Your Future

Computers Are Your Future Networks: Communicating and Sharing Resources. Network Fundamentals What You Will Learn About Basic networking concepts Advantages and disadvantages of networks Peer-to-peer and