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Chapter 5 LANs And WLANS (了 解) Contents Network Building Blocks (Section A) Wired Networks (Section B) Wireless Networks (Section C) Using LANs (Section D) Security Through Encryption (Section E) Computer Concepts 2 CHAPTER OBJECTIVES Describe the characteristics of PANs(个人域网), NANs, LANs, MANs(区域网), and WANs Diagram the five most common network topologies(拓扑) Diagram Shannon's model of a communications network List the types of cables and other links typically used for data communications networks Make a list of network devices and explain the role of each one Computer Concepts 3 CHAPTER OBJECTIVES Describe the role of communications protocols Explain the difference between packet switching and circuit switching technology Describe how to set up wired and wireless networks List various ways to share files over a LAN List security measures for wired and wireless networks List and define types of encryption(加密) that help secure computer networks and data Computer Concepts 4 Section A Network Building Blocks Network Classifications P198-199 How are computer networks classified? Networks can be classified according to their size and geographic scope. A PAN.---- (personal area network) refers to the interconnection of personal digital devices within a range of about 30 feel and without the use of wires or cables. A NAN (neighborhood area network) provides connectivity within a limited geographical area, usually spread over several buildings. A LAN ---(local area network) connects personal computers within a very limited geographical area-usually a single building. A MAN ----(metropolitan area network) is a public high-speed network capable of voice and data transmission within a range of about 50 miles (80 km). A WAN -----(wide area network) covers a large geographical area and usually consists of several smaller networks. Computer Concepts 5 LANs Standards P199 What are LAN standards ? LAN technologies are standardized by the Institute of Electrical and Electronics Engineers (IEEE) Project 802Local Network Standards. What are the most popular LAN standards? Several LAN standards including ARCnet, Token Ring, and FDDI(光纤分布数据接口), were popular in the past. Today, most LANs are configured with Ethernet technology and use compatible Wi-Fi standards in applications that require wireless access. More specifics about these in sections B and C. Computer Concepts 6 Network device such as Router , hub , switch, repeater. Network Peripheral Such as printer, scanner Storage device Computer Network Devices P200 Network interface card (NIC) Concepts 7 Client, Servers ,And Peers P201 What is the difference between a network client and a server? A server is a computer that provides services to other computers called clients. Application Server File Server Print Server Computer Concepts 8 Client, Servers ,And Peers P201 Can a network function without a server? Files and applications can he shared among workstations operating in peer-to-peer mode. A network can function in client/server mode when necessary and also exchange data in peer-to-peer fashion. Computer Concepts 参考: http://docs.huihoo.com/p2p/1/index.html 9 Physical Topology p202 How are the devices on a LAN physically arranged? The arrangement of devices in a network is referred to as its physical topology. Computer Concepts 10 Physical Topology p202 Can various networks he interconnected? Yes. Two similar networks can be connected by a device called a bridge, which simply transfers data without regard to its format. Networks that use different topologies and technologies can be interconnected by using gateways(通道). Computer Concepts 11 Network Links p203 What connects the nodes of a network ? Data in a network with wired links travels from one device to another over cables Networks without wires transport data through the air What's bandwidth ? Bandwidth is the transmission capacity of a communications channel. The bandwidth of a channel carrying digital data is usually measured in bits per second (bps). ※ Broadband ※ Narrowband Computer Concepts 12 Communications Protocols p204 What is a protocol ? A protocol is a set of rules for interacting(相互作用) and negotiating(处 理). A communications protocol refers to a set of rules for efficiently transmitting data from one network node to another. The best-known communications protocol is probably TCP/IP. How does data over a network ? Computer Concepts 13 Communications Protocols p205-207 Your file is chopped up(切开) into small pieces called packet to transmit. A packet(信息包) is a parcel of data that is sent across a computer network. Each packet contains the address of its sender, the destination address, a sequence number, and some data. How are packets routed to their destinations? Every packet that travels over a network includes the address of its destination device. Two commonly used addresses are MAC addresses :is a unique number assigned to a network interface card when it is manufactured. IP addresses : is a series of numbers used to identify a network device. such as 204.127.129.1 Computer Concepts 14 Section B Wired Networks Wired Networks Basics p208-209 What is a wired network? A wired network is one that uses cables to connect network devices. What are the advantages of wired networks? Wired networks are fast, secure, and simple to configure. What are the disadvantages of wired networks? The cables that offer speed and security for a wired network are also its main weakness. Computer Concepts 15 Wired Networks Basics p208-209 Today ,the most popular LAN technology is Ethernet. Alternatives such as HomePNA and HomePlug technology are available but much less frequently use. 有关HOMEPNA AND POWERLINE NETWORKS的相关知 识在P209-210,作为选学内容。 Computer Concepts 16 Ethernet p210-211 How does Ethernet work? Computer Concepts 17 Ethernet p211-216 How fast is an Ethernet network(以太网 )? What equipment do I need for an Ethernet network? Two or more Ethernet-ready computers An Ethernet router Surge strip(防浪涌插座) or UPS Cables for each computer Internet access device, such as cable modem or DSL modem and corresponding cables Computer Concepts 18 Ethernet Equipment p212 HOW can I tell if a computer is Ethernet ready? Computer Concepts 19 Ethernet Setup p214 What's the general procedure for setting up Ethernet? Run Cables from the router to each workstation or server Run a cable between the router and the device used for your Internet Connection Configure each workstation Configure the router Computer Concepts 20 Section C Wireless networks Wireless Networks Basic P217 What Is a wireless network? A wireless network transports data from one device to another without the use of cables or wires. It transports data from radio signals, microwaves, and infrared light. How do radio signals transport data? RF signals (radio frequency signals) are sent and received by a transceiver (a combination of a transmitter and a receiver) that is equipped with an antenna. How do microwaves transport data? Microwaves are electromagnetic signals. It can be aimed in a single direction and have more carrying capacity than radio waves. How do infrared(红外线) transport data? Infrared can also carry data signals, but only for short distances and with a clear line of sight. Computer Concepts 21 Wireless Networks Basic P217-218 What are the advantages of wireless networks? The main advantage of wireless networks is mobility. What are the disadvantages of wireless networks? The main disadvantages of wireless networks are speed, range, licensing, and security. Why is wireless slower than wired? Wireless signals are susceptible(敏感的) to interference(干扰) from devices . When interference affects a wireless signal, data must de retransmitted. What limits the range of a wireless network? It can be limited by the type of signal, the transmitter strength, and the physical environment. Computer Concepts 22 Wireless Networks Basic P217-218 Note: To make wireless network data useless to intruders(入侵者). it should be encrypted(编码). To broadcast at most frequencies, a license is required. What are the most popular technologies for wireless networks? By far the most popular wireless LAN technology is Wi-Fi. A second wireless technology called Bluetooth is useful for some applications. Computer Concepts 23 Bluetooth P219 What is Bluetooth? Bluetooth is a short-range wireless network technology that's designed to make its own connections between electronic devices, without wires, cables or any direct action from a user. Where is Bluetooth use ? Anyone can set up a Bluetooth network. Bluetooth connectivity replaces the short cables that would otherwise tether (拴系)a mouse, keyboard, or printer to a computer. Computer Concepts 24 Wi-Fi P220 What is Wi-Fi ? Wi-Fi refers to a set of wireless networking technologies defined by IEEE 802.11 standards that are compatible with Ethernet. A Wi-Fi network transmits data as radio waves over 2.4 GHz or 5.8 GHz frequencies. How do the speed and range of Wi-Fi compare to other network technologies? Wireless network speed and range, are often theoretical maximums. Although Wi-Fi 802.11n is capable of 200 Mbps speeds, in actual performance it is unlikely to match Fast Ethernet and is far slower than Gigabit Ethernet. Computer Concepts 25 Wi-Fi Equipment P221 What equipment is required for a Wi-Fi network? Computer Concepts 26 Wi-Fi Setup p222 What's the general procedure for setting up Wi-Fi network? Computer Concepts 27 Section D Using LANs LAN Advantages And Challenges p226-227 Why are LANs advantageous? LANs enable people to work together Sharing networked software can reduce costs Sharing data on a LAN can increase productivity Sharing networked hardware can reduce costs Sharing networked hardware can provide access to a wide range of services and specialized peripheral devices Computer Concepts 28 LAN Advantages And Challenges p226-227 Do LANs have disadvantages? when a network malfunctions(失灵), all the resources you're accustomed to accessing are unavailable until the network is repaired. their vulnerability(弱点) to unauthorized access. more vulnerable than standalone computers to malicious(怀恶意的) code. Computer Concepts 29 Sharing Files p228 How do I access network resource? If you use Windows, it automatically detects available LANs any time you turn on a workstation. You can access shared data on other workstations in a variety of ways. Such as Windows Explorer Driver mapping Computer Concepts 30 Sharing Files p229 How do I specify which resources can be shared by other workstations? You can allow other network users to view and edit files in the folders you've designated as shared, or you can limit access only to viewing. Computer Concepts 31 Sharing Files p230 What is file server? A file server is a computer whose primary purpose is to be a repository(仓库) for files that can be accessed by network workstations. Are file servers a good idea for home networks? Whereas file servers are an essential component of most business networks, in many home networks, files are stored on workstations in shared folders rather than on a file server. Computer Concepts 32 Sharing Printers p230 How can I set up a printer for network access? Computer Concepts 33 Sharing Printers p231 How does printer sharing work? ① Connect the printer to one of the workstations ② Enable printer sharing ③ turn on printer and workstation Any workstation on the network can send print jobs to the printer. How do I enable printer sharing? Computer Concepts 34 Sharing Printers p231 How do I send a print job to a shared printer? you have to make sure that the printer driver is installed on your computer Computer Concepts 35 Troubleshooting p232 What if my network stops working? Cables Signal strength Interference Network devices Security Computer Concepts 36 Section E Security Through Encryption Wi-Fi Security p234 What are the threats to my wireless network? wireless networks are much more susceptible to unauthorized access and use. Evil twin LAN jacking War chalking How can I secure my wireless network? Wireless encryption(编密码) scrambles(加密) the data transmitted between wireless devices and then unscrambles the data only on devices that have a valid encryption key. What are the types of wireless encryption? WEP WPA http://myhard.yesky.com/net/441/2152441.shtml http://www.rcdaily.com.cn/html/wuxian/20080220/71.html Computer Concepts 37 Encryption p237 Exactly what is encryption? Encryption transforms a message in such a way that its contents are hidden from unauthorized readers. How does encryption work? An original message---one that has not yet been encrypted-is referred to as plaintext(明文). An encrypted message is referred to as ciphertext(暗文). The process of converting plaintext into ciphertext is called encryption. The reverse process converting ciphertext into plaintext is called decryption. Computer Concepts 38 Encryption p237 What's the difference between strong and weak encryption? weak encryption is easy to decrypt even without the algorithm and key. Strong encryption is loosely defined as "very difficult to break." How long does it take to break strong encryption ? Encryption methods can be broken by the use of expensive, specialized, code-breaking computers. A 32-bit key (232) numbers less than a day A 40-bit key (240) numbers a week 128-bit encryption and 256-bit encryption are probably secure for several years. Most encryption today uses a 128-bit key. Computer Concepts 39 THE END