CH-7-9 Wide Area Networks – Network+ Guide to Networks : Chapter Notes

This Document Contains Chapters 7 to 9 Chapter 7 Wide Area Networks At a Glance Instructor’s Manual Table of Contents • Overview • Objectives • Teaching Tips • Quick Quizzes • Class Discussion Topics • Additional Projects • Additional Resources • Key Terms Lecture Notes Overview A WAN is a network that connects two or more geographically distinct LANs. One might assume that WANs are the same as LANs, only bigger. Although a WAN is based on the same principles as a LAN, including reliance on the OSI model, its distance requirements affect its entire infrastructure. As a result, WANs differ from LANs in nearly every respect. This chapter discusses the technical differences between LANs and WANs and describes WAN transmission media and methods in detail. It also notes the potential pitfalls in establishing and maintaining WANs. In addition, it introduces the student to remote connectivity for LANs - a technology that, in some cases, can be used to extend a LAN into a WAN. Remote connectivity and WANs are significant concerns for organizations attempting to meet the needs of telecommuting workers, global business partners, and Internet-based commerce. Chapter Objectives After reading this chapter and completing the exercises, the student will be able to: • Identify a variety of uses for WANs • Explain different WAN topologies, including their advantages and disadvantages • Compare the characteristics of WAN technologies, including their switching type, throughput, media, security, and reliability • Describe several WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, broadband over powerline, ATM, and SONET Teaching Tips WAN Essentials 1. Define and describe a WAN. 2. Point out that the Internet is the largest WAN in existence today. 3. Describe why any business or government institution with sites scattered over a wide geographical area needs a WAN. Provide examples. 4. Discuss the fundamental properties WANs and LANs have in common. 5. Discuss the differences between WANs and LANs. 6. Define and explain the term NSPs (network service providers). 7. Define the term, dedicated line and explain the advantages it provides. 8. Define and describe a WAN link. 9. Use Figure 7-1 to illustrates the difference between WAN and LAN connectivity. Teaching Tip Students may read a brief history report covering the largest WAN in existence today (the Internet) at http://www.isoc.org/internet/history/brief.shtml WAN Topologies 1. Explain how WAN topologies differ from LAN topologies. Bus 1. Define the bus WAN topology. 2. Describe the similarities and differences of WAN, and LAN bus topologies. 3. Note the type of WAN best suited for a bus WAN topology. 4. Use Figure 7-2 to illustrate a bus WAN topology. Ring 1. Define the ring WAN topology. 2. Describe the similarities and differences of WAN, and LAN ring topologies. 3. Note the type of WAN best suited for a ring WAN topology. 4. Use Figure 7-3 to illustrate a ring WAN topology. Star 1. Describe the star WAN topology. 2. Use Figure 7-4 to illustrate a ring WAN topology. 3. Describe the benefits of a star WAN topology. 4. Mention the one drawback of the star WAN topology. Mesh 1. Describe the mesh WAN topology. 2. Describe the benefits of a mesh WAN topology. 3. Emphasize and explain why mesh WANs are the most fault-tolerant type of WAN. 4. Use Figure 7-5 to illustrate a mesh WAN topology. 5. Define and describe a full-mesh WAN. 6. Mention one drawback of the full-mesh WAN topology. 7. Define and describe a partial-mesh WAN. 8. Use Figure 7-5 to illustrate a full-mesh WAN and a partial-mesh WAN. Tiered 1. Define and describe a tiered topology WAN. 2. Use Figure 7-6 to illustrate a tiered WAN topology. 3. Explain how the flexibility of these types of WANs allows many variations. 4. Note how this flexibility also affects the creation of tiered WANs in terms of requiring careful consideration of geography, usage patterns, and growth potential. PSTN 1. Define and describe a PSTN. 2. Mention that the name POTS also refers to a PSTN. 3. Note how PSTNs originally carried data and compare it to today’s methods. 4. Explain why it is helpful to understand how the PSTN provided WAN connectivity when the Internet first became popular in the 1990s. 5. Define dial-up connections and explain how their use in early PSTN and WAN access. 6. Explain why modems are usually necessary when computers connect to a public or private data network via the PSTN. 7. Use Figure 7-7 to describe the main stages of dial-up Internet access. Teaching Tip Point out to the students that, as represented in Figure 7-7, the WAN of the regional offices is represented as a cloud. On networking diagrams, packet-switched networks (including the Internet) are depicted as clouds, because of the indeterminate nature of their traffic patterns. 8. Use Figure 7-8 to illustrate the local loop portion for dial-up WAN access. 9. Describe the implementations of various digital local loops, including optical technologies. 10. Use Figure 7-9 to illustrate a passive optical network. 11. Explain the purpose of the demarcation point. 12. Describe the advantages of using the PSTN for an Internet connection. 13. Describe the disadvantages of using the PSTN for an Internet connection. X.25 and Frame Relay 1. Define and describe the ITU X.25 standard protocol. 2. Explain the advantage and disadvantage of having transmissions verified at every node. 3. Define and describe frame relay. 4. Compare X.25 and frame relay in terms of error checking, and throughput. 5. Describe a virtual circuit and its advantage. 6. Note that both X.25 and frame relay implement virtual networks. 7. Explain SVCs (switched virtual circuits). 8. Explain PVCs (permanent virtual circuits). 9. Note that both X.25 and frame relay implement SVCs and PVCs. 10. Describe how lease contracts work for X.25 and frame relay circuits. 11. Define the term CIR (committed information rate). 12. Describe how the lease works for a PVC circuit. 13. Discuss frame relay lease advantages. 14. Discuss frame relay and X.25 disadvantages. 15. Explain why frame relay and X.25 easily upgrade to T-carrier dedicated lines. 16. Use Figure 7-10 to illustrate a WAN using frame relay. Teaching Tip Students may find more information on X.25 at http://docwiki.cisco.com/wiki/X.25 Teaching Tip Students may find more information on frame relay at http://docwiki.cisco.com/wiki/Frame_Relay ISDN 1. Briefly describe the history of ISDN. 2. Point out where ISDN protocols operate in the OSI model. 3. Describe the ISDN transmission medium. 4. Describe the two types of ISDN connections: a. Dial-up b. Dedicated 5. Define and explain the two types of ISDN channels on which connections are based: a. B channels b. D channels 6. Describe a BRI (Basic Rate Interface). 7. Define the term bonding. 8. Use Figure 7-11 to illustrate a BRI link. 9. Describe a PRI (Primary Rate Interface). 10. Compare and contrast PRI and BRI connections. 11. Describe how a NT2 (Network Termination 2) device is used. 12. Use Figure 7-12 to illustrate a PRI link. T-Carriers 1. Introduce T-carrier technology. 2. Point out where T-carrier protocols operate in the OSI model. 3. Explain how a T-carrier divides a single channel into multiple channels. 4. Describe the T-carrier transmission medium. Types of T-Carriers 1. Use Table 7-1 to illustrate the various T-carrier circuit specifications. 2. Point out the most common T-carrier implementations. 3. Describe a T1 circuit’s operation and throughput. 4. Describe a T3 circuit’s operation and throughput. 5. Define the term signal level and its implications in T-carrier speed. 6. Describe common uses for T1 and T3 circuits. 7. Define a fraction T1 lease and its advantages. T-Carrier Connectivity 1. Introduce characteristics of T-carrier connectivity hardware used at both the customer site and the local telecommunications providers switching facility. 2. Mention that T-carrier lines require different media, depending on their throughput. 3. Describe the physical wiring component T1 technology uses. 4. Define and explain the functions of a smart jack. 5. Use Figure 7-15 to illustrate a T1 smart jack. 6. Define and explain the functions of CSUs (channel service units) and DSUs (data service units). 7. Use Figure 7-16 to illustrate a stand-alone CSU/DSU. 8. Use Figure 7-17 to illustrate a typical use of smart jacks and CSU/DSUs with a point-to-point T1-connected WAN. 9. Define and describe the use of terminal equipment on a typical T1-connected data network. a. Include a description of how terminal equipment such as a router or switch interacts with CSU/DSU signals. 10. Use Figure 7-18 to illustrate how a router with an integrated CSU/DSU can be used to connect a LAN with a T1 WAN link. Quick Quiz 1 1. True or False: A WAN link is a connection between one WAN site and another site. Answer: True 2. WANs that use the ____ topology are only practical for connecting fewer than four or five locations. a. tiered b. ring c. star d. mesh Answer: B 3. True or False: X.25 is quite suitable for time-sensitive applications, such as audio or video. Answer: False 4. True or False: PVCs are dedicated, individual links. Answer: False 5. ISDN BRI (Basic Rate Interface) uses ____ B channels and one D channel. a. zero b. one c. two d. three Answer: C 6. A ____ provides T-carrier digital signal termination. a. DSU b. CSU c. smart jack d. terminal adapter Answer: B DSL (Digital Subscriber Line) 1. Define and describe characteristics of a DSL (digital subscriber line). Types of DSL 1. Define the term xDSL. 2. Describe the better-known DSL varieties. 3. Note the two categories of DSL types can be divided into asymmetrical and symmetrical. 4. Explain the concepts of downstream and upstream data transmission. 5. Describe asymmetrical communications. 6. Describe symmetrical communications. 7. Describe how DSL versions differ in the type of modulation they use. 8. Describe how DSL versions differ in terms of their capacity and maximum line length. 9. Mention that DSL types vary according to how they use the PSTN. 10. Use Table 7-2 to compare current specifications for six DSL types. DSL Connectivity 1. Explain how an ADSL connection flows from a home computer, through the local loop, and to the telecommunications carriers switching facility. 2. Define the term DSL modem. 3. Use Figure 7-19 to illustrate a DSL modem. 4. Explain what a DSLAM (DSL access multiplexer) is and what it does. 5. Use Figure 7-20 to illustrate a DSL connection. 6. Mention the competition of DSL. 7. Review DSL installation costs. 8. Discuss the major drawback of DSL. Teaching Tip Students may find more information on DSL at http://support.gateway.com/s/tutorials/index/Tutorials.asp?cat=3&subcat=18&topic=115&series=1415 Broadband Cable 1. Introduce broadband cable. 2. Describe the transmission media it uses. 3. Compare the theoretical transmission rates with the real transmission rates. 4. Discuss best use scenarios for broadband cable. 5. Define a cable modem and explain its purpose in broadband communication. 6. Use Figure 7-21 to illustrate a cable modem. 7. Describe the infrastructure required for broadband cable to operate. 8. Use Figure 7-22 to illustrate the infrastructure of a cable system. 9. Point out that broadband cable provides a dedicated, or continuous, connection that does not require dialing up a service provider. 10. Describe the drawback of broadband cable that raises concerns about security and actual throughput. 11. Mention that cable broadband access continues to service the majority of residential customers, whereas DSL is more popular among business customers. Teaching Tip Students may find more information on cable modems at http://www.howstuffworks.com/cable-modem.htm Teaching Tip Students may find more information on cable technologies at http://docwiki.cisco.com/wiki/Cable_Access_Technologies BPL (Broadband Over Powerline) 1. Point out where BPL protocols operate in the OSI model. 2. Explain the shared nature of BPL and the potential reach of BPL. 3. Explain that BPL technologies peaked in the mid-2000s and never achieved widespread deployment. ATM (Asynchronous Transfer Mode) 1. Point out where ATM protocols operate in the OSI model. 2. Describe the asynchronous communications method as it is referenced in ATM. 3. Point out that like Ethernet, ATM specifies Data Link layer framing techniques. 4. Explain what sets ATM apart from Ethernet. 5. Explain that in ATM, a packet is called a cell and the cell always consists of 48 bytes of data plus a 5-byte header. 6. Describe a drawback of a smaller packet size and explain how the drawback is overcome by cell efficiency. 7. Explain how ATM relies on virtual circuits. 8. Explain how ATM guarantees specific QoS (quality of service). 9. Discuss how ATM’s developers have made certain ATM is compatible with other leading network technologies. 10. Mention ATMs significant throughput potential. 11. Point out the cost disadvantage inherent with ATM. Teaching Tip Students may find a tutorial on ATM at http://www.techfest.com/networking/atm/atm.htm SONET (Synchronous Optical Network) 1. Describe the four key strengths of SONET. 2. Explain what is meant by synchronous in SOMET technology. 3. Explain the interoperability advantage of SONET. 4. Explain the fault tolerant advantage of SONET. 5. Use Figure 7-23 to illustrate a SONET ring. 6. Describe the SONET ring. 7. Use Figure 7-24 to illustrate the devices necessary to connect a WAN site with a SONET ring. 8. Define the term OC (Optical Carrier) level and explain its relation in determining the data rate of a particular SONET ring. 9. Use Table 7-3 to list the OC levels and their maximum throughput. 10. Explain the best use of SONET. Teaching Tip Students may find a tutorial on SONET at http://compnetworking.about.com/od/hardwarenetworkgear/l/aa092800a.htm WAN Technologies Compared 1. Use Table 7-4 to summarize the media and throughputs offered by each technology discussed so far. Quick Quiz 2 1. True or False: Broadband cable relies on the PSTN for transmission medium. Answer: False 2. ____ communication occurs when the downstream throughput is higher than the upstream throughput. a. DSU b. CSU c. Symmetrical d. Asymmetrical Answer: D 3. ____ sets ATM apart from Ethernet. a. Fixed packet size b. Security c. Wiring d. Throughput Answer: A 5. True or False: An advantage of SONET is its fault tolerance. Answer: True 6. ____________________ refers to dialing directly into a private network’s or ISP’s remote access server to log on to a network. Answer: Dial-up networking 7. True or False: ATM is a widely deployed technology that could one day overtake the Ethernet. Answer: False 8. True or False: BPL is a cost-effective technology that will maximize the widely deployed electrical grid as infrastructure. Answer: False 9. ____________________ is an open source system designed to allow one workstation to remotely manipulate and receive screen updates from another workstation. Answer: VNC (virtual network computing Virtual network computing VNC Class Discussion Topics 1. Take a class poll to determine what kind of Internet access students have at home. Discuss the availability of DSL in the area, and the pros and cons of each available access type. 2. Discuss the security implication of always-on technologies like DSL in remote home offices. What concerns are there? Are they justified? Is the technology worth the security risks, if any? Additional Projects 1. Have students compare cable broadband and DSL services in their residential areas. Each student should write a report summarizing his or her findings. 2. Have students research a remote virtual computing software product not covered in this lesson. Each student should write a report summarizing his or her findings. Additional Resources 1. Local Loop http://en.wikibooks.org/wiki/Communication_Networks/Local_Loop 2. Resource page providing support for virtual private network (VPN) technologies in Microsoft Windows http://technet.microsoft.com/en-us/network/bb545442.aspx 3. DSL resource http://www.dslreports.com/ 4. Cisco Internetworking Technology Handbook http://www.cisco.com/en/US/docs/internetworking/technology/handbook/ito_doc.html 5. Cable Networks http://en.wikibooks.org/wiki/Communication_Networks/Cable Key Terms  asymmetrical The characteristic of a transmission technology that affords greater bandwidth in one direction (either from the customer to the carrier, or vice versa) than in the other direction.  asymmetrical DSL A variation of DSL that offers more throughput when data travels downstream, downloading from a local carrier’s switching facility to the customer, than when data travels upstream, uploading from the customer to the local carrier’s switching facility.  asynchronous A transmission method in which data being transmitted and received by nodes do not have to conform to any timing scheme. In asynchronous communications, a node can transmit at any time and the destination node must accept the transmission as it comes.  Asynchronous Transfer Mode See ATM.  ATM (Asynchronous Transfer Mode) A Data Link layer technology originally conceived in the early 1980s at Bell Labs and standardized by the ITU in the mid-1990s. ATM relies on fixed packets, called cells, that each consist of 48 bytes of data plus a 5-byte header. ATM relies on virtual circuits and establishes a connection before sending data. The reliable connection ensured by ATM allows network managers to specify QoS levels for certain types of traffic.  B channel In ISDN, the “bearer” channel, so named because it bears traffic from point to point.  Basic Rate Interface See BRI.  bonding The process of combining more than one bearer channel of an ISDN line to increase throughput. For example, BRI’s two 64-Kbps B channels are bonded to create an effective throughput of 128 Kbps.  BPL (broadband over powerline) High-speed Internet access delivered over the electrical grid.  BRI (Basic Rate Interface) A variety of ISDN that uses two 64-Kbps bearer channels and one 16-Kbps data channel, as summarized by the notation 2B+D. BRI is the most common form of ISDN employed by home users.  broadband cable A method of connecting to the Internet over a cable network. In broadband cable, computers are connected to a cable modem that modulates and demodulates signals to and from the cable company’s head-end.  broadband over powerline See BPL.  bus topology WAN A WAN in which each location is connected to no more than two other locations in a serial fashion.  cable drop The fiber-optic or coaxial cable that connects a neighborhood cable node to a customer’s house.  cable modem A device that modulates and demodulates signals for transmission and reception via cable wiring.  cable modem access See broadband cable.  cell A packet of a fixed size. In ATM technology, a cell consists of 48 bytes of data plus a 5-byte header.  central office See CO.  channel service unit See CSU.  CIR (committed information rate) The guaranteed minimum amount of bandwidth selected when leasing a frame relay circuit. Frame relay costs are partially based on CIR.  CO (central office) The location where a local or long-distance telephone service provider terminates and interconnects customer lines.  committed information rate See CIR.  CSU (channel service unit) A device used with T-carrier technology that provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. Typically, a CSU is combined with a DSU in a single device, a CSU/DSU.  CSU/DSU A combination of a CSU (channel service unit) and a DSU (data service unit) that serves as the connection point for a T1 line at the customer’s site. Most modern CSU/DSUs also contain a multiplexer. A CSU/DSU may be a separate device or an expansion card in another device, such as a router.  D channel In ISDN, the “data” channel is used to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals.  data service unit See DSU.  dedicated A continuously available link or service that is leased through another carrier. Examples of dedicated lines include ADSL, T1, and T3.  dial-up A type of connection in which a user connects to a distant network from a computer and stays connected for a finite period of time. Most of the time, the term dial-up refers to a connection that uses a PSTN line.  digital subscriber line See DSL.  downstream A term used to describe data traffic that flows from a carrier’s facility to the customer. In asymmetrical communications, downstream throughput is usually much higher than upstream throughput. In symmetrical communications, downstream and upstream throughputs are equal.  DS0 (digital signal, level 0) The equivalent of one data or voice channel in T-carrier technology, as defined by ANSI Physical layer standards. All other signal levels are multiples of DS0.  DSL (digital subscriber line) A dedicated WAN technology that uses advanced data modulation techniques at the Physical layer to achieve extraordinary throughput over regular phone lines. DSL comes in several different varieties, the most common of which is Asymmetric DSL (ADSL).  DSL access multiplexer See DSLAM.  DSL modem A device that demodulates an incoming DSL signal, extracting the information and passing it to the data equipment (such as telephones and computers) and modulates an outgoing DSL signal.  DSLAM (DSL access multiplexer) A connectivity device located at a telecommunications carrier’s office that aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the Internet backbone.  DSU (data service unit) A device used in T-carrier technology that converts the digital signal used by bridges, routers, and multiplexers into the digital signal used on cabling. Typically, a DSU is combined with a CSU in a single device, a CSU/DSU.  E1 A digital carrier standard used in Europe that offers 30 channels and a maximum of 2.048-Mbps throughput.  E3 A digital carrier standard used in Europe that offers 480 channels and a maximum of 34.368-Mbps throughput.  fiber to the home See FTTH.  fiber to the premises See FTTP.  fractional T1 An arrangement that allows a customer to lease only some of the channels on a T1 line.  frame relay A digital, packet-switched WAN technology whose protocols operate at the Data Link layer. The name is derived from the fact that data is separated into frames, which are then relayed from one node to another without any verification or processing. Frame relay offers throughputs between 64 Kbps and 45 Mbps. A frame relay customer chooses the amount of bandwidth he requires and pays for only that amount.  FTTH (fiber to the home) A service in which a residential customer is connected to his carrier’s network with fiber-optic cable.  FTTP (fiber to the premises) A service in which a residential or business customer is connected to his carrier’s network using fiber-optic cable.  full-mesh WAN A version of the mesh topology WAN in which every site is directly connected to every other site. Full-mesh WANs are the most fault-tolerant type of WAN.  head-end A cable company’s central office, which connects cable wiring to many nodes before it reaches customers’ sites.  HFC (hybrid fiber-coax) A link that consists of fiber cable connecting the cable company’s offices to a node location near the customer and coaxial cable connecting the node to the customer’s house. HFC upgrades to existing cable wiring are required before current TV cable systems can provide Internet access.  hybrid fiber-coax See HFC.  Integrated Services Digital Network See ISDN.  ISDN (Integrated Services Digital Network) An international standard that uses PSTN lines to carry digital signals. It specifies protocols at the Physical, Data Link, and Transport layers of the OSI model. ISDN lines may carry voice and data signals simultaneously. Two types of ISDN connections are used in North America: BRI (Basic Rate Interface) and PRI (Primary Rate Interface). Both use a combination of bearer channels (B channels) and data channels (D channels).  LAN Emulation See LANE.  LANE (LAN Emulation) A method for transporting token ring or Ethernet frames over ATM networks. LANE encapsulates incoming Ethernet or token ring frames, then converts them into ATM cells for transmission over an ATM network.  last mile See local loop.  local loop The part of a phone system that connects a customer site with a telecommunications carrier’s switching facility.  mesh topology WAN A type of WAN in which several sites are directly interconnected. Mesh WANs are highly fault tolerant because they provide multiple routes for data to follow between any two points.  network interface unit See NIU.  network service provider See NSP.  Network Termination 1 See NT1.  Network Termination 2 See NT2.  NIU (network interface unit) The point at which PSTN-owned lines terminate at a customer’s premises. The NIU is usually located at the demarc.  NSP (network service provider) A carrier that provides long-distance (and often global) connectivity between major data-switching centers across the Internet. AT&T, Verizon, and Sprint are all examples of network service providers in the United States. Customers, including ISPs, can lease dedicated private or public Internet connections from an NSP.  NT1 (Network Termination 1) A device used on ISDN networks that connects the incoming twisted pair wiring with the customer’s ISDN terminal equipment.  NT2 (Network Termination 2) An additional connection device required on PRI to handle the multiple ISDN lines between the customer’s network termination connection and the local phone company’s wires.  OC (Optical Carrier) An internationally recognized rating that indicates throughput rates for SONET connections.  OLT (optical line terminal) A device located at the carrier’s endpoint of a passive optical network. An ONU contains multiple optical ports, or PON interfaces and a splitter that subdivides the capacity of each port into up to 32 logical channels, one per subscriber.  ONU (optical network unit) In a passive optical network, the device near the customer premises that terminates a carrier’s fiber-optic cable connection and distributes signals to multiple endpoints via fiber-optic cable, in the case of FTTP, or via copper or coax cable.  Optical Carrier See OC.  optical line terminal See OLT.  optical network unit See ONU.  partial-mesh WAN A version of a mesh topology WAN in which only critical sites are directly interconnected and secondary sites are connected through star or ring topologies. Partial-mesh WANs are less expensive to implement than full-mesh WANs.  passive optical network See PON.  permanent virtual circuit See PVC.  plain old telephone service (POTS) See PSTN.  PON (passive optical network) A network in which a carrier uses fiber-optic cabling to connect with multiple endpoints—for example, many businesses on a city block. The word passive applies because in a PON no repeaters or other connectivity devices intervene between a carrier and its customer.  POTS See PSTN.  PRI (Primary Rate Interface) A type of ISDN that uses 23 bearer channels and one 64-Kbps data channel, represented by the notation 23B+D. PRI is less commonly used by individual subscribers than BRI, but it may be used by businesses and other organizations needing more throughput.  PSTN (Public Switched Telephone Network) The network of lines and carrier equipment that provides telephone service to most homes and businesses. Now, except for the local loop, nearly all of the PSTN uses digital transmission. Its traffic is carried by fiber-optic or copper twisted pair cable, microwave, and satellite connections.  Public Switched Telephone Network See PSTN.  PVC (permanent virtual circuit) A point-to-point connection over which data may follow any number of different paths, as opposed to a dedicated line that follows a predefined path. X.25, frame relay, and some forms of ATM use PVCs.  registered jack 48 See RJ-48.  ring topology WAN A type of WAN in which each site is connected to two other sites so that the entire WAN forms a ring pattern.  RJ-48 (registered jack 48) A standard for terminating wires in an eight-pin connector. RJ-48 is the preferred connector type for T1 connections that rely on twisted pair wiring.  SDH (Synchronous Digital Hierarchy) The international equivalent of SONET.  self-healing A characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed.  signal level An ANSI standard for T-carrier technology that refers to its Physical layer electrical signaling characteristics. DS0 is the equivalent of one data or voice channel. All other signal levels are multiples of DS0.  smart jack A termination for T-carrier wire pairs that is located at the customer demark and which functions as a connection protection and monitoring point.  SONET (Synchronous Optical Network) A high-bandwidth WAN signaling technique that specifies framing and multiplexing techniques at the Physical layer of the OSI model. It can integrate many other WAN technologies (for example, T-carriers, ISDN, and ATM technology) and allows for simple link additions and removals. SONET’s topology includes a double ring of fiber-optic cable, which results in very high fault tolerance.  star topology WAN A type of WAN in which a single site acts as the central connection point for several other points. This arrangement provides separate routes for data between any two sites; however, if the central connection point fails, the entire WAN fails.  SVC (switched virtual circuit) A logical, point-to-point connection that relies on switches to determine the optimal path between sender and receiver. ATM technology uses SVCs.  switched virtual circuit See SVC.  symmetrical A characteristic of transmission technology that provides equal throughput for data traveling both upstream and downstream and is suited to users who both upload and download significant amounts of data.  symmetrical DSL A variation of DSL that provides equal throughput both upstream and downstream between the customer and the carrier.  synchronous A transmission method in which data being transmitted and received by nodes must conform to a timing scheme.  Synchronous Digital Hierarchy See SDH.  Synchronous Optical Network See SONET.  T1 A digital carrier standard used in North America and most of Asia that provides 1.544-Mbps throughput and 24 channels for voice, data, video, or audio signals. T1s rely on time division multiplexing and may use shielded or unshielded twisted pair, coaxial cable, fiber optics, or microwave links.  T3 A digital carrier standard used in North America and most of Asia that can carry the equivalent of 672 channels for voice, data, video, or audio, with a maximum data throughput of 44.736 Mbps (typically rounded up to 45 Mbps for purposes of discussion). T3s rely on time division multiplexing and require either fiber-optic or microwave transmission media.  T-carrier The term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s.  TA (terminal adapter) A device used to convert digital signals into analog signals for use with ISDN phones and other analog devices. TAs are sometimes called ISDN modems.  TE (terminal equipment) The end nodes (such as computers and printers) served by the same connection (such as an ISDN, DSL, or T1 link).  terminal adapter See TA.  terminal equipment See TE.  tiered topology WAN A type of WAN in which sites that are connected in star or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings.  upstream A term used to describe data traffic that flows from a customer’s site to a carrier’s facility. In asymmetrical communications, upstream throughput is usually much lower than downstream throughput. In symmetrical communications, upstream and downstream throughputs are equal.  virtual circuit A connection between network nodes that, although based on potentially disparate physical links, logically appears to be a direct, dedicated link between those nodes.  WAN link A point-to-point connection between two nodes on a WAN.  X.25 An analog, packet-switched WAN technology optimized for reliable, long-distance data transmission and standardized by the ITU in the mid-1970s. The X.25 standard specifies protocols at the Physical, Data Link, and Network layers of the OSI model. It provides excellent flow control and ensures data reliability over long distances by verifying the transmission at every node. X.25 can support a maximum of only 2-Mbps throughput.  xDSL The term used to refer to all varieties of DSL. Chapter 8 Wireless Networking At a Glance Instructor’s Manual Table of Contents • Overview • Objectives • Teaching Tips • Quick Quizzes • Class Discussion Topics • Additional Projects • Additional Resources • Key Terms Lecture Notes Overview The Earth’s atmosphere provides an intangible means of transporting data over networks. For decades, radio and TV stations have used the atmosphere to transport information via analog signals. Such analog signals are also capable of carrying data. Networks that transmit signals through the atmosphere via radio frequency (RF) waves are known as wireless networks or WLANs (wireless local area networks). Wireless transmission media is now common in business and home networks and necessary in some specialized network environments. In this chapter, the student will learn how data travels through the air and how to make it happen on their network. Chapter Objectives After reading this chapter and completing the exercises, the student will be able to: • Explain how nodes exchange wireless signals • Identify potential obstacles to successful wireless transmission and their repercussions, such as interference and reflection • Understand WLAN (wireless LAN) architecture • Specify the characteristics of popular WLAN transmission methods, including 802.11 a/b/g/n • Install and configure wireless access points and their clients • Describe wireless WAN technologies, including 802.16 (WiMAX), HSPA+, LTE and satellite communications Teaching Tips The Wireless Spectrum 1. Define the term wireless spectrum. 2. Explain how wireless spectrum waves are arranged. 3. Use Figure 8-1 to illustrate the wireless spectrum and the major wireless services associated with each frequency range. 4. Describe the role of the FCC with respect to managing the wireless spectrum in the United States. 5. Describe the role of the ITU with respect to managing the wireless spectrum internationally. Teaching Tip The FCC Wireless Telecommunications Bureau (WTB) handles nearly all FCC domestic wireless telecommunications programs, policies, and outreach initiatives. Go to http://wireless.fcc.gov and review the services and materials available. Characteristics of Wireless Transmission 1. Describe the characteristics wireless transmissions have in common with wired transmissions. 2. Describe the differences between wireless and wired transmissions. 3. Explain how wireless signals travel from the transmitter to the receiver. a. Emphasize the role of the antenna. 4. Use Figure 8-2 to illustrate wireless transmission and reception. Antennas 1. Introduce the concept of an antenna noting that each type of wireless service requires an antenna specifically designed for that service. 2. Define the term radiation pattern. 3. Define the term directional antenna and provide examples of its use. 4. Define the term omnidirectional antenna and provide examples of its use. 5. Define and explain the term range. Signal Propagation 1. Introduce the concept of signal propagation noting that ideally, a wireless signal would travel directly in a straight line from its transmitter to its intended receiver. 2. Define and explain LOS (line-of-sight) propagation. 3. Explain the options available when an obstacle stands in a signal’s way. a. The signal may pass through the object. b. The signal may be absorbed by the object. c. The signal may be subject to any of the following phenomena: reflection, diffraction, or scattering. 4. Note that the object’s geometry governs which of these three phenomena occurs. 5. Define and explain the term reflection. 6. Define and explain the term diffraction. 7. Define and explain the term scattering. 8. Define multipath signals noting the advantage and disadvantage they present. 9. Use Figure 8-3 to illustrate multipath signals caused by reflection, diffraction, and scattering. Signal Degradation 1. Define and explain fading. 2. Define and explain attenuation. 3. Describe the impact of noise on wireless signals. 4. Explain why interference is a significant problem for wireless communications. Frequency Ranges 1. Describe the 2.4-GHz band. 2. Define the term unlicensed. 3. Describe the 5-GHz band. Narrowband, Broadband, and Spread Spectrum Signals 1. Introduce narrowband, broadband, and spread spectrum signals noting that they define wireless spectrum use. 2. Define and explain narrowband. 3. Define an explain broadband. 4. Define and explain spread-spectrum. 5. Define and describe FHSS (frequency hopping spread spectrum). 6. Define and describe DSSS (direct-sequence spread spectrum). Fixed versus Mobile 1. Describe fixed communication wireless systems. 2. Describe mobile communication wireless systems. Quick Quiz 1 1. True or False: All wireless signals are carried through the air by electromagnetic waves. Answer: True 2. The ____________________ is a continuum of the electromagnetic waves used for data and voice communication. Answer: wireless spectrum 3. ____________________ are used for both the transmission and reception of wireless signals. Answer: Antennas 4. ____ signals follow a number of different paths to their destination because of reflection, diffraction, and scattering. a. Multipath b. Opened c. Closed d. Variable Answer: A 5. Wireless signals cannot depend on a(n) ____________________ or shielding to protect them from extraneous EMI. Answer: conduit 6. True or False: Spread-spectrum signaling is a popular way of making wireless transmissions more secure. Answer: True WLAN (Wireless LAN) Architecture 1. Explain why wireless networks are not laid out using the same topologies as wired networks. 2. Describe an ad hoc WLAN. 3. Define an access point and provide alternative names for it. 4. Use Figure 8-6 to illustrate an ad hoc WLAN. 5. Describe an infrastructure WLAN. 6. Use Figure 8-7 to illustrate an infrastructure WLAN. 7. Note that it is common for a WLAN to include several access points. 8. Explain why mobile networking allows roaming wireless nodes. 9. Explain why wireless technology can be used to connect two different parts of a LAN or two separate LANs. 10. Use Figure 8-8 to illustrate wireless LAN interconnection. 11. Explain the advantage of having WLANs support the same protocols (for example, TCP/IP) and operating systems (for example, UNIX, Linux, or Windows) as wired LANs. 802.11 WLANs 1. Introduce 802.11 WANs, noting that the evolution of wireless access methods did not follow one direct and cooperative path, but grew from the efforts of multiple vendors and organizations. 2. Introduce wireless technology standards. 3. Introduce Wi-Fi (wireless fidelity) standards. Access Method 1. Introduce and describe 802.11 MAC services frame modifications. 2. Note the significance of using the same physical addressing scheme as Ethernet. 3. Describe three characteristics of wireless devices that distinguish them from wired devices. a. Emphasize the difference in access method. 4. Explain the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) access method. a. Note the significance of using ACK packets to verify every transmission. 5. Describe the RTS/CTS (Request to Send/Clear to Send) protocol. Association 1. Introduce the concept of association by noting that association involves a number of packet exchanges between an access point and a computer. a. Note that association is another function of the MAC sublayer described in the 802.11 standard. 2. Define the term scanning. 3. Describe active scanning and passive scanning. 4. Define an SSID and explain its significance. 5. Define the BSS (basic service set) and explain its significance. 6. Define the ESS (extended service set) and explain its significance. 7. Use Figure 8-10 to illustrate a network with a single BSS. 8. Use Figure 8-11 to illustrate a network encompassing multiple BSSs that form an ESS. 9. Emphasize what happens if a station detects the presence of several access points. a. Explain why this process can present a security risk for any station within range of a powerful, rogue access point. 10. Explain why a network with several authorized access points in an ESS requires a station to be able to associate with any access point while maintaining network connectivity. 11. Define and explain reassociation. 12. Note that on a network with multiple access points, network managers can take advantage of the stations’ scanning feature to automatically balance transmission loads between those access points. Teaching Tip Explain why it is best to use access points manufactured by the same company when designing an 802.11 network. Frames 1. Review the types of overhead required to manage access to the 802.11 wireless networks. 2. Note that for each function, the 802.11 standard specifies a frame type at the MAC sublayer: a. ACKs, probes, beacons 3. Introduce and describe the three groups for these multiple frame types: a. Control, management, data 4. Compare a basic 802.11 data frame with an Ethernet_II (DIX) frame (Figure 8-12). 5. Describe the significant fields in an 802.11 data frame contributing to data frame overhead. 6. Point out that although 802.11b, 802.11a, 802.11g, and 802.11n share all of the MAC sublayer characteristics described in the previous sections, they differ in their modulation methods, frequency usage, and ranges. 802.11b 1. Describe the 802.11b standard. 802.11a 1. Describe the 802.11a standard. 802.11g 1. Describe the 802.11g standard. 802.11n 1. Describe the 802.11n standard. 2. Note how the 802.11n standard differs from 802.b. 3. Note how the 802.11n standard differs from 802.11a and 802.11g. 4. Describe 802.11n innovations: a. MIMO (multiple input-multiple output) b. Channel bonding c. Higher modulation rates d. Frame aggregation 5. Use Figure 8-13 to illustrate an 802.11n access point with three antennas. 6. Use Figure 8-15 to illustrate the relatively low overhead of an aggregated 802.11n frame. 7. Note that 802.11n is backward compatible with previous Wi-Fi standards; however in mixed environments, some of the new standard’s techniques for improving throughput will not be possible. Teaching Tip Provide a live demonstration by navigating to the Wi-Fi Alliance homepage at http://www.wi-fi.org and reviewing the material available at the site. 8. Use Table 8-1 to compare the common wireless networking standards, their ranges, and throughputs. Implementing a WLAN 1. Introduce the topics covered in this section: a. Designing a small WLAN b. Formation of larger, enterprise-wide WANs c. Installing and configuring access points and clients d. Implementation pitfalls Determining the Design 1. Describe how an access point might function if there is only one in the network. a. Note considerations involved with access point WLAN placement. 2. Use Figure 8-16 to illustrate a home or small office WLAN arrangement. 3. Explain why in larger WLAN environments, a systematic approach to access point placement is necessary. 4. Define and describe a site survey. 5. Point out the enterprise-wide WLAN design consideration. 6. Use Figure 8-17 to illustrate an enterprise-wide WLAN. Configuring Wireless Connectivity Devices 1. Review the steps to configure an access point. Configuring Wireless Clients 1. Review the steps to configure a Windows 7 client using a graphical interface. 2. Note that the iwconfig command may be used in UNIX and Linux environments to view and set wireless interface parameters. 3. Use Figure 8-18 to illustrate output from the iwconfig command. Avoiding Pitfalls 1. Describe the items that may cause issues in wireless configuration and explain how to avoid or correct them. Wireless WANs 1. Introduce and describe wireless broadband. 2. Review how access points figure into home networks and enterprise wide LANs. a. Note that most networks use the 802.11b or 802.11g access methods. 3. Define and describe a hotspot. b. Explain that a hotspot may accept a user’s connection based on his or her MAC address. Teaching Tip Provide an example of a commercial hotspot by visiting the T-mobile hot spot Web site at https://selfcare.hotspot.t-mobile.com/locations/viewLocationMap.do and reviewing the material available there. Cellular 1. Define and describe cellular networks. 2. Explain the architecture of cellular networks using Figure 8-22. 3. Describe the performance characteristics of the digital cellular networks. 4. Use Table 8-2 to describe the characteristics of some of the latest wireless WAN services. 802.16 (WiMAX) 5. Define and describe WiMAX. 6. Describe the two distinct advantages WiMAX has over Wi-Fi. 7. Discuss possible best uses for WiMAX. 8. Review residential installation of WiMAX. 9. Use Figure 8-21 to illustrate WiMAX residential service installation. 10. Use Figure 8-20 to illustrate a WiMAX residential antenna. 11. Describe WiMAX MAN service. 12. Note the one big disadvantage of WiMAX at this time. Teaching Tip Provide a live demonstration by navigating to the Discovery Channel site at http://dsc.discovery.com/technology/tech-10/wireless-cities-top.html to illustrate 10 cities with widespread wireless Internet. Satellite Internet Access 1. Introduce satellite Internet access by explaining where it is best utilized. 2. Define and describe geosynchronous orbit. 3. Define and describe LEO (low Earth orbiting) satellites. 4. Use Figure 8-23 to illustrate satellite communication. 5. Define and describe MEO (medium Earth orbiting) satellites. 6. Note that geosynchronous orbiting satellites are the most popular for satellite Internet access. 7. Describe satellite frequencies. 8. Note the bands that satellite Internet access providers use. 9. Describe satellite Internet services. a. Explain the dial return arrangement service. b. Explain the satellite return arrangement service. Teaching Tip Provide a live demonstration by navigating to the Clearwire Web site at http://www.clearwire.com to illustrate their Internet access offerings. Quick Quiz 2 1. ____________________ networking allows wireless nodes to roam from one location to another within a certain range of their access point. 2. Answer: Mobile 3. The four 802.11 standards (802.11b, 802.11a, 802.11g, 802.11n) are collectively known as ____. a. WiMAX b. Wi-Fi c. Bluetooth d. Open Answer: B 4. True or False: 802.11 networks use the same access method as Ethernet networks. Answer: False 5. The 802.11 standard specifies a frame type at the ____________________ sublayer. Answer: MAC 6. ____ orbiting satellites are the type used by the most popular satellite Internet access service providers. Answer: Geosynchronous Class Discussion Topics 1. Take a student poll of Wi-Fi use (802.11b, 802.11a, 802.11g, and 802.11n). Which standard is used the most by the class? Have the class discuss their experiences with the technology they use. Ask students to explain why they have or have not moved to the newer 802.11n standard. 2. WiMAX showed great promise for convenient and fast connectivity; however, deployment has stalled and there is a great deal of competition from cellular technologies, especially LTE. Discuss the technology in terms of its potential positive and negative impacts to society. Additional Projects 1. Have students research the AT&T network of hot spots across the nation. Each student should write a report summarizing his or her findings. 2. Have students research satellite Internet access. Students may select a vendor supplying the service, a manufacturer, or a technology. Each student should write a report summarizing his or her findings. Additional Resources 1. The ABCs of securing your wireless network http://arstechnica.com/security/news/2008/04/wireless-security.ars 2. Wi-Fi Certified Products http://www.wi-fi.org/wi-fi-certified%E2%84%A2-products 3. IEEE Commentary: WiMax and Wi-Fi: Separate and Unequal http://www.spectrum.ieee.org/mar04/3977 4. 10 Cities With Widespread Wireless Internet http://dsc.discovery.com/technology/tech-10/wireless-cities-top.html 5. How WiFi Works http://computer.howstuffworks.com/wireless-network.htm Key Terms  1G The first generation of mobile phone services, popular in the 1970s and 1980s, which were entirely analog.  2.4-GHz band The range of radio frequencies from 2.4 to 2.4835 GHz. The 2.4-GHz band, which allows for 11 unlicensed channels, is used by WLANs that follow the popular 802.11b and 802.11g standards. However, it is also used for cordless telephone and other transmissions, making the 2.4-GHz band more susceptible to interference than the 5-GHz band.  2G Second-generation mobile phone service, popular in the 1990s. 2G was the first standard to use digital transmission, and as such, it paved the way for texting and media downloads on mobile devices.  3G Third-generation mobile phone service, released in the early 2000s, that specifies throughputs of 384 Kbps and packet switching for data (but not voice) communications.  4G Fourth-generation mobile phone service that is characterized by an all-IP, packet-switched network for both data and voice transmission. 4G standards, released in 2008, also specify throughputs of 100 Mbps for fast-moving mobile clients, such as those in cars, and 1 Gbps for slow-moving mobile clients, such as pedestrians.  5-GHz band A range of frequencies that comprises four frequency bands: 5.1 GHz, 5.3 GHz, 5.4 GHz, and 5.8 GHz. It consists of 24 unlicensed bands, each 20-MHz wide. The 5-GHz band is used by WLANs that follow the 802.11a and 802.11n standards.  802.11a The IEEE standard for a wireless networking technique that uses multiple frequency bands in the 5-GHz frequency range and provides a theoretical maximum throughput of 54 Mbps. 802.11a’s high throughput, compared with 802.11b, is attributable to its use of higher frequencies, its unique method of encoding data, and more available bandwidth.  802.11b The IEEE standard for a wireless networking technique that uses DSSS (direct-sequence spread spectrum) signaling in the 2.4–2.4835-GHz frequency range (also called the 2.4-GHz band). 802.11b separates the 2.4-GHz band into 14 overlapping 22-MHz channels and provides a theoretical maximum of 11-Mbps throughput.  802.11g The IEEE standard for a wireless networking technique designed to be compatible with 802.11b while using different encoding techniques that allow it to reach a theoretical maximum capacity of 54 Mbps. 802.11g, like 802.11b, uses the 2.4-GHz frequency band.  802.11n The IEEE standard for a wireless networking technique that may issue signals in the 2.4- or 5-GHz band and can achieve actual data throughput between 65 and 600 Mbps. It accomplishes this through several means, including MIMO, channel bonding, and frame aggregation. 802.11n is backward compatible with 802.11a, b, and g.  802.16 An IEEE standard for wireless MANs. 802.16 networks may use frequencies between 2 and 66 GHz. Their antennas may operate in a line-of-sight or non-line-of-sight manner and cover 50 kilometers (or approximately 30 miles). 802.16 connections can achieve a maximum throughput of 70 Mbps, though actual throughput diminishes as the distance between transceivers increases. Several 802.16 standards exist. Collectively, they are known as WiMAX.  802.16e Currently, the most widely implemented version of WiMAX. With 802.16e, IEEE improved the mobility and QoS characteristics of the technology, making it better suited to VoIP and mobile phone users. 802.16e is capable of 70-Mbps throughput, but because bandwidth is shared and service providers cap data rates, most users actually experience 1–4Mbps throughput.  802.16m Also known as WiMAX 2, the IEEE standard for a version of 802.16 that achieves theoretical throughputs of 330 Mbps with lower latency and better quality for VoIP applications than previous WiMAX versions. 802.16m has been approved as a true 4G technology. Manufacturers expect it to reach throughputs of 1 Gbps in the near future. access point A device used on wireless LANs that transmits and receives wireless signals to and from multiple nodes and retransmits them to the rest of the network segment. Access points can connect a group of nodes with a network or two networks with each other. They may use directional or omnidirectional antennas.  active scanning A method used by wireless stations to detect the presence of an access point. In active scanning, the station issues a probe to each channel in its frequency range and waits for the access point to respond.  ad hoc A type of wireless LAN in which stations communicate directly with each other (rather than using an access point).  AP See access point.  association In the context of wireless networking, the communication that occurs between a station and an access point to enable the station to connect to the network via that access point.  backhaul An intermediate connection between subscriber networks and a telecommunications carrier’s network.  base station See access point.  basic service set See BSS.  basic service set identifier See BSSID.  beacon frame In the context of wireless networking, a frame issued by an access point to alert other nodes of its existence.  bounce See reflection.  BSS (basic service set) In IEEE terminology, a group of stations that share an access point.  BSSID (basic service set identifier) In IEEE terminology, the identifier for a BSS (basic service set).  Carrier Sense Multiple Access with Collision Avoidance See CSMA/CA.  cell In a cellular network, an area of coverage serviced by an antenna and base station.  channel bonding In the context of 802.11n wireless technology, the combination of two 20-MHz frequency bands to create one 40-MHz frequency band that can carry more than twice the amount of data that a single 20-MHz band could. It’s recommended for use only in the 5-GHz range because this band has more available channels and suffers less interference than the 2.4-GHz band.  CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) A network access method used on 802.11 wireless networks. In CSMA/CA, before a node begins to send data it checks the medium. If it detects no transmission activity, it waits a brief, random amount of time, and then sends its transmission. If the node does detect activity, it waits a brief period of time before checking the channel again. CSMA/CA does not eliminate, but minimizes, the potential for collisions.  diffraction In the context of wireless signal propagation, the phenomenon that occurs when an electromagnetic wave encounters an obstruction and splits into secondary waves. The secondary waves continue to propagate in the direction in which they were split. If you could see wireless signals being diffracted, they would appear to be bending around the obstacle. Objects with sharp edges—including the corners of walls and desks—cause diffraction.  direct-sequence spread spectrum See DSSS.  directional antenna A type of antenna that issues wireless signals along a single direction, or path.  downlink In the context of wireless transmission, the connection between a carrier’s antenna and a client’s transceiver—for example, a smartphone.  DSSS (direct-sequence spread spectrum) A transmission technique in which a signal’s bits are distributed over an entire frequency band at once. Each bit is coded so that the receiver can reassemble the original signal upon receiving the bits.  ESS (extended service set) A group of access points and associated stations (or basic service sets) connected to the same LAN.  ESSID (extended service set identifier) A special identifier shared by BSSs that belong to the same ESS.  extended service set See ESS.  extended service set identifier See ESSID.  fading A variation in a wireless signal’s strength as a result of some of the electromagnetic energy being scattered, reflected, or diffracted after being issued by the transmitter.  FHSS (frequency hopping spread spectrum) A wireless signaling technique in which a signal jumps between several different frequencies within a band in a synchronization pattern known to the channel’s receiver and transmitter.  fixed A type of wireless system in which the locations of the transmitter and receiver are static. In a fixed connection, the transmitting antenna focuses its energy directly toward the receiving antenna. This results in a point-to-point link.  frequency hopping spread spectrum See FHSS.  GEO (geosynchronous earth orbit) The term used to refer to a satellite that maintains a constant distance from a point on the equator at every point in its orbit. Geosynchronous orbit satellites are the type used to provide satellite Internet access.  geosynchronous earth orbit See GEO.  handoff The transition that occurs when a cellular network client moves from one antenna’s coverage area to another.  High Speed Packet Access Plus See HSPA+.  HSPA+ (High Speed Packet Access Plus) A 3G mobile wireless technology released in 2008 that uses MIMO and sophisticated encoding techniques to achieve a maximum 84-Mbps downlink throughput and 11-Mbps uplink throughput in its current release. Advances in more efficiently using limited channels and incorporating more antennas in MIMO promise to push the maximum downlink data rate to 336 Mbps.  infrastructure WLAN A type of WLAN in which stations communicate with an access point and not directly with each other.  iwconfig A command-line utility for viewing and setting wireless interface parameters on Linux and UNIX workstations.  line-of-sight See LOS.  Long Term Evolution See LTE.  LOS (line-of-sight) A wireless signal or path that travels directly in a straight line from its transmitter to its intended receiver. This type of propagation uses the least amount of energy and results in the reception of the clearest possible signal.  LTE (Long Term Evolution) A 4G cellular network technology that achieves downlink data rates of up to 1 Gbps and uplink rates up to 500 Mbps. AT&T and Verizon have adopted LTE for their high-speed wireless data networks.  MIMO (multiple input-multiple output) In the context of 802.11n wireless networking, the ability for access points to issue multiple signals to stations, thereby multiplying the signal’s strength and increasing their range and data-carrying capacity. Because the signals follow multipath propagation, they must be phase-adjusted when they reach their destination.  mobile A type of wireless system in which the receiver can be located anywhere within the transmitter’s range. This allows the receiver to roam from one place to another while continuing to pick up its signal.  mobile switching center See MSC.  mobile telecommunications switching office See MSC.  MSC (mobile switching center) A carrier’s facility to which multiple cellular base stations connect. An MSC might be located inside a telephone company’s central office or it might stand alone and connect to the central office via fiber-optic cabling or a microwave link. Equipment at an MSC manages mobile clients, monitoring their location and usage patterns, and switches cellular calls. It also assigns each mobile client an IP address.  MTSO (mobile telecommunications switching office) See MSC.  multipath The characteristic of wireless signals that follow a number of different paths to their destination (for example, because of reflection, diffraction, and scattering).  multiple input-multiple output See MIMO.  narrowband A type of wireless transmission in which signals travel over a single frequency or within a specified frequency range.  omnidirectional antenna A type of antenna that issues and receives wireless signals with equal strength and clarity in all directions. This type of antenna is used when many different receivers must be able to pick up the signal, or when the receiver’s location is highly mobile.  passive scanning In the context of wireless networking, the process in which a station listens to several channels within a frequency range for a beacon issued by an access point.  probe In 802.11 wireless networking, a type of frame issued by a station during active scanning to find nearby access points.  radiation pattern The relative strength over a three-dimensional area of all the electromagnetic energy an antenna sends or receives.  range The geographical area in which signals issued from an antenna or wireless system can be consistently and accurately received.  reassociation In the context of wireless networking, the process of a station establishing a connection (or associating) with a different access point.  reflection In the context of wireless, the phenomenon that occurs when an electromagnetic wave encounters an obstacle and bounces back toward its source. A wireless signal will bounce off objects whose dimensions are large compared with the signal’s average wavelength.  Request to Send/Clear to Send See RTS/CTS.  roaming In wireless networking, the process that describes a station moving between BSSs without losing connectivity.  RTS/CTS (Request to Send/Clear to Send) An exchange in which a wireless station requests the exclusive right to communicate with an access point and the access point confirms that it has granted that request.  scanning The process a wireless station undergoes to find an access point. See also active scanning and passive scanning.  scattering The diffusion of a wireless signal that results from hitting an object that has smaller dimensions compared with the signal’s wavelength. Scattering is also related to the roughness of the surface a wireless signal encounters. The rougher the surface, the more likely a signal is to scatter when it hits that surface.  service set identifier See SSID.  site survey In the context of wireless networking, an assessment of client requirements, facility characteristics, and coverage areas to determine an access point arrangement that will ensure reliable wireless connectivity within a given area.  spread spectrum A type of wireless transmission in which lower-level signals are distributed over several frequencies simultaneously. Spread-spectrum transmission is more secure than narrowband.  SSID (service set identifier) A unique character string used to identify an access point on an 802.11 network.  station An end node on a network; used most often in the context of wireless networks.  transponder The equipment on a satellite that receives an uplinked signal from Earth, amplifies the signal, modifies its frequency, then retransmits it (in a downlink) to an antenna on Earth.  uplink In the context of wireless transmission, the connection between a client’s transceiver and a carrier’s antenna.  WAP (wireless access point) See access point.  Wi-Fi See 802.11.  WiMAX See 802.16.  WiMAX 2 See 802.16m.  wireless A type of signal made of electromagnetic energy that travels through the air.  wireless access point See access point.  wireless gateway An access point that provides routing functions and is used as a gateway.  wireless LAN See WLAN.  wireless router An access point that provides routing functions.  wireless spectrum A continuum of electromagnetic waves used for data and voice communication. The wireless spectrum (as defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300 GHz. Each type of wireless service can be associated with one area of the wireless spectrum.  WLAN (wireless LAN) A LAN that uses wireless connections for some or all of its transmissions.  Worldwide Interoperability for Microwave Access (WiMAX) See 802.16a. Chapter 9 In-Depth TCP/IP Networking At a Glance Instructor’s Manual Table of Contents • Overview • Objectives • Teaching Tips • Quick Quizzes • Class Discussion Topics • Additional Projects • Additional Resources • Key Terms Lecture Notes Overview In Chapter 4, students learned about core protocols and subprotocols in the TCP/IP protocol suite, addressing schemes, and host and domain naming. Students also learned that TCP/IP is a complex and highly customizable protocol suite. This chapter builds on these basic concepts, examining how TCP/IP-based networks are designed and analyzed. It also describes the services and applications that TCP/IP-based networks commonly support. Chapter Objectives After reading this chapter and completing the exercises, the student will be able to: • Describe methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation • Explain the differences between public and private TCP/IP networks • Describe protocols used between mail clients and mail servers, including SMTP, POP3, and IMAP4 • Employ multiple TCP/IP utilities for network discovery and troubleshooting Teaching Tips Designing TCP/IP-Based Networks 1. Describe how most modern networks rely on the TCP/IP protocol suite. 2. Review TCP/IP fundamentals. 3. Note the two versions of IP. a. Explain why this discussion on IP addressing focuses on IPv4. 4. Review these IPv4 address expressions: a. Binary and dotted decimal 5. Remind students that many networks assign IP addresses and host names dynamically, using DHCP, rather than statically. 6. Review network classes. a. Emphasize that a node’s network class provides information about the segment or network to which the node belongs. Subnetting 1. Define the term subnetting. 2. Discuss how networks are commonly subnetted. a. Geographic locations b. Departmental boundaries c. Technology types 3. Discuss three reasons why a network administrator might separate traffic. 4. Review IPv4 addressing conventions on a network that does not use subnetting. 5. Introduce and explain classful addressing in IPv4. 6. Remind students that all IPv4 addresses consist of network and host information. 7. Explain where the network information portion of an IPv4 address (the network ID) is located in classful addressing: a. First 8 bits in a Class A address b. First 16 bits in a Class B address c. First 24 bits in a Class C address 8. Explain where the host information portion of an IPv4 address is located in classful addressing: a. Last 24 bits for a Class A address b. Last 16 bits in a Class B address c. Last 8 bits in a Class C address 9. Use Figure 9-1 to illustrate examples of IPv4 addresses separated into network and host information according to the classful addressing convention. 10. Introduce and describe IPv4 subnet masks. 11. Use Table 9-1 to illustrate how each network class is associated with a default subnet mask. a. Remind students that an octet composed of all 1s in binary notation equals 255 in decimal notation and an octet composed of all 0s in binary notation equals 0 in decimal notation. 12. Define and explain the concept of ANDing. a. Explain how to calculate a host’s network ID given its IPv4 address and subnet mask. b. Use Table 9-2 to illustrate ANDing. c. Use Figure 9-3 to illustrate and example of calculating a host’s network ID. Teaching Tip Point out that several online sites and operating systems provide calculators that calculate AND operations. Provide a class demonstration of the Windows operating system calculator by navigating to the Accessories area containing the calculator. Change the calculator view to scientific if necessary. Select “bin” for input and practice ANDing two binary numbers of various numeric contents and lengths. 13. Define and explain the concept of reserved addresses. a. Describe why the network ID is considered a reserved address. b. Describe why the broadcast address is considered a reserved address. c. Explain why only the numbers 1 through 254 can be used for host information in an IPv4 address. 14. Introduce and explain IPv4 subnetting techniques. a. Note that subnetting breaks the rules of classful IPv4 addressing. b. Describe how some bits in an IP address that represent host information in classful addressing are changed to represent network information instead. c. Emphasize the consequence of subnetting in terms of the number of useable host addresses available per subnet. d. Use Table 9-5 to illustrate the numbers of subnets and hosts that can be created by subnetting a Class B network. e. Use Table 9-5 to illustrate the numbers of subnets and hosts that can be created by subnetting a Class C network. 15. Introduce the topic of calculating IPv4 subnets. a. Present and explain the formula for determining how to modify a default subnet mask. b. Walk through an example that utilizes a leased Class C network with network ID of 199.34.89.0 and then divides it into six subnets. c. Use Table 9-6 to illustrate a listing of the network ID, broadcast address, and usable host addresses for each of the six subnets in the example Class C network. d. Point out that the extended network prefix for each subnet is based on which of the additional (borrowed) network information bits are set to equal 1. e. Point out that Class A, Class B, and Class C networks can all be subnetted; however, each class reserves a different number of bits for network information and each class has a different number of host information bits that can be used for subnet information. f. Explain how subnetting on a LAN affects LAN devices. g. Use Figure 9-4 to illustrate and explain a situation in which a LAN running IPv4 has been granted the Class C range of addresses that begin with 199.34.89. Teaching Tip Point out that several Web sites provide excellent tools to assist network administrators in calculating subnet information. Provide a classroom demonstration by navigating to http://www.subnetmask.info to illustrate one such site. CIDR (Classless Interdomain Routing) 1. Introduce and explain CIDR (Classless Interdomain Routing). 2. Mention that CIDR is sometimes called classless routing or supernetting. 3. Walk through an example of CIDR in which a subnet boundary moves to the left. a. Emphasize that moving the subnet boundary to the left allows an administrator to use more bits for host information and, therefore, generate more usable IP addresses on the network. b. Mention that a subnet created by moving the subnet boundary to the left is known as a supernet. 4. Use Figure 9-5 to contrast examples of a Class C supernet mask with a subnet mask. a. In Figure 9-5, point out that 27 bits are used for network information in the subnet mask, whereas in the superset mask, only 22 bits are used for network information. 5. Walk through an example where an organization has leased the Class C range of IPv4 addresses that shares the network ID 199.34.89.0 and, because of growth in the company, the network administrator needs to increase the number of host addresses this network allows by default. a. Use Figure 9-6 to illustrate the process of calculating a host’s network ID on a supernetted network. 6. Describe CIDR notation (or slash notation). 7. Define and describe a CIDR block. 8. Wrap up this topic by emphasizing that to take advantage of classless routing, a network’s routers must be able to interpret IP addresses that do not adhere to conventional network class parameters. a. Routers that rely on older routing protocols, such as RIP, are not capable of interpreting classless IP addresses. Teaching Tip Point out that CIDR is pronounced cider. Subnetting in IPv6 1. Explain that IPv6 addresses are classless. 2. Explain that an IPv6 address divides into a 64-bit subnet prefix and 64-bit interface identifier. 3. Use Figure 9-7 to show the prefix and interface portions of an IPv6 address. 4. Remind students that they may see IPv6 addresses containing a slash, such as 2608:FE10:1:A::/64, but that the left-most 64 bits of any IPv6 address are the subnet portion of the address. 5. Explain how subnet prefixes may be assigned from a national NSP down to a local ISP level, using Figure 9-8. Internet Gateways 1. Define and explain a gateway. 2. Define the term default gateway. 3. Explain characteristics of default gateways. 4. Use Figure 9-9 to illustrate the use of default gateways. 5. Define and describe the advantages of a default router. 6. Describe two default gateway connections. 7. Note that routers used as gateways must maintain routing tables. 8. Describe the gateways that make up the Internet. 9. Define a core gateway. Teaching Tip Student may read more about “Using Internet Gateway Device Discovery and Control” at http://windowshelp.microsoft.com/Windows/en-US/help/670718ec-7d51-49ed-87f1-b8a98ced11a41033.mspx Address Translation 1. Define the term public network and provide examples. 2. Define the term private network and provide examples. 3. Explain how hiding IP addresses on private networks allows network managers more flexibility in assigning addresses. 4. Define the term NAT (Network Address Translation). 5. Describe reasons for using address translation. 6. Define and describe SNAT (Static Network Address Translation). 7. Use Figure 9-10 to illustrate SNAT. 8. Define and describe DNAT (Dynamic Network Address Translation). 9. Mention that DNAT is also called IP masquerading. 10. Define and describe PAT (Port Address Translation). 11. Use Figure 9-11 to illustrate an example of PAT usage. 12. Explain how the gateway might instead operate on a network host. 13. Describe how in Windows operating systems, ICS (Internet Connection Sharing) can be used to translate network addresses and allow clients to share an Internet connection. Teaching Tip Student may find a “Description of Internet Connection Sharing” at http://support.microsoft.com/kb/234815 Quick Quiz 1 1. True or False: DHCP may be used to assign IP addresses and host names dynamically. Answer: True 2. A node’s network ____ provides information about the segment or network to which the node belongs. a. frame b. location c. class d. routing table Answer: C 3. Subnetting separates a network into multiple logically defined segments, or ____________________. Answer: subnets 4. True or False: Subnet masks are only used in IPv4 classful addressing. Answer: False 5. A broadcast address is known as a(n) ____ address for a network or segment. a. reserved b. default c. open d. informative Answer: A 6. True or False: In CIDR, conventional network class distinctions exist. Answer: False TCP/IP Mail Services 1. Explain why it is important to understand how mail services work. 2. Point out that all Internet mail services rely on the same principles of mail delivery, storage, and pickup, though they may use different types of software to accomplish these functions. 3. Explain the function of mail servers. 4. Explain the function of mail clients. 5. Emphasize that e-mail servers and clients communicate through special TCP/IP Application layer protocols. SMTP (Simple Mail Transfer Protocol) 1. Define and describe SMTP. 2. Point out that SMTP transports mail and holds it in a queue. 3. Mention that in Internet e-mail transmission, higher-level mail protocols such as POP and IMAP may attempt to figure out what went wrong with an undeliverable message. 4. Describe how to configure a client to use SMPT. Teaching Tip Student may find more information on SMTP at http://www.cisco.com/en/US/docs/ios/sw_upgrades/interlink/r2_0/user/ugsmtp.html MIME (Multipurpose Internet Mail Extensions) 1. Explain the drawbacks of SMTP. 2. Define and describe MIME as a solution to the ASCII character limit of 1,000. a. Note that MIME is a standard for encoding and interpreting binary files, images, video, and non-ASCII character sets within an e-mail message. b. Point out that MIME identifies each element of a mail message according to content type. c. Mention that MIME encodes different content types so that SMTP is fooled into thinking it is transporting an ASCII message stream. 3. Emphasize that MIME does not replace SMTP, but works in conjunction with it. 4. Note that most modern e-mail clients and servers support MIME. POP (Post Office Protocol) 1. Define and describe POP. 2. Note the most current version. 3. Describe how POP3 mail is stored and delivered. 4. Describe the advantages of using POP3. 5. Emphasize that mail is deleted from the server after it is downloaded. a. Explain why this can be troublesome for mobile users. IMAP (Internet Message Access Protocol) 1. Point out that IMAP is a mail retrieval protocol that was developed as a more sophisticated alternative to POP3. 2. Describe the advantages of IMAP. 3. Describe the features of IMAP. 4. Describe the disadvantages of IMAP. Teaching Tip Students may find more information on how e-mail works at http://communication.howstuffworks.com/email.htm Additional TCP/IP Utilities 1. Note that there are many points of failure in a TCP transmission. 2. Explain how TCP/IP attempts to help an administrator track down most TCP/IP-related problems without using expensive software or hardware to analyze network traffic. 3. Emphasize why students should be familiar with TCP/IP diagnostic tools. 4. Review the Telnet, ARP, and ping utilities from Chapter 4. 5. Explain the benefits of the command prompt in accessing TCP/IP utilities. 6. Note that utility command syntax may differ, depending on the client’s operating system. Ipconfig 1. Define and explain the ipconfig utility. a. Review the command switches. b. Note that this command operates with Windows-based systems. 2. Use Figure 9-12 to illustrate the output of an ipconfig command on a Windows workstation. Teaching Tip Students may find more information on the syntax and options for using the ipconfig diagnostic utility for network connections at http://support.microsoft.com/kb/117662 Ifconfig 1. Define and explain the ifconfig utility. a. Review the command switches. b. Note that ifconfig is the UNIX and Linux version of ipconfig. 2. Use Figure 9-13 to illustrate detailed information available through ifconfig. Teaching Tip Students may find more information on the syntax and options for the ifconfig command at http://en.wikipedia.org/wiki/Ifconfig Netstat 1. Define and explain the netstat utility. a. Review the command switches. 2. Use Figure 9-14 to illustrate detailed output of a netstat –a command. Teaching Tip Students may read information on adding a GUI front end to the netstat command line utility at http://articles.techrepublic.com.com/5100-10878_11-5149569.html Nbtstat 1. Define and explain the nbtstat utility. a. Note that nbtstat is useful only on networks that run Windows-based operating systems and NetBIOS. b. Review the command switches. Teaching Tip Students may find more information on nbtstat at http://technet.microsoft.com/en-us/library/cc940106.aspx Hostname, Host, and Nslookup 1. Define and explain the hostname utility. a. Note that the hostname utility is useful to a computer running the Windows, UNIX, or Linux operating systems. 2. Define and explain the host utility. a. Note that Windows requires a third-party version of host. 3. Define and explain the nslookup utility. a. Note that this utility is useful in troubleshooting DNS resolution problems. b. Use Figure 9-15 to illustrate the result of running a simple nslookup command at a Linux shell prompt. c. Review how to get help with the nslookup command switches. Dig 1. Define and explain the dig utility. a. Compare the dig command to the nslookup command. b. Mention that dig is useful for helping network administrators diagnose DNS problems. c. Point out that the dig utility is included with UNIX and Linux operating systems. d. Mention that for Windows-based operating system, an administrator must obtain the code for the dig utility from a third party and install it on your system. 2. Use Figure 9-16 to illustrate the output of a simple dig command. Whois 1. Review the basic steps that occur when a domain name is registered with ICAN. 2. Define and explain the whois utility. a. Mention that whois utility is helpful in troubleshooting network problems. b. Review the command syntax. c. Mention that there are Web-based interfaces for running the whois command Teaching Tip Demonstrate the use of the Whois command by navigating to http://www.networksolutions.com/whois/index.jsp. Search for various organizations. Traceroute (Tracert) 1. Define and explain the traceroute utility. a. Note that the utility is known as tracert on Windows-based systems and tracepath on some Linux systems. b. Walk through the steps traceroute takes to trace the path from one networked node to another. c. Describe the simplest form of the traceroute command. 2. Use Figure 9-17 to illustrate output of a traceroute command. 3. Review popular switches. Mtr (my traceroute) 1. Define and explain the mtr utility. a. Mention that it comes with UNIX and Linux operating systems. b. Emphasis that the mtr utility combines the functions of the ping and traceroute utilities and delivers an easy-to-read chart as its output. c. Describe the simplest form of the mtr command. d. Describe some popular MTR utility switches. 2. Use Figure 9-18 to illustrate the output of the command mtr –c 100 –r www.cengage.com 3. Describe a program similar to mtr, pathping, which is available as a command-line utility in Windows XP, Vista, Server 2003, and Server 2008. Route 1. Define and explain the route utility. a. Describe the route command syntax for various operating systems and Cisco-brand routers. 2. Use Figure 9-19 to illustrate an example of a routing table. 3. Use Table 9-7 to explain the fields belonging to routing tables on UNIX or Linux systems. 4. Review some options available for use with the route command. 5. Describe how to get help with route command options. Quick Quiz 2 1. True or False: MIME is a standard for encoding and interpreting binary files, images, video, and non-ASCII character sets within an e-mail message. Answer: True 2. True or False: The MIME standard replaces SMTP. Answer: False 3. ____________________ is a mail retrieval protocol that was developed as a more sophisticated alternative to POP3. Answer: MAP (Internet Message Access Protocol), Internet Message Access Protocol, IMAP 4. True or False: The ipconfig utility is the TCP/IP configuration and management utility used on UNIX and Linux systems. Answer: False 5. ____ combines the functions of the ping and traceroute utilities a. Tracert b. Mtr c. Whois d. Route Answer: B Class Discussion Topics 1. Discuss the benefits of subnetting. 2. Discuss why IMAP is preferred over POP3. Additional Projects 1. Have the student research their favorite e-mail service. The students should determine which Application layer protocols the e-mail system supports (SMTP, MIME, POP, POP3, IMAP, etc.) and write a report on their findings. The report should also include a description of the protocol set-up or configurations, if applicable. 2. Have student select five random companies, and issue the whois and traceroute commands for each one. The student should prepare a report describing the results. Require the use of screen shots to back up the reported findings. Additional Resources 1. ARIN https://www.arin.net/ 2. SMTP http://www.cisco.com/en/US/docs/ios/sw_upgrades/interlink/r2_0/user/ugsmtp.html 3. IMAP http://en.wikipedia.org/wiki/Internet_Message_Access_Protocol 4. RFC 1009 Requirements for Internet Gateways (Historic) http://tools.ietf.org/html/rfc1009 5. RFC 5034 The Post Office Protocol (POP3) http://tools.ietf.org/html/rfc5034 Key Terms  ANDing A logical process of combining bits. In ANDing, a bit with a value of 1 plus another bit with a value of 1 results in a 1. A bit with a value of 0 plus any other bit results in a 0.  CIDR (Classless Interdomain Routing) An IP addressing and subnetting method in which network and host information is manipulated without adhering to the limitations imposed by traditional network class distinctions. CIDR is also known as classless routing or supernetting. Older routing protocols, such as RIP, are not capable of interpreting CIDR addressing schemes.  CIDR block In CIDR notation, the number of bits used for an extended network prefix. For example, the CIDR block for 199.34.89.0/22 is /22.  CIDR notation In CIDR, a method of denoting network IDs and their subnet boundaries. Slash notation takes the form of the network ID followed by a slash (/), followed by the number of bits that are used for the extended network prefix.  classful addressing An IP addressing convention that adheres to network class distinctions, in which the first 8 bits of a Class A address, the first 16 bits of a Class B address, and the first 24 bits of a Class C address are used for network information.  Classless Interdomain Routing See CIDR.  classless routing See CIDR.  core gateway A gateway that operates on the Internet backbone.  default gateway The gateway that first interprets a device’s outbound requests, and then interprets its inbound requests to and from other subnets. In a Postal Service analogy, the default gateway is similar to a local post office.  default router See default gateway.  dig (domain information groper) A TCP/IP utility that queries the DNS database and provides information about a host given its IP address or vice versa. Dig is similar to the nslookup utility, but provides more information, even in its simplest form, than nslookup can.  DNAT (Dynamic Network Address Translation) A type of address translation in which a limited pool of Internet-valid IP addresses is shared by multiple private network hosts.  domain information groper See dig.  Dynamic Network Address Translation See DNAT.  extended network prefix The combination of an IP address’s network ID and subnet information. By interpreting the address’s extended network prefix, a device can determine the subnet to which an address belongs.  host A TCP/IP utility that at its simplest returns either the IP address of a host if its host name is specified or its host name if its IP address is specified.  hostname A TCP/IP utility used to show or modify a client’s host name.  ICS (Internet Connection Sharing) A service provided with Windows operating systems that allows one computer, the ICS host, to share its Internet connection with other computers on the same network.  ICS host On a network using the Microsoft Internet Connection Sharing service, the computer whose Internet connection other computers share. The ICS host must contain two network interfaces: one that connects to the Internet and one that connects to the LAN.  IMAP (Internet Message Access Protocol) A mail retrieval protocol that improves on the shortcomings of POP. The single biggest advantage IMAP4 has relative to POP is that it allows users to store messages on the mail server, rather than always having to download them to the local machine. The most current version of IMAP is version 4 (IMAP4).  IMAP4 (Internet Message Access Protocol, version 4) The most commonly used form of the Internet Message Access Protocol (IMAP).  Internet Connection Sharing See ICS.  Internet Message Access Protocol See IMAP.  Internet Message Access Protocol, version 4 See IMAP4.  IP masquerading See DNAT.  MIME (Multipurpose Internet Mail Extensions) A standard for encoding and interpreting binary files, images, video, and non-ASCII character sets within an e-mail message.  mtr (my traceroute) A route discovery and analysis utility that comes with UNIX and Linux operating systems. Mtr combines the functions of the ping and traceroute commands and delivers an easily readable chart as its output.  Multipurpose Internet Mail Extensions See MIME.  my traceroute See mtr.  NAT (Network Address Translation) A technique in which IP addresses used on a private network are assigned a public IP address by a gateway when accessing a public network.  nbtstat A TCP/IP troubleshooting utility that provides information about NetBIOS names and their addresses. If you know the NetBIOS name of a workstation, you can use nbtstat to determine its IP address.  NetBIOS A protocol that runs in the Session and Transport layers of the OSI model and associates NetBIOS names with workstations. NetBIOS alone is not routable because it does not contain Network layer information. However, when encapsulated in another protocol such as TCP/IP, it can be routed.  netstat A TCP/IP troubleshooting utility that displays statistics and the state of current TCP/IP connections. It also displays ports, which can signal whether services are using the correct ports.  Network Address Translation See NAT.  network number See network ID.  network prefix See network ID.  nslookup A TCP/IP utility that allows you to look up the DNS host name of a network node by specifying its IP address, or vice versa. This ability is useful for verifying that a host is configured correctly and for troubleshooting DNS resolution problems.  PAT (Port Address Translation) A form of address translation that uses TCP port numbers to distinguish each client’s transmission, thus allowing multiple clients to share a limited number of Internet-recognized IP addresses.  pathping A command-line utility that combines the functionality of the tracert and ping commands (similar to UNIX’s mtr command) and comes with Windows operating systems.  POP (Post Office Protocol) An Application layer protocol used to retrieve messages from a mail server. When a client retrieves mail via POP, messages previously stored on the mail server are downloaded to the client’s workstation, and then deleted from the mail server.  POP3 (Post Office Protocol, version 3) The most commonly used form of the Post Office Protocol.  Port Address Translation See PAT.  Post Office Protocol See POP.  Post Office Protocol, version 3 See POP3.  private network A network whose access is restricted to only clients or machines with proper credentials.  public network A network that any user can access with no restrictions. The most familiar example of a public network is the Internet.  route A utility for viewing or modifying a host’s routing table.  route prefix The prefix in an IPv6 address that identifies a route. Because route prefixes vary in length, slash notation is used to define them. For example, the route prefix indicated by 2608:FE10::/32 includes all subnets whose prefixes begin with 2608:FE10 and, consequently, all interfaces whose IP addresses begin with 2608:FE10.  Simple Mail Transfer Protocol See SMTP.  slash notation See CIDR notation.  SMTP (Simple Mail Transfer Protocol) The Application layer TCP/IP subprotocol responsible for moving messages from one e-mail server to another.  SNAT (Static Network Address Translation) A type of address translation in which each private IP address is correlated with its own Internet-recognized IP address.  Static Network Address Translation See SNAT.  subnet prefix The 64-bit prefix in an IPv6 address that identifies a subnet. A single IPv6 subnet is capable of supplying 18,446,744,073,709,551,616 IPv6 addresses.  supernet In IPv4, a type of subnet that is created by moving the subnet boundary to the left and using bits that normally would be reserved for network class information.  supernet mask A 32-bit number that, when combined with a device’s IPv4 address, indicates the kind of supernet to which the device belongs.  supernetting See CIDR.  tracepath A version of the traceroute utility found on some Linux distributions.  traceroute (tracert) A TCP/IP troubleshooting utility that uses ICMP to trace the path from one networked node to another, identifying all intermediate hops between the two nodes. Traceroute is useful for determining router or subnet connectivity problems. On Windows-based systems, the utility is known as tracert. Instructor Manual for Network+ Guide to Networks Tamara Dean 9781133608196, 9781133608257, 9781337569330