Guide to Networking Essentials, Fifth Edition 13-1 Chapter 13 Enterprise and 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 Technical Notes for Hands-On Projects Guide to Networking Essentials, Fifth Edition 13-2 Lecture Notes Overview Chapter 13 offers an introduction to enterprise and wide area networks. Students learn how large networks can be implemented with a variety of devices (i.e., repeaters, bridges, switches, routers, and gateways). They also learn about the different technologies used in implementing WANs and are exposed to a significant amount of new terminology related to WANs. Finally, they learn how to configure remote access protocols. Objectives Explain how large networks can be implemented with a variety of devices Discuss the technologies used in constructing WANs Explain some terminology used in implementing WANs Configure and describe remote access protocols Teaching Tips Creating Larger Networks 1. Provide a brief introduction to how network capabilities can be stretched or expanded. Repeaters 1. Use Figure 13-1 to explain how repeaters work. 2. Students may review Simulation 2-1 to see that when a signal is sent to one computer, all computers attached to the hub receive the signal, but only the intended destination processes the information. 3. Use Table 13-1 to discuss the advantages and disadvantages of using repeaters to expand a network. Bridges 1. Explain how bridges work. Be sure to introduce the terms transparent bridge, bridging table, and source-routing bridge. 2. Use Table 13-2 to discuss the advantages and disadvantages of using bridges to extend a network. Be sure to introduce the term broadcast storm. Guide to Networking Essentials, Fifth Edition 13-3 Switches 1. Explain how switches work. Students may review Simulation 2-2 to see how a switch uses a table to forward frames. Stress the differences between bridges and switches. Teaching For more information on network switches, read: Tip http://en.wikipedia.org/wiki/Network_switch. 2. Use Table 13-3 to explain how cut-through, store-and-forward, and fragment free switching works. To see an animated representation of cut-through switching and store- and-forward switching, run Simulation 13-1. 3. Explain that a benefit of switching technology is its capability to dedicate bandwidth to each port on the switch. 4. Use Figure 13-2 to explain that another important feature available on switches but not on bridges or repeaters is the capability to segment a network into virtual local area networks (VLANs). Routers 1. Use Figure 13-3 to explain how routers work. Explain that each network segment, also called a subnetwork (or subnet), is assigned a network address, and each node on a subnet is also assigned an address. Introduce the term routing table. Teaching For more information on routers, read: http://en.wikipedia.org/wiki/Router. Tip 2. Stress the differences between routers and bridges/switches. 3. Use Simulation 13-2 to show how a packet travels from one network to another through routers. 4. Routing Tables. Use Table 13-4 to explain how a router uses a routing table. Explain the difference between static and dynamic routing, and between the distance-vector algorithm and the link-state algorithm. Stress that dynamic routers are easier to maintain and provide better route selection than static routers, but the routing table updates and discovery generate additional network traffic. 5. Use Table 13-5 to discuss the advantages and disadvantages of routers. Gateways 1. Describe the role of a gateway. Explain that a gateway usually operates at the Application layer, but it can also operate at the Network or Session layers. Guide to Networking Essentials, Fifth Edition 13-4 2. Stress that a gateway is generally harder to install, slower, and more expensive. Quick Quiz 1 1. What is a repeater and how does it work? Answer: A repeater accepts a signal, cleans it, regenerates it, and sends it down the line, effectively doubling the length of the network. Repeaters operate at the Physical layer (Layer 1) of the OSI model without concern for the type of data being transmitted, the packet address, or the protocol. Repeaters operate only with bits and can’t perform any filtering or translation on the actual data. 2. ____________________ bridges, used primarily in token ring networks, rely on the frame’s source to include path information. Answer: Source-routing 3. What is a switch? Answer: A switch is really a high-speed multiport bridge, an intelligent device that maintains a switching table and keeps track of which hardware addresses are located on which network segments. 4. ____________________ are advanced devices that connect separate logical networks to form an internetwork. Answer: Routers Wide Area Network (WAN) Transmission Technologies 1. Explain that WANs are often constructed by linking WANs. Mention the different communication links that can be purchased or leased to construct WANs. 2. Note that WAN technologies can be analog, digital, or packet switching. Analog Connectivity 1. Use Figure 13-4 to explain that to establish a WAN link to remote computers and networks, a LAN can use the same telecommunications network you use to talk on the phone. 2. Explain that because PSTN lines require modems to transmit digital computer data over the analog telephone network, data transmission is extremely slow. Also, because PSTN is a circuit-switched network, connection quality is highly inconsistent; a link is only as reliable and fast as the circuits linked to establish the pathway. Guide to Networking Essentials, Fifth Edition 13-5 Note that recently, telcos upgraded some PSTN lines to support data Teaching transmission more reliably. They are now installing fiber-optic cable to support Tip the increasing demand for high-bandwidth data communications. 3. Explain that one way to improve the quality of a PSTN connection is to lease a dedicated line or circuit. Introduce the term line conditioning. 4. Briefly discuss the factors that should be considered when deciding between a dial-up or dedicated PSTN connection. 5. Modems in Network Communications. Define the term modem. Table 13-6 shows some of the V-series standards the International Telecommunications Union (ITU) developed to define modem speed. Explain that the term baud is sometimes used to denote modem speed. A baud represents the oscillation of a sound wave that carries one bit of data. For earlier modems, the terms baud and bits per second (bps) are used interchangeably; a Teaching 300 bps modem has 300 oscillations of sound waves each second. However, with Tip new compression technologies, the number of bits per second has increased way beyond the number of oscillations per second. For example, a modem that transmits at 28,800 bps might actually be transmitting at 9600 baud. 6. Types of Modems. Explain that two types of modems are used today: asynchronous and synchronous. Note that the type you use depends on the type of phone lines and the network requirements. Use Figure 13-5 to explain how asynchronous communication works. Note that the most common asynchronous modem standard for connecting to the Internet is the V.90 standard. Use Figures 13-6 and 13-7 to explain how this standard works. Introduce the term Pulse Code Modulation (PCM). Explain that there are two caveats with V.90 communications: There must be only one analog circuit between the modem and the Internet, and 56 Kbps communication works in only one direction—the download direction. Introduce the term asymmetric communication. Use Figure 13-8 to explain how synchronous modems work. Stress that because synchronous modems have so little overhead in terms of error checking, they are much faster than asynchronous modems. Note that there are three primary synchronous communication protocols: Synchronous Data Link Control (SDLC), High-level Data Link Control (HDLC), and Binary Synchronous (bisync). Note that synchronous modems were not designed for use over regular phone lines; instead, they are generally found in dedicated, leased-line environments. Teaching For more information on modems, read: http://en.wikipedia.org/wiki/Modem. Tip Guide to Networking Essentials, Fifth Edition 13-6 Digital Connectivity 1. Explain why digital connectivity makes more sense than analog connectivity. 2. Explain what Digital Data Service (DDS) lines are. Mention some DDS examples (e.g., ISDN, T1, T3, switched 56K). 3. Use Figure 13-9 to explain the role of a CSU/DSU in DDS networks. 4. Digital Modems. Explain that the term “digital modem” is frequently used in situations in which there is actually no modulation/demodulation between analog/digital signals; e.g., ISDN (NT and TA), cable modems, and DSL modems. Note that some CATV systems do indeed use analog signaling, so the term “cable modem” is correct in these cases. Briefly discuss how cable modem and DSL technologies work, stressing their advantages and disadvantages. Be sure to introduce the terms ADSL and SDSL. Teaching Stress that ADSL is ideal for home Internet users because the bulk of traffic in Tip these connections travels in the download direction. Teaching For more information on cable modems, see: Tip http://en.wikipedia.org/wiki/Cable_modem. Teaching For more information on DSL technology, see: www.dslreports.com and Tip http://electronics.howstuffworks.com/dsl.htm. 5. T1. Explain what T1 is. Note that organizations purchase or lease T1 lines, and that subscribing to one or more channels instead of an entire T1 is possible with fractional T1. Use Table 13-7 to explain that in some countries, the E1 technology is used. Use Table 13-8 to introduce the term multiplexing and to explain that muxing can increase DS-1 rates up to DS-4 speeds. 6. T3. Briefly describe the T3 technology. Teaching For more information on T1 and T3, read: http://en.wikipedia.org/wiki/T-carrier. Tip 7. Switched 56K. Briefly describe the switched 56K technology. Note that this technology is only used today when multiple 56 Kbps channels are aggregated for frame relay services or when other specialized dedicated digital leased lines are needed. Guide to Networking Essentials, Fifth Edition 13-7 8. Integrated Services Digital Networks. Briefly describe the ISDN technology. Describe the characteristics of the two available formats/rates: BRI and PRI. Briefly introduce B- ISDN. For more information on ISDN, read: Teaching www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm and Tip http://en.wikipedia.org/wiki/ISDN. Packet-Switching Networks 1. Explain how packet switching networks work. Stress that they are fast, efficient, and highly reliable. Note that the Internet is a packet switched network. 2. Explain that data delivery does not depend on a single pathway, which means that packets may take different routes and may need to be rearranged on delivery. Teaching For a packet switching simulation, visit: Tip www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_switching_flash.html. 3. Discuss the advantages of dividing data in small packets (mainly, efficient retransmission and fast switching/processing). 4. Virtual Circuits. Explain that many packet-switching networks use virtual circuits to provide temporarily “dedicated” pathways between two points. Explain how virtual circuits are created. Explain the difference between SVCs and PVCs. 5. X.25. Provide a brief introduction to this technology. Note that X.25 is an SVC network that originally used POTS lines as communication links. Explain that error checking and retransmission schemes that were added later improved success of transmissions but dampened speed. For more information on X.25, read: Teaching www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.htm and Tip http://en.wikipedia.org/wiki/X.25. 6. Frame Relay. Use Figure 13-10 to briefly describe the frame relay technology. Note that it is a point-to-point PVC, digital, packet-switched technology that does not use error checking (for improved throughput). Introduce the term Committed Information Rate (CIR). Stress that because customers can pay for a customized bandwidth solution, frame relay is sometimes preferred to T1 because it’s generally less expensive. Guide to Networking Essentials, Fifth Edition 13-8 For more information on frame relay, read: Teaching www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm and Tip http://en.wikipedia.org/wiki/Frame_relay. WAN Implementation Basics 1. This section discusses how WANs are implemented. Customer Equipment 1. Introduce the terms CPE and demarcation point. Note that the CPE might be owned or leased by the client, and that it includes devices such as routers, modems, and CSUs/DSUs. Provider Equipment 1. Introduce the terms CO, local loop, and last mile. 2. Explain that for wired connections, a cable runs from the customer site demarcation point to the CO of the WAN service provider. Note that this cable is usually copper or fiber-optic, and it is the provider’s responsibility. Going the Last Mile 1. Use Figure 13-11 to introduce the terms data circuit-terminating equipment (DCE) and data terminal equipment (DTE), and to help explain the relationship between the different concepts introduced in this section. Remote Access Networking 1. Stress that for a network to be even more effective, you might need to allow users dial- in access from their homes, remote sites, or hotel rooms. Use Figure 13-12 to explain that a simple way to do this in a Windows Server network is to use Routing and Remote Access Service (RRAS). 2. Note that all versions of Windows, starting with Windows 95, include Dial-Up Networking (DUN) software to make an RRAS connection. Note that the option for users to dial in to a Windows remote access server is Teaching disabled by default for security reasons. This feature must be enabled in a user’s Tip account information. Guide to Networking Essentials, Fifth Edition 13-9 3. Two protocols, discussed in the following sections, are available for remote access: Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP). Serial Line Internet Protocol (SLIP) 1. Describe the role of SLIP. Note that it relies on hardware for error checking and correction. 2. Explain why it requires no addressing. Introduce CSLIP. Stress that SLIP is not used much in today’s environment. Point-to-Point Protocol (PPP) 1. Describe the role of PPP. Note that PPP provides both physical and data link layer services; thus, it effectively turns a modem into a NIC. 2. Stress that PPP supports multiple protocols, and that it inherently supports compression and error checking. 3. Explain that PPP supports dynamic assignment of IP addresses. 4. Stress that PPP has replaced SLIP as the remote protocol of choice for TCP/IP connections. Quick Quiz 2 1. What is a modem? Answer: A modem is a device for making an analog connection between computers over a telephone line, effectively making a WAN connection between computers or networks. 2. What is T1? Answer: One of the most widely used high-speed digital lines is the T1, a DDS technology that uses two two-wire pairs to transmit full-duplex data signals at a maximum rate of 1.544 Mbps. 3. Many packet-switching networks use ____________________ to provide temporarily “dedicated” pathways between two points. Answer: virtual circuits 4. The connection between the demarcation point and the CO is called the local loop or ____________________. Answer: last mile Guide to Networking Essentials, Fifth Edition 13-10 Class Discussion Topics 1. Have students used SLIP or PPP before? If so, ask them to mention when they have done so. Tip: some students may have had dial-up Internet access since the early Internet days, when the use of SLIP was very common. 2. Have any of the students switched from cable modem to DSL services or the other way around? If so, ask them to explain why they did so. Additional Projects 1. Ask students to compile a list of prices of hubs, switches, routers, and gateways for SOHOs. The list should include the model, vendor, characteristics, and price. 2. Ask students to do some research to find out what WAN services are available in their area (e.g., T1/T3 leased lines, ISDN, frame relay, cable modem, dsl, etc.). Additional Resources 1. Network Switch: http://en.wikipedia.org/wiki/Network_switch 2. Router: http://en.wikipedia.org/wiki/Router 3. Modem: http://en.wikipedia.org/wiki/Modem 4. Cable Modem: http://en.wikipedia.org/wiki/Cable_modem 5. Integrated Services Digital Network: www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm 6. Integrated Services Digital Network: http://en.wikipedia.org/wiki/ISDN 7. How DSL Works: http://electronics.howstuffworks.com/dsl.htm 8. T-Carrier: http://en.wikipedia.org/wiki/T-carrier 9. X.25: www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.htm Guide to Networking Essentials, Fifth Edition 13-11 10. X.25: http://en.wikipedia.org/wiki/X.25 11. Frame Relay: www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm 12. Frame Relay: http://en.wikipedia.org/wiki/Frame_relay 13. SLIP/PPP Homepage: http://sunsite.nus.sg/pub/slip-ppp/ Key Terms asymmetric communication — Communication in which data travels in the download direction at a speed different from the speed of the upload direction. Asymmetric Digital Subscriber Line (ADSL) — A digital telecommunications technology that uses different speeds for downloading and uploading data. asynchronous — A communication method that sends data in a stream with start and stop bits that indicate where data begins and ends. Basic Rate Interface (BRI) — An ISDN version that provides two 64 Kbps B- channels. Generally used for remote connections. baud — A measurement of modem speed that describes the number of state transitions occurring per second on an analog phone line. Binary Synchronous (bisync) — One of the primary synchronous communication protocols. bridges — Networking devices that work at the Data Link layer of the OSI model. They filter traffic according to a packet’s hardware destination address. bridging table — A reference table created by a bridge to track hardware addresses and to track on which network segment each address is located. Broadband ISDN (B-ISDN) — An ISDN variation that supports much higher data rates than standard ISDN and works with other technologies, such as ATM, SONET, and frame relay. broadcast storm — A phenomenon that occurs when a network device malfunctions and floods the network with broadcast packets. Channel Service Unit/Data Service Unit (CSU/DSU) — A device that links a computer or network to a DDS communications link. Committed Information Rate (CIR) — A guaranteed minimum transmission rate offered by the service provider. Customer premises equipment (CPE) — The equipment at the customer site that’s usually the responsibility of the customer. cut-through switching — The fastest switching method, in which the switch reads only enough of the incoming frame to determine where to forward the frame. data circuit-terminating equipment (DCE) — The device that sends data to (and receives data from) the local loop, usually a CSU/DSU or modem. data terminal equipment (DTE) — The device that passes data from the customer LAN to the DCE, usually a router. Guide to Networking Essentials, Fifth Edition 13-12 demarcation point — The point at which the CPE ends and the provider’s equipment responsibility begins. Dial-Up Networking (DUN) — The Windows program (beginning with Windows 95) that allows connectivity to servers running RAS or RRAS. Digital Data Service (DDS) — A type of point-to-point synchronous communication link offering 2.4, 4.8, 9.6, or 56 Kbps transmission rates. digital modem — A hardware device used to transmit digital signals across an ISDN link. distance-vector algorithm — One method of determining the best route available for a packet. Distance-vector protocols count the number of routers (hops) between the source and destination. The best path has the least number of hops. dynamic routing — The process by which routers dynamically learn from each other the available paths. fractional T1 — One or more of the 24 channels (but not all) of a T1 connection. fragment-free switching — A switching method in which the switch reads in enough of the frame to guarantee that the frame is not less than the minimum frame size allowed for the network type. frame fragment — A frame error that occurs because the frame is less than the allowable minimum size for the network type. A frame fragment usually occurs because of a collision or a device malfunction. frame relay — A point-to-point permanent virtual circuit (PVC) technology that offers WAN communications over a fast, reliable, digital packet-switching network gateway — A networking device that translates information between protocols or between completely different networks, such as from TCP/IP to SNA. High-level Data Link Control (HDLC) — One of the primary synchronous communication protocols. hop — A packet traveling through a router on its way to the destination network. Integrated Services Digital Network (ISDN) — A WAN technology that offers increments of 64 Kbps connections, most often used by SOHO (small office/home office) users. last mile — The connection between a WAN’s demarcation point and the central office (CO). See also local loop. line conditioning — A feature that sustains a consistent transmission rate, improves overall quality, and reduces interference noise levels. link-state algorithm — A method used by routers to determine a packet’s best path. In addition to the number of routers involved, routers using link-state algorithms take network traffic and link speed into account to determine the best path. local loop — The connection between a WAN’s demarcation point and the central office (CO). See also last mile. metric — A value that describes the distance to the destination network. modem — A device computers use to convert digital signals to analog signals for transmission over telephone lines. The receiving computer then converts the analog signals to digital signals. multiplexing — A technology that enables several communication streams to travel simultaneously over the same cable segment packet assembler/disassembler (PAD) — A device that supports X.25 communications for low-speed, character-based terminals. Guide to Networking Essentials, Fifth Edition 13-13 permanent virtual circuits (PVCs) — Pathways between two communication points that are established as permanent logical connections; therefore, the pathway exists even when it’s not in use. plain old telephone service (POTS) — Also known as PSTN, the normal telephone communications system. See also public switched telephone network (PTSN). Point-to-Point Protocol (PPP) — A remote access protocol that supports many protocols, including IP, NetBEUI, and IPX. Primary Rate Interface (PRI) — An ISDN version that provides 23 64-Kbps B- channels. propagation delay — Signal delay created when a number of repeaters connect in a line. To prevent this, many network architectures limit the number of repeaters on a network. public data networks (PDNs) — WAN services, usually provided by private companies, for the purpose of enabling WAN technologies, such as X.25. public switched telephone network (PSTN) — Another term for the public telephone system. pulse code modulation (PCM) — A technique for digitizing analog signals. PCM introduces less noise into the signal than traditional modulation/demodulation techniques, thus boosting the total number of bits per second. routers — Networking devices that operate at the Network layer of the OSI model. A router connects networks with different physical media and translates between different network architectures, such as token ring and Ethernet. routing table — A reference table that includes network information and the next router in line for a particular path. Serial Line Internet Protocol (SLIP) — The dial-up protocol originally used to connect PCs directly to the Internet. source-routing bridges — A type of bridge used in IBM token ring networks that learns its bridging information from information in the frame’s structure. static routing — A type of routing in which the router is configured manually with all possible routes. store-and-forward switching — A switching method in which the switch reads the entire frame to check for errors before forwarding the frame. switched 56K — Digital point-to-point leased communication links offered by local and long-distance telcos. Lease terms are based on per-minute use charges, not on 24- hour, seven-day dedicated circuits. switched virtual circuits (SVCs) — A communication circuit that’s established when needed and then terminated when the transmission is completed. Symmetric Digital Subscriber Line (SDSL) — A digital telecommunications technology that uses equivalent speeds for downloading and uploading data. synchronous — A communication method in which computers rely on exact timing and sync bits to maintain data synchronization. Synchronous Data Link Control (SDLC) — One of the primary synchronous communication protocols. T1 — A DDS technology that uses two two-wire pairs to transmit full-duplex data signals at a maximum rate of 1.544 Mbps. T3 — A communication line that has 28 T1s or 672 channels and supports a data rate of 44.736 Mbps. translation bridges — A type of bridge that can translate between network architectures. Guide to Networking Essentials, Fifth Edition 13-14 transparent bridges — Generally used in Ethernet networks, these bridges build their bridging tables automatically as they receive packets. virtual circuits — A logical sequence of connections with bandwidth allocated for a specific transmission pathway. virtual local area networks (VLANs) — A feature of switches that allows network administrators to group users and resources logically, regardless of their physical location. V-series — The ITU standards that specify how data communication takes place over the telephone network. X.25 — A WAN protocol that defines how devices communicate over an internetwork. X.25 networks are SVC networks, meaning they create the best available pathway for transmission at the time of transmission. Technical Notes for Hands-On Projects Hands-On Project 13-1: In this project, students enable and configure RRAS on Windows Server 2003. This project requires a server with at least two network connections. Hands-On Project 13-2: This project requires a Windows XP Professional computer with a modem already installed. Hands-On Project 13-3: In this project, students set up a VPN connection using Windows XP (Start Control Panel Network Connections). Hands-On Project 13-4: This project requires a Web browser and Internet access. Hands-On Project 13-5: In this project, students use the Trace Route program (tracert in Windows or traceroute in Linux). Hands-On Project 13-6: In this project, students use the route Windows command-line utility.
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