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					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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