Guide to Networking Essentials, Fifth Edition 13-1
Enterprise and Wide Area Networks
At a Glance
Instructor’s Manual Table of Contents
Class Discussion Topics
Technical Notes for Hands-On Projects
Guide to Networking Essentials, Fifth Edition 13-2
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
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
Creating Larger Networks
1. Provide a brief introduction to how network capabilities can be stretched or expanded.
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.
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
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:
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
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.
For more information on routers, read: http://en.wikipedia.org/wiki/Router.
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
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.
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.
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.
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.
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
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
transmission more reliably. They are now installing fiber-optic cable to support
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
300 bps modem has 300 oscillations of sound waves each second. However, with
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
For more information on modems, read: http://en.wikipedia.org/wiki/Modem.
Guide to Networking Essentials, Fifth Edition 13-6
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:
Teaching For more information on DSL technology, see: www.dslreports.com and
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.
For more information on T1 and T3, read: http://en.wikipedia.org/wiki/T-carrier.
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-
For more information on ISDN, read:
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:
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:
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:
WAN Implementation Basics
1. This section discusses how WANs are implemented.
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
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
disabled by default for security reasons. This feature must be enabled in a user’s
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
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
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
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.
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.).
1. Network Switch:
4. Cable Modem:
5. Integrated Services Digital Network:
6. Integrated Services Digital Network:
7. How DSL Works:
Guide to Networking Essentials, Fifth Edition 13-11
11. Frame Relay:
12. Frame Relay:
13. SLIP/PPP Homepage:
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
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
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
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
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
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-
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
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
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
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
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
translation bridges — A type of bridge that can translate between network
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
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.