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Chapter 12
Wide Area Networks
Applying Concepts: Internet Down
One evening, you’re up late working to meet a fast-approaching deadline when suddenly
your Internet connection fails. Much of your work requires Internet access for research,
but you belay the panic for a few moments to evaluate the situation:
• You try a couple of different websites in your browser, then open a different
browser and try a couple of websites again. None of the sites will load.
• You check all the cable connections between your computer and your network’s
demarc. Everything looks normal.
• You check the Network Connections status on your computer and confirm that
you have a functioning connection with your network.
• You try again to navigate to a website in your browser, but the page still won’t
load.
• You open a Command Prompt window and ping one of Google’s servers at
8.8.8.8. The ping works.
• You ping Google’s website at google.com, but this time it doesn’t work.
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• You pull up an outage reporting website for your ISP on your smartphone, and
find that a few hundred other people have reported the outage in your area, too.
With a quick adjustment, you get your Internet service functioning again and continue
with your work. Which of the following did you do and why?
a. You switched out the Ethernet cable connecting your modem to your router because
the cable was damaged.
b. You used ipconfig to release the IP address on your computer and get a new one
c. You changed the DNS settings on your router to point to Google’s DNS servers
instead of the DNS servers of your ISP because the ISP’s DNS servers were down.
d. You switched to a different ISP because the former ISP’s service was unreliable.
e. You replaced the router with a new router you had ready to go, knowing that the old
router had already exceeded its life expectancy and had finally ceased to function.
f. You created an ad hoc network with another computer on your network and used that
computer’s access to the Internet to continue your research because the Wi-Fi radio
on your computer had died and will need to be replaced.
g. You performed a factory reset on your modem so it would reinitiate a connection with
the ISP.
h. You updated the default gateway on your computer because it was unable to
communicate with the router.
i. You restarted your computer because Windows had updates that needed to be
installed.
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Applying Concepts: Test Your WAN Connection’s Speed
You can test your own WAN connection to see what the current upload and download
speeds are using a bandwidth speed tester, or a speed test website. During the test, data
will be sent to your computer and then requested from your computer in order to measure
download and upload speeds, respectively. Complete the following steps:
1. In your browser, go to speedtest.net. At the time of this writing, you start the test
by clicking GO. The test begins, as shown in Figure 12-4.
[[Insert Figure 12-4 here]]
2. Wait for the test to complete, then write down your speed test results. What are
your current download and upload speeds?
Answer: Answers may vary.
3. Let’s try another site and compare results. Go to verizon.com/speedtest, start the
test (see Figure 12-5), and wait for it to finish. What are the results this time?
How do they compare to your first results?
Answer: Answers may vary.
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[[Insert Figure 12-5 here]]
Applying Concepts: Determine a Cable Modem’s DOCSIS Version
You can determine the DOCSIS version of a cable modem on a SOHO (small
office/home office) network with a little detective work. This project requires a SOHO
network serviced by cable broadband and a computer (Windows, Linux, or Mac)
connected to the network. Complete the following steps to identify the DOCSIS version
of a cable modem:
1. Examine the labels on the cable modem to determine the device’s manufacturer and
2. Research the manufacturer and model number information online. You might find the
DOCSIS information while conducting your research. If not, the minimum
information you need is the cable modem’s default internal IP address (such as
3. Enter the default internal IP address in a web browser and log on if necessary.
Explore the user interface to locate the cable modem’s hardware information. Figure
12-15 shows the hardware information for a cable modem made by ARRIS. What is
the DOCSIS version of your cable modem?
Answer: Answers may vary.
[[Insert Figure 12–15 here]]
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Review Questions
1. What is the lowest layer of the OSI model at which LANs and WANs support the
same protocols?
a. Layer 2
b. Layer 3
c. Layer 4
d. Layer 5
2. An organization can lease a private _________________ that is not shared with
other users, or a _________________ that can be physically configured over
shared lines in the carrier’s cloud.
a. PVC (permanent virtual circuit), SVC (switched virtual circuit)
b. SVC (switched virtual circuit), dedicated line
c. dedicated line, virtual circuit
d. SVC (switched virtual circuit), PVC (permanent virtual circuit)
3. What kind of device can monitor a connection at the demarc but cannot interpret
data?
a. CSU/DSU
b. NID
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c. NIU
d. Smart jack
4. What kind of network is the PSTN?
a. Packet-switched
b. Circuit-switched
c. Virtual circuit
d. Dedicated line
5. How many channels are in an ISDN PRI connection?
a. 2B+D
b. 2D+B
c. 23D+B
d. 23B+D
6. What specifications define the standards for cable broadband?
a. ATM
b. Digital signal
c. ANSI
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d. DOCSIS
7. ______________ in SONET are analogous to the ________________ of T-
carriers.
a. Throughput, digital signal levels
b. OC levels, digital signal levels
c. QoS levels, OC levels
d. OC levels, carrier levels
8. Which DSL standard has the fastest speeds immediately outside the CO?
a. VDSL
b. ADSL
c. SDSL
d. ADSL2+
9. What method does a GSM network use to separate data on a channel?
a. SIM
b. CDMA
c. TDMA
d. TDM
10. Where does an MPLS label go in a PDU?
a. Layer 1
b. Between Layers 2 and 3
c. Between Layers 1 and 2
d. Layer 3
11. What are two types of virtual circuits?
12. What are three examples of Layer 2 LAN or PAN standards that also function at
Layer 1?
13. What information is typically included in a Layer 1 frame?
14. Which ISDN channel carries signaling information?
15. What two types of modulation does DSL use to carry data?
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16. What device must be installed on a DSL network to protect the sound quality of
phone calls?
17. What type of network combines fiber with coax?
18. What is the maximum capacity of a T1 line?
19. Which protocol can provide VoIP services over a Metro Ethernet connection?
20. How large is an ATM cell?
Hands-On Projects
Project 12-1: Research CSU/DSU Devices
Just as you might go shopping for a modem in order to get specific features, you can also
shop for a CSU/DSU to meet particular needs when you have a T1 or T3 line. In this
project, you will research CSU/DSU devices. Complete the following steps to find an
appropriate device for each scenario:
1. You’ve just been hired by a small company that is ready to lease its first fractional T1
line. Find a Cisco second-generation WIC (WAN interface connector) that can
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provide a fractional T1 connection. List the product description details that indicate
the WIC you found will meet these requirements, and be sure to include the price and
the website where you found your device. Find at least three reviews of the product
and include that information as well.
2. Your company has grown over the past year, and is ready to upgrade to a full T1 line.
You’ve also decided to upgrade the router at the same time, so you decide to purchase
a router-CSU/DSU bundle. Find a device that includes the router and the CSU/DSU
capabilities, and that is rack-mountable. List the product description details that
indicate the device you found will meet these requirements, and be sure to include the
price and the website where you found your device. Find at least one review of the
product and include that information as well.
3. Your company has grown even more, and merged with another, larger company.
Your new employer is ready to upgrade to a T3 line. You’ll need a new CSU/DSU,
and this time you decide to get a dedicated CSU/DSU device. Find a device that
includes CSU/DSU capabilities for a full-rate T3 line and that is rack-mountable. List
the product description details that indicate the device you found will meet these
requirements, and be sure to include the price and the website where you found your
device.
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Project 12-2: Develop a Plan to Troubleshoot a WAN Connection
In this project, you’ll research suggestions online for troubleshooting Internet connection
problems, and develop your own list of procedures to follow the next time you encounter
this type of problem.
1. In a web browser, do a search for tips, tricks, hints, and steps for troubleshooting
Internet connection issues. Make a list of ideas from at least three different sources
that you can use for future reference.
2. Think about the ideas you’ve gathered, and consider which steps should be completed
first, middle, and last, to narrow down and identify a problem as quickly as possible
without a great deal of backtracking. Make sure your troubleshooting steps cover a
wide variety of potential problems.
3. Rearrange and edit your list so that the steps would be easy to follow, beginning to
end, in a troubleshooting scenario. Draw a troubleshooting diagram using the same
style as the troubleshooting diagram in Figure 1-21 at the beginning of this text.
Explain why you placed the steps in the order you chose, and list one or more
potential problems that each step is designed to detect. Include your information
sources with your diagram and explanations.
Project 12-3: Explore WAN Options in Your Area
Selecting a particular WAN solution because its theoretical maximum speed is faster than
another solution’s theoretical maximum speed won’t help much if your local carrier
doesn’t actually offer service at that speed. Selecting a WAN solution for a corporation