SYSTEM ADMINISTRATION
Chapter 20
Troubleshooting Small
Office/Home Office Network
Failures
Small Office/Home Office
(SOHO) Environments
• In the SOHO environment, many users connect to
some type of network remotely. That is, they are not
connected directly to the network. Instead, they
connect indirectly, or on demand.
• For example, a user might use a modem to dial into
a remote access server.
• Once users are authenticated, they may or may not
be required to log on a second time through the
appropriate network client, i.e., the Novell Client for
NetWare Networks or the Microsoft Client for
Microsoft Networks.
(continued)
Small Office/Home Office
(SOHO) Environments
• Once users are authenticated, they have access to
network resources, just like any other network client.
• In a small office environment, users may have a
small peer-to-peer or client-server network setup.
They may or may not need access to anything
outside of their own network, other than the Internet.
• Users of a small office network commonly access
the Internet through a shared connection, such as a
DSL line using Internet Connection Sharing.
Digital Subscriber Line (DSL)
• Digital Subscriber Line (DSL) is a broadband
technology that makes use of unused frequencies
on normal telephone lines to transmit data at varying
speeds, depending on the type of DSL being used.
• One of the primary benefits of DSL is that voice and
data traffic can be sent simultaneously over the
same phone line.
• DSL is always on; therefore, a connection is always
available while working on a client workstation.
• There are two primary types of DSL service,
asymmetric and symmetric.
Asymmetric DSL
• Residential DSL uses a type of DSL called
asymmetric DSL or ADSL, which uses its own phone
line to send and receive data traffic.
• The term asymmetric means that data sent from
your computer (uploading or upstream) will travel at
different speeds from data sent to your computer
(downloading or downstream).
• For home users, ADSL is normally optimized for
faster download speeds than upload speeds. There
are several different types of ADSL available.
(continued)
Asymmetric DSL
(continued)
• Full rate (ADSL)
– Offers speeds up to 6 Mbps of data per second.
Voice and data are sent simultaneously over an
existing telephone line. Full-rate is the most
common type of DSL used by businesses and
residential customers.
• G.lite
– Targeted specifically at the home Internet user
market. G.lite supports speeds up to 1.5 Mbps
downstream and up to 500 Kbps upstream.
(continued)
Asymmetric DSL
(continued)
• Rate adaptive (RADSL)
– A nonstandard version of ADSL.
• Very-high-bit-rate (VDSL)
– Supports data transfer speeds up to 26 Mbps
over short distances, usually not more than 50
meters.
Symmetric DSL
Symmetric DSL usually requires its own dedicated
phone line and allows uploads and downloads to travel
at the same speeds There are several different types
of symmetric DSL.
• Symmetric DSL (SDSL)
– A proprietary version of DSL that supports data
transfer speeds from 128 Kbps to 2.32 Mbps.
– SDSL is a generic term for a number of
supplier-specific implementations that use a
single copper wire pair that supports variable
transfer rates of symmetric service.
(continued)
Symmetric DSL
(continued)
• Symmetric high-bit-rate DSL (SHDSL)
– An industry standard that achieves 20% better
loop-reach than older versions of symmetric DSL.
– SHDSL supports data transfer speeds ranging
from 192 Kbps to 2.3 Mbps with less crosstalk
between cable pairs.
– One pair of wires may be used for short loops
while two wire pairs may be used for longer loops.
– SHDSL is designed specifically for data transfers
that need fast upload speeds. For that reason,
SHDSL is aimed primarily at business customers.
(continued)
Symmetric DSL
(continued)
• High-data-rate DSL (HDSL)
– Service that supports speeds up to 2.3 Mbps with
both uploads and downloads.
– HDSL is available at both 1.5 and 2.3 Mbps, and
uses one, two, or three pairs of twisted copper
wire. The newer generation of HDSL is HDSL2,
which requires only one wire pair.
• 2nd generation HDSL (HDSL2)
– Provides upload and download speeds of 1.5
Mbps and supports voice, data, and video using
either asynchronous transfer mode (ATM) or
frame relay over a single copper wire pair.
– HDSL2 does not provide voice telephone service
on the same wire pair.
– HSDL2 requires only one wire pair to support data
transfer.
(continued)
Symmetric DSL
(continued)
•
Integrated Services Digital Network DSL (IDSL)
– Supports data transfer rates up to 144 Kbps using
standard phone lines.
– IDSL has the ability to deliver services through a
digital loop carrier (DLC), which is a device often
placed in newer neighborhood telephone cabinets.
– The DLC is designed to simplify the distribution of
cable and wiring for the phone company.
– ADSL and its G.lite variation are implemented
directly into these DLCs.
– Keep in mind that DSL will not be available in all
areas due to distance limitations. That is, in order to
obtain DSL service, you must be within a specific
distance from the central telephone office.
Connecting to DSL
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After obtaining the necessary service from your
provider, you will need to establish the physical
connection.
First, you will need to install a network interface card in
the computer. After the card is installed, start the
computer and install the appropriate driver when
prompted.
Following the directions provided by your DSL
provider, you will also need to install and configure a
client and the necessary protocols, normally a
Microsoft Client for Microsoft Networks and TCP/IP.
An Ethernet cable will then be connected from the
back of the network card into a DSL modem or router.
A standard telephone cable is then connected at the
modem or router on one end and into a standard
telephone wall jack on the other, completing the
connection.
Troubleshooting an Established
DSL Connection
•
If your DSL connection was working correctly and
suddenly stopped, begin by conducting some
simple checks of the DSL modem or router.
• Most DSL hardware contains an array of lights that
will give you an idea whether the problem is with
the DSL line, equipment, or the computer.
• When checking the status of the network interface
card, begin by checking the link and collision
lights.
• If they are operating correctly, check and replace,
if necessary, the Ethernet cable between the
network card and the DSL modem or router.
(continued)
Troubleshooting an Established
DSL Connection (continued)
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•
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If the lights are not lit, check the Device Manager
utility to ensure the network card is configured
correctly.
Check the status of the adapter to ensure it is
functioning correctly.
– If it is not, press the Troubleshoot button to
begin the troubleshooting process.
Finally, check the telephone wiring at your home
or office.
Troubleshooting a New DSL
Connection
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Many of the steps used for an established connection
can be used to troubleshoot a new connection.
With a new connection always suspect that some
configuration parameter is incorrect.
If checks of those parameters disclose that everything
is correct, the DSL hardware is always a good place to
check.
Begin by checking the lights, as they will most likely
point you to where the problem is.
Also, always make sure the phone company has
accomplished the work that is necessary or all of your
troubleshooting efforts will be for nothing.
Cable
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A cable connection works with the cable television
service that runs into your home.
The service is provided by your local cable television
provider and, like DSL, may or may not be available in
all areas.
The installation of cable service is fairly straightforward. First, the incoming television cable is cut and
connected to one side of a splitter.
The end of the cable going to the TV set will be
connected to an “Out” port.
Next, a new piece of cable will be connected to
another “Out” port.
(continued)
Cable
(continued)
•
The other end of the new cable will be connected to a
cable modem.
•
It is important to note here that there should be no
devices between the cable splitter and the cable
modem. The signal from the cable modem is very
strong. If a television is connected in the path between
the modem and the splitter, the signal to the television
would be disturbed.
•
A cable modem is a different from a standard modem,
although it still modulates and demodulates signals.
•
Cable modems perform more functions than a
standard phone line modem, such as routing and
tuning of the signal.
•
An Ethernet cable attaches the cable modem to a
network interface card that is installed inside the
workstation.
(continued)
Cable
(continued)
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Cable is always on; therefore a connection is always
available while working on a client workstation.
Cable modem speeds vary by service and direction of
data traffic. Two terms that you need to be familiar with
are upstream and downstream.
– Upstream is the data that is traveling from your
computer to another destination.
– Downstream is traffic that is being transmitted to
your computer.
Currently, cable modem speeds for downstream traffic
typically top out at about 1.5 Mbps, with actual
performance in the 1.0 – 1.5 Mbps range.
Upstream speeds generally top out at 256Kbps.
One advantage that cable has over DSL is that cable is
not subject to the distance limitations of DSL. The
distance capability for cable is virtually unlimited.
Troubleshooting an Established
Cable Connection
•
If your cable connection was working correctly and
suddenly stopped, begin by conducting some simple
checks of the cable modem.
•
Although features vary from brand to brand and model
to model, most cable modems include an array of
lights that will give you an idea whether the problem is
with the cable line, equipment, or the computer.
•
When checking the status of the network interface
card, begin by checking the link and collision lights.
– If they are operating correctly, check and replace, if
necessary, the Ethernet cable between the network
card and the modem.
– If the lights are not lit, to check the Device Manager
utility to ensure the network card is configured
correctly.
(continued)
Troubleshooting an Established
Cable Connection (continued)
•
•
Finally, check the cable wiring at your home or office.
All you can test is the wiring inside of your home or
office building.
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Always make sure that all connections are secure.
If none of your cable devices work, suspect the external
line.
If only one of several devices is experiencing problems,
use a cable tester to check the cable on the nonworking
device or just replace the cable with a known good
cable.
If the cables are good, try replacing the splitter, although
these items seldom fail.
If all of the internal components appear to be working,
you will need to contact the cable company.
Troubleshooting a New Cable
Connection
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•
•
•
With a new connection always suspect that some
configuration parameter is incorrect.
If checks of those parameters disclose that
everything is correct, the cable hardware is always
a good place to check.
Begin by checking the lights on the network card
and modem, as they will most likely point you to
where the problem is.
Also, always make sure the cable company has
accomplished the work that is necessary or all of
your troubleshooting efforts will be for nothing.
Home Satellite
• Satellite communication systems send and receive
signals between Earth-based stations and
geosynchronous space satellites.
• Broadcast centers, also known as Earth centers, are
used to transmit high-powered, high-frequency
signals to the satellite.
– The signals are referred to as uplink.
• The satellite then transmits that information back to
Earth, to satellite dishes that are within the coverage
area of the satellite.
– These signals are referred to as downlink.
(continued)
Home Satellite
(continued)
• The data from the satellite is then patched into an
existing network, allowing computers to
communicate.
• This operation works in reverse whenever data is
transmitted from the satellite dish to the Internet or
to another network.
• There are several advantages to using satellite
technology in networking.
– It is always on.
– Satellites allow users to be mobile.
(continued)
Home Satellite
(continued)
There are also several disadvantages to the use of
satellite technology.
• Latency
– Latency is the delay in data transmission that
occurs when the satellite communicates back
and forth between Earth-based systems, such
as the broadcast center and a home satellite
dish. This delay is due to the distance that the
data must travel between the satellite and
Earth-based systems.
(continued)
Home Satellite
(continued)
• Noise
– The strength of a signal sent by a satellite begins
to weaken as it travels. Since these signals travel
a long way, you end up with a low signal-to-noise
ratio. In essence, this means you have less signal
and more noise.
• Bandwidth
– The radio frequency spectrum is fairly narrow,
meaning that the amount of bandwidth available
is limited.
(continued)
Home Satellite
(continued)
There are several varieties of satellites in use:
• Low-earth Orbit (LEOs)
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Located closest to the Earth, at about 900 miles away
from the Earth’s surface.
Because they are so close, they have a small footprint.
However, since they are close, there is little delay in
the signal, which equates to a fast response time when
sending and receiving data.
• Medium-Earth Orbit (MEO)
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Travel above the Earth in the 5,000 to 8,000 mile
range.
Since they have a higher orbit than LEOs, they have a
broader footprint.
Unfortunately, as distance away from the Earth
increases, so does the delay in data travel.
(continued)
Home Satellite
(continued)
•
Geosynchronous-Earth Orbit (GEO)
– Operate in high stationary orbits 22,300 miles above
the Earth.
– They cover a very large area with a large footprint,
but suffer from significant delays (about half a
second) in transferring data traffic back and forth to
the Earth.
(continued)
Home Satellite
(continued)
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The standard home setup consists of a small, (about
24" x 36") satellite dish, also called an antenna, that is
mounted on or near your home.
The dish must have a clear, unobstructed view of the
sky. The dish is connected to a satellite modem using
coaxial cable.
There are internal and external modems.
– If the modem is internal, it is installed directly into an
open slot in your computer and the cable is
connected directly to the back of it.
– If it is external, the modem is connected to a
computer through an Ethernet cable which connects
to a network interface card or a USB cable.
(continued)
Home Satellite
(continued)
• Home satellite systems typically provide download
speeds in the range of 150 - 500 Kbps, and upload
speeds of 128 Kbps.
• It is important to note that some systems are
"receive only" systems, which means that you must
use a telephone line and a modem to transmit data.
In order to transmit, you must either keep your
existing dial-up ISP account or get a new one, which
will add to the cost.
Troubleshooting a Satellite
Connection
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First, it must be correctly installed, which means that
the Earth-based satellite receiver must be set to the
proper parameters.
•
For example, after the Earth-based satellite system is
set up and connected, the installer must be able to
locate a signal.
•
Once the signal is located, you must be able to make
adjustments to items such as azimuth, elevation, and
antenna polarization. The correct adjustments ensure
maximum signal strength accuracy.
•
If the system was previously installed and working
correctly, but you’ve noticed a marked drop in
bandwidth, or no bandwidth at all, you will need to
recheck these settings.
(continued)
Troubleshooting a Satellite
Connection (continued)
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Since the connection between the antenna and
computer is coaxial cable, check the connections to
make sure they are tight and that the connectors have
not separated from the wire.
If you are sure that the antenna is adjusted to the
correct parameters and the cable is working properly,
the next step in the chain is the satellite modem.
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Most modems have a set of lights on the front, just like
cable modems, to give you an idea if everything is
working correctly.
Then check the network card using the procedures that
were outlined earlier.
Keep in mind that rain and snow will affect the
performance of your satellite system, just as they do
with satellite-based television.
Wireless
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In a typical wireless LAN (WLAN) configuration, a
device that both transmits and receives, commonly
referred to as an access point (AP), connects to the
wired network from a fixed location using a standard
Ethernet cable.
The access point receives, buffers, and transmits data
between wireless components, such as a laptop
computer with a wireless network adapter installed and
the wired network.
An access point can support a small group of users
and generally has a range up to several hundred feet.
The access point can be installed anywhere provided
there is good radio coverage.
This type of wireless network operates in infrastructure
mode.
Troubleshooting a Wireless
Connection
•
Always perform a communications test. Probably
the easiest test to perform is to PING the hardware.
– Begin by PINGing your local computer to ensure
that it is working correctly. Next, PING the AP’s IP
address.
– If the AP doesn’t respond to the PING , suspect a
malfunctioning AP.
– Try cycling the power on the AP to reset it.
(continued)
Troubleshooting a Wireless
Connection (continued)
•
Wait a few minutes and then try PINGing the AP again.
If both PINGs still fail, check the configuration of the
AP:
– Verify that the service set identifier (SSID) is correct.
Each wireless network has its own SSID. If it is
incorrect, the computer will ignore the AP and
search for an AP with the specified SSID.
– Verify the WEP key. Check to see if the wired
equivalent privacy (WEP) encryption configuration is
configured correctly for the network card and AP
you are using. Each network card and AP requires
you to specify the WEP encryption key differently.
(continued)
Troubleshooting a Wireless
Connection (continued)
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Test the signal strength. Most manufacturers of
wireless equipment have some mechanism, usually
a software utility, that is designed to measure signal
strength.
Change channels on the AP and the wireless client
to see if signal strength improves.
Keep in mind that a wireless phone or microwave
oven may interfere with wireless clients. Try
unplugging the wireless phone and turning off the
microwave to see if the situation improves.
Plain Old Telephone System
(POTS)
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The plain old telephone system (POTS), also
referred to as the public switched telephone
network (PSTN), is the standard phone system
that you use to place phone calls or to connect to
an ISP using a modem.
The signal that enters and leaves your phone is
analog. That analog signal is transmitted over a
twisted pair cable. Once the signal reaches the
telephone company, it is digitized, providing a 64
Kbps data stream.
Troubleshooting POTS
•
When your local telephone stops working, begin
by checking the telephone wiring at your home or
office.
Troubleshooting Modems
Connected to POTS
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Always check the telephone wiring.
If you can rule out the wiring as a cause of your
problem, check the modem.
You may also try issuing commands to the modem.
Most modems have a standard set of commands that
can be issued through a terminal window.
Typically, a modem will begin responding to new
commands the next time it is used. Occasionally you
will have to restart the computer for the change to take
effect.
If a modem does not support an issued command, it
will report an error.
Most Windows operating systems give you the ability
to log the steps that your modem takes when trying to
establish a connection.