1. technology and computing
2. hardware
3. computer networking
4. router

Unit 2: LAN Configurations
Lesson 2-2: Data Transmission
At a Glance
In this lesson, the process of transmitting data is examined. Computers
encode and transmit data, voice, and video over networks via various
transmission media. Encoding is the process of transforming information
into digital and analog signals. This lesson covers the basics of how data is
encoded, decoded, and transmitted. Data packet structure and its
relationship to the OSI layers is also covered.
What You Will learn
After completing this lesson, you will be able to:
•
Define technical terms associated with data signaling and
transmission.
•
Describe the characteristics of digital and analog signaling.
•
Explain how packets and frames are structured, and describe their
relationship to the OSI model.
•
Convert binary and hexadecimal digits to decimal digits.
•
Use Sniffer Basic software to capture and analyze packets.
ST0025803A
143
Lesson 2-2: Data Transmission
Tech Talk
•
AmplitudeCharacteristic of a wave measuring wave height from the
base to the peak of a waveform. Indicates the strength of the signal.
•
Analog SignalAnalog signals change continuously as opposed to
digital signals, which are discretely valued. For example, sound is an
analog signal; it is continuous and varies in strength.
•
ASCII CodeAmerican Standard Code for Information Interchange. A
7-bit coding scheme that assigns unique numeric values to letters,
numbers, punctuation, and control characters.
•
Baudot CodeA 5-bit coding scheme used for transmitting data.
•
Binary NumbersA number system based on two states, 0 and 1.
Computers use combinations of binary numbers to represent and
encode all kinds of data including words, sounds, colors, and pictures.
•
Connection-Oriented CommunicationA form of network
communication, where the transmitting device must establish a
connection with the receiving device before data can be transmitted,
(for example, telephone). In connection-oriented communication, the
receiving device acknowledges receipt of the data.
•
Connectionless CommunicationA form of communication over
networks where the transmitting device can send a message without
establishing a connection with the receiving device (for example, radio).
Signals are sent, but there is no mechanism for acknowledging receipt.
•
Digital SignalData transmitted in discrete states, for example, on
and off. These discrete states can be represented by binary numbers,
and vice versa.
•
Full-DuplexTwo-way, simultaneous data transmission. Each device
has a separate communication channel.
•
EBCDIC CodeExtended Binary Coded Decimal Interchange Code.
An 8-bit coding scheme used by IBM for data representation in
mainframe environments.
•
Logical AddressAn OSI model Layer 3 address.
•
FrameBasic unit of data transfer at OSI Layer 2.
•
Half- DuplexTwo-way data transmission that is not simultaneous.
Only one device can communicate at a time.
•
PacketBasic unit of data transfer at OSI Layer 3.
•
Physical AddressA OSI model Layer 2 address.
•
144
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Data Transmission
Data is transmitted over networks using signals, which are transformed, or
encoded, by computers into the voice, video, graphics, and/or the print we
see on our computer screens. The signals used by computers to transmit
data are either digital or analog.
•
Analog signals are continuous signals that vary in strength. Sound is
an example of an analog signal. Sound is actually a wave and is quite
similar, or analogous, to electromagnetic waves, hence the name
analog. Telephones have transmitters that encode sound waves into
electromagnetic waves, which then travel over wires toward their
destination. The receiving telephone decodes the electromagnetic
waves back into sound waves. Our brains then decode the sound waves
into the words we hear. Computer modems use the same principle.
Analog signals can be represented digitally. For instance, a high
electromagnetic voltage could be interpreted as 1 and low voltage as 0.
Telephone Encoding/Decoding
Encode
Decode
Cable
Source
•
Destination
Digital signals are discrete rather than continuous. Either there is a
signal or there isn't a signal. Telegraphs transmit data with discrete
signals. You either hear a tap or you do not hear a tap. Discrete
signals can be represented by on and off pulses. The duration of a
discrete signal can be varied, as with dots and dashes in Morse Code.
Telegraph Encoding/Decoding
Encode
Decode
Cable
Source
Destination
ST0025803A
145
Lesson 2-2: Data Transmission
Discrete signals can also be represented digitally. The presence of a signal
could be coded as a 1 and the absence of a signal coded as a 0. The digits 0
and 1 are used because computer circuitry is based on binary digital data.
Codes are used to group a set number of bits together and have a group of
bits represent a letter, number, or other character. The computer’s brain,
the central processing unit (CPU), transforms these codes of 0s and 1s into
the voice, video and data we see. One coding scheme, ASCII, codes an “a”
as the binary number 0110-0001.
Digital data is based on two states, on or off. The binary numbering
system uses only two digits, 0 and 1, so it makes sense to use the binary
numbering system. One digit, 0 represents off, the other digit represents
on. A single 0 or 1 is called a bit. One byte is equal to eight bits (also
called an octet when discussing TCP/IP). In ASCII code, one octet is the
equivalent of one alphabetic or numeric character. In order to appreciate
how computers communicate over networks, it is necessary to be aware of
how they encode information.
Connection-Oriented and Connectionless Transmissions
Data transmission may be:
•
Connection-oriented
•
Connectionless
The main difference between the two is that with a connection-oriented
transmission, the destination device acknowledges receipt. Whereas, with
connectionless, there is no acknolwedgement.
In connection-oriented transmissions, the sending (source) device
establishes a connection with the receiving (destination) device. The
connection is continued until all data packets have been transmitted and
the source device receives notification that the data was received by the
destination device and has been checked for errors.
A telephone conversation is an example of a connection-oriented
transmission. When a call is made, data is transmitted across phone lines,
the receiving party picks up the phone, and a conversation takes place.
The individual making the call knows that it arrived at the correct
destination and that it was understood.
In a connectionless transmission, the source device transmits data but the
connection is not maintained. The source device does not wait for
notification that the destination device actually received the information
accurately. This method is faster than connection-oriented, however less
reliable since there is no notification of whether the data is received or not.
It is more common to find connectionless transmissions on LANs.
To understand a connectionless transmission, think of a radio broadcast: A
radio disc jockey tells his/her friends to be sure to listen to her/his program
146
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
at 9:00 p.m. At that time the disk jockey broadcasts a message to them.
Did they receive the message? Although it is quite likely, the disk jockey
cannot be sure that they turned the radio on, listened, or understood the
message.
Synchronous and Asynchronous Transmission
Computers need to know when to expect data and where a character
begins and ends. When receiving data, timing on both computer devices
must be coordinated if they are to work together efficiently. This
coordination is called clocking, timing, or framing. There are two protocols
for the timing or coordination of data signals:
•
Synchronous
•
Asynchronous
When transferring data, both the transmitting and receiving nodes need to
agree when the signal begins and ends so the signals can be correctly
measured and interpreted. This timing process is called bit
synchronization, framing, or clocking.
Imaginehowdifficultitwouldbetoreadifyoudidnotknowwhenawordstartedan
dwhenawordendediftherewerenopunctuationandnospacesyoucandoitbecaus
ethereareseveraldifferentcharactersanditisnotincodewhatifthiswerecodedas
zerosandonesthenyouwouldhaverealproblems. As you can see,
synchronization of data is very important.
Clocking is somewhat like timing in music. There are a specific number of
beats expected per bar. When computer devices are synchronized, a
specific number of signals or “beats” are expected within a set amount of
time. Timing is important because it helps you be prepared. In many
schools, every 50 minutes, a new class period starts. Students watch the
clock and expect a signal. Usually, they are already prepared to leave the
classroom. That is because they expected the signal.
Synchronous transmission requires the communicating devices to maintain
synchronous clocks during the entire connection. The sending device
transmits on a specific schedule and the receiving device accepts the data
on that same fixed schedule. The receiving device knows the timing of the
sending device because the timing information is embedded within the
preamble of the frame. Synchronous transmissions are common in
internal computer communications and usually are sent as entire frames.
Synchronous transmission is common when large blocks of data are
transferred, since it is efficient and has a low overhead (number of bytes of
data/control + data bytes).
Asynchronous data transmission does not involve synchronizing the clocks
of the sending and receiving devices. Instead, start and stop bits are used
for synchronization of data signals. The start and stop bits tell the
ST0025803A
147
Lesson 2-2: Data Transmission
receiving device how to interpret the data. Asynchronous sends one
character at a time.
Data transmission may be half-duplex; meaning data is transferred in only
one direction at a time. An example of half-duplex is a CB radio where
only one person can talk at a time. Or, transmission may be full duplex,
transmitted in two directions simultaneously. A telephone conversation
illustrates full-duplex communication.
Check Your Understanding
♦ Why do the variations in data transmission signals need to be
synchronized?
♦ Explain how the two binary numbers, 0s and 1s, are used to
interpret data.
♦ Distinguish between connectionless and connection-oriented data
transmissions. Give an example of when you think a connectionoriented transmission might be useful.
Analog Signals
Analog signals, which are electromagnetic waves, are continuous and look
like a copy of the original sound wave. Transmission of data is
accomplished by varying one or more the waves’ properties.
Analog Signal
Analog
+
0
-
All waves have three characteristics, amplitude (strength), frequency, and
phase. Variations, called modulations, in wave characteristics are used to
encode analog signals to digital signals. Amplitude-Shift Keying
(variations in strength) and Frequency-Shift Keying are two examples.
148
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Amplitude-Shift Keying uses a change of the voltages for interpretation.
When there is a voltage change from high to low, the binary digit
represented changes. If high voltage were 1 then low voltage would be 0.
Amplitude-Shift Keying
1
1
0
0
0
ASK
Frequency-Shift Keying uses the frequency of the waves for interpretation.
When there is a frequency change from high to low, the binary digit
changes. If high frequency were 1 then low frequency would be 0 .
ST0025803A
149
Lesson 2-2: Data Transmission
Frequency-Shift Keying
1
0 0
1
FSK
Digital Signals
With digital signaling, either there is or there isn’t a signal. There are
various encoding schemes that use the “on” “off” signal to represent data.
Digital
+
0
-
Depending upon the type of network, different digital encoding schemes
are used. For example, Ethernet and Token Ring LANs do not use the
same encoding scheme. For computer devices to interpret the data
correctly, both the transmitter and receiver must agree on the encoding
scheme in order to determine data elements and their values. When new
technologies are invented, new encoding protocols often need to be
established.
Check Your Understanding
♦ What are the three characteristics of waves that are used when
transmitting data?
♦ Why will new technologies need new encoding schemes?
150
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Data Transmission and the OSI Model
When transmitting data over networks, conforming to the OSI model is
important. As discussed in the previous lesson, data travels vertically
through the seven OSI layers. Data is encapsulated at each layer of the
transmitting device from top to bottom and stripped at the receiving device
in the reverse direction. The protocols of the OSI model are used to
organize the data into packets, with headers and trailers.
OSI Model Original Data with Headers and Trailers
Hp
Hs
Ht
Hn
Hd
Data
Application Layer
Data
Presentation Layer
Data
Session Layer
Data
Transport Layer
Data
Data
Network Layer
Data Link Layer
Data
T
T
Physical Layer
OSI communication is as follows:
•
Each layer communicates with layers both immediately above and
below it.
•
Each layer from the sending (source) station also communicates with
its peer layer at the receiving (destination) computer.
•
Data starts at the application layer of the source device and descends
through the remaining layers before being transmitted to the
destination device.
•
As each layer receives the data from the layer above, it adds, in the
form of headers, its data. This data contains various protocols that
enable communication.
•
The original data, with the new header and the headers from the
previous layers, is then sent to the next layer down.
•
When the data reaches the Physical Layer, it is transmitted across
various media to the destination device.
ST0025803A
151
Lesson 2-2: Data Transmission
•
The destination device receives the entire frame and sends it up
through the layers, one after the other in sequence.
•
Each layer strips the header added by its peer layer at the source
device.
Ethernet packets can contain approximately 1,000 bytes. If the data being
transmitted is larger than 1,000 bytes then the computer breaks it down
into packets. Each packet is transmitted and received separately. Packets
are sequentially numbered. This allows the receiving computer to recreate
the data in the correct order. Depending upon the protocols used, packet
size can change.
Transmission of Data through the OSI Layers
Data transfer begins at the application layer of the source device and each
OSI layer adds header and/or trailer information to help ensure efficient,
error free transfer of data. The destination device receives the data and
the data is transferred up through the layers. Each strips the information
added by its peer layer and moves the remaining data to the next layer.
Eventually, the data is returned to its original form at the application
layer.
Application Layer
Data
The application layer serves as an interface between user applications and
network services, such as electronic mail. Data input by the user is then
sent to the next layer, the presentation layer.
Presentation Layer
Hp
Data
Header information is added by presentation layer protocols. This layer is
responsible for translation, encryption, and compression of data. If
necessary, it is this layer that translates local data, such as ASCII and
EBCDIC.
152
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Session Layer
Hs Hp
Data
At the session layer, checkpoints are built in to ensure successful data
transmission. If transmissions are proceeding smoothly, they continue. If
not, retransmission of data takes place. This layer provides the user
interface, in the form of passwords and logins, which allow network access.
Transport Layer
H t Hs Hp
Data
The transport layer provides for message segmentation and ensures errorfree delivery, without loss or duplication.
Network Layer
Hn H t H s Hp
Data
At the network layer, header information identifies the “logical” source and
destination addresses of the network. The logical network differs from the
physical MAC address. The logical address assists with the routing of data
from network to network. Factors affecting routing decisions include cost,
speed, network conditions, and priorities.
Data Link Layer
Hd Hn H t Hs Hp
Data
T
Frames are built at the data link layer. The headers and trailers added at
this layer control error handling and synchronization over the local
segment. This is where the “physical” address of the destination and the
source address of the sender are added.
ST0025803A
153
Lesson 2-2: Data Transmission
Physical Layer
The physical layer of the OSI controls the electrical aspects of data
transfer, such as voltage levels, signal timing, and encoding.
Physical Layer Frame with Preamble, Headers, and Trailers
Transport
Header
Data Link
Presentation
Header
Header
Hd Hn H t Hs Hp
Physical
Preamble
Session
Header
Header
Network
Header
Data
T
Trailer
Although real network applications don’t always incorporate protocols from
every layer, or sometimes combine the functions of two layers, it is
important to understand how the OSI model is used as a framework for the
protocols used when transmitting data.
Transmission of data packets occurs in both directions. Peer layers
communicate back and forth when a data packet is being sent. What is
actually taking place is a checking sequence. For example, does the
address match, is there any congestion, which is the best route, are the
destination and source devices synchronized, is it time to terminate the
connection? All of this takes place in a fraction of a second.
154
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Check Your Understanding
♦ What is the difference between half-duplex and full duplex
transmission?
♦ How is sending a registered letter through the mail similar to
sending data over a network?
ST0025803A
155
Lesson 2-2: Data Transmission
Try It Out
Converting Binary and Hexadecimal to Decimal Numerals
Computers are electrical devices. Electrical pulses can be turned “on” or
“off.” Binary digits 0 and 1 can be used to represent “on” and “off” pulses.
Computers use these 0s and 1s to represent data, which they then
interpret using various codes. In computer language, each 0 or 1 is
considered a bit and eight bits are equal to an octet (byte). One octet
generally represents one character of data.
We use and understand a base-10 numbering system in everyday life.
Base-10 uses the digits 0-9. In order to understand how computers
transmit data, it is necessary to understand two additional numbering
systems, base-2 and base-16. Two digits, 0 and 1, are used for base-2
numbering and 10 digits plus 6 characters from our alphabet are used for
base-16 numbering.
ASCII code uses the base-2, or binary, numbering system and hexadecimal
code, uses the base-16, or hex, numbering system.
In hexadecimal numbering, there are 16 symbols for the decimal numbers
0-15. The numbers 0 to 9 represent the decimal numerals 0 to 9. The
decimal numbers 10 to 15 are represented by the alphabetic characters A
to F, e.g., A=10, B=11, C=12, D=13, E=14, F=15. Hexadecimal numbers
can be used to represent 8 bits as two hexadecimal digits. MAC addresses,
which you will learn about later in this course, use hex numbers for
address identification.
Materials Needed
•
None
In this activity, you will attempt to convert decimal, binary, and
hexadecimal numbers. Use the data from the following tables to help with
conversions.
156
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Number Equivalents
Decimal
Binary
Hexadecimal
0
0000
0
1
0001
1
2
0010
2
3
0011
3
4
0100
4
5
0101
5
6
0110
6
7
0111
7
8
1000
8
9
1001
9
10
1010
A
11
1011
B
12
1100
C
13
1101
D
14
1110
E
15
1111
F
When numbering, we give each digit column a name or positional value.
We do this for convenience when reading numbers. The column value is
determined by raising the base (decimal, binary, or hexadecimal) to a
power as shown in the charts below.
ST0025803A
157
Lesson 2-2: Data Transmission
When using a base-10 number such as 34,752, each of the numbers has a
decimal positional value based on the powers of 10. 2 is in the 1s position,
5 in the 10s position, 7 in the 100s position, 4 in the 1,000 position, and 3
in the 10,000 position.
Decimal (Base 10) Positional (Column) Values
100 = 1s column/position
101 = 10s column/position
102 = 100s column/position
103 = 1,000s column/position
104 = 10,000s column/position
Or: 3 4, 7 5 2
Ones position
Tens position
Hundreds position
Thousands position
Ten thousands position
Binary (Base 2) Positional (Column) Values
When you use a base-2 number such as 11011001, each of the numbers
has a decimal positional value based on the powers of 2. Starting from
the right, 1 is in the 1s position, 0 in the 2s position, 0 in the 4s position, 1
in the 8s position, and 1 in the 16s position, 0 in the 32s position, 1 in the
64s position, and 1 in the 128s position.
158
20
= 1s column
21
= 2s column
22
= 4s column
23
= 8s column
24
= 16s column
28
= 32s column
216
= 64s column
2128
= 128s column
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Or, 1 1 0 1 1 0 0 1
1s
2s
4s
8s
16s
32s
64s
128s
Hexadecimal (Base 16) Positional (Column) Values
When you use a base-16 number such as B620A each of the numbers has
a decimal positional value based on the powers of 16. Starting from the
right, A is in the 1s position, 0 in the 16s position, 2 in the 256s position, 6
in the 4,096 position, and B in the 65,536s position.
160
= 1s column/position
161
= 16s column/position
162
= 256s column/position
163
= 4,096s column/position
164
= 65,536s column/position
Or, B 6 2 0 A
Ones position
Sixteens position
Two hundred fifty-sixes position
Four thousand ninety-sixes position
Sixty-five thousands, five hundred
thirty-sixes position
ST0025803A
159
Lesson 2-2: Data Transmission
Converting a Binary Number to a Decimal Number
Example: Convert the Binary number 101100 to a decimal number.
1. To change from a binary number to a decimal number you must first
determine the binary digit’s positional value, see chart on previous
page. Start at the right: 0=1, 0=2, 1=4, 1=8, 0=16, and 1=32.
Binary Digit
Value
0
0
1
1
0
1
Positional
Value
1
2
4
8
16
32
2. Multiply the binary digit value and the positional value for each digit.
0x1=0, 0x2=0, 1x4=4, 1x8=8, 1x32=32.
Binary Digit
Value
0
0
1
1
0
1
Positional
Value
1
2
4
8
16
32
Product of Binary
Digit and
Positional Values
0
0
4
8
0
32
3. Add the products together: 0 + 0 + 4 + 8 + 0 + 32 = 44.
4. The sum of the products of the binary digit and positional values is
equal to the decimal number. Binary number 101100 is equal to a
decimal value of 44.
160
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Convert the following binary numbers to decimals. Follow the steps above.
Show your work.
a. 110011
b. 0011
c. 010101
d. 1111
e. 01010101
Converting a Hexadecimal Number to a Decimal Number
Example: Convert the hex number 5B6A to a decimal number.
1. To change from a hexadecimal number to a decimal number you must
first change the hex value to a decimal value. Look on the number
equivalents chart and change the hex digits to decimal digits. 5 = 5; B=
11; 6 = 6; A = 10.
Hexadecimal
Value
5
B
6
A
Decimal
Value
5
11
6
10
ST0025803A
161
Lesson 2-2: Data Transmission
2. Determine the positional value for each hex digit (see Positional Value
Tables): 5 is in the fourth position so the positional value is 4,096. B is
in the third position so the positional value is 256; 6 is in the second
position so the positional value is 16; and A is in the first position so
the positional value is 1.
Hexadecimal
Value
5
B
6
A
Decimal
Value
5
11
6
10
Hex Positional
Value
4,096
256
16
1
3. Multiply the decimal value and the positional value for each
hexadecimal. 5 x 4,096 = 20,480; 11 x 256 = 2,816; 6 x 16 = 96; 10 x 1 =
10.
Hexadecimal
Value
5
B
6
A
Decimal
Value
5
11
6
10
Hex
Positional
Value
Product of
Decimal and Hex
Positional Values
4,096
256
16
1
20,480
2,816
96
10
4. Step 4: Add the products together. 20,480 + 2,816 + 96 + 10 = 23,402.
Hexadecimal
Value
5
B
6
A
Decimal
Value
5
11
6
10
Hex
Positional
Value
Product of
Decimal and Hex
Positional Values
4,096
256
16
1
20,480
2,816
96
10
5. Step 5: The sum of the products of the decimal and hex positional
values is equal to the decimal number. Hexadecimal number 5B6A =
decimal number 23,402.
162
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Try the following hexadecimal numbers to decimal numbers. Follow the
steps listed above. Show your work.
a. 237AF
b. 57
c. 392
d. FFF
e. BB41A
Rubric: Suggested Evaluation Criteria and Weightings
Criteria
%
Accurate conversions
40
All work shown
60
TOTAL
Your Score
100
ST0025803A
163
Lesson 2-2: Data Transmission
Stretch Yourself: Launching Sniffer Basic
Capturing Packets
Sniffer Basic is software used by information services technicians to help
analyze networks and locate problems. In this activity, data packets will
be captured and stored. If Sniffer Basic is not installed on your computer,
see your instructor. Be sure you are connected to a network when
completing this activity.
Materials Needed
•
Basic Sniffer Software (NetXRay)
•
Network Connection
•
Internet Connection (optional)
1. Double-click the Sniffer Basic desktop icon, or select it from the Start
menu/Programs list. If you have more than one NIC adapter, a screen
similar to the one below will be displayed and you will be prompted to
choose an adapter to monitor.
164
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
2. From the toolbar, select Help Topics. A screen similar to the following
will appear. Should you have any problems when you use Sniffer Basic,
the help menu is very useful.
ST0025803A
165
Lesson 2-2: Data Transmission
3. Close the Help window.
4. On the Capture menu, click Start. In the Profile box, select default and
click
to start capture.
5. You should see a screen similar to the following:
♦ Is the packet capture gauge incrementing?
6. Spend some time exploring this software. You will be using it
throughout the course.
7. In the Capture Panel window, click
to stop capture. Then click
.
8. In the View window, you will notice three separate windows:
•
The top window lists the packets that were captured.
•
The middle window lists all packet specific information in a verbal
description.
•
The bottom window displays the actual packet data in hexadecimal.
9. Print each of these screens and save.
166
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Generating Traffic
1. Keep Sniffer Basic in capture mode. You are going to generate some
traffic over your network.
2. From your desktop, double-click the Network Neighborhood icon: You
will recognize a list of the computers in your network (if not, notify your
instructor).
3. Double-click one of the names.
♦ What workstation’s node name did you choose?
4. Copy a file from your local PC to the computer you chose in step 2.
5. Now verify the file copy was successful.
♦ How did you do this?
Viewing Captured Data
Return to the Sniffer Basic application.
10. In the Capture Panel window, click
to stop capture. Then click
.
11. In the View window, you will notice three separate windows:
•
The top window lists the packets that were captured.
•
The middle window lists all packet specific information in verbal
description.
•
The bottom window displays the actual packet data in hexadecimal.
12. Print each of these screens and save.
13. In the top window, select a row that has NetBIOS in the Layer column.
14. Scroll down through the information in the middle window and look for
workstation node names. Find the one that you copied your file to.
ST0025803A
167
Lesson 2-2: Data Transmission
15. Scroll to the top of the middle window to the address field. There are
two MAC addresses, the one on the left is the source address, and the
one on the right is the destination address.
♦ What is the node name in the packet you are viewing?
♦ What are the source and destination MAC addresses? What do you
think the source and destination addresses are for?
♦ What data link protocol is being used?
Protocol Distribution
1. Close the packet capture window and do not save the data.
2. From the toolbar, click Tools, then Protocol Distribution button.
3. After a few seconds, you should see several different protocols being
displayed.
♦ Which protocol do you see?
♦ Which protocol generated the most traffic?
4. Go back and copy that file back from the computer you copied it to.
Notice how the chart changes.
5. If you are connected to the Internet, use your browser and hit several
web sites. Again notice the changes on the chart.
♦ Describe changes you noticed. Why do you think there are so many
changes?
168
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Host Table
7. From the toolbar, select Tools then click the Host Table button. This
displays, in pie chart fashion, the busiest nodes on the network.
8. From the toolbar on the left of this window, you can change the display
to a bar chart, outline, or detail view.
♦ How many hardware addresses are listed?
♦ Which nodes do they represent?
♦ How can you find out which nodes are represented by each
hardware address?
♦ The data represented by the Host Table is from which layer of the
OSI model?
Summary
In this lab, you launched Sniffer Basic and captured network traffic to view
packets, determine the type of protocols used, and the amount of traffic
generated in your network. Save the printed data from the three windows
and place them in your portfolio.
How do you think a network administrator uses this information to assist
him/her with the job of managing and planning network expansions?
Write a short essay on this topic and submit it to your teacher.
ST0025803A
169
Lesson 2-2: Data Transmission
Rubric: Suggested Evaluation Criteria and Weightings
Criteria
%
Essay on how a network administrator would use
information gathered from Sniffer Basic software.
40
Directions followed, data recorded as specified,
and questions answered completely and
accurately.
35
Printed materials placed in portfolio
10
Participation and active engagement
15
TOTAL
170
Your Score
100
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Network Wizards
Code Research
Select one of the following topics to research.
Materials Needed
•
Internet Connection
•
ASCII code from another source
1. Search the Internet for the code for interpreting ASCII.
2. Using ASCII code, write the following sentence: Hello, how are you?
Look at the length of the code. Search the Internet to determine how
much time it takes for a byte of information to be sent over a network.
How long would it take to send this message? Calculate how many
bytes are in your name. How long would it take for your name to be
sent over the network? Can you see why computers need to break data
into packets? Explain why this is the case. Prepare a one-page
summary of your findings. Present your findings to the class. Create a
visual display for your presentation.
3. Baudot, ASCII, and EBCDIC are three codes used for the transmission
of data. Research these codes and their history. Prepare a one-page
summary of your findings. Present your findings to the class. Create a
visual display for your presentation.
Rubric: Suggested Evaluation Criteria and Weightings
Criteria
%
On time delivery of assignment
10
Content and quality of one-page summary
25
Content and quality of class presentation
25
Creativity, originality, and quality of visual aid
25
Organization, spelling, and grammar
15
TOTAL
Your Score
100
ST0025803A
171
Lesson 2-2: Data Transmission
Summary
In this lesson, you learned the following:
•
Technical definitions associated with data signaling and transmission.
•
The characteristics of digital signaling, analog signaling.
•
What packets and frames are, how they are structured, and their
relationship to the OSI model.
•
How to convert binary and hexadecimal digits to decimal digits.
•
How to use Sniffer Basic software to capture and analyze packets.
Review Questions
Name___________________
Lesson 2-2: Data Transmission
Part A
1. Describe analog signals. How are they used to transmit data?
2. Describe digital signals.
3. Describe synchronous data transmission.
4. Describe asynchronous data transmission.
5. What is the difference between half-duplex and full duplex
transmissions?
172
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
6. There is a timing process that signals the beginning and ending of data
so it can be correctly measured. This process is called what?
a. Digital signaling
b. Analog signaling
c. Bit synchronization
d. Asynchronous
e. Synchronous
7. Which type of signaling scheme represents data sent as discrete
signals?
a. Digital signaling
b. Analog signaling
c. Asynchronous
d. Synchronous
8. Which type of signaling scheme represents continuously changing data?
a. Digital signaling
b. Analog signaling
c. Asynchronous
d. Synchronous
9. Which type of bit synchronization transmission requires both a start bit
and a stop bit for clocking purposes?
a. Digital signaling
b. Analog signaling
c. Asynchronous
d. Synchronous
ST0025803A
173
Lesson 2-2: Data Transmission
10. Group of bits, including data and control signals, arranged in a specific
format and transmitted as a whole, are called what?
a. Clocking
b. Sequencing
c. Synchronization
d. Packets
Part B
1. Describe the difference between analog and digital signaling
waves/pulses.
2. What is binary notation and how is it used to transfer data signals over
network media?
3. List three characteristics of waves that are used to encode data.
Part C
1. Use the OSI model as your reference and explain how data packets are
structured. Give several examples of information that may be
contained within headers . Draw a diagram showing packet addition at
each layer.
174
ST0025803A
Internetworking Fundamentals
Unit 2: LAN Configurations
Scoring
Rubric: Suggested Evaluation Criteria and Weightings
Criteria
%
Part A: Technical definitions associated with
data signaling and transmission.
30
Part B: Describe the characteristics of digital
signaling, analog signaling.
35
Part C: What packets and frames are, how
they are structured, and their relationship to
the OSI model.
35
TOTAL
100
Try It Out: How to convert binary and
hexadecimal digits to decimal digits.
100
Stretch Yourself: How to use Sniffer Basic
software to capture and analyze packets.
100
Network Wizards
100
FINAL TOTAL
400
Your Score
Resources
Aschermann, Robert (1998). MCSE Networking Essentials for Dummies.
IDG Books Worldwide, Inc. Forest City, California.
Baker, R. (1996). Data Communications Home Page. Available:
www.georcoll.on.ca/staff/rbaker /intro.sht [1999, May 13].
Bert Glen (1998). MCSE Networking Essentials: Next Generation
Training Second Edition. New Riders Publishing. Indianapolis Indiana.
Chellis, James; Perkins, Charles; & Strebe Matthew (1997). MCSE
Networking Essentials Study Guide. Sybex Inc. Alameda California
CMP Media, Inc. (1999). FDDI fundamentals. In Data Communications
Tech Tutorials [Online]. Available:
www.data.com/Tutorials/FDDI_Fundamentals [1999, April 20].
Computer and Information Science, Ohio State University (No date). Data
Communications Cabling FAQ. [Online].Available: www.cis.ohiostate.edu/hypertext/faq/usenet/LANs/cabling-faq/faq.html [1999, May 13].
ST0025803A
175
Lesson 2-2: Data Transmission
Derfler, Jr., Frank J., & Freed, L. (1998). How Networks Work, Fourth
Edition. Macmillan Computer Publishing/Que Corporation. Indianapolis,
Indiana.
Hayden, Matt. (1998). Sam's Teach Yourself Networking in 24 Hours.
Sam's Publishing, Indianapolis, Indiana.
Microsoft Corporation (1998). Dictionary of Computer Terms, Microsoft
Press, Redmond, Washington.
Nortel Networks (1998). Internetworking Fundamentals: Student Guide.
Bay Networks Inc. Billerica, Massachusetts.
Palmer , Michael J. (1998) Hands-On Networking Essentials with
Projects, Course Technology, Inc. Cambridge, Massachusetts.
176
ST0025803A
Internetworking Fundamentals