Building a Simple Network - Study Notes

Building a Simple IT Network
Study Notes for
+W Series - Technology Skills For Women1
http://SlideShare.net/OxfordCambridge
1
Men too are allowed to read, if they wish, as the language style and the document format are universal.

Study Notes http://SlideShare.net/OxfordCambridge
2 | P a g e B u i l d i n g a S i m p l e I T N e t w o r k
Contents
About “+W Series - Technology Skills For Women” ................................................................................ 5
A. Application sharing through networks.................................................................................................... 6
1. Major components of a computer system.......................................................................................... 6
Question ................................................................................................................................................ 10
Quiz........................................................................................................................................................ 11
2. Network interface card...................................................................................................................... 12
Quiz........................................................................................................................................................ 13
Quiz........................................................................................................................................................ 14
Summary................................................................................................................................................ 15
B. Understanding binary basics ................................................................................................................. 16
1. Bits, bytes and measurement terms ................................................................................................. 16
Quiz........................................................................................................................................................ 19
2. Conversion between decimal and binary.......................................................................................... 20
Quiz........................................................................................................................................................ 22
Quiz........................................................................................................................................................ 24
3. Conversion between binary and hexadecimal .................................................................................. 24
Quiz........................................................................................................................................................ 28
Quiz........................................................................................................................................................ 30
Summary................................................................................................................................................ 30
C. Using a PC on a network........................................................................................................................ 31
1. Basic Networking Terminology.......................................................................................................... 31
2. Network Applications ........................................................................................................................ 32
3. Computer Networks .......................................................................................................................... 34
Summary................................................................................................................................................ 36
D. Working with PC technology ................................................................................................................. 37
1. Exercise overview .............................................................................................................................. 37
2. Task 1: Identifying PC components ................................................................................................... 37
Step 1 of 1.................................................................................................................................................. 38
Result......................................................................................................................................................... 38
3. Task 2: Interpreting numerical systems ............................................................................................ 39
Step 1 of 5.............................................................................................................................................. 39
Result..................................................................................................................................................... 39
Step 2 of 5.............................................................................................................................................. 40
Result..................................................................................................................................................... 40
Step 3 of 5.............................................................................................................................................. 40

Result..................................................................................................................................................... 40
Step 4 of 5.............................................................................................................................................. 41
Result..................................................................................................................................................... 41
Step 5 of 5.............................................................................................................................................. 41
Result..................................................................................................................................................... 41
E. OSI model layers and functions............................................................................................................. 42
1. Origins of the OSI reference model................................................................................................... 42
Quiz............................................................................................................................................................ 44
Answer....................................................................................................................................................... 44
2. OSI layers and functions.................................................................................................................... 45
Quiz............................................................................................................................................................ 50
Answer....................................................................................................................................................... 51
3. Data communications........................................................................................................................ 51
Quiz............................................................................................................................................................ 53
Answer....................................................................................................................................................... 54
Quiz............................................................................................................................................................ 58
Answer....................................................................................................................................................... 58
4. The TCP/IP protocol stack.................................................................................................................. 58
Quiz............................................................................................................................................................ 60
Answer....................................................................................................................................................... 60
Summary................................................................................................................................................ 60
F. Working with the OSI model ................................................................................................................. 62
Exercise overview.................................................................................................................................. 62
Task1: Networking terms and functions................................................................................................ 62
Result..................................................................................................................................................... 62
Step 2 of 3.............................................................................................................................................. 63
Result..................................................................................................................................................... 63
Step 3 of 3.............................................................................................................................................. 64
Result..................................................................................................................................................... 64
Task 2: Functions of the OSI model....................................................................................................... 64
1 of 1...................................................................................................................................................... 65
Result......................................................................................................................................................... 65
Task 3: The data encapsulation process................................................................................................ 65
Step 1 of 1.............................................................................................................................................. 66
Result..................................................................................................................................................... 66
G. Glossary ................................................................................................................................................. 67

H. Quizzes’ Answers................................................................................................................................... 96

About “+W Series - Technology Skills For Women”
Study Notes in the field of technology will be put together under this category for the following reasons:
 to encourage ladies, who wish to do so, to stand up and look over the fence into technology related
topics;
 with apprehension or fear;
 and perhaps consider embracing a career move into this technological path;
 or simply as to broaden their general knowledge; after all ICT is in most aspects of everyday life;
 no matter the decision, their skills, professional strengths, and contribution can only be something
positive for technical and technological fields.

Building a Simple Network
A. Application sharing through networks
B. Understanding binary basics
C. Using a PC on a network
D. Working with PC technology
E. OSI model layers and functions
F. Working with the OSI model
A. Application sharing through networks
After completing this topic, you should be able to identify the major components of a computer system and
their functionality, and list the resources required to install a NIC.
1. Major components of a computer system
2. Network interface card
Summary
1. Major components of a computer system
There are several fundamental elements involved in the networking of computers, including computers
themselves and their components that are designed for network connectivity, as well as other network
devices, such as bridges, hubs, and routers.

Some of the major hardware elements of computers that allow network connectivity include the central
processing unit (CPU), the bus, drives, memory components, ports, and cards.
Many networking devices are special-purpose computers and have many of the same parts as normal PCs.
For you to be able to use the computer as a reliable means of obtaining information, it must be in good
working order.
If the need arises to troubleshoot a simple hardware or software problem, you should be able to recognize,
name, and state the purpose of PC components.
 Drives
 CPU
 Expansion slots
 Bus
 Backplane components
 Motherboard
Drives
There are different drive types – for example the CD-ROM drive, the floppy disk drive, and the hard
disk drive.
The CD-ROM drive is a compact disc read-only memory drive that can read information from a CD-
ROM (combined CD-ROM/DVD-ROM are used nowadays).
The floppy disk drive is a disk drive that can read and write to floppy disks (rarely used nowadays).
The hard disk drive is the device that reads and writes data on a hard disk.
CPU
The CPU is the "brain" of the computer, where most of the calculations take place.
The microprocessor is a silicon chip contained within a CPU.

Expansion slots
The expansion slots are openings in a computer into which you can insert a circuit board to add new
capabilities to the computer.
The expansion card is a printed circuit board that provides added capabilities to the computer.
Bus
A bus is a collection of wires through which data is transmitted from one part of a computer to
another.
The bus connects all the internal computer components to the CPU. The Industry-Standard
Architecture (ISA) and the Peripheral Component Interconnect (PCI) are two types of buses.
Backplane components
The backplane is an area of the computer into which you plug external devices.

The following items are backplane components of a PC:
- interface
- mouse port
- network card
- parallel port
- power cord
- serial port
- sound card
- video card
The interface is a piece of hardware, such as a modem connector, that allows two devices to be
connected together.
The mouse port is a port that is designed for connecting a mouse to a PC.
The network card is an expansion board inserted into a computer to enable connection to a
network.
The parallel port is an interface capable of transferring more than one bit simultaneously, and is
used for connecting external devices, such as printers.
The power cord is a cord connecting an electrical device to an electrical outlet to provide power to
the device.
The serial port is an interface that can be used for serial communication in which only one bit is
transmitted at a time.
The sound card is an expansion board that handles sound functions.
The video card is a board that plugs into a PC to give it display capabilities.
Motherboard
The motherboard is the main circuit board of a computer.

The motherboard utilizes the following primary components:
- power supply
- printed circuit board (PCB)
- random access memory (RAM)
- read-only memory (ROM)
- system unit
The power supply is the component that supplies power to a computer.
The printed circuit board (PCB) is a thin plate on which chips (integrated circuits) and other
electronic components are placed.
Random access memory (RAM) is memory that has new data written into it as well as stored data
read from it. It is also known as read-write memory.
A drawback of RAM is that it requires electrical power to maintain data storage. If the computer is
turned off or loses power, all data stored in RAM is lost unless the data was previously saved to disk.
The read-only memory (ROM) is the computer memory on which data has been pre-recorded.
The system unit is the main part of a PC. It is a term that encompasses the chassis, the
microprocessor, the main memory, the bus, and the ports. The system unit does not include the
keyboard, the monitor, or any other external devices connected to the computer.
Because computers are important building blocks in a network, you should be able to identify their major
components.
Questioni
Match the PC components to their descriptions.

Options:
1. Backplane
2. Bus
3. CPU
4. Expansion slots
5. Floppy drive (rarely used nowadays).
Targets:
a. A disk drive that can read and write to floppy disks
b. A part of the computer that allows external devices to be connected
c. Where most of the calculations take place
d. Connects all the internal computer components to the CPU
e. Openings in a computer into which you can insert a circuit board
Laptop computers and notebook computers have become very popular. There are few differences between
the two.
The main difference between PCs and laptops is that laptop components are smaller than those found in a
PC, they are designed to fit together into a smaller physical space, and they use less power when operated.
These smaller components can be difficult to remove.
In a laptop, the expansion slots become Personal Computer Memory Card International Association
(PCMCIA) card slots, or PC slots, through which NICs, modems, hard drives, and other useful devices (usually
the size of a thick credit card) are connected.
PCs are more powerful than laptops, but laptops have the advantage of being portable, which makes it more
convenient to work from home and while traveling between offices.
Quizii
What are the main differences between the components of a desktop PC and a laptop?
Options:
1. It is easier to remove the components from a laptop than the components from a PC
2. Laptops use less power than PCs
3. Laptop components are smaller than those in a PC
4. The slots you connect devices to are called expansion slots in a PC and PCMCIA slots in a laptop

2. Network interface card
A network interface card (NIC) is a printed circuit board that provides network communication capabilities to
and from a personal computer.
Also called a LAN adapter, the NIC plugs into a motherboard and provides a port for connecting to the
network. The NIC constitutes the computer interface with the local area network (LAN).
The NIC communicates with the network through a serial connection, and with the computer
through a parallel connection.
When a NIC is installed in a computer, it requires an interrupt request line (IRQ), an input/output (I/O)
address, a memory space for the operating system (such Windows), and drivers in order to perform its
function.
An IRQ is a signal that informs a CPU that an event needing its attention has occurred. An IRQ is sent over a
bus line to the microprocessor.
An example of an interrupt request being issued is when a key is pressed on a keyboard, and the CPU must
move the character from the keyboard to RAM.

An I/O address is a location in memory used by an auxiliary device to enter or retrieve data from a computer.
When selecting a NIC for a network, you should consider the following:
 type of network
 type of media
 type of expansion slot
type of network
You must choose a NIC to suit the type of network you have. Ethernet NICs are designed for Ethernet
LANs.
type of media
The type of port or connector used by the NIC for network connection is specific to the type of
media, such as twisted-pair.
type of expansion slot
With regard to the type of expansion slot to use, you should consider that because PCI slots are
faster than ISA slots, the latter are being phased out.
Quiziii
Which of the following should you take into account when selecting a NIC for a network?
Options:
1. The type of CPU
2. The type of media
3. The type of network
4. The type of expansion slot
The ability to install a NIC correctly is an important aspect of preparing a computer for network connectivity.

To install a NIC, you must know about the following:
 Network card configuration
 Network card diagnostics
 Hardware resource conflicts
Network card configuration
You must know how the network card is configured, including jumpers, "plug-and-play" software,
and erasable programmable read-only memory (EPROM).
Network card diagnostics
You must know the network card diagnostics, including the vendor-supplied diagnostics and
loopback tests (see the documentation that comes with the card).
Hardware resource conflicts
You must know how to resolve hardware resource conflicts, including IRQ, I/O base address, and
direct memory access (DMA), which is used to transfer data from RAM to a device without going
through the CPU.
Quiziv
Which options correctly describe the information needed to install a NIC?
Options:
1. Knowledge of how to resolve hardware resource conflicts
2. Knowledge of all types of network cards
3. Knowledge of how the network card is configured
4. Knowledge of how to use the network card diagnostics

Summary
There are several PC components, which include the motherboard, the backplane, the central processing
unit (CPU), the bus, drives, expansion slots, memory components, ports, and cards. A laptop is a portable PC
that uses smaller components, is more power efficient than a PC, and has Personal Computer Memory Card
International Association (PCMCIA) card slots instead of expansion slots.
A network interface card (NIC) is a circuit board that allows a personal computer to communicate with a
network. You need to consider the type of network, media, and expansion slot when selecting a NIC. To
install a NIC, you should know how to configure it, how to use its diagnostics, and be able to resolve
hardware resource conflicts.

B. Understanding binary basics
After completing this topic, you should be able to distinguish between the processes used to convert
between decimal, binary, and hexadecimal numbering systems.
1. Bits, bytes and measurement terms
2. Conversion between decimal and binary
3. Conversion between binary and hexadecimal
Summary
1. Bits, bytes and measurement terms
At the most basic level, computers perform their computations by using 1s and 0s instead of the decimal
system.
Computers are made up of electronic switches. At the lowest levels of computation, computers depend on
these electronic switches to make decisions. Computers react only to electrical impulses, understood by the
computer as either "on" or "off" states (1s or 0s).
Computers can understand and process only data that is in a binary format, represented by 0s and 1s. These
0s and 1s represent the two possible states of an electrical impulse and are referred to as binary digits (bits).
Most computer coding schemes use eight bits to represent a number, letter, or symbol. A series of eight bits
is referred to as a byte. One byte represents a single addressable storage location.

The following are commonly used computer measurement terms:
 Bit (b)
 Byte (B)
 Kilobit (Kb)
 Kilobyte (KB)
 Megabit (Mb)
 Megabyte (MB)
 Gigabit (Gb)
 Gigabyte (GB)
Bit (b)
A bit is the smallest unit of data in a computer. A bit equals 1 or 0 in the binary format in which data
is processed by computers.
Bits per second (bps) is a standard unit of measurement for data transmission.
Byte (B)
A byte is a unit of measure used to describe the size of a data file, the amount of space on a disk or
other storage medium, or the amount of data being sent over a network. One byte equals eight bits
of data.
Bytes per second (Bps) is a standard unit of measurement of the data transmission rate over a
network connection.
Kilobit (Kb)
A kilobit is approximately 1000 bits (1024 bits exactly).
Kilobits per second (Kbps) is a standard unit of measurement of the data transmission rate over a
network connection.

Kilobyte (KB)
A kilobyte is approximately 1000 bytes (1024 bytes exactly).
Kilobytes per second (KBps) is another standard unit of measurement for data transmission.
Megabit (Mb)
A megabit is approximately 1 million bits.
Megabits per second (Mbps) is a standard unit of measurement of the data transmission rate over a
network connection.
Megabyte (MB)
A megabyte is approximately 1 million bytes (1,048,576 bytes exactly). A megabyte is sometimes
referred to as a "meg."
Megabytes per second (MBps) is a standard unit of measurement for data transmission.
Gigabit (Gb)
A gigabit is equal to approximately one billion bits.
Gigabits per second (Gbps) is a standard unit of measurement of the data transmission rate over a
network connection.
Gigabyte (GB)
A gigabyte is equal to approximately one billion bytes.
Gigabytes per second (GBps) is a standard unit of measurement for data transmission.
It is a common error to confuse KB with Kb and MB with Mb. You should remember to do the proper
calculations when comparing transmission speeds that are measured in KBps and those measured in Kbps.
For example, modem software usually shows the connection speed in kilobits per second (for example, 45
Kbps). However, popular browsers display file-download speeds in kilobytes per second, meaning that with a
45-Kbps connection, the download speed would be a maximum of 5.76 KBps. In practice, this download speed
cannot be reached because of other factors consuming bandwidth at the same time.
The following are speed measurement terms commonly used for microprocessors:
 Hz
 MHz

 GHz
Hz
A hertz (hz) is a unit of frequency. It is the rate of change in the state or cycle in a sound wave,
alternating current, or other cyclical waveform. It represents one cycle per second and is used to
describe the speed of a computer microprocessor.
MHz
A megahertz (MHz) represents one million cycles per second. This is a common unit of measurement
of the speed of a processing chip, such as a computer microprocessor.
GHz
A gigahertz (GHz) represents one billion (1,000,000,000) cycles per second. This is a common unit of
measurement of the speed of a processing chip, such as a computer microprocessor.
PC processors are getting faster all the time. The microprocessors used on PCs in the 1980s typically ran
under 10 MHz (the original IBM PC was 4.77 MHz). Today they are measured in GHz.
Quizv
Match the measurement terms with their definitions.
Options:
1. Bit
2. Byte
3. GB
4. KB
5. Mb
6. MB
Targets:
a. It equals 1 or 0 in binary format
b. It is equal to 8 bits
c. It is equal to approximately 1000 bytes
d. It is equal to approximately one billion bytes
e. It is equal to approximately one million bits
f. It is equal to approximately one million bytes

2. Conversion between decimal and binary
Converting a decimal number to a binary number is one of the most common procedures performed in
computer operations.
Computers recognize and process data using the binary, or base 2, numbering system. The binary numbering
system uses only two symbols (0 and 1) instead of the ten symbols used in the decimal numbering system.
The position, or place, of each digit represents the number 2 (the base number) raised to a power
(exponent), based on its position (2^0, 2^1, 2^2, 2^3, 2^4, and so on).
Suppose you want to convert the decimal number 253 to a binary number. You can do this by dividing the
number by two each time and taking note of the remaining number.
First you divide 253 by 2, which is equal to 126 with 1 remaining.

Then you divide 126 by 2, which is equal to 63 with 0 remaining.
Finally you divide 1 by 2, which is equal to 0 with 1 remaining.
You should write the binary number in the order of the last bit first. In this case, the binary equivalent of 253
is 11111101.
Suppose you want to convert the decimal number 153 to binary.
Suppose you want to convert the number 35 to a binary number. You can do this using the following steps:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5
Step 1

Step 1: Looking at the figure, you must identify what is the greatest power of 2 that is less than or
equal to 35. Starting with the largest number, 2^5 (32) is smaller than 35. You place a "1" in that
column, a "0" in each preceding place, and calculate how much is left over by subtracting 32 from
35. The result is 3.
Step 2
Step 2: Next you check to see if 16 (the next lower power of 2) fits into 3. Because it does not, a "0"
is placed in that column. The value of the next number is 8, which is larger than 3, so a "0" is placed
in that column too.
Step 3
Step 3: The next value is 4, which is still larger than 3, so it too receives a "0."
Step 4
Step 4: The next value is 2, which is smaller than 3. Because 2 fits into 3, place a "1" in that column.
Now subtract 2 from 3, and the result is 1.
Step 5
Step 5: The value of the last number is 1, which fits in the remaining number. Therefore, you place a
"1" in the last column. The binary equivalent of the decimal number 35 is 100011.
In this case, the place values of 128 and 64 are too high to be considered for the calculation.
Quizvi
Which number is the binary equivalent of 197?
Options:
1. 10000101
2. 10100101
3. 11000101
4. 11100101
You can also convert binary numbers to decimal format.

As with decimal-to-binary conversion, there is usually more than one way to convert binary numbers to
decimal numbers.
The figure illustrates one conversion method. Each binary digit has a corresponding decimal position value.
To work out the decimal position values, you start with 1 and then multiply each number by 2.
For example, 1 multiplied by 2 is equal to 2, 2 multiplied by 2 is 4, 4 multiplied by 2 is 8, and so on.
Consider the 8 digits that make up the binary number. If a digit is 1, then you count the corresponding
position value whereas if the digit is 0, then you ignore it.
Next, suppose you want to convert the binary number 10111001 to a decimal number. You can do this using
the following steps:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5

Step 1
Step 1: The binary number has a 1 in the 2^7 (128) bit position, so 128 is added to the decimal total.
Step 2
Step 2: Next the binary number has a 0 in the 2^6 (64) bit position so 64 is not added to the decimal
total (128+0=128). Next there is a 1 in the 2^5 (32) bit position, so the decimal total becomes
128+32=160.
Step 3
Step 3: Next there is a 1 in the 2^4 (16) bit position. Adding the value to the decimal total gives
160+16=176. Then the 2^3 (8) bit position has the binary digit 1, so the value 8 needs to be added to
the decimal total: 176+8=184.
Step 4
Step 4: Next there are 0s in the 2^2 and 2^1 bit positions, so you add 0s to the decimal total:
184+0+0=184.
Step 5
Step 5: Finally, there is a 1 in the 2^0 (1) bit position, so you add 1 to 184 to give the result 185. The
decimal equivalent of the binary number 10111001 is 185.
Quizvii
Convert the binary number 11011000 to decimal.
3. Conversion between binary and hexadecimal
The base 16, or hexadecimal (hex), numbering system is used frequently when working with computers
because it can be used to represent binary numbers in a more readable form.
The computer performs computations in binary, but there are instances when the binary output of a
computer is expressed in hexadecimal format to make it easier to read.

Converting a hexadecimal number to binary, and vice versa, is a common task when dealing with the 16-bit
configuration register in Cisco routers. That 16-bit binary number can be represented as a four-digit
hexadecimal number. For example, 0010000100000010 in binary is equal to 2102 in hex.
The most common way for computers and software to express hexadecimal output is using "0x" in front of
the hexadecimal number. Thus, whenever you see "0x," you know that the number that follows is a
hexadecimal number. For example, 0x1234 means 1234 in base 16.
It is referred to as base 16 because it uses 16 symbols. Combinations of these symbols can represent all
possible numbers. Because there are only 10 symbols that represent digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and base
16 requires six more symbols, the extra symbols are the letters A, B, C, D, E, and F.
The "A" represents the decimal number 10, "B" represents 11, "C" represents 12, "D" represents 13, "E"
represents 14, and "F" represents 15.

The position of each symbol (digit) in a hex number represents the base number 16 raised to a power
(exponent) based on its position. Moving from right to left, the first position represents 16^0 (or 1), the
second position represents 16^1 (or 16), the third position represents 16^2 (or 256), and so on.
Network layer 2 MAC addresses are typically written in hex. For Ethernet and Token Ring topologies, these
addresses are 48 bits, or six octets (one octet is eight bits). Because these addresses consist of six distinct
octets, you can write them as 12 hex numbers.
Instead of writing
10101010.11110000.11000001.11100010.011101 11.01010001
you can write the much shorter hex equivalent: AA.F0.C1.E2.77.51. To make handling hex versions of MAC
addresses even easier, the dots are placed only after each four hex digits, as in AAF0.C1E2.7751.
Converting binary to hex is easy because base 16 (hexadecimal) is a power of base 2 (binary). Every four
binary digits (bits) are equal to one hexadecimal digit.
The table compares the binary and hexadecimal numbering systems.

If there is a binary number that looks like 01011011, you can break it into two groups of four bits: 0101 and
1011. When converting these two groups to hex, they become 5 and B, so the hexadecimal equivalent of the
binary 01011011 is 5B.
No matter how large the binary number, you always apply the same conversion.
First you start from the right of the binary number and break the number into groups of four.
If the far left group does not contain four digits, add zeros to the left end until there are four digits (bits) in
every group.
Then you convert each group of four to its hex equivalent.
Suppose you want to convert the binary number 01001110000100110101011110001101 to hexadecimal.

Quizviii
Which options are hexadecimal equivalents of 1010110100010011111000111101100?
Options:
1. 1451880940
2. 5689F1EC
3. AD13E3D4
4. 0x5689F1EC
You can also convert hexadecimal numbers to binary format. To convert from hexadecimal to binary, you
convert every hex digit into four binary digits (bits).
For example, to convert hex AC (0xAC) to binary, you first convert hex A, which is 1010 binary, and then
convert hex C, which is 1100 binary. So the conversion of hex AC is 10101100 binary.

Suppose you want to convert the hexadecimal number 1245F7DC9 to binary.
Make sure you include four binary digits for each hexadecimal character, adding zeros to the left of the
number when necessary.

Quizix
Match the binary numbers to their hexadecimal equivalent.
Options:
1. 1100011101011000010
2. 10101101110110101000101
3. 10100101010110001000101000100100011
4. 1011000100111111110
Targets:
a. 52AC45123
b. 56ED45
c. 589FE
d. 63AC2
Summary
The binary numbering system is made up of 0s and 1s. The most common measurement terms are bit, byte,
kilobit (Kb), kilobyte (KB), megabit (Mb), megabyte (MB), gigabit (Gb), and gigabyte (GB). The microprocessor
speeds are hertz (Hz), megahertz (MHz), and gigahertz (GHz).
The decimal numbering system uses ten symbols – 0 - 9. Decimal numbers can be converted to binary. One
way of doing this is to divide the decimal number by two each time, taking note of the remaining number. All
the remaining numbers form the binary equivalent. You can also convert binary numbers to decimal.
The hexadecimal numbering system uses 16 symbols – 0 - 9, and A - F. Hexadecimal numbers often have 0x
in front of them. You can easily convert binary numbers to hexadecimal as each group of four binary digits is
equal to one hexadecimal digit. You can also convert hexadecimal numbers to binary by converting every
hex digit into four binary digits (bits).

C. Using a PC on a network
To review basic networking technologies and common network applications, and identify the main purposes
and functions of networking.
1. Basic Networking Terminology
2. Network Applications
3. Computer Networks
Summary
1. Basic Networking Terminology
Computer networking, like most industries, has its own jargon, which includes technical terms,
abbreviations, and acronyms. Without a good grasp of the terminology, it will be difficult to understand the
concepts and processes involved in networking. The following list of terms and their definitions is intended
to be a quick reference that defines some of the most important words, phrases, and acronyms related to
computer networking:
 A network interface card (NIC), pronounced "nick," is also called the LAN adapter, or just the
network interface. This card typically goes into an ISA, PCI, or PCMCIA (PC card) slot in a computer
and connects to the network medium. It then connects to other computers through the network
media.
 Media refers to the various physical environments through which transmission signals pass.
Common network media include twisted-pair, coaxial, and fiber-optic cable, and even the earth's
atmosphere through which wireless transmission occurs.
 A protocol is a set of rules. In the case of a network protocol, it is a set of rules by which computers
communicate. The term "protocol suite" describes a set of several protocols that perform different
functions related to different aspects of the communication process.
 Cisco IOS software which runs on Cisco equipment and devices, is the industry-leading and most
widely deployed network system software. It delivers intelligent network services for enabling the
rapid deployment of Internet applications.
Cisco IOS software provides a wide range of functionality, from basic connectivity, security, and
network management to technically advanced services. The functionality of Cisco IOS software is the
result of a technological evolution. First-generation networking devices could only store and forward
data packets.
Today, Cisco IOS software can recognize, classify, and prioritize network traffic, optimize routing,
support voice and video applications, and much more. Cisco IOS software runs on most Cisco routers
and Cisco switches. These network devices carry most of the Internet traffic today.
 Network operating system (NOS) usually refers to server software such as Windows NT, Windows
2000 Server, Windows Server 2003, Novell NetWare, UNIX, and Linux. The term sometimes refers to
the networking components of a client operating system such as Windows 95 or the Macintosh OS.
 Connectivity devices refer to several different device types, all of which are used to connect cable
segments, connect two or more smaller networks (or subnets) into a larger network, or divide a
large network into smaller ones. The term encompasses repeaters, hubs, switches, bridges, and
routers.

The following are three categories of networks:
 A local-area network (LAN) is a network that is confined to a limited geographic area. This area can
be a room, a floor, a building, or even an entire campus.
 A metropolitan-area network (MAN) is a network that is larger in size than a LAN and smaller in size
than a WAN. This is a network that covers approximately the area of a large city or metropolitan
area.
 A wide-area network (WAN) is made up of interconnected LANs. It spans wide geographic areas by
using WAN links such as telephone lines or satellite technology to connect computers in different
cities, countries, or even different continents.
Network structure is described in the following two ways:
 The logical topology is the path that the signals take from one computer to another. The logical
topology may or may not correspond to the physical topology. For instance, a network can be a
physical "star," in which each computer connects to a central hub, but inside the hub the data can
travel in a circle, making it a logical "ring."
 The physical topology refers to the layout or physical shape of the network, and includes the
topologies in this table.
Topologies
Bus Computers arranged so that cabling goes from one to another in a linear fashion
Ring When there are no clear beginning points or endpoints within a topology, forming a circle
Star If the systems "meet in the middle" by connecting to a central hub
Mesh When multiple redundant connections make pathways to some or all of the endpoints
2. Network Applications
Network applications are software programs that run between different computers connected together on a
network.
Some of the more common uses of network applications include using a web browser program to find
content from the World Wide Web, or using an e-mail program to send e-mails over the Internet.

Network applications are selected based on the type of work that needs to be done. A complete set of
application-layer programs is available to interface with the Internet. Each application program type is
associated with its own application protocol. Some examples include:
 HTTP is the World-Wide-Web communications protocol used to connect to web servers. Its primary
function is to establish a connection with a web server and transmit HTML pages to the client
browser.
 Post Office Protocol 3 (POP3) is an application-layer protocol supported by e-mail programs for the
retrieval of electronic mail. POP3 is a standard e-mail server commonly used on the Internet. It
provides a message storage container that holds incoming e-mail until users log on and download
their messages.
 File Transfer Protocol (FTP) is a simple file utility program for transferring files between remote
computers, which also provides for basic user authentication.
 Telnet is a remote access application and protocol for connecting to remote computer consoles,
which also provides for basic user authentication. Telnet is not a graphical user interface but is
command-line driven or character mode only.
 Simple Network Management Protocol (SNMP) is used by network management programs for
monitoring the network device status and activities.
It is important to emphasize that the application layer is just another protocol layer in the OSI model or
TCP/IP protocol stack. The programs interface with application layer protocols.
E-mail client applications, such as Microsoft Outlook, Lotus Notes, Pegasus Mail, Mozilla's Thunderbird,
Eudora, KMail, all work with the POP (Post Office Protocol) and IMAP4 (Message Access Protocol) protocols.
Electronic mail enables you to send messages between connected computers. The procedure for sending an
e-mail document involves two separate processes – sending the e-mail to the user's post office, which is a
computer running the POP3 server software, and delivering the e-mail from that post office to the user's e-
mail client computer, which is the recipient.
While popular protocols for retrieving mail include POP3 and IMAP4, sending mail is usually done using the
SMTP protocol.
A user's mailbox can be accessed in two dedicated ways. POP allows the user to download messages one at a
time and only deletes them from the server after they have been successfully saved on local storage. It is
possible to leave messages on the server to permit another client to access them.
Alternatively, IMAP allows users to keep messages on the server, flagging them as appropriate. IMAP
provides folders and sub-folders, which can be shared among different users with possibly different access
rights.
Another important standard supported by most email clients is MIME, which is used to send binary file email
attachments. Attachments are files that are not part of the email proper, but are sent with the email.

The same principle is true with web browsers. The two most popular web browsers are Google Chrome,
Mozilla Firefox, Internet Explorer, Opera, and Safari. The appearance of these web browser programs might
be different, but they both work with the application layer HTTP protocol.
3. Computer Networks
One of the primary purposes of a network is to increase productivity by linking computers and computer
networks, so that people have easy access to information regardless of differences in time, place, or type of
computer system.
Because companies have adopted networks as part of their business strategy, they typically subdivide and
map corporate networks to the corporate business structure. In the figure, the network is defined based on
the grouping of employees (users) into a main office and various remote access locations.
A main office is a site where everyone is connected via a LAN and where the bulk of corporate information is
located. A main office can have hundreds or even thousands of people who depend on network access to do
their jobs. It may have several LANs, or it may be a campus that contains several buildings. Because everyone
needs access to central resources and information, it is common to see a high-speed backbone in a LAN as
well as a datacentre with high-performance computers or servers and networked applications.
A variety of remote access locations connect to the main office or each other using WAN services as follows:
 In branch offices, smaller groups of people work and connect to each other via a LAN. To connect to
the main office, these users must use WAN services such as Asymmetric digital subscriber line
(ADSL). Although some corporate information may be stored at a branch office, it is more likely that
branch offices have local network resources, such as printers, but have to access information directly
from the main office.
 A home office is where individuals are set up to work from their own home. Home office workers
most likely require on-demand connections to the main office or a branch office to access
information or use network resources such as file servers.
 Individuals who are mobile users connect to the main office LAN when they are at the main office, at
the branch office, or on the road. Their network access needs are based on where they are located.
In order to understand what types of equipment and services to deploy in a network and when to deploy
them, it is important to understand the business and user needs. The figure shows how to map an
organization's business or user requirements to a network.

In this example, the business needs may require LAN connectivity within the campus to interconnect the
servers and end-user PCs, and WAN connectivity to connect the campus to the remote branch office and
telecommuters. The WAN connection to the remote branch office requires a permanent connection, such as
a leased line, and the home office connection requires a dial-up connection, such as ADSL.
Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data
communications technology that enables faster data transmission over copper telephone lines than a
conventional voice band modem can provide. It does this by utilizing frequencies that are not used by a voice
telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service
and voice calls at the same time. ADSL can generally only be distributed over short distances from the
telephone exchange (the last mile), typically less than 4 kilometres (2 mi).
At the telephone exchange the line generally terminates at a digital subscriber line access multiplexer
(DSLAM) where another frequency splitter separates the voice band signal for the conventional phone
network. Data carried by the ADSL are typically routed over the telephone company's data network and
eventually reach a conventional Internet Protocol network.
A digital subscriber line access multiplexer (DSLAM) is a network device, often located in telephone
exchanges, which connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital
communications channel using multiplexing techniques.

Summary
When working with computer applications, it is important that you are familiar with networking
terminology. There are three categories of networks – a LAN, a MAN, and a WAN. The physical topology of a
network is the physical structure of a network. The logical topology of a network is the path that signals
follow through the network.
Network applications are software programs that run between different computers connected on a network.
Each application type has associated protocols depending on the function of the application. HTTP is used by
applications that access the Internet, POP3 is used by applications that access email services, FTP is used by
applications that transfer files, Telnet is used by applications that remotely access other machines, and
SNMP is used by applications that monitor the operation of the network.
Applications interface with protocols in the application layer of the OSI model or TCP/IP stack.
By creating a computer network, you enable access between computers regardless of time, place, or type of
computer system. Because networks are incorporated into the business strategy of a company, a company's
network will usually replicate its business structure. Typically, a network will be subdivided to facilitate the
branch, home, and main office of the company as well as its mobile users.

D. Working with PC technology
After completing this topic, you should be able to identify the purpose of major computer components, and
calculate conversions between binary, decimal, and hexadecimal numerical systems.
1. Exercise overview
2. Task 1: Identifying PC components
3. Task 2: Interpreting numerical systems
1. Exercise overview
In this exercise, you're required to identify the internal components of a PC and calculate conversions
between the three numerical systems – binary, decimal, and hexadecimal.
This involves the following tasks:
 identifying PC components
 converting between numerical systems
2. Task 1: Identifying PC components
Let's look at the internal components of a PC.

Step 1 of 1
Match the PC components to their descriptions.
Options:
1. CD Rom drive
2. Hard disk drive
3. RAM
4. NIC
5. CPU
Targets:
a. A compact disk read-only memory drive
b. A device that reads and writes data on a hard disk
c. An expansion board inserted into a computer to enable connection to a network
d. A silicon-based microprocessor where most of the computer's calculations take place
e. Memory that has new data written into it and has stored data read from it
Resultx
A CD Rom drive is a compact disk read-only memory drive, a hard disk drive is a device that reads and writes
data on a hard disk, RAM is memory that has new data written into it and stored data read from it, a NIC is
an expansion board inserted into a computer to enable connection to a network, and a CPU is a silicon-based
microprocessor where most of the computer's calculations take place.
A CD-ROM drive can read information from a CD-ROM disk.
A hard disk drive reads data from a hard disk. Unlike a CD-ROM drive it can also write data to a disk.
RAM is also known as read-write memory.
The NIC plugs into a motherboard and provides a port for connecting to the network. It is also known as a
LAN adapter.
A CPU acts as the "brain" of the computer.

3. Task 2: Interpreting numerical systems
Let's look at the binary, decimal, and hexadecimal numerical systems.
Step 1 of 5
Match the numerical systems to their descriptions.
Options:
1. Binary
2. Decimal
3. Hexadecimal
Targets:
a. This system uses 16 symbols
b. This system uses 10 symbols
c. This system uses 2 symbols
Resultxi
Binary uses 2 symbols, decimal uses 10 symbols, and hexadecimal uses 16 symbols.
The binary system uses 2 symbols – 0 and 1 – and is also known as base 2.
The decimal system uses 10 symbols – 0 to 9 – and is also known as base 10.
The hexadecimal system uses 16 symbols – 0-9, A-F – and is also known as base 16.
Let's look at some binary conversions.

Step 2 of 5
See if you can convert the binary number 10101000 to decimal.
Resultxii
The decimal equivalent of the binary number 10101000 is 168.
Step 3 of 5
What is the hexadecimal equivalent of 100011000101111?
Options:
1. 462C
2. 462D
3. 462E
4. 462F
Result
The hexadecimal equivalent of 100011000101111 is 462F.
Option 1 is incorrect. 462C is actually the hexadecimal equivalent of 100011000101100.
Option 2 is incorrect. 462D is actually the hexadecimal equivalent of 100011000101101.
Option 3 is incorrect. 462E is actually the hexadecimal equivalent of 100011000101110.
Option 4 is correct. 462F is the hexadecimal equivalent of 100011000101111 – 100 is 4, 0110 is 6, 0010 is 2,
and 1111 is F.
Let's look at a conversion from decimal to binary.

Step 4 of 5
See if you can convert the decimal number 68 to binary.
Result
The decimal number 68 is 1000100 in binary.
Let's look at a conversion from hexadecimal to binary.
Step 5 of 5
What is the binary equivalent of 812C?
Options:
1. 1000000100101011
2. 1000000100101100
3. 1000000100101101
4. 1000000100101110
Result
The binary equivalent of 812C is 1000000100101100.
Option 1 is incorrect. 1000000100101011 is actually the binary equivalent of 812B.
Option 2 is correct. 1000000100101100 is actually the binary equivalent of 812C – 8 is 1000, 1 is 0001, 2 is
0010, and 1100 is C.
Option 3 is incorrect. 1000000100101101 is actually the binary equivalent of 812D.
Option 4 is incorrect. 1000000100101110 is actually the binary equivalent of 812E.

E. OSI model layers and functions
After completing this topic, you should be able to distinguish between the OSI reference model and the
TCP/IP stack.
1. Origins of the OSI reference model
2. OSI layers and functions
3. Data communications
4. The TCP/IP protocol stack
Summary
1. Origins of the OSI reference model
The early development of LANs, MANs, and WANs was chaotic in many ways. The early 1980s saw
tremendous increases in the number and sizes of networks.
As companies realized that they could save money and gain productivity by using networking technology,
they added networks and expanded existing networks as rapidly as new network technologies and products
were introduced.
By the middle of the 1980s, companies began to experience difficulties from all the expansions they had
made. It became more difficult for networks using different specifications and implementations to
communicate with each other.
The companies realized that they needed to move away from proprietary networking systems, those
systems which are privately developed, owned, and controlled.
A standard or technology may be
 proprietary
 open
proprietary
Proprietary means that one company or a small group of companies control(s) all usage of the
technology. In the computer industry, proprietary is the opposite of open.

open
Open means that free usage of the technology is available to the public.
To address the problem of networks being incompatible and unable to communicate with each other, the
International Organization for Standardization (ISO) researched different network schemes.
As a result of this research, the ISO created a model that would help vendors create networks that would be
compatible with, and operate with, other networks.
The Open Systems Interconnection (OSI) reference model, released in 1984, was the descriptive scheme that
the ISO had created. It provided vendors with a set of standards that ensured greater compatibility and
interoperability between the various types of network technologies produced by companies around the
world.
Although other models exist, most network vendors today relate their products to the OSI reference model,
especially when they want to educate customers on the use of their products. It is considered the best tool
available for teaching people about sending and receiving data on a network.
The OSI reference model has seven numbered layers, each illustrating a particular network function. This
separation of networking functions is called layering.

The OSI reference model defines the network functions that occur at each layer.
More importantly, the OSI reference model facilitates an understanding of how information travels
throughout a network.
In addition, the OSI reference model describes how data travels from application programs (for example,
spreadsheets), through a network medium, to an application program located in another computer, even if
the sender and receiver are connected using different network media.
Quiz
Which of the following statements about the OSI model are correct.
Options:
1. It defines the network functions that occur at each layer
2. It is a conceptual framework that specifies how information travels through networks
3. It is a model that describes how data makes its way from one application program to another
throughout a network
4. It was developed in order to help companies communicate with each other using proprietary
network systems.
Answerxiii
(See Endnotes).

2. OSI layers and functions
The practice of moving information between computers is divided into seven techniques in the OSI reference
model.
Each of the seven techniques is represented by its own layer in the model.
The seven layers of the OSI reference model are as follows:
 Layer 7: Application layer
 Layer 6: Presentation layer
 Layer 5: Session layer
 Layer 4: Transport layer
 Layer 3: Network layer
 Layer 2: Data-link layer
 Layer 1: Physical layer
Dividing the network into seven layers provides the following advantages:
 accelerates evolution
 ensures interoperable technology
 facilitates modular engineering
 reduces complexity
 standardizes interfaces
 simplifies teaching and learning
accelerates evolution
Layering accelerates evolution by providing for effective updates and improvements to individual
components without affecting other components or having to rewrite the entire protocol.
ensures interoperable technology
Layering prevents changes in one layer from affecting the other layers, allowing for quicker
development, and ensuring interoperable technology.
facilitates modular engineering
Layering allows different types of network hardware and software to communicate with each other,
thereby facilitating modular engineering.
reduces complexity
Layering breaks network communication into smaller, simpler parts and reduces complexity.
standardizes interfaces

Layering standardizes network component interfaces to allow multiple-vendor development and
support.
simplifies teaching and learning
Layering breaks network communication into smaller components to make learning easier, thereby
simplifying teaching.
Each OSI layer contains a set of functions performed by programs to enable data packets to travel from a
source to a destination on a network.
Now we will look at each layer in the OSI reference model.
The application layer is the OSI layer that is closest to the user. This layer provides network services to the
user's applications. It differs from the other layers in that it does not provide services to any other OSI layer,
but rather, only to applications outside the OSI model.
The application layer establishes the availability of intended communication partners and synchronizes and
establishes agreement on procedures for error recovery and control of data integrity.
The presentation layer ensures that the information that the application layer of one system sends out is
readable by the application layer of another system.
For example, a PC program communicates with another computer, one using extended binary coded decimal
interchange code (EBCDIC) and the other using ASCII to represent the same characters.
If necessary, the presentation layer translates between multiple data formats by using a common format.

The session layer establishes, manages, and terminates sessions between two communicating hosts. It
provides its services to the presentation layer. The session layer also synchronizes dialogue between the
presentation layers of the two hosts and manages their data exchange.
For example, web servers have many users, so there are many communication processes open at a given
time. It is important to keep track of which user communicates on which path.
In addition to session regulation, the session layer offers provisions for efficient data transfer, class of
service, and exception reporting of session layer, presentation layer, and application layer problems.
The transport layer segments data from the sending host's system and reassembles the data into a data
stream on the receiving host's system.
For example, business users in large corporations often transfer large files from field locations to a corporate
site.

Reliable delivery of the files is important, so the transport layer will break down large files into smaller
segments that are less likely to incur transmission problems.
The boundary between the transport layer and the session layer can be thought of as the boundary
between application protocols and data-flow protocols. Whereas the application, presentation, and session
layers are concerned with application issues, the lower four layers are concerned with data transport issues.
The transport layer attempts to provide a data-transport service that shields the upper layers from transport
implementation details. Specifically, issues such as reliability of transport between two hosts are the concern
of the transport layer.
In providing communication service, the transport layer establishes, maintains, and properly terminates
virtual circuits.
Transport error detection and recovery and information flow control are used to provide reliable service.
The network layer provides connectivity and path selection between two host systems that may be located
on geographically separated networks. The growth of the Internet has increased the number of users
accessing information from sites around the world, and it is the network layer that manages this
connectivity.

The data-link layer defines how data is formatted for transmission and how access to the network is
controlled.
The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating,
maintaining, and deactivating the physical link between end systems.
Characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission
distances, physical connectors, and other similar attributes are defined by physical layer specifications.
In summary, the functions of the layers in the OSI model are as follows:
 application network services
 data representation
 interhost communication
 end-to-end connections
 data delivery

 media access
 binary transmission
application network services
The application layer provides network services to any applications requiring access to the network.
data representation
The presentation layer handles data representation. It ensures data is readable, and formats and
structures data. It also negotiates data transfer syntax for the application layer.
interhost communication
The session layer provides interhost communication. In doing this it establishes, manages, and
terminates sessions between applications.
end-to-end connections
The transport layer facilitates end-to-end communications. It handles transportation issues between
hosts and ensures data transport reliability. It also establishes, maintains, and terminates virtual
circuits, and provides reliability through fault detection and recovery information flow control.
data delivery
The network layer ensures data delivery. It provides connectivity and path selection between two
host systems, routes data packets and selects the best path to deliver data.
media access
The data-link layer provides access to the network media. It defines how data is formatted and how
access to the network is controlled.
binary transmission
The physical layer handles binary transmission. It defines the electrical, mechanical, procedural, and
functional specifications for activating, maintaining, and deactivating the physical link. It is
responsible for transmitting the data onto the physical media.
Quiz
What is the function of the session layer?
Options:
1. It routes data packets
2. It ensures reliable transport of data
3. It ensures received data is readable
4. It regulates communication processes

Answerxiv
(See Endnotes).
3. Data communications
All communications on a network originate at a source and are sent to a destination.
The information sent on a network is referred to as data or data packets. If one computer (Host A) wants to
send data to another computer (Host B), the data must first be packaged by a process called encapsulation.
The encapsulation process can be thought of as putting a letter inside an envelope, and then properly
writing the recipient's mail address on the envelope so it can be properly delivered by the postal system.
Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the
data moves down through the layers of the OSI model, each OSI layer adds a header (and a trailer if
applicable) to the data before passing it down to a lower layer.
The headers and trailers contain control information for the network devices and receiver to ensure proper
delivery of the data and to ensure that the receiver can correctly interpret the data.

The figure illustrates how encapsulation occurs. It shows the manner in which data travels through the
layers.
The following eight steps occur in order to encapsulate data:
 Step 1
 Step 2
 Step 3
 Step 4
 Step 5
 Step 6
 Step 7
 Step 8
Step 1
Step 1: The user data is sent from an application to the application layer.
Step 2

Step 2: The application layer adds the application layer header (Layer 7 header) to the user data. The
Layer 7 header and the original user data become the data that is passed down to the presentation
layer.
Step 3
Step 3: The presentation layer adds the presentation layer header (Layer 6 header) to the data. This
then becomes the data that is passed down to the session layer.
Step 4
Step 4: The session layer adds the session layer header (Layer 5 header) to the data. This then
becomes the data that is passed down to the transport layer.
Step 5
Step 5: The transport layer adds the transport layer header (Layer 4 header) to the data. This then
becomes the data that is passed down to the network layer.
Step 6
Step 6:The network layer adds the network layer header (Layer 3 header) to the data. This then
becomes the data that is passed down to the data-link layer.
Step 7
Step 7: The data-link layer adds the data-link-layer header and trailer (Layer 2 header and trailer) to
the data. A Layer 2 trailer is usually the frame check sequence (FCS), which is used by the receiver to
detect whether or not the data is in error. This then becomes the data that is passed down to the
physical layer.
Step 8
Step 8:The physical layer then transmits the bits onto the network media.
Quiz
When a user sends information across a network it first traverses the application layer.
Rank the layers of the OSI model in the order in which encapsulation occurs, after the application layer.
Options
Option Description
A Data Link
B Network
C Physical
D Presentation
E Session
F Transport

Answerxv
(See Endnotes).
When the remote device receives a sequence of bits, the physical layer at the remote device passes the bits
to the data-link layer for manipulation.
The data-link layer performs the following tasks:
 Task 1
 Task 2
 Task 3
 Task 4
Task 1
Task 1: It checks the data-link trailer (the FCS) to see if the data is in error.
Task 2
Task 2: If the data is in error, it may be discarded, and the data-link layer may ask for the data to be
retransmitted.

Task 3
Task 3: If the data is not in error, the data-link layer reads and interprets the control information in
the data-link header.
Task 4
Task 4: It strips the data-link header and trailer, and then passes the remaining data up to the
network layer based on the control information in the data-link header.
This process is referred to as de-encapsulation. Each subsequent layer performs a similar de-encapsulation
process. Think of de-encapsulation as the process of reading the address on a letter to see if it is for you or
not, and then removing the letter from the envelope if the letter is addressed to you.

So that data packets can travel from the source to the destination, each layer of the OSI model at the source
must communicate with its peer layer at the destination.
This form of communication is referred to as peer-to-peer communication. During this process, the protocols
at each layer exchange information, called protocol data units (PDUs), between peer layers.
Data packets on a network originate at a source and then travel to a destination. Each layer depends on the
service function of the OSI layer below it.
To provide this service, the lower layer uses encapsulation to put the PDU from the upper layer into its data
field. It then adds whatever headers the layer needs to perform its function. As the data moves down
through Layers 7 through 5 of the OSI model, additional headers are added. The grouping of data at the
Layer 4 PDU is called a segment.
The network layer provides a service to the transport layer, and the transport layer presents data to the
internetwork subsystem.
The network layer moves the data through the internetwork by encapsulating the data and attaching a
header to create a packet (the Layer 3 PDU). The header contains information required to complete the
transfer, such as source and destination logical addresses.

The data-link layer provides a service to the network layer by encapsulating the network layer packet in a
frame (the Layer 2 PDU).
The frame header contains the physical addresses required to complete the data-link functions, and the
frame trailer contains the FCS.
The physical layer provides a service to the data-link layer, encoding the data-link frame into a pattern of 1s
and 0s (bits) for transmission on the medium (usually a wire) at Layer 1.
Network devices such as hubs, switches, and routers work at the lower three layers. Hubs are at Layer 1 –
the physical layer, switches are at Layer 2 – the data-link layer, and routers are at Layer 3 – the network
layer.

Quiz
Match the communication process with its definition.
Options:
1. Encapsulation
2. De-encapsulation
3. Peer-to-peer communication
Targets:
a. This is the process that wraps data with the necessary protocol information before network transit.
b. This is the process that checks for errors, and begins the process of stripping the header and trailer
from received data.
c. This is the process that facilitates the communication between OSI peer layers during data transfer.
Answerxvi
(See Endnotes).
4. The TCP/IP protocol stack
Although the OSI reference model is universally recognized, the historical and technical open standard of the
Internet is the TCP/IP protocol stack.
The TCP/IP protocol stack has four layers – the application layer, the transport layer, the Internet layer, and
the network access layer.
It is important to note that although some of the layers in the TCP/IP protocol stack have the same names as
layers in the OSI model, the layers have different functions in each model.
The following are the TCP/IP protocol stack layers.
 Application
 Transport
 Internet
 Network access

Application
The application layer handles high-level protocols, including issues of representation, encoding, and
dialog control. The TCP/IP model combines all application-related issues into one layer and ensures
that this data is properly packaged for the next layer.
Transport
The transport layer deals with quality-of-service issues of reliability, flow control, and error
correction. One of its protocols, the Transmission Control Protocol (TCP), provides for reliable
network communications.
Internet
The purpose of the Internet layer is to send source packets from any network on the internetwork
and have them arrive at the destination, regardless of the path they took to get there.
Network access
The network access layer is also called the host-to-network layer. It includes the LAN and WAN
protocols, and all the details in the OSI physical and data-link layers.
There are similarities and differences between the TCP/IP protocol stack and the OSI reference model.
The main similarities between the TCP/IP protocol stack and the OSI reference model are
 application layers
 packet-switched technology
 transport and network layers
application layers
Both have application layers, though they include different services.
packet-switched technology
Both assume packet-switched technology, not circuit-switched. (Analog telephone calls are an
example of circuit-switched.)
transport and network layers

Both have comparable transport and network layers.
The main differences between the TCP/IP protocol stack and the OSI reference model are
 data-link and physical layers
 implementation of standards
 presentation and session layers
data-link and physical layers
TCP/IP combines the OSI data-link and physical layers into the network access layer.
implementation of standards
TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP protocol
stack gains credibility just because of the widespread implementation of its protocols. In contrast,
networks are not typically built on the OSI model, even though the OSI model is used as a guide.
presentation and session layers
TCP/IP combines the OSI presentation and session layers into its application layer.
Quiz
In the TCP/IP protocol stack, which layer deals with reliability, flow control, and error correction?
Options:
1. Application
2. Internet
3. Network access
4. Transport
Answerxvii
(See Endnotes).
Summary
The advent of LANs, WANs, and MANs in the 1980s and 1990s was largely unregulated and no standard for
network communication was available. As a result it became more difficult for networks using different
specifications and implementations to communicate with each other. To resolve this, the ISO created and
released the OSI reference model in 1984 to provide vendors with a set of standards to ensure greater
compatibility and interoperability between various types of network technologies.
The OSI reference model comprises seven layers – the application, presentation, session, transport, network,
data-link, and physical layer. Each layer has its own function. The application layer provides network services
to the user applications. The presentation layer presents the data in a format that will be understood by the
receiving application. The session layer regulates the session between the communicating hosts. The
transport layer ensures reliable transport of the data. The network layer routes the packets through the
network. The data-link layer controls access to the network. The physical layer sends the data along the
physical wire.

Encapsulating wraps data with the necessary protocol information before sending it across the network. De-
encapsulation strips the protocol information when the data is received. Each OSI layer at the source
communicates with its peer layer at the destination – this is called peer-to-peer communication.
The TCP/IP protocol stack has four layers – the application layer, transport layer, internet layer, and network
access layer. There are both similarities and differences between the TCP/IP protocol stack and the OSI
reference model. The TCP/IP protocol stack is widely implemented whereas the OSI reference model is
widely used for reference.

F. Working with the OSI model
After completing this topic, you should be able to distinguish between basic computer and networking
terms, and between the principles of the OSI reference model and the TCP/IP protocol stack.
Exercise overview
Task1: Networking terms and functions
Task 2: Functions of the OSI model
Task 3: The data encapsulation process
Exercise overview
In this exercise, you are required to identify networking terms and functions, and the functions of the OSI
reference model. You will also examine data communication methods.
This involves the following tasks:
 identifying networking terms and functions
 defining the functions of each OSI layer
 examining the data encapsulation process
Task1: Networking terms and functions
The topology of a network describes the layout of the wire and devices as well as the paths used by data
transmissions.
Match the schematic description with its function.
Options:
1. Logical topology
2. Physical topology
Targets:
a. This defines the structure of the paths that the signals take within a network
b. This describes the physical layout or structure of the network
Result
The logical topology is the structure of the paths that the signals take within a network and the physical
topology refers to the physical layout or structure of the network.

The logical topology defines the structure of the paths that the signals take within a network. Although the
logical topology does not have to correspond to the physical topology, it is often the same as the physical
topology.
The physical topology is the actual physical shape of the network. Networks can be arranged in a bus, star,
ring, or mesh format.
Network applications are software programs that run between different computers connected on a network.
Each application type has an associated protocol depending on the function of the application.
Step 2 of 3
Which application transfers files between remote computers?
Options:
1. FTP
2. HTTP
3. POP3
4. SMNP
Result
File transfer protocol (FTP) is used to transfer files between remote computers.
Option 1 is correct. FTP is a simple file utility program used for transferring files between remote computers.
Option 2 is incorrect. Hypertext Transfer Protocol (HTTP) establishes a connection between a browser and a
web server allowing the client to view web pages in the web browser.
Option 3 is incorrect. When you send an email it is usually Post Office Protocol version 3 (POP3) that will
hold the mail in a storage container until the receiver is ready to download it.
Option 4 is incorrect. Simple network monitoring protocol (SNMP) is used for monitoring network device
status and activities.

A LAN covers a smaller geographic area than a MAN or a WAN.
Step 3 of 3
Home office users are most likely to connect to the main office LAN using what WAN technology?
Options:
1. Frame Relay
2. ADSL
3. Leased lines
4. X.25
Result
Home office users are most likely to connect to the main office LAN using an ADSL connection.
Option 1 is incorrect. Frame Relay provides a permanent serial connection. Due to the cost of such
connections, this is not an effective solution for home office users
Option 2 is correct. An ADSL connection is a dial-up connection, and is often used by home office users to
connect to a LAN.
Option 3 is incorrect. A WAN connection to the remote branch office requires a permanent connection such
as a leased line. Home office users will most often use a dial-up technology.
Option 4 is incorrect. X.25 is an older form of permanent serial connection, not used very often in modern
networks. Due to the cost of such connections, this is not an effective solution for home office users.
Task 2: Functions of the OSI model
The OSI reference model has seven layers, each illustrating a particular network function. This separation of
networking functions is called layering.

1 of 1
What layer defines voltage levels, timing of voltage changes and maximum transmission distances?
Options:
1. The data-link layer
2. The network layer
3. The physical layer
4. The session layer
5. The transport layer
Result
The physical layer defines voltage levels, timing of voltage changes and maximum transmission distances.
Option 1 is incorrect. The data-link layer controls network access and formats data before it is transmitted to
ensure that it will be properly received.
Option 2 is incorrect. The network layer provides connectivity and path selection for data when moving
between different network locations.
Option 3 is correct. The physical layer defines the hardware specifications required for end-system
communications.
Option 4 is incorrect. The session layer regulates the communication processes of conversations between
hosts.
Option 5 is incorrect. The transport layer is responsible for the reliable transfer of data between network
hosts.
Task 3: The data encapsulation process
Data packets are packaged in a process known as encapsulation before they travel safely across a network.

Step 1 of 1
Which of the following describes the first step of data encapsulation?
Options:
1. A data-link header is stripped from the message
2. The frame is converted into binary format
3. The data-link layer checks the data-link trailer to see if the data is in error
4. The user data is sent from an application to the application layer
Result
The first step of data encapsulation is when the user data is sent from an application to the application layer.
Option 1 is incorrect. This occurs during de-encapsulation. When a message arrives at the data-link layer, it is
checked for errors. If no errors exist, it is then stripped of its data-link header and trailer, and passed on up
to the network layer.
Option 2 is incorrect. Conversion to binary is one of the last processes that occurs before the data frame is
transmitted onto the network media.
Option 3 is incorrect. The FCS trailer is checked after the data has been received from the network and has
been passed from the physical layer to the data-link layer. This is actually a part of the de-encapsulation
process.
Option 4 is correct. When data is sent from an application for transmission on the network, the
encapsulation process begins. Encapsulation begins at the application layer and wraps data with the
necessary protocol information before network transit.

G. Glossary
ABR
Acronym for available bit rate. See UBR.
access list
List kept by Cisco routers to control access to or from the router for a number of services (for
example, to prevent packets with a certain IP address from leaving a particular interface on the
router).
acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example,
receipt of a message) has occurred. Sometimes abbreviated ACK.
active hub
Multiport device that amplifies LAN transmission signals.
adapter
An adapter is a physical device that allows one hardware or electronic interface to be adapted
(accommodated without loss of function) to another hardware or electronic interface. In a
computer, an adapter is often built into a card that can be inserted into a slot on the computer's
motherboard. The card adapts information that is exchanged between the computer's
microprocessor and the devices that the card supports.
adaptive routing
See dynamic routing.
address
Data structure or logical convention used to identify a unique entity, such as a particular process or
network device.
Address Resolution Protocol
Abbreviated to ARP.
administrative distance
A rating of the trustworthiness of a routing information source. In Cisco routers, administrative
distance is expressed as a numerical value between 0 and 255. The higher the value, the lower the
trustworthiness rating.
ADSL
Acronym for asymmetric digital subscriber line. One of four DSL technologies. ADSL is designed to
deliver more bandwidth downstream (from the central office to the customer site) than upstream.
Downstream rates range from 1.5 to 9 Mbps, while upstream bandwidth ranges from 16 to 640
kbps. ADSL transmissions work at distances up to 18,000 feet (5,488 meters) over a single copper
twisted pair.
algorithm
Well-defined rule or process for arriving at a solution to a problem. In networking, algorithms are
commonly used to determine the best route for traffic from a particular source to a particular
destination.
American National Standards Institute
See ANSI.
American Standard Code for Information Interchange
See ASCII
ANSI
Acronym for American National Standards Institute. Voluntary organization comprised of corporate,
government, and other members that coordinates standards-related activities, approves U.S.
national standards, and develops positions for the United States in international standards
organizations. ANSI helps develop international and U.S. standards relating to, among other things,
communications and networking. ANSI is a member of the IEC and the ISO.
API

Acronym for application programming interface. Specification of function-call conventions that
defines an interface to a service.
application layer
Layer 7 of the OSI reference model. This layer provides services to application processes (such as
electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The
application layer identifies and establishes the availability of intended communication partners (and
the resources required to connect with them), synchronizes cooperating applications, and
establishes agreement on procedures for error recovery and control of data integrity. Corresponds
roughly with the transaction services layer in the SNA model.
application programming interface
See API.
ARP
Acronym for Address Resolution Protocol. Internet protocol used to map an IP address to a MAC
address. Defined in RFC 826. Compare with RARP.
ASCII
Acronym for American Standard Code for Information Interchange. 8-bit code for character
representation (7 bits plus parity).
asymmetric digital subscriber line
Abbreviated to ADSL.
asynchronous timedivision multiplexing
See ATDM
Asynchronous Transfer Mode
See ATM.
asynchronous transmission
Term describing digital signals that are transmitted without precise clocking. Such signals generally
have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate
individual characters in control bits (called start and stop bits) that designate the beginning and end
of each character.
ATDM
Acronym for asynchronous time-division multiplexing. Method of sending information that
resembles normal TDM, except that time slots are allocated as needed rather than preassigned to
specific transmitters. See FDM.
ATM
Acronym for Asynchronous Transfer Mode. International standard for cell relay in which multiple
service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length
cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to
take advantage of high-speed transmission media such as E3, SONET, and T3.
attachment unit interface
See AUI.
attenuation
Loss of communication signal energy.
attribute
Configuration data that defines the characteristics of database objects such as the chassis, cards,
ports, or virtual circuits of a particular device. Attributes might be preset or user-configurable.
AUI
Attachment unit interface. IEEE 802.3 interface between an MAU and a NIC (network interface card).
The term AUI can also refer to the rear panel port to which an AUI cable might attach, such as those
found on a Cisco LightStream Ethernet access card. Also called transceiver cable.
autonomous system

Collection of networks under a common administration sharing a common routing strategy.
Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique
16-bit number by the IANA. Sometimes abbreviated AS.
back end
Node or software program that provides services to a front end. Usually transparent to the user.
backbone
The part of a network that acts as the primary path for traffic that is most often sourced from, and
destined for, other networks.
backbone cabling
Cabling that provides interconnections between wiring closets, wiring closets and the POP, and
between buildings that are part of the same LAN. Also known as vertical cabling.
backplane
The backplane is a large circuit board that contains sockets for expansion cards.
backward explicit congestion notification
See BECN.
bandwidth
The difference between the highest and lowest frequencies available for network signals. The term is
also used to describe the rated throughput capacity of a given network medium or protocol.
baseband
Characteristic of a network technology where only one carrier frequency is used. Ethernet is an
example of a baseband network. Also called narrowband.
Basic Rate Interface
See BRI.
baud
Unit of signaling speed equal to the number of discrete signal elements transmitted per second.
Baud is synonymous with bits per second (bps), if each signal element represents exactly 1 bit.
B-channel
The name for a bearer channel. DS0 time slot that carries analog voice or digital data over ISDN. In
ISDN, a full-duplex, 64-kbps channel used to send user data.
BECN
Acronym for backward explicit congestion notification. Bit set by a Frame Relay network in frames
traveling in the opposite direction of frames encountering a congested path. DTE receiving frames
with the BECN bit set can request that higher-level protocols take flow control action as appropriate.
Compare with FECN.
BGP
Acronym for Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP
exchanges reachability information with other BGP systems. It is defined by RFC 1163.
BGP4
BGP Version 4. Version 4 of the predominant interdomain routing protocol used on the Internet.
BGP4 supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables.
Bit
The smallest unit of data in a computer. A bit equals 1 or 0, and is the binary format in which data is
processed by computers.
Border Gateway Protocol
See BGP.
BPDU
Acronym for bridge protocol data unit. Spanning-Tree Protocol hello packet that is sent out at
configurable intervals to exchange information among bridges in the network.
BRI
Acronym for Basic Rate Interface. ISDN interface composed of two B channels and one D channel for
circuit-switched communication of voice, video, and data.

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