Building Simple Network

7/31/2019 Building Simple Network

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Lesson Objectives

Building a Simple Network

identify the major components of a computer system and their functionality, and list the

resources required to install a NIC.distinguish between the processes used to convert between decimal, binary, and

hexadecimal numbering systems.

identify the main purposes and functions of networking.identify the purpose of major computer components, and calculate conversions between

binary, decimal, and hexadecimal numerical systems.

distinguish between the OSI reference model and the TCP/IP stack.distinguish between basic computer and networking terms, and between the principles

of the OSI reference model and the TCP/IP protocol stack.

Ref: http://www.webopedia.com/TERM/C/computer.html

Computer:

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A programmable machine. The two principal characteristics of a computer are:

o It responds to a specific set ofinstructionsin a well-defined manner.

o It canexecutea prerecorded list of instructions (aprogram).

Modern computers are electronic anddigital. The actual machinery -- wires,transistors,and circuits -- is called hardware; the instructions and data are calledsoftware.

All general-purpose computers require the following hardware components:

o Memory : Enables a computer to store, at least temporarily, data and programs.

o Mass storage device : Allows a computer to permanently retain large amounts of

data. Common mass storage devices includedisk drives andtape drives.

o Input device : Usually a keyboard andmouse, the input device is the conduit

through which data and instructions enter a computer.

o Output device : A display screen,printer, or other device that lets you see what the

computer has accomplished.

o Central processing unit (CPU): The heart of the computer, this is the component

that actually executes instructions.

In addition to these components, many others make it possible for the basic components to

work together efficiently. For example, every computer requires abus that transmits datafrom one part of the computer to another.

Computers can be generally classified by size and power as follows, though there is

considerable overlap:

o Personal computer : A small, single-usercomputer based on a microprocessor. In

addition to the microprocessor, a personal computer has a keyboard for entering

data, a monitorfor displaying information, and a storage device forsaving data.

o Workstation : A powerful, single-user computer. A workstation is like a personal

computer, but it has a more powerful microprocessor and a higher-quality monitor.

o Minicomputer : A multi-usercomputer capable of supporting from 10 to hundreds

of users simultaneously.

o Mainframe : A powerful multi-user computer capable of supporting many

hundreds or thousands of users simultaneously.

o Supercomputer : An extremely fast computer that can perform hundreds of

millions of instructions per second.

Memory:

Internalstorage areas in the computer. The term memory identifiesdata storage that comes

in the form ofchips, and the wordstorage is used for memory that exists on tapes ordisks.

Moreover, the term memory is usually used as a shorthand forphysicalmemory, which

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refers to the actual chips capable of holding data. Some computers also use virtual memory,

which expandsphysical memory onto ahard disk.

Every computer comes with a certain amount of physical memory, usually referred to asmain memory orRAM. You can think ofmain memory as an array of boxes, each of which

can hold a singlebyte of information. A computer that has 1megabyteof memory,therefore, can hold about 1 million bytes (orcharacters) of information.

There are several different types of memory:

o RAM (random-access memory): This is the same as main memory. When used by

itself, the termRAMrefers to readandwrite memory; that is, you can both writedata into RAM andread data from RAM. This is in contrast to ROM, which

permits you only to read data. Most RAM is volatile, which means that it requires a

steady flow of electricity to maintain its contents. As soon as the power is turnedoff, whatever data was in RAM is lost.

o ROM (read-only memory): Computers almost always contain a small amount ofread-only memory that holds instructions for starting up the computer. Unlike

RAM, ROM cannot be written to.

o PROM (programmable read-only memory): A PROM is a memory chip on

which you canstore aprogram. But once the PROM has been used, you cannotwipe it clean and use it to store something else. Like ROMs, PROMs are non-

volatile.

o EPROM (erasable programmable read-only memory): An EPROM is a special

type of PROM that can be erased by exposing it to ultraviolet light.

o EEPROM (electrically erasable programmable read-only memory): An

EEPROM is a special type of PROM that can be erased by exposing it to an

electrical charge.

Mass Storage:

Refers to various techniques anddevices forstoring large amounts ofdata. The earliest

storage devices were punched paper cards, which were used as early as 1804 to controlsilk-weaving looms. Modern mass storage devices include all types ofdisk drivesand tape

drives. Mass storage is distinct frommemory, which refers to temporary storage areas

within the computer. Unlikemain memory, mass storage devices retain data even when the

computer is turned off.

The main types of mass storage are:

o Floppy disks : Relatively slow and have a small capacity, but they areportable,

inexpensive, and universal.

o Hard disks : Very fast and with more capacity than floppy disks, but also more

expensive. Some hard disksystemsare portable (removable cartridges), but most

are not.

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o Optical disks : Unlike floppy and hard disks, which use electromagnetism to

encode data, optical disk systems use a laser toread andwrite data. Optical disks

have very large storage capacity, but they are not as fast as hard disks. In addition,

the inexpensive optical disk drives are read-only. Read/write varieties areexpensive.

o Tapes: Relatively inexpensive and can have very large storage capacities, but theydo not permitrandom accessof data.

Mass storage is measured inkilobytes (1,024bytes),megabytes (1,024 kilobytes),

gigabytes (1,024 megabytes) andterabytes (1,024 gigabytes).

Mass storage is sometimes called auxiliary storage.

Input Device:

Any machine that feedsdata into a computer. For example, a keyboard is an input device,

whereas a display monitoris anoutput device. Input devices other than the keyboard aresometimes called alternate input devices.Mice,trackballs, and light pens are all alternate

input devices.

Output Device:

Any machine capable of representing information from a computer. This includesdisplay

screens,printers, plotters, and synthesizers.

Central Processing Unit:

Abbreviation ofcentralprocessingunit, and pronounced as separate letters. The CPU isthe brains of the computer. Sometimes referred to simply as theprocessororcentral

processor, the CPU is where most calculations take place. In terms of computing power,the CPU is the most important element of a computer system.

On large machines, CPUs require one or moreprinted circuit boards. Onpersonalcomputers and smallworkstations, the CPU is housed in a single chip called a

microprocessor.

Two typical components of a CPU are:

The arithmetic logic unit(ALU), which performs arithmetic and logical operations.

The control unit(CU), which extracts instructions frommemory and decodes and

executes them, calling on the ALU when necessary.

U-NET Reference:

Major Hardware Elements of a computer system:

Major hardware elements of computers that allow network connectivity include the CPU,

the bus, drives, memory components, ports and cards.

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Backplane components:

o Power cord: cord connecting an electric device to an electrical outlet to provide

power to the device

o Mouse Port: Port that is designed for connecting a mouse to a PC.

o Parallel Port: An interface capable of transferring more than one bit simultaneously,used for connecting external devices, such as printers.

o Serial port: An interface that can be used for serial communication in which only

one bit is transmitted at a time.

o Sound card: An expansion board that handles sound functions.

o Video card: A board that plugs into a PC to give its display capabilities.

o Network card: An expansion board inserted into a computer to enable connection to

a network.

o Interface: A piece of hardware, such as modern connector, that allows two devices

to be connected together.

Drives:There are different types of drives the CD-ROM drive, the floppy disk drive, and the hard

disk drive.

o CD-ROM drive: A compact disc read only memory drive that can read information

from a CD-ROM.

o Floppy disk drive: Disk drive that can read and write to floppy disks.

o Hard disk drive: Device that reads and writes data on a hard drive.

CPU:

The CPU is the brain of the computer where most of the calculations take place. Themicroprocessor is a silicon chip contained within a CPU.

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.

Expansion Slots:

These are the openings in computer into which you can insert a circuit board to add newcapabilities to the computer. The expansion card is a printed circuit board that provides the

added capabilities to the computer.

Motherboard:

The Motherboard is the main circuit board of a computer. The important components on

the motherboard are -

o The power supply is the component that supplies power to the computer.

o The system unit is the main part of a PC. It is the term that encompasses the

chassis, the microprocessor, the main memory, the bus, and the ports. The system

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unit does not contain the keyboard, the monitor, or any other external devices

connected to the computer.

o ROM Read Only Memory is the computer memory on which data has been

prerecorded.

o PCB Printed Circuit Board is a thin plate on which chips (integrated circuits) and

other electronic components are placed.o RAM Random Access Memory 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 previously saved to disk.

Laptop Vs PC:

Laptop computers and notebook computers have become very popular. There are few

differences between the two.

o 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 physicalspace, and they use less power when operated. These smaller components can be

difficult to remove.

o In a laptop, the expansion slots become Personal Computer Memory Card

International Association (PCMCIA) card slots, or PC slots, through which NIC,

modems, hard drives, and other useful devices (usually the size of a thick creditcard) are connected.

o 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.

Application sharing through networks:Network Interface card:

o A network interface card (NIC) is a printed circuit board that provides network

communication capabilities to and from a personal computer.

o Also called a LAN adapter, the NIC plugs into a motherboard and provides port for

connecting to the network. The NIC constitutes the computer with the local areas

network (LAN).

o The NIC communicates with the network through a serial connection, and with the

computer through a parallel connection.

o 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 as

DOS or Windows), and drivers in order to perform its function.o 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.

o 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.

o An I/O address is a location in memory used by an auxiliary device to enter or

retrieve data from a computer.

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When selecting a NIC card for a network, one should consider the following:

o Type of network: You must choose a NIC to suit the type of network you have,

Ethernet NICs are designed for Ethernet LANs.

o 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.

o Type of Expansion Slot: With regard to the type of expansion slot to use, oneshould consider that because PCI slots are faster than ISA slots, the latter are being

phased out.

To install a NIC, one should know about these issues:

o One must know how the network card is configured, including jumpers, plug-and-

play software, and erasable programmable read only memory (EPROM).

o One must know the network card diagnostics; including the vendor supplied

diagnostics and loopback tests (see the documentation that comes with the card).

o 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 fromRAM to a device without going through the CPU.

Understanding Binary Basics:

At the most basic level, computers perform their computations by using 1s and 0s insteadof 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).

Bits, bytes and measurement terms:

Computers can understand and process only data that in a binary format, represented by 0s

and 1s. These 0s and 1s represent the two possible states of an electrical impulse and

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 storagelocation.

BIT (b): A bit is the smallest unit of data in a computer. A bit equals 1 or 0 in the binaryformat 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.

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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.

1byte = 8 bits.

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 networkconnection.

1Kilobit = 1000 bits

Kilobyte (KB): 1000 bytes = 8000 bits =1Kilobyte [KBps]

Megabit (Mb): 1 million bits = 1 Megabit (Mbps)

Megabyte (MB): 1million bytes (1,048,576 bytes exactly) = 8 million bits = 1 Megabyte(MBps)

Gigabit (Gb): 1 billion bits = 1 Gigabit (Gbps)

Gigabyte (GB): 1 billion bytes = 8 billion bits = 1Gigabyte (GBps)

Footnote: 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 with Kbps. For example, modern software usuallyshows the connection speed in kilobits per second (for example 45Kbps). However,

popular browsers display file-download speeds in kilobytes per second, meaning that with

a 45-Kbps.

Speed Measurement terms commonly used for microprocessors:

o 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.

o 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.

o GHz: A gigahertz (GHz) represents one billion 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 1980z

typically ran 10MHz (the original IBM PC was 4.77 MHz). Today they are measured inGHz.

Understanding Binary Basics:

Converting a decimal number to a binary number is one of the most common procedures

performed in computer operations.

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Conversion between decimal and binary:

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 usedin the decimal numbering system.

Example: Convert 100 to binary

2 100

2 50 0

2 25 0

2 12 1

2 6 0

2 3 0

1 1

The binary number for 100 is 1100100

Reference from Google:

Converting Binary to Decimal -

Steps:

1. Get the last digit of the hex number, call this digit the currentDigit.

2. Make a variable, let's call it power. Set the value to 0.3. Multiply the current digit with (2^power), store the result.

4. Increment power by 1.

5. Set the current Digit to the previous digit of the hex number.6. Repeat step 3 until all digits have been multiplied.

7. Sum the result of step 3 to get the answer number.

Example

Convert BINARY 11101 to DECIMAL

NOTES MULTIPLICATION RESULT

start from the last digit, which is 1, 1*(2^0) 1

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multiply that digit with 2^0, note

that the power of 0 of any number

is always 1

11101 (current digit is in bold)

process the previous digit, whichis 0, multiply that digit with the

increasing power of 2

11101(current digit is in bold)

0*(2^1) 0

process the previous digit, which

is 1, note that 2^2 means 2*2


1*(2^2) 4


is 1, note that 2^3 means 2*2*2


1*(2^3) 8


is 1, note that 2^4 means 2*2*2*2


1*(2^4) 16

here, we stop because there's no

more digit to process

this number comes from the sumof the RESULTS ANSWER 29

Basically, this is the same as saying:

1*(2^4) + 1*(2^3) + 1*(2^2) + 0*(2^1) + 1*(2^0)

or

1*(16) + 1*(8) + 1*(4) + 0*(2) + 1*(1)

The reason it's easier to start backward is because:

Counting the number of digits takes extra time, and you might count wrongly.

If you don't remember what a particular power-of-2 value, it's easy to calculate it

from the previous value. For instance, if you don't remember what the value of2*2*2 is, then just double the value of 2*2 (which you already have - if you had

started backward).

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Another Example

Convert BINARY 1010 to DECIMAL

MULTIPLICATION RESULT

0*(2^0) 0

1*(2^1) 2

0*(2^2) 0

1*(2^3) 8

ANSWER 10

Is constructing a table like above required? No, it just depends on your preference. Some

people are visual, and the table might help. Without a table, it's also easy. If you want to

be a speed counter, just remember that the value of the multiplier is always the double ofthe previous one.

1, 2, 4, 8, 16, 32, 64, 128, 256, 512, ...

POWER OF 2s RESULT

2^0 1

2^1 = 2 2

2^2 = 2*2 4

2^3 = 2*2*2 82^4 = 2*2*2*2 16

Example

Convert BINARY 1010001 to DECIMAL.

Again, I'm starting backward here:

(1*1) + (0*2) + (0*4) + (0*8) + (1*16) + (0*32) + (1*64) =

1 + 0 + 0 + 0 + 16 + 0 + 64 = 81

BINARY

Computers work on the principle of number manipulation. Inside the computer, thenumbers are represented inbits andbytes. For example, the number three is represented by

a byte with bits 0 & 1 set; 00000011. This is numbering system using base 2. Peoplecommonly use a decimal or Base 10 numbering system. What this means is that in Base 10,

count from 0 to 9 before adding another digit. The number 22 in Base 10 means we have 2

sets of 10's and 2 sets of 1's.

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Base 2 is also known asbinary since there can only be two values for a specific digit; either

a 0 = OFF or a 1 = ON. You cannot have a number represented as 22 in binary notation.

The decimal number 22 is represented in binary as 00010110 which by following the belowchart breaks down to:

Bit Position 7 6 5 4 3 2 1 01 1 1 1 1 1 1 1

Decimal 128 64 32 16 8 4 2 1

22 or 00010110:

All numbers representing 0 are not counted, 128, 64, 32, 8, 1 because 0 represents OFF

However, numbers representing 1 are counted, 16 + 4 + 2 = 22 because 1 represents ON

Decimal Values and Binary Equivalents chart:

DECIMAL BINARY

1 1

2 10

3 11

4 100

5 101

6 110

7 111

8 1000

9 1001

10 1010

16 10000

32 100000

64 1000000

100 1100100

256 100000000

512 1000000000

1000 1111110100

1024 10000000000HEXADECIMAL

The other major numbering system used by computers is hexadecimal, or Base 16. In thissystem, the numbers are counted from 0 to 9, then letters A to F before adding another

digit. The letter A through F represents decimal numbers 10 through 15, respectively. The

below chart indicates the values of the hexadecimal position compared to 16 raised to a

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power and decimal values. It is much easier to work with large numbers using hexadecimal

values than decimal.

To convert a value from hexadecimal to binary, you merely translate each hexadecimal

digit into its 4-bit binary equivalent. Hexadecimal numbers have either and 0x prefix or an

h suffix. For example, the hexadecimal number:0x3F7A

Translates into, Using the Binary chart and the below chart for Hex:0011 1111 0111 1010

DECIMAL HEXADECIMAL BINARY

0 0 00001 1 0001

2 2 0010

3 3 0011

4 4 0100

5 5 0101

6 6 0110

7 7 0111

8 8 1000

9 9 100110 A 1010

11 B 1011

12 C 1100

13 D 1101

14 E 1110

15 F 1111

From U learning

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 readableform. 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.

Conversion between binary and hexadecimal:

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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 commonly way for computers and software to express hexadecimal output isusing 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 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 theletters A, B, C, D, E, F. The A represents the decimal 10, B represents the decimal 11,

C represents the decimal 12, D represents the decimal 13, E represents the decimal

14, and F represents the decimal 15.

Decimal Binary Hex

0 00000000 00

1 00000001 01

2 00000010 02

3 00000011 03

4 00000100 04

5 00000101 05

6 00000110 06

7 00000111 07

8 00001000 08

9 00001001 0910 00001010 0A

11 00001011 0B

12 00001100 0C

13 00001101 0D

14 00001110 0E

15 00001111 0F

16 00010000 10

32 00100000 20

64 01000000 40

128 10000000 80

255 11111111 FF

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.

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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.

10101010 11110000 11000001 11100010 01110111 01010001

Octet Bit

Converting binary to hex is easy because base 16 (hexadecimal) is a power of base 2

(binary). Every four digits (bits) are equal to one hexadecimal digit. The figure 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 thefar left group does not contain four digits, add zero to the left and until there are four digits

(bits) in every group.

100100100010111110111110111001001 can be split as follows:

1 0010 0100 0101 1111 0111 1101 1100 1001 As per the rule add three zero to the

left, therefore the number becomes

0001 0010 0100 0101 1111 0111 1101 1100 1001

And the Hex number is 1245F7DC9

You can also convert hexadecimal numbers to binary format. To convert from hexadecimalto 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.

NOTE: Make sure you include four binary digits for each hexadecimal character, adding

zeros to the left of the number when necessary.

Using a PC on a Network

This article discusses basic networking technologies and common network applications. It

identifies the main purposes and functions of networking.

Basic Networking Terminology

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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 bedifficult 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:o 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.

o Media refers to the various physical environments through which transmission

signals pass. Common network media include twisted-pair, coaxial, and fiber-opticcable, and even the earth's atmosphere through which wireless transmission occurs.

o Aprotocolis 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.o 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 networkingdevices 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 onmost Cisco routers and Cisco switches. These network devices carry most of the Internet

traffic today.

o 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.

o Connectivity devices refer to several different device types, all of which are used to

connect cable segments, connect two or 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:

o 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.

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o 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.

o 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 differentcontinents.

Network structure is described in the following two ways:

o 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. Forinstance, 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."

o Thephysical topology refers to the layout or physical shape of the network, andincludes the topologies in this table.

Table1: 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 acircle

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

Network Applications

Network applications are software programs that run between different computers

connected together on a network.

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Network applications


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. Eachapplication program type is associated with its own application protocol. Some examples

include:

o HTTPis the World-Wide-Web communications protocol used to connect to web

servers. Its primary function is to establish a connection with a web server andtransmit HTML pages to the client browser.

o 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 holdsincoming e-mail until users log on and download their messages.

o File Transfer Protocol(FTP) is a simple file utility program for transferring filesbetween remote computers, which also provides for basic user authentication.

o Telnetis 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.

o Simple Network Management Protocol(SNMP) is used by network management

programs for monitoring the network device status and activities.

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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.

Sending e-mail

E-mail client applications, (such as Eudora, Microsoft Mail, Pegasus, and Netscape Mail)

all work with the POP3 protocol. The same principle is true with web browsers. The two

most popular web browsers are Microsoft Internet Explorer and Netscape Communicator.The appearance of these two web browser programs is very different, but they both work

with the application layer HTTP protocol.

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 therecipient.

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.

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Components of a network

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 andvarious remote access locations.

A main office is a site where everyone is connected via a LAN and where the bulk ofcorporate 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 centralresources and information, it is common to see a high-speed backbone in a LAN as well as

a data center with high-performance computers or servers and networked applications.

A variety of remote access locations connect to the main office or each other using WANservices as follows:

o 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

Integrated Services Digital Network (ISDN). Although some corporate informationmay 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.o 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 abranch office to access information or use network resources such as file servers.

o 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.

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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.

Computer networks

In this example, the business needs may require LAN connectivity within the campus tointerconnect 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 officeconnection requires a dial-up connection, such as ISDN.

Summary

When working with computer applications, it is important that you are familiar withnetworking 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.


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 isused 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.

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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.

Functions of networking:

OSI model layers and functions

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 size of networks. As companies

realized that they could save money and gain productivity by using networking technology,they added networks and expanded existing network 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 differentspecifications 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

o 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.

o 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 helpvendors create network 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 standardsthat ensured greater compatibility and interoperability between the various types od

network technologies produced by companies around the world.

Although other models exist, most network vendors today relate their products to the OSI

reference mode, 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 andreceiving data on a network.

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The OSI reference model has seven numbered layers, each illustrating a particular network

function. This separation of networking functions is called layering.

1. Physical Layer

2. Data0link Layer3. Network Layer

4. Transport Layer

5. Session Layer6. Presentation Layer

7. Application Layer

The OSI reference model defines the network functions that occur at each layer. Moreimportantly, 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 networkmedia.

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 are as follows:

1. Physical Layer

2. Data0link Layer

3. Network Layer4. Transport Layer

5. Session Layer

6. Presentation Layer

7. Application Layer

Dividing the network into seven layers provides the following advantages:

o 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.

o Ensures interoperable technology: Layering prevents changes in one layer from

affecting the other layers, allowing for quicker development, and ensuring

interoperable technology.

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o Facilitates modular engineering: Layering allows different types of network

hardware and software to communicate with each other, thereby facilitating

modular engineering.

o Reduces complexity: Layering breaks network communication into smaller,

simpler parts and reduces complexity.

o Standardizes interfaces: Layering standardizes network component interfaces toallow multiple-vendor development and support.

o 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 totravel from a source to a destination on a network. The functions are as follows

Application Layer:

The application layer is the OSI layer that is closest to the user. This layer provides

network services to the users 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 OSImodel.

The application layer establishes the availability of intended communication partners and

synchronizes and establishes agreement on procedures for error recovery and control ofdata integrity.

Presentation Layer:

The presentation layer ensures that the information that the application layer of one system

sends out is readable by an application layer of another system.

For example, a PC program communicates with another computer, one using extendedbinary 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.

Session Layer:

The session layer establishes, manages and terminates sessions between two

communicating hosts. It provides its services to the presentation layer. The session layeralso 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 processesopen at a given time. It is important to keep track of which user communicates on which

path.

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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.

Transport Layer:

The transport layer segments data from the sending hosts system and reassembles the datainto a data stream on the receiving hosts system.

For example, business users in large corporations often transfer large files from fieldlocations 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 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 layersfrom 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.

Network Layer:

The network layer provides connectivity and path selection between two host systems that

may be located on geographically separated network. The growth of the internet hasincreased the number of users accessing information from sites around the world, and it is

the network layer that manages this connectivity.

Data-Link Layer:

The data-link layer defines how data is formatted for transmission and how access to the

network is controlled.

Physical Layer:

The Physical layer defines the electrical, mechanical, procedural, and functional

specifications for activating, maintaining, and deactivating the physical link between endsystems.

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 these are the functions of the layers in the OSI model:

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o Application network services: The application layer provides network services to

any applications requiring access to the network.

o 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.o Interhost communication: The session layer provides Interhost communication. In

doing this it establishes, manages, and terminates sessions between applications.

o 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.

o Data Delivery: The network layer ensures data delivery. It provides connectivity

and path selection between two host systems, routes data packets and selects thepath to deliver data.

o Media access: The data-link layer provides access to the network media. It defineshow data is formatted and how access to the network is controlled.

o 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 thedata onto the physical media.

Reference from GOOGLE:

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The protocols defined by ISO based on the OSI 7 layer mode are as follows:

Application ACSE: Association Control Service Element

CMIP: Common Management Information Protocol

CMIS: Common Management Information Service

CMOT: CMIP over TCP/IP

FTAM: File Transfer Access and Management

ROSE: Remote Operation Service Element

RTSE: Reliable Transfer Service Element Protocol

VTP: ISO Virtual Terminal Protocol

X.400: Message Handling Service (ISO email

transmission service) Protocols

X.500: Directory Access Service Protocol (DAP)

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Presentation

LayerISO-PP: OSI Presentation Layer Protocol

ASN.1: Abstract Syntax Notation One

Session Layer ISO-SP: OSI Session Layer Protocol

Transport LayerISO-TP: OSI Transport Protocols: TP0, TP1, TP2, TP3,

TP4

Network Layer ISO-IP: CLNP: Connectionless Network Protocol

CONP: Connection-Oriented Network Protocol

ES-IS: End System to Intermediate System Routing

Exchange protocol

IDRP: Inter-Domain Routing Protocol

IS-IS: Intermediate System to Intermediate System

Data Link HDLC: High Level Data Link Control protocol

LAPB: Link Access Procedure Balanced for X.25

http://www.javvin.com/osimodel.html

DATA Communication:

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. Of one computer (Host

A) wants to send data to another computer (HOST B), the data must first be packaged by aprocess called encapsulation.

The encapsulation process can be thought of as putting a letter inside an envelope, and then

properly writing the recipients mail address on the envelope so it can be properly deliveredby 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 the 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.

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.

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The data-link layer performs the following tasks:

o It checks the data-link trailer (the FCS) to see if the data is in error.

o If the data is in error, it may be discarded, and the data-link layer may ask for the

data to be retransmitted.

o If the data is not in error, the data-link layer reads and interprets the controlinformation in the data-link header.

o 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 similarde-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 ofcommunication 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. Itthen adds whatever headers the layer needs to perform its function. As the data moves

down through Layers 7 through 5 of the OSI model, the additional headers are added. The

grouping of data at the Layer 4 (transport) PDU is called 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 3PDU). 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 by encapsulating the network layer

packet in a frame (the Layer 2PDU). The frame header contains the physical addressesrequired 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 1sand 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 routerare at Layer 3 the network layer.


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Each protocol creates a Protocol Data Unit (PDU) for transmission that includes headers

required by that protocol and data to be transmitted. This data becomes the Service DataUnit (SDU) of the next layer below it. This diagram shows a 7 layer PDU consisting of a

layer 7 header (L7H) and application data. When this is passed to layer 6, it becomes a

layer 6SDU. The layer 6 protocol prepends to it a layer 6 header (L6H) to create a layer

6PDU, which is passed to layer 5. The encapsulation process continues all the way down tolayer 2, which creates a layer 2 PDU in this case shown with both a header and footer

that is converted to bits and sent at layer 1.

The TCP/IP protocol stack

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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 eachmodel.

Application Layer:

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 Layer: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 forreliable network communications.

Internet Layer:

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 look to get

there.

Network access Layer:

The network access layer is also called the host-to-network layer. It includes LAN and

WAN protocols, and all the details in the OSI physical and data-link layers.

Similarities and differences b/w TCP/IP protocol stack and the OSI reference model:

Main Similarities:

o Application layers Both have the application layers, though they include

different services.

o Packet-switched technology - Both assume packet-switched technology, not

circuit-switched. (Analog telephone calls are an example of circuit switched.)

o Transport and network layers Both have comparable transport and network

layers.

Main Differences:

o Data-link and physical layers TCP/IP combines the OSI data-link and physical

layers into the network access layer.

o 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 wide spread implementation of its protocols. In contrast, networks are nottypically built on the OSI model, even though the OSI model is used as a guide.

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o Presentation and session layers TCP/IP combines the OSI presentation and

session layers into its application layer.


Layer Function Protocols NetworkComponents

Application

User Interface

used for applications

specifically written to runover the network

allows access to network

services that support

applications;

directly represents the

services that directly

support user applications

handles network access,

flow control and error

recovery

Example apps are filetransfer,e-mail, NetBIOS-

based applications

DNS; FTP; TFTP;

BOOTP;SNMP;RLOGIN;

SMTP; MIME;

NFS; FINGER;

TELNET; NCP;APPC; AFP; SMB

Gateway

Presentation

Translation

Translates from application

to network format andvice-versa

all different formats fromall sources are made into acommon uniform format

that the rest of the OSI

model can understand

responsible for protocol

conversion, character

conversion,dataencryption / decryption,

expanding graphics

commands, data

compression

sets standards for different

systems to provide

seamless communicationfrom multiple protocol

stacks

not always implemented in

Gateway

Redirector

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a network protocol

Session

"syncs and

sessions"

establishes, maintains and

ends sessions across the

network

responsible for namerecognition (identification)

so only the designated

parties can participate inthe session

provides synchronization

services by planning checkpoints in the data stream

=> if session fails, only

data after the most recentcheckpoint need be

transmitted manages who can transmit

data at a certain time andfor how long

Examples are interactive

login and file transferconnections, the session

would connect and re-

connect if there was an

interruption; recognize

names in sessions andregister names in history

NetBIOS

Names Pipes

Mail Slots

RPC

Gateway

Transport

packets; flow

control &

error-handling

additional connectionbelow the session layer

manages the flow control

of data between parties

across the network

divides streams of data into

chunks or packets; the

transport layer of thereceiving computer

reassembles the messagefrom packets

"train" is a good analogy

=> the data is divided into

identical units

provides error-checking toguarantee error-free data

delivery, with on losses or

TCP, ARP, RARP;

SPX

NWLink

NetBIOS /

NetBEUI

ATP

Gateway

Advanced Cable

Tester

Brouter

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duplications

provides acknowledgment

of successfultransmissions; requests

retransmission if some

packets dont arrive error-free

provides flow control and

error-handling

Network

addressing;

routing

translates logical network

address and names to theirphysical address (e.g.

computername ==> MAC

address)

responsible for

o addressingo determining routes

for sending

o managing network

problems such aspacket switching,

data congestion and

routing

if router cant send dataframe as large as the source

computer sends, the

network layer compensatesby breaking the data into

smaller units. At the

receiving end, the networklayer reassembles the data

think of this layer stamping

the addresses on each train

car

IP; ARP; RARP,

ICMP; RIP; OSFP;

IGMP;

IPX

NWLink

NetBEUI

OSI

DDP

DECnet

Brouter

Router

Frame Relay

Device

ATM Switch

Advanced Cable

Tester

Data Link

data frames tobits

turns packets into raw bits100101 and at the receiving

end turns bits into packets. handles data frames

between the Network and

Physical layers

the receiving end packagesraw data from the Physical

layer into data frames for

Logical Link

Control

error

correction and

flow control manages link

control anddefines SAPs

Bridge

Switch

ISDN Router

Intelligent Hub

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delivery to the Network

layer

responsible for error-freetransfer of frames to other

computer via the Physical

Layer

this layer defines themethods used to transmit

and receive data on the

network. It consists of thewiring, the devices use to

connect the NIC to the

wiring, the signaling

involved to transmit /receive data and the ability

to detect signaling errorson the network media

802.1 OSI Model

802.2 Logical Link

Control

NIC

Advanced Cable

Tester

Media AccessControl

communicateswith the

adapter card controls the

type of media

being used:

802.3 CSMA/CD

(Ethernet)

802.4 Token Bus

(ARCnet)

802.5 Token Ring

802.12 DemandPriority

Physical

hardware;

raw bit stream

transmits raw bit stream

over physical cable

defines cables, cards, and

physical aspects

defines NIC attachments tohardware, how cable isattached to NIC

defines techniques to

transfer bit stream to cable

IEEE 802

IEEE 802.2

ISO 2110

ISDN

Repeater

Multiplexer

Hubs

Passive

Active

TDR

Oscilloscope

Amplifier

The 7 Layers of the OSI Model

The OSI, or Open System Interconnection, model defines a networking framework for

implementing protocols in seven layers. Control is passed from one layer to the next,

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starting at the application layer in one station, proceeding to the bottom layer, over the

channel to the next station and back up the hierarchy.

Application(Layer 7)

This layer supports application and end-user processes. Communication

partners are identified, quality of service is identified, userauthenticationand privacy are considered, and any constraints on data syntax are

identified. Everything at this layer is application-specific. This layerprovides application services for file transfers, e-mail, and othernetworksoftwareservices. Telnet and FTP are applications that exist entirely in the

application level. Tiered application architectures are part of this layer.

Presentation

(Layer 6)

This layer provides independence from differences in data representation

(e.g.,encryption) by translating from application to network format, andvice versa. The presentation layer works to transform data into the form

that the application layer can accept. This layer formats and encrypts data

to be sent across a network, providing freedom from compatibility

problems. It is sometimes called thesyntax layer.

Session

(Layer 5)

This layer establishes, manages and terminates connections betweenapplications. The session layer sets up, coordinates, and terminates

conversations, exchanges, and dialogues between the applications at each

end. It deals with session and connection coordination.

Transport

(Layer 4)

This layer providestransparent transfer of data between end systems, orhosts, and is responsible for end-to-end error recovery andflow control. It

ensures complete data transfer.

Network

(Layer 3)

This layer providesswitchingand routing technologies, creating logical

paths, known as virtual circuits, for transmitting data from node to node.

Routing and forwarding are functions of this layer, as well as addressing,internetworking, error handling, congestion control andpacket sequencing.

Data Link

(Layer 2)

At this layer, data packets are encoded and decoded intobits. It furnishes

transmission protocol knowledge and management and handles errors in

the physical layer, flow control and frame synchronization. The data link

layer is divided into two sublayers: The Media Access Control (MAC)layer and the Logical Link Control (LLC) layer. The MAC sublayer

controls how a computer on the network gains access to the data and

permission to transmit it. The LLC layer controls frame synchronization,flow control and error checking.

Physical

(Layer 1)

This layer conveys thebitstream - electrical impulse, light or radio signal-- through the network at the electrical and mechanical level. It provides the

hardware means of sending and receiving data on a carrier, includingdefining cables, cards and physical aspects. Fast Ethernet,RS232, and

ATM are protocols with physical layer components.

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Reference from Google CISCO:

Open System Interconnection Protocols

Background

The Open System Interconnection (OSI) protocol suite is comprised of numerous standard

protocols that are based on the OSI reference model. These protocols are part of aninternational program to develop data-networking protocols and other standards that

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