View Full Version : Networking Basics

24-02-2006, 11:43 AM
Connecting to the Internet
Requirements for Internet connection

This page will describe the physical and logical requirements for an Internet connection.
The Internet is the largest data network on earth. The Internet consists of many large and small networks that are interconnected. Individual computers are the sources and destinations of information through the Internet. Connection to the Internet can be broken down into the physical connection, the logical connection, and applications.

A physical connection is made by connecting an adapter card, such as a modem or a NIC, from a PC to a network.

The physical connection is used to transfer signals between PCs within the local-area network (LAN) and to remote devices on the Internet.

The logical connection uses standards called protocols. A protocol is a formal de******ion of a set of rules and conventions that govern how devices on a network communicate. Connections to the Internet may use multiple protocols. The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is the primary set of protocols used on the Internet. The TCP/IP suite works together to transmit and receive data, or information.

The last part of the connection are the applications, or software programs, that interpret and display data in an understandable form. Applications work with protocols to send and receive data across the Internet. A Web browser displays HTML as a Web page. Examples of Web browsers include Internet Explorer and Netscape. File Transfer Protocol (FTP) is used to download files and programs from the Internet. Web browsers also use proprietary plug-in applications to display special data types such as movies or flash animations.

24-02-2006, 11:46 AM
thank you innerpeace456
and we wann more

24-02-2006, 12:35 PM
PC basics

Computers are important building blocks in a network. Therefore, you must be able to identify the major components of a PC. Many networking devices are special purpose computers, with many of the same components as general purpose PCs.

A computer must work properly before it can be used to access information such as Web-based content. This will require troubleshoot basic hardware and software problems. Therefore, You must be familiar with the following small, discreet PC components:

You should also be familiar with the following PC subsystems:

Transistor – Device that amplifies a signal or opens and closes a circuit.
Integrated circuit – Device made of semiconductor material that contains many transistors and performs a specific task.
Resistor – An electrical component that limits or regulates the flow of electrical current in an electronic circuit.
Capacitor – Electronic component that stores energy in the form of an electrostatic field that consists of two conducting metal plates separated by an insulating material.
Connector – The part of a cable that plugs into a port or interface.
Light emitting diode (LED) – Semiconductor device that emits light when a current passes through it.
Printed circuit board (PCB) – A circuit board which has conducting tracks superimposed, or printed, on one or both sides. It may also contain internal signal layers and power and ground planes. Microprocessors, chips and integrated circuits and other electronic components are mounted on the PCB.
CD-ROM drive – A device that can read information from a CD-ROM.
Central processing unit (CPU) – The part of a computer that controls the operation of all the other parts. It gets instructions from memory and decodes them. It performs math and logic operations, and translates and executes instructions.
Floppy disk drive – A computer drive that reads and writes data to a 3.5-inch, circular piece of metal-coated plastic disk. A standard floppy disk can store approximately 1 MB of information.
Hard disk drive – A computer storage device that uses a set of rotating, magnetically coated disks called platters to store data or programs. Hard drives come in different storage capacity sizes.
Microprocessor– A microprocessor is a processor which consists of a purpose-designed silicon chip and is physically very small. The microprocessor utilizes Very Large-Scale Integration (VLSI) circuit technology to integrate computer memory, logic, and control on a single chip. A microprocessor contains a CPU.
Motherboard – The main printed circuit board in a computer. The motherboard contains the bus, the microprocessor, and integrated circuits used for controlling any built-in peripherals such as the keyboard, text and graphics display, serial ports and parallel ports, joystick, and mouse interfaces.
Bus– A collection of wires on the motherboard through which data and timing signals are transmitted from one part of a computer to another.
Random-access memory (RAM) – Also known as read-write memory because new data can be written to it and stored data can be read from it. RAM requires electrical power to maintain data storage. If a computer is turned off or loses power all data stored in RAM is lost.
Read-only memory (ROM) – Computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.
System unit – The main part of a PC, which includes the chassis, microprocessor, main memory, bus, and ports. The system unit does not include the keyboard, monitor, or any external devices connected to the computer.
Expansion slot – A socket on the motherboard where a circuit board can be inserted to add new capabilities to the computer. Figure shows Peripheral Component Interconnect (PCI) and Accelerated Graphics Port (AGP) expansion slots. PCI is a fast connection for boards such as NICs, internal modems, and video cards. The AGP port provides a high bandwidth connection between the graphics device and the system memory. AGP provides a fast connection for 3-D graphics on computer systems.
Power supply– The component that supplies power to a computer.

The following backplane components are also important:

Backplane – A backplane is an electronic circuit board containing circuitry and sockets into which additional electronic devices on other circuit boards or cards can be plugged; in a computer, generally synonymous with or part of the motherboard.
Network interface card (NIC) – An expansion board inserted into a computer so that the computer can be connected to a network.
Video card– A board that plugs into a PC to give it display capabilities.
Audio card – An expansion board that enables a computer to manipulate and output sounds.
Parallel port – An interface capable of transferring more than one bit simultaneously that is used to connect external devices such as printers.
Serial port – An interface that can be used for serial communication in which only one bit is transmitted at a time.
Mouse port – A port used to connect a mouse to a PC.
USB port– A Universal Serial Bus connector. A USB port connects devices such as a mouse or printer to the computer quickly and easily.
Firewire– A serial bus interface standard offering high-speed communications and isochronous real-time data services.
Power cord – A cord used to connect an electrical device to an electrical outlet that provides power to the device.
Think of the internal components of a PC as a network of devices that are all attached to the system bus.

24-02-2006, 12:42 PM
Network Interface Card

This page will explain what a NIC is and how it works. You will also learn how to select the best NIC for a PC.

A NIC, or LAN adapter, provides network communication capabilities to and from a PC. On desktop computer systems, it is a printed circuit board that resides in a slot on the motherboard and provides an interface connection to the network media. On laptop computer systems, it is commonly integrated into the laptop or available on a small, credit card-sized PCMCIA card. PCMCIA stands for Personal Computer Memory Card International Association. PCMCIA cards are also known as PC cards. The type of NIC must match the media and protocol used on the local network.

The NIC uses an interrupt request (IRQ), an input/output (I/O) address, and upper memory space to work with the operating system. An IRQ value is an assigned location where the computer can expect a particular device to interrupt it when the device sends the computer signals about its operation. For example, when a printer has finished printing, it sends an interrupt signal to the computer. The signal momentarily interrupts the computer so that it can decide what processing to do next. Since multiple signals to the computer on the same interrupt line might not be understood by the computer, a unique value must be specified for each device and its path to the computer. Prior to Plug-and Play (PnP) devices, users often had to set IRQ values manually, or be aware of them, when adding a new device to a computer.

These considerations are important in the selection of a NIC:

Protocols – Ethernet, Token Ring, or FDDI
Types of media – Twisted-pair, coaxial, wireless, or fiber-optic
Type of system bus – PCI or ISA

24-02-2006, 01:00 PM
NIC and modem istallation

This page will explain how an adapter card, which can be a modem or a NIC, provides Internet connectivity. You will also learn how to install a modem or a NIC.

A modem, or modulator-demodulator, is a device that provides the computer with connectivity to a telephone line. A modem converts data from a digital signal to an analog signal that is compatible with a standard phone line. The modem at the receiving end demodulates the signal, which converts it back to digital. Modems may be installed internally
or attached externally to the computer using a phone line.

A NIC must be installed for each device on a network. A NIC provides a network interface for each host. Different types of NICs are used for various device configurations. Notebook computers may have a built-in interface or use a PCMCIA card. Figure
shows PCMCIA wired, wireless network cards, and a Universal Serial Bus (USB) Ethernet adapter. Desktop systems may use an internal network adapter , called a NIC, or an external network adapter that connects to the network through a USB port.

Situations that require NIC installation include the following:

Installation of a NIC on a PC that does not already have one
Replacement of a malfunctioning or damaged NIC
Upgrade from a 10-Mbps NIC to a 10/100/1000-Mbps NIC
Change to a different type of NIC, such as wireless
Installation of a secondary, or backup, NIC for network security reasons
To perform the installation of a NIC or modem the following resources may be required:

Knowledge of how the adapter, jumpers, and plug-and-play software are configured
Availability of diagnostic tools
Ability to resolve hardware resource conflicts

24-02-2006, 01:09 PM
Overview of High-speed and dial-up connectivity

This page will explain how modem connectivity has evolved into high-speed services.

In the early 1960s, modems were introduced to connect dumb terminals to a central computer. Many companies used to rent computer time since it was too expensive to own an on-site system. The connection rate was very slow. It was 300 bits per second (bps), which is about 30 characters per second.

As PCs became more affordable in the 1970s, bulletin board systems (BBSs) appeared. These BBSs allowed users to connect and post or read messages on a discussion board. The 300-bps speed was acceptable since it was faster than the speed at which most people could read or type. In the early 1980s, use of bulletin boards increased exponentially and the 300 bps speed quickly became too slow for the transfer of large files and graphics. In the 1990s, modems could operate at 9600 bps. By 1998, they reached the current standard of 56,000 bps, or 56 kbps.

Soon the high-speed services used in the corporate environment such as Digital Subscriber Line (DSL) and cable modem access moved to the consumer market. These services no longer required expensive equipment or a second phone line. These are "always on" services that provide instant access and do not require a connection to be established for each session. This provides more reliability and flexibility and has simplified Internet connection sharing in small office and home networks.

24-02-2006, 01:15 PM
TCP/IP de******ion and configuration

This page will introduce the Transmission Control Protocol/Internet Protocol (TCP/IP).

TCP/IP is a set of protocols or rules that have been developed to allow computers to share resources across a network. The operating system tools must be used to configure TCP/IP on a workstation. The process is very similar for Windows or Mac operating systems.

24-02-2006, 01:23 PM
Testing connectivity with ping

This page will explain how the ping command is used to test network connectivity.

Ping is a basic program that verifies a particular IP address exists and can accept requests. The computer acronym ping stands for Packet Internet or Inter-Network Groper. The name was contrived to match the submariners' term for the sound of a returned sonar pulse from an underwater object.

The ping command works by sending special Internet Protocol (IP) packets, called Internet Control Message Protocol (ICMP) Echo Request datagrams, to a specified destination. Each packet sent is a request for a reply. The output response for a ping contains the success ratio and round-trip time to the destination. From this information, it is possible to determine if there is connectivity to a destination. The ping command is used to test the NIC transmit and receive function, the TCP/IP configuration, and network connectivity. The following types of ping commands can be issued:

ping – This is a unique ping and is called an internal loopback test. It is used to verify the TCP/IP network configuration.
ping IP address of host computer – A ping to a host PC verifies the TCP/IP address configuration for the local host and connectivity to the host.
ping default-gateway IP address – A ping to the default gateway indicates if the router that connects the local network to other networks can be reached.
ping remote destination IP address – A ping to a remote destination verifies connectivity to a remote host.

24-02-2006, 01:54 PM
Web browser and plug-ins

This page will explain what a Web browser is and how it performs the following functions:

Contacts a Web server
Requests information
Receives information
Displays the results on the screen

A Web browser is software that interprets HTML, which is one of the languages used to code Web page content. Some new technologies use other markup languages with more advanced features. HTML, which is the most common markup language, can display graphics or play sound, movies, and other multimedia files. Hyperlinks that are embedded in a Web page provide a quick link to another location on the same page or a different Internet address.

Two of the most popular Web browsers are Internet Explorer (IE) and Netscape Communicator. These browsers perform the same tasks. However, there are differences between them. Some websites may not support the use of one of these browsers. It is a good idea to have both programs installed.

Here are some features of Netscape Navigator:

Was the first popular browser
Uses less disk space
Displays HTML files
Performs e-mail and file transfers

Here are some features of IE:

Is powerfully integrated with other Microsoft products
Uses more disk space
Displays HTML files
Performs e-mail and file transfers

There are also many special, or proprietary, file types that standard Web browsers are not able to display. To view these files the browser must be configured to use the plug-in applications. These applications work with the browser to launch the programs required to view special files:

Flash – Plays multimedia files created by Macromedia Flash
Quicktime – Plays video files created by Apple
Real Player – Plays audio files

Use the following procedure to install the Flash plug-in:

1- Go to the Macromedia website.
2- Download the latest flash player installer file.
3- Run and install the plug-in in Netscape or IE.
4- Access the Cisco Academy website to verify the installation and proper operation.

Computers also perform many other useful tasks. Many employees use a set of applications in the form of an office suite such as Microsoft Office. Office applications typically include the following:

- Spreadsheet software contains tables that consist of columns and rows and it is often used with formulas to process and analyze data.
- Modern word processors allow users to create documents that include graphics and richly formatted text.
- Database management software is used to store, maintain, organize, sort, and filter records. A record is a collection of information identified by some common theme such as customer name.
- Presentation software is used to design and develop presentations to deliver at meetings, classes, or sales presentations.
- A personal information manager includes an e-mail utility, contact lists, a calendar, and a to-do list.

Office applications are now a part of daily work, as typewriters were before PCs.

25-02-2006, 10:18 AM
Network Math

Binary presentation of data

This page will explain how computers use the binary number system to represent data.

Computers work with and store data using electronic switches that are either ON or OFF. Computers can only understand and use data that is in this two-state or binary format. The 1s and 0s are used to represent the two possible states of an electronic component in a computer. 1 is represented by an ON state, and 0 is represented by an OFF state. They are referred to as binary digits or bits.

American Standard Code for Information Interchange (ASCII) is the code that is most commonly used to represent alpha-numeric data in a computer. ASCII uses binary digits to represent the symbols typed on the keyboard. When computers send ON or OFF states over a network, electrical, light, or radio waves are used to represent the 1s and 0s. Notice that each character is represented by a unique pattern of eight binary digits.

Because computers are designed to work with ON/OFF switches, binary digits and binary numbers are natural to them. Humans use the decimal number system, which is relatively simple when compared to the long series of 1s and 0s used by computers. So the computer binary numbers need to be converted to decimal numbers.

Sometimes binary numbers are converted to hexadecimal numbers. This reduces a long string of binary digits to a few hexadecimal characters. It is easier to remember and to work with hexadecimal numbers.

25-02-2006, 10:24 AM
Bits and bytes

This page will explain what bits and bytes are.

A binary 0 might be represented by 0 volts of electricity.

A binary 1 might be represented by +5 volts of electricity.

Computers are designed to use groupings of eight bits. This grouping of eight bits is referred to as a byte. In a computer, one byte represents a single addressable storage location. These storage locations represent a value or single character of data, such as an ASCII code. The total number of combinations of the eight switches being turned on and off is 256. The value range of a byte is from 0 to 255. So a byte is an important concept to understand when working with computers and networks.

25-02-2006, 10:36 AM
Base 10 number system

Numbering systems consist of symbols and rules for their use. This page will discuss the most commonly used number system, which is decimal, or Base 10.

Base 10 uses the ten symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. These symbols, can be combined to represent all possible numeric values.

The decimal number system is based on powers of 10. Each column position of a value, from right to left, is multiplied by the base number 10 raised to a power, which is the exponent. The power that 10 is raised to depends on its position to the left of the decimal point. When a decimal number is read from right to left, the first or rightmost position represents 100, which equals 1. The second position represents 101, which equals 10. The third position represents 102, which equals 100. The seventh position to the left represents 106, which equals 1,000,000. This is true no matter how many columns the number has.

Here is an example:

2134 =
(2x10^3) + (1x10^2) + (3x10^1) + (4x10^0)

This review of the decimal system will help you understand the Base 2 and Base 16 number systems. These systems use the same methods as the decimal system.

25-02-2006, 10:50 AM
Base 2 number system

This page will discuss the number system that computers use to recognize and process data, which is binary, or Base 2.
The binary system uses only two symbols, which are 0 and 1. The position of each digit from right to left in a binary number represents the base number 2 raised to a power or exponent. These place values are, from right to left, 20, 21, 22, 23, 24, 25, 26, and 27, or 1, 2, 4, 8, 16, 32, 64, and 128 respectively.

Here is an example:

101102 =
(1 x 2^4 = 16) + (0 x 2^3 = 0) + (1 x 2^2 = 4) + (1 x 2^1 = 2) + (0 x 2^0 = 0) = 22 (16 + 0 + 4 + 2 + 0)

This example shows that the binary number 10110 is equal to the decimal number 22.

25-02-2006, 11:01 AM
Converting decimal numbers to 8-bit binary numbers

This page will teach you how to convert decimal numbers to binary numbers.

Conversion exercise:

Use the example below to convert the decimal number 168 to a binary number:

128 is less than 168 so the left most bit in the binary number is a 1. 168 - 128 = 40.
64 is not less than or equal to 40 so the second bit from the left is a 0.
32 is less than 40 so the third bit from the left is a 1. 40 - 32 = 8.
16 is not less than or equal to 8 so the fourth bit from the left is a 0.
8 is equal to 8 so the fifth bit from the left is a 1. 8 - 8 = 0. Therefore, the bits to the right are all 0.

This example shows that the decimal number 168 is equal to the binary number 10101000.

25-02-2006, 11:19 AM
Converting 8-bit binary numbers to decimal numbers

This page will teach you how to convert binary numbers to decimal numbers.

Here is an example:

Convert the binary number 01110000 to a decimal number.

Work from right to left. Remember that anything raised to the 0 power is 1.

0 x 20 = 0

0 x 2^1 = 0

0 x 2^2 = 0

0 x 2^3 = 0

1 x 2^4 = 16

1 x 2^5 = 32

1 x 2^6 = 64

0 x 2^7 = 0


= 112

25-02-2006, 11:48 AM
Four-octet dotted decimal representation of 32-bit binary numbers

This page will explain how binary numbers are represented in dotted decimal notation.

Currently, addresses assigned to computers on the Internet are 32-bit binary numbers. To make it easier to work with these addresses, the 32-bit binary number is broken into a series of decimal numbers. First the binary number is split into four groups of eight binary digits. Then each group of eight bits, or octet, is converted into its decimal equivalent. This conversion can be performed as shown on the previous page.

When written, the complete binary number is represented as four groups of decimal digits separated by periods. This is called dotted decimal notation and provides a compact and easy way to refer to 32-bit addresses. This representation is used frequently later in this course, so it is necessary to understand it. For dotted decimal to binary conversions, remember that each group of one to three decimal digits represents a group of eight binary digits. If the decimal number that is being converted is less than 128, zeros will be needed to be added to the left of the equivalent binary number until there are a total of eight bits.

Try the following conversions for practice:

Convert to its 32-bit binary equivalent.

Convert 10000000 01011101 00001111 10101010 to its dotted decimal equivalent.

01-03-2006, 03:54 AM

This page will teach you about the hexadecimal number system. You will also learn how hexadecimal is used to represent binary and decimal numbers.

The hexadecimal or Base 16 number system is commonly used to represent binary numbers in a more readable form. Computers perform computations in binary. However, there are several instances when the binary output of a computer is expressed in hexadecimal to make it easier to read.

The configuration register in routers often requires hexadecimal to binary and binary to hexadecimal conversions. routers have a configuration register that is 16 bits long. The 16-bit binary number can be represented as a four-digit hexadecimal number. For example, 0010000100000010 in binary equals 2102 in hexadecimal. A hexadecimal number is often indicated with a 0x. For example, the hexadecimal number 2102 would be written as 0x2102.

Like the binary and decimal systems, the hexadecimal system is based on the use of symbols, powers, and positions. The symbols that hexadecimal uses are the digits 0 through 9 and the letters A through F.

All combinations of four binary digits can be represented with one hexadecimal symbol. These values require one or two decimal symbols. Two hexadecimal digits can efficiently represent any combination of eight binary digits. The decimal representation of an eight-bit binary number will require either two or three decimal digits. Since one hexadecimal digit always represents four binary digits, hexadecimal symbols are easier to use than decimal symbols when working with large binary numbers. Using hexadecimal representation also reduces the confusion of reading long strings of binary numbers and the amount of space it takes to write binary numbers. Remember that 0x may be used to indicate a hexadecimal value. The hexadecimal number 5D might be written as 0x5D.

01-03-2006, 04:04 AM
Boolean or binary logic

This page will introduce Boolean logic and explain how it is used.

Boolean logic is based on digital circuitry that accepts one or two incoming voltages. Based on the input voltages, output voltage is generated. For computers the voltage difference is represented as an ON or OFF state. These two states are associated with a binary 1 or 0.

Boolean logic is a binary logic that allows two numbers to be compared and makes a choice based on the numbers. These choices are the logical AND, OR, and NOT. With the exception of the NOT, Boolean operations have the same function. They accept two numbers, which are 1 and 0, and generate a result based on the logic rule.

The NOT operation takes the value that is presented and inverts it. A 1 becomes a 0 and a 0 becomes a 1. Remember that the logic gates are electronic devices built specifically for this purpose. The logic rule that they follow is whatever the input is, the output is the opposite.

The AND operation compares two input values. If both values are 1, the logic gate generates a 1 as the output. Otherwise it outputs a 0. There are four combinations of input values. Three of these combinations generate a 0, and one combination generates a 1.

The OR operation also takes two input values. If at least one of the input values is 1, the output value is 1. Again there are four combinations of input values. Three combinations generate a 1 and the fourth generates a 0.

The two networking operations that use Boolean logic are subnetwork and wildcard masking. The masking operations are used to filter addresses. The addresses identify the devices on the network and can be grouped together or controlled by other network operations.

01-03-2006, 05:55 AM
IP addresses and network masks

This page will explain the relationship between IP addresses and network masks.

When IP addresses are assigned to computers, some of the bits on the left side of the 32-bit IP number represent a network. The number of bits designated depends on the address class. The bits left over in the 32-bit IP address identify a particular computer on the network. A computer is referred to as a host. The IP address of a computer consists of a network and a host part.

To inform a computer how the 32-bit IP address has been split, a second 32-bit number called a subnetwork mask is used. This mask is a guide that determines how the IP address is interpreted. It indicates how many of the bits are used to identify the network of the computer. The subnetwork mask sequentially fills in the 1s from the left side of the mask. A subnet mask will always be all 1s until the network address is identified and then it will be all 0s to the end of the mask. The bits in the subnet mask that are 0 identify the computer or host.

Some examples of subnet masks are as follows:

written in dotted decimal as

written in dotted decimal as

In the first example, the first eight bits from the left represent the network portion of the address, and the last 24 bits represent the host portion of the address. In the second example the first 16 bits represent the network portion of the address, and the last 16 bits represent the host portion of the address.

The IP address
in binary form is 00001010.00100010.00010111.10000110.

A Boolean AND of the IP address and the subnet mask produces the network address of this host:


The dotted decimal conversion is which is the network portion of the IP address when the mask is used.

A Boolean AND of the IP address and the subnet mask produces the network address of this host:


The dotted decimal conversion is which is the network portion of the IP address when the mask is used.

This is a brief illustration of the effect that a network mask has on an IP address. The importance of masking will become much clearer as more work with IP addresses is done. For right now it is only important that the concept of the mask is understood.

01-03-2006, 06:00 AM

Decimal representation of IP addresses and network masksThis page summarizes the topics discussed in this module.

A connection to a computer network can be broken down into the physical connection, the logical connection, and the applications that interpret the data and display the information. Establishment and maintenance of the physical connection requires knowledge of PC components and peripherals. Connectivity to the Internet requires an adapter card, which may be a modem or a network interface card (NIC).

In the early 1960s modems were introduced to provide connectivity to a central computer. Today, access methods have progressed to services that provide constant, high-speed access.

The logical connection uses standards called protocols. The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is the primary group of protocols used on the Internet. TCP/IP can be configured on a workstation using operating system tools. The ping utility can be used to test connectivity.

A web browser is software that is installed on the PC to gain access to the Internet and local web pages. Occasionally a browser may require plug-in applications. These applications work in conjunction with the browser to launch the program required to view special or proprietary files.

Computers recognize and process data using the binary, or Base 2, numbering system. Often the binary output of a computer is expressed in hexadecimal to make it easier to read. The ablility to convert decimal numbers to binary numbers is valuable when converting dotted decimal IP addresses to machine-readable binary format. Conversion of hexadecimal numbers to binary, and binary numbers to hexadecimal, is a common task when dealing with the configuration register in routers.

Boolean logic is a binary logic that allows two numbers to be compared and a choice generated based on the two numbers. Two networking operations that use Boolean logic are subnetting and wildcard masking.

The 32-bit binary addresses used on the Internet are referred to as Internet Protocol (IP) addresses.

01-03-2006, 06:28 AM
Networking Terminology

Data networks

This page will discuss the evolution of data networks.

Data networks developed as a result of business applications that were written for microcomputers. The microcomputers were not connected so there was no efficient way to share data among them. It was not efficient or cost-effective for businesses to use floppy disks to share data. Sneakernet created multiple copies of the data. Each time a file was modified it would have to be shared again with all other people who needed that file. If two people modified the file and then tried to share it, one of the sets of changes would be lost. Businesses needed a solution that would successfully address the following three problems:

How to avoid duplication of equipment and resources
How to communicate efficiently
How to set up and manage a network

Businesses realized that computer networking could increase productivity and save money. Networks were added and expanded almost as rapidly as new network technologies and products were introduced. The early development of networking was disorganized. However, a tremendous expansion occurred in the early 1980s.

In the mid-1980s, the network technologies that emerged were created with a variety of hardware and software implementations. Each company that created network hardware and software used its own company standards. These individual standards were developed because of competition with other companies. As a result, many of the network technologies were incompatible with each other. It became increasingly difficult for networks that used different specifications to communicate with each other. Network equipment often had to be replaced to implement new technologies.

One early solution was the creation of local-area network (LAN) standards. LAN standards provided an open set of guidelines that companies used to create network hardware and software. As a result, the equipment from different companies became compatible. This allowed for stability in LAN implementations.

In a LAN system, each department of the company is a kind of electronic island. As the use of computers in businesses grew, LANs became insufficient.

A new technology was necessary to share information efficiently and quickly within a company and between businesses. The solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs). Because WANs could connect user networks over large geographic areas, it was possible for businesses to communicate with each other across great distances.

01-03-2006, 06:47 AM
Network history

This page presents a simplified view of how the Internet evolved.

The history of computer networking is complex. It has involved many people from all over the world over the past 35 years. Presented here is a simplified view of how the Internet evolved. The processes of invention and commercialization are far more complicated, but it is helpful to look at the fundamental development.

In the 1940s computers were large electromechanical devices that were prone to failure.
In 1947 the invention of a semiconductor transistor opened up many possibilities for making smaller, more reliable computers.
In the 1950s large institutions began to use mainframe computers, which were run by punched card programs.
In the late 1950s the integrated circuit that combined several, and now millions, of transistors on one small piece of semiconductor was invented.
In the 1960s mainframes with terminals and integrated circuits were widely used.

In the late 1960s and 1970s smaller computers called minicomputers were created. However, these minicomputers were still very large by modern standards.
In 1977 the Apple Computer Company introduced the microcomputer, which was also known as the Mac.
In 1981 IBM introduced its first PC. The user-friendly Mac, the open-architecture IBM PC, and the further micro-miniaturization of integrated circuits led to widespread use of personal computers in homes and businesses.

In the mid-1980s PC users began to use modems to share files with other computers. This was referred to as point-to-point, or dial-up communication. This concept was expanded by the use of computers that were the central point of communication in a dial-up connection. These computers were called bulletin boards. Users would connect to the bulletin boards, leave and pick up messages, as well as upload and download files. The drawback to this type of system was that there was very little direct communication and then only with those who knew about the bulletin board. Another limitation was that the bulletin board computer required one modem per connection. If five people connected simultaneously it would require five modems connected to five separate phone lines. As the number of people who wanted to use the system grew, the system was not able to handle the demand. For example, imagine if 500 people wanted to connect at the same time.

From the 1960s to the 1990s the U.S. Department of Defense (DoD) developed large, reliable, wide-area networks (WANs) for military and scientific reasons. This technology was different from the point-to-point communication used in bulletin boards. It allowed multiple computers to be connected together through many different paths. The network itself would determine how to move data from one computer to another. One connection could be used to reach many computers at the same time. The WAN developed by the DoD eventually became the Internet.

01-03-2006, 07:18 AM
Networking devices

This page will introduce some important networking devices.

Equipment that connects directly to a network segment is referred to as a device. These devices are broken up into two classifications. The first classification is end-user devices. End-user devices include computers, printers, scanners, and other devices that provide services directly to the user. The second classification is network devices. Network devices include all the devices that connect the end-user devices together to allow them to communicate.

End-user devices that provide users with a connection to the network are also referred to as hosts. These devices allow users to share, create, and obtain information. The host devices can exist without a network, but without the network the host capabilities are greatly reduced. NICs are used to physically connect host devices to the network media. They use this connection to send e-mails, print reports, scan pictures, or access databases.

A NIC is a printed circuit board that fits into the expansion slot of a bus on a computer motherboard. It can also be a peripheral device. NICs are sometimes called network adapters. Laptop or notebook computer NICs are usually the size of a PCMCIA card. Each NIC is identified by a unique code called a Media Access Control (MAC) address. This address is used to control data communication for the host on the network. More about the MAC address will be covered later. As the name implies, the NIC controls host access to the network.

There are no standardized symbols for end-user devices in the networking industry. They appear similar to the real devices to allow for quick recognition.

Network devices are used to extend cable connections, concentrate connections, convert data formats, and manage data transfers. Examples of devices that perform these functions are repeaters, hubs, bridges, switches, and routers. All of the network devices mentioned here are covered in depth later in the course. For now, a brief overview of networking devices will be provided.

A repeater is a network device used to regenerate a signal. Repeaters regenerate analog or digital signals that are distorted by transmission loss due to attenuation. A repeater does not make intelligent decision concerning forwarding packets like a router.

Hubs concentrate connections. In other words, they take a group of hosts and allow the network to see them as a single unit. This is done passively, without any other effect on the data transmission. Active hubs concentrate hosts and also regenerate signals.

Bridges convert network data formats and perform basic data transmission management. Bridges provide connections between LANs. They also check data to determine if it should cross the bridge. This makes each part of the network more efficient.

Workgroup switches add more intelligence to data transfer management. They can determine if data should remain on a LAN and transfer data only to the connection that needs it. Another difference between a bridge and switch is that a switch does not convert data transmission formats.

Routers have all the capabilities listed above. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances. None of the other devices can provide this type of connection.

01-03-2006, 07:53 AM
Network topology

This page will introduce you to the most common physical and logical network topologies.

Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the hosts access the media to send data.
The physical topologies that are commonly used are as follows:


A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone.
A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable.
A star topology connects all cables to a central point.
An extended star topology links individual stars together by connecting the hubs or switches.
A hierarchical topology is similar to an extended star. However, instead of linking the hubs or switches together, the system is linked to a computer that controls the traffic on the topology.
A mesh topology is implemented to provide as much protection as possible from interruption of service. For example, a nuclear power plant might use a mesh topology in the networked control systems. As seen in the graphic, each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.

The logical topology of a network determines how the hosts communicate across the medium.
The two most common types of logical topologies are broadcast and token passing.

The use of a broadcast topology indicates that each host sends its data to all other hosts on the network medium. There is no order that the stations must follow to use the network. It is first come, first serve. Ethernet works this way as will be explained later in the course.

The second logical topology is token passing. In this type of topology, an electronic token is passed sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI). A variation of Token Ring and FDDI is Arcnet. Arcnet is token passing on a bus topology.


The diagram in Figure shows many different topologies connected by network devices. It shows a network of moderate complexity that is typical of a school or a small business. The diagram includes many symbols and networking concepts that will take time to learn.

01-03-2006, 08:10 AM
Network protocols

This page will explain what network protocols are and why they are important.

Protocol suites are collections of protocols that enable network communication between hosts. A protocol is a formal de******ion of a set of rules and conventions that govern a particular aspect of how devices on a network communicate. Protocols determine the format, timing, sequencing, and error control in data communication. Without protocols, the computer cannot make or rebuild the stream of incoming bits from another computer into the original format.

Protocols control all aspects of data communication, which include the following:

How the physical network is built
How computers connect to the network
How the data is formatted for transmission
How that data is sent
How to deal with errors

These network rules are created and maintained by many different organizations and committees. Included in these groups are the Institute of Electrical and Electronic Engineers (IEEE), American National Standards Institute (ANSI), Telecommunications Industry Association (TIA), Electronic Industries Alliance (EIA) and the International Telecommunications Union (ITU), formerly known as the Comité Consultatif International Téléphonique et Télégraphique (CCITT).

01-03-2006, 08:18 AM
Local-area networks (LANs)

This page will explain the features and benefits of LANs.

LANs consist of the following components:

Network interface cards
Peripheral devices
Networking media
Network devices

LANs allow businesses to locally share computer files and printers efficiently and make internal communications possible. A good example of this technology is e-mail. LANs manage data, local communications, and computing equipment.

Some common LAN technologies include the following:

Token Ring

01-03-2006, 09:24 AM
بجد يا innerpeace456
معلومات جامدة

04-03-2006, 06:31 AM
كويس يااسمايل ان الموضوع عجبك .. تابع بقى الباقى

Wide-area networks (WANs)

This page will explain the functions of a WAN.

WANs interconnect LANs, which then provide access to computers or file servers in other locations. Because WANs connect user networks over a large geographical area, they make it possible for businesses to communicate across great distances. WANs allow computers, printers, and other devices on a LAN to be shared with distant locations. WANs provide instant communications across large geographic areas.

Collaboration software provides access to real-time information and resources and allows meetings to be held remotely. WANs have created a new class of workers called telecommuters. These people never have to leave their homes to go to work.

WANs are designed to do the following:

Operate over a large and geographically separated area
Allow users to have real-time communication capabilities with other users
Provide full-time remote resources connected to local services
Provide e-mail, Internet, file transfer, and e-commerce services

Some common WAN technologies include the following:

Integrated Services Digital Network (ISDN)
Digital subscriber line (DSL)
Frame Relay
T1, E1, T3, and E3
Synchronous Optical Network (SONET)

04-03-2006, 06:36 AM
Metropolitan-area networks (MANs)

This page will explain how MANs are used.

Wireless bridge technologies that send signals across public areas can also be used to create a MAN. A MAN usually consists of two or more LANs in a common geographic area. For example, a bank with multiple branches may utilize a MAN. Typically, a service provider is used to connect two or more LAN sites using private communication lines or optical services. A MAN can also be created using wireless bridge technology by beaming signals across public areas.

04-03-2006, 06:48 AM
Storage-area networks (SANs)

This page will discuss the features of SANs.

A storage-area network (SAN) is a dedicated, high-performance network used to move data between servers and storage resources. Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers.

SAN technology allows high-speed server-to-storage, storage-to-storage, or server-to-server connectivity. This method uses a separate network infrastructure that relieves any problems associated with existing network connectivity.

SANs offer the following features:

Performance – SANs allow concurrent access of disk or tape arrays by two or more servers at high speeds. This provides enhanced system performance.
Availability – SANs have built-in disaster tolerance. Data can be duplicated on a SAN up to 10 km (6.2 miles) away.
Scalability – A SAN can use a variety of technologies. This allows easy relocation of backup data, operations, file migration, and data replication between systems.

04-03-2006, 06:55 AM
Virtual private network (VPN)

This page will explain what a VPN is and how it is used.

A vitual private network (VPN) is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can remotely access the network of the company headquarters.


Through the Internet, a secure tunnel can be built between the PC of the telecommuter and a VPN router at the company headquarters.

04-03-2006, 07:04 AM
Benefits of VPNs

This page will introduce the three main types of VPNs and explain how they work.

A VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure such as the Internet. VPNs maintain the same security and management policies as a private network. The use of a VPN is the most cost-effective way to establish a point-to-point connection between remote users and an enterprise network.

The following are the three main types of VPNs:

Access VPNs provide remote access for mobile and small office, home office (SOHO) users to an Intranet or Extranet over a shared infrastructure. Access VPNs use analog, dialup, ISDN, DSL, mobile IP, and cable technologies to securely connect mobile users, telecommuters, and branch offices.

Intranet VPNs use dedicated connections to link regional and remote offices to an internal network over a shared infrastructure. Intranet VPNs differ from Extranet VPNs in that they allow access only to the employees of the enterprise.

Extranet VPNs use dedicated connections to link business partners to an internal network over a shared infrastructure. Extranet VPNs differ from Intranet VPNs in that they allow access to users outside the enterprise.

04-03-2006, 07:12 AM
Intranets and extranets

This page will teach you about intranets and extranets.

One common configuration of a LAN is an intranet. Intranet Web servers differ from public Web servers in that the public must have the proper permissions and passwords to access the intranet of an organization. Intranets are designed to permit users who have access privileges to the internal LAN of the organization. Within an intranet, Web servers are installed in the network. Browser technology is used as the common front end to access information on servers such as financial, graphical, or text-based data.

Extranets refer to applications and services that are Intranet based, and use extended, secure access to external users or enterprises. This access is usually accomplished through passwords, user IDs, and other application-level security. An extranet is the extension of two or more intranet strategies with a secure interaction between participant enterprises and their respective intranets.

04-03-2006, 07:28 AM

Importance of bandwidth

This page will describe the four most important characteristics of bandwidth.

Bandwidth is defined as the amount of information that can flow through a network connection in a given period of time. It is important to understand the concept of bandwidth for the following reasons.


Bandwidth is finite. Regardless of the media used to build a network, there are limits on the network capacity to carry information. Bandwidth is limited by the laws of physics and by the technologies used to place information on the media. For example, the bandwidth of a conventional modem is limited to about 56 kbps by both the physical properties of twisted-pair phone wires and by modem technology. DSL uses the same twisted-pair phone wires. However, DSL provides much more bandwidth than conventional modems. So, even the limits imposed by the laws of physics are sometimes difficult to define. Optical fiber has the physical potential to provide virtually limitless bandwidth. Even so, the bandwidth of optical fiber cannot be fully realized until technologies are developed to take full advantage of its potential.

Bandwidth is not free. It is possible to buy equipment for a LAN that will provide nearly unlimited bandwidth over a long period of time. For WAN connections, it is usually necessary to buy bandwidth from a service provider. In either case, individual users and businesses can save a lot of money if they understand bandwidth and how the demand will change over time. A network manager needs to make the right decisions about the kinds of equipment and services to buy.

Bandwidth is an important factor that is used to analyze network performance, design new networks, and understand the Internet. A networking professional must understand the tremendous impact of bandwidth and throughput on network performance and design. Information flows as a string of bits from computer to computer throughout the world. These bits represent massive amounts of information flowing back and forth across the globe in seconds or less.

The demand for bandwidth continues to grow. As soon as new network technologies and infrastructures are built to provide greater bandwidth, new applications are created to take advantage of the greater capacity. The delivery of rich media content such as streaming video and audio over a network requires tremendous amounts of bandwidth. IP telephony systems are now commonly installed in place of traditional voice systems, which further adds to the need for bandwidth. The successful networking professional must anticipate the need for increased bandwidth and act accordingly.

04-03-2006, 07:45 AM
The desktop

This page will present two analogies that may make it easier to visualize bandwidth in a network.

Bandwidth has been defined as the amount of information that can flow through a network in a given time. The idea that information flows suggests two analogies that may make it easier to visualize bandwidth in a network.

Bandwidth is like the width of a pipe. A network of pipes brings fresh water to homes and businesses and carries waste water away. This water network is made up of pipes of different diameters. The main water pipes of a city may be 2 meters in diameter, while the pipe to a kitchen faucet may have a diameter of only 2 cm. The width of the pipe determines the water-carrying capacity of the pipe. Therefore, the water is like the data, and the pipe width is like the bandwidth. Many networking experts say that they need to put in bigger pipes when they wish to add more information-carrying capacity.

Bandwidth is like the number of lanes on a highway. A network of roads serves every city or town. Large highways with many traffic lanes are joined by smaller roads with fewer traffic lanes. These roads lead to narrower roads that lead to the driveways of homes and businesses. When very few automobiles use the highway system, each vehicle is able to move freely. When more traffic is added, each vehicle moves more slowly. This is especially true on roads with fewer lanes. As more traffic enters the highway system, even multi-lane highways become congested and slow. A data network is much like the highway system. The data packets are comparable to automobiles, and the bandwidth is comparable to the number of lanes on the highway. When a data network is viewed as a system of highways, it is easy to see how low bandwidth connections can cause traffic to become congested all over the network.

04-03-2006, 07:50 AM

This page will explain how bandwidth is measured.

In digital systems, the basic unit of bandwidth is bits per second (bps). Bandwidth is the measure of how many bits of information can flow from one place to another in a given amount of time. Although bandwidth can be described in bps, a larger unit of measurement is generally used. Network bandwidth is typically described as thousands of bits per second (kbps), millions of bits per second (Mbps), billions of bits per second (Gbps), and trillions of bits per second (Tbps). Although the terms bandwidth and speed are often used interchangeably, they are not exactly the same thing. One may say, for example, that a T3 connection at 45 Mbps operates at a higher speed than a T1 connection at 1.544 Mbps. However, if only a small amount of their data-carrying capacity is being used, each of these connection types will carry data at roughly the same speed. For example, a small amount of water will flow at the same rate through a small pipe as through a large pipe. Therefore, it is usually more accurate to say that a T3 connection has greater bandwidth than a T1 connection. This is because the T3 connection is able to carry more information in the same period of time, not because it has a higher speed.

04-03-2006, 07:55 AM

This page describes the limitations of bandwidth.

Bandwidth varies depending upon the type of media as well as the LAN and WAN technologies used. The physics of the media account for some of the difference. Signals travel through twisted-pair copper wire, coaxial cable, optical fiber, and air. The physical differences in the ways signals travel result in fundamental limitations on the information-carrying capacity of a given medium. However, the actual bandwidth of a network is determined by a combination of the physical media and the technologies chosen for signaling and detecting network signals.

For example, current information about the physics of unshielded twisted-pair (UTP) copper cable puts the theoretical bandwidth limit at over 1 Gbps. However, in actual practice, the bandwidth is determined by the use of 10BASE-T, 100BASE-TX, or 1000BASE-TX Ethernet. The actual bandwidth is determined by the signaling methods, NICs, and other network equipment that is chosen. Therefore, the bandwidth is not determined solely by the limitations of the medium.

04-03-2006, 08:01 AM

This page explains the concept of throughput.

Bandwidth is the measure of the amount of information that can move through the network in a given period of time. Therefore, the amount of available bandwidth is a critical part of the specification of the network. A typical LAN might be built to provide 100 Mbps to every desktop workstation, but this does not mean that each user is actually able to move 100 megabits of data through the network for every second of use. This would be true only under the most ideal circumstances.

Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network. Unfortunately, for many reasons, throughput is often far less than the maximum possible digital bandwidth of the medium that is being used. The following are some of the factors that determine throughput:

Internetworking devices
Type of data being transferred
Network topology
Number of users on the network
User computer
Server computer
Power conditions

The theoretical bandwidth of a network is an important consideration in network design, because the network bandwidth will never be greater than the limits imposed by the chosen media and networking technologies. However, it is just as important for a network designer and administrator to consider the factors that may affect actual throughput. By measuring throughput on a regular basis, a network administrator will be aware of changes in network performance and changes in the needs of network users. The network can then be adjusted accordingly.

04-03-2006, 08:16 AM
Data transfer calculation

This page provides the formula for data transfer calculation.

Network designers and administrators are often called upon to make decisions regarding bandwidth. One decision might be whether to increase the size of the WAN connection to accommodate a new database. Another decision might be whether the current LAN backbone is of sufficient bandwidth for a streaming-video training program. The answers to problems like these are not always easy to find, but one place to start is with a simple data transfer calculation.

Using the formula transfer time = size of file / bandwidth (T=S/BW) allows a network administrator to estimate several of the important components of network performance. If the typical file size for a given application is known, dividing the file size by the network bandwidth yields an estimate of the fastest time that the file can be transferred.

Two important points should be considered when doing this calculation.

The result is an estimate only, because the file size does not include any overhead added by encapsulation.
The result is likely to be a best-case transfer time, because available bandwidth is almost never at the theoretical maximum for the network type. A more accurate estimate can be attained if throughput is substituted for bandwidth in the equation.

Although the data transfer calculation is quite simple, one must be careful to use the same units throughout the equation. In other words, if the bandwidth is measured in megabits per second (Mbps), the file size must be in megabits (Mb), not megabytes (MB). Since file sizes are typically given in megabytes, it may be necessary to multiply the number of megabytes by eight to convert to megabits.

04-03-2006, 08:30 AM
Digital versus analog

This page will explain the differences between analog and digital signals.

Radio, television, and telephone transmissions have, until recently, been sent through the air and over wires using electromagnetic waves. These waves are called analog because they have the same shapes as the light and sound waves produced by the transmitters. As light and sound waves change size and shape, the electrical signal that carries the transmission changes proportionately. In other words, the electromagnetic waves are analogous to the light and sound waves.

Analog bandwidth is measured by how much of the electromagnetic spectrum is occupied by each signal. The basic unit of analog bandwidth is hertz (Hz), or cycles per second. Typically, multiples of this basic unit of analog bandwidth are used, just as with digital bandwidth. Units of measurement that are commonly seen are kilohertz (KHz), megahertz (MHz), and gigahertz (GHz). These are the units used to describe the frequency of cordless telephones, which usually operate at either 900 MHz or 2.4 GHz. These are also the units used to describe the frequencies of 802.11a and 802.11b wireless networks, which operate at 5 GHz and 2.4 GHz.

While analog signals are capable of carrying a variety of information, they have some significant disadvantages in comparison to digital transmissions. The analog video signal that requires a wide frequency range for transmission cannot be squeezed into a smaller band. Therefore, if the necessary analog bandwidth is not available, the signal cannot be sent.

In digital signaling all information is sent as bits, regardless of the kind of information it is. Voice, video, and data all become streams of bits when they are prepared for transmission over digital media. This type of transmission gives digital bandwidth an important advantage over analog bandwidth. Unlimited amounts of information can be sent over the smallest or lowest bandwidth digital channel. Regardless of how long it takes for the digital information to arrive at its destination and be reassembled, it can be viewed, listened to, read, or processed in its original form.

It is important to understand the differences and similarities between digital and analog bandwidth. Both types of bandwidth are regularly encountered in the field of information technology. However, because this course is concerned primarily with digital networking, the term ‘bandwidth’ will refer to digital bandwidth.

05-03-2006, 04:31 AM
Networking Models
Using layers to analyze problems in a flow of materials

This page explains how layers are used to describe communications between computers.

The concept of layers is used to describe communication from one computer to another.
Figure shows a set of questions that are related to flow, which is defined as the motion through a system of either physical or logical objects. These questions show how the concept of layers helps describe the details of the flow process. This process could be any kind of flow, from the flow of traffic on a highway system to the flow of data through a network.
Figure shows several examples of flow and ways that the flow process can be broken down into details or layers.

A conversation between two people provides a good opportunity to use a layered approach to analyze information flow. In a conversation, each person wishing to communicate begins by creating an idea. Then a decision is made on how to properly communicate the idea. For example, a person could decide to speak, sing or shout, and what language to use. Finally the idea is delivered. For example, the person creates the sound which carries the message.

This process can be broken into separate layers that may be applied to all conversations. The top layer is the idea that will be communicated. The middle layer is the decision on how the idea is to be communicated. The bottom layer is the creation of sound to carry the communication.

The same method of layering explains how a computer network distributes information from a source to a destination. When computers send information through a network, all communications originate at a source then travel to a destination.

The information that travels on a network is generally referred to as data or a packet. A packet is a logically grouped unit of information that moves between computer systems. As the data passes between layers, each layer adds additional information that enables effective communication with the corresponding layer on the other computer.

The OSI and TCP/IP models have layers that explain how data is communicated from one computer to another. The models differ in the number and function of the layers. However, each model can be used to help describe and provide details about the flow of information from a source to a destination.

05-03-2006, 04:38 AM
Using layers to describe data communication

This page describes the importance of layers in data communication.

In order for data packets to travel from a source to a destination on a network, it is important that all the devices on the network speak the same language or protocol. A protocol is a set of rules that make communication on a network more efficient. For example, while flying an airplane, pilots obey very specific rules for communication with other airplanes and with air traffic control.

A data communications protocol is a set of rules or an agreement that determines the format and transmission of data.

Layer 4 on the source computer communicates with Layer 4 on the destination computer. The rules and conventions used for this layer are known as Layer 4 protocols. It is important to remember that protocols prepare data in a linear fashion. A protocol in one layer performs a certain set of operations on data as it prepares the data to be sent over the network. The data is then passed to the next layer where another protocol performs a different set of operations.

Once the packet has been sent to the destination, the protocols undo the construction of the packet that was done on the source side. This is done in reverse order. The protocols for each layer on the destination return the information to its original form, so the application can properly read the data.

05-03-2006, 04:47 AM
OSI model

This page discusses how and why the OSI model was developed.

The early development of networks was disorganized in many ways. The early 1980s saw tremendous increases in the number and size of networks. As companies realized the advantages of using networking technology, networks were added or expanded almost as rapidly as new network technologies were introduced.

By the mid-1980s, these companies began to experience problems from the rapid expansion. Just as people who do not speak the same language have difficulty communicating with each other, it was difficult for networks that used different specifications and implementations to exchange information. The same problem occurred with the companies that developed private or proprietary networking technologies. Proprietary means that one or a small group of companies controls all usage of the technology. Networking technologies strictly following proprietary rules could not communicate with technologies that followed different proprietary rules.

To address the problem of network incompatibility, the International Organization for Standardization (ISO) researched networking models like Digital Equipment Corporation net (DECnet), Systems Network Architecture (SNA), and TCP/IP in order to find a generally applicable set of rules for all networks. Using this research, the ISO created a network model that helps vendors create networks that are compatible with other networks.

The Open System Interconnection (OSI) reference model released in 1984 was the de******ive network model that the ISO created. It provided vendors with a set of standards that ensured greater compatibility and interoperability among various network technologies produced by companies around the world.

The OSI reference model has become the primary model for network communications. Although there are other models in existence, most network vendors relate their products to the OSI reference model. This is especially true when they want to educate users on the use of their products. It is considered the best tool available for teaching people about sending and receiving data on a network.

05-03-2006, 05:17 AM
OSI layers

This page discusses the seven layers of the OSI model.

The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media.

In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function.
Dividing the network into seven layers provides the following advantages:

It breaks network communication into smaller, more manageable parts.
It standardizes network components to allow multiple vendor development and support.
It allows different types of network hardware and software to communicate with each other.
It prevents changes in one layer from affecting other layers.
It divides network communication into smaller parts to make learning it easier to understand.

05-03-2006, 05:33 AM
Peer-to-peer communications

This page explains the concept of peer-to-peer communications.

In order for data to 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. During this process, the protocols of each layer exchange information, called protocol data units (PDUs). Each layer of communication on the source computer communicates with a layer-specific PDU, and with its peer layer on the destination computer .

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. Then it adds whatever headers and trailers the layer needs to perform its function. Next, as the data moves down through the layers of the OSI model, additional headers and trailers are added. After Layers 7, 6, and 5 have added their information, Layer 4 adds more information. This grouping of data, 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 has the task of moving the data through the internetwork. It accomplishes this task by encapsulating the data and attaching a header creating 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. It encapsulates the network layer information in a frame (the Layer 2 PDU). The frame header contains information (for example, physical addresses) required to complete the data link functions. The data link layer provides a service to the network layer by encapsulating the network layer information in a frame.

The physical layer also provides a service to the data link layer. The physical layer encodes the data link frame into a pattern of 1s and 0s (bits) for transmission on the medium (usually a wire) at Layer 1.

05-03-2006, 11:08 AM
TCP/IP model

This page discusses the TCP/IP reference model, which is the historical and technical standard of the Internet.

The U.S. Department of Defense (DoD) created the TCP/IP reference model, because it wanted to design a network that could survive any conditions, including a nuclear war. In a world connected by different types of communication media such as copper wires, microwaves, optical fibers and satellite links, the DoD wanted transmission of packets every time and under any conditions. This very difficult design problem brought about the creation of the TCP/IP model.

Unlike the proprietary networking technologies mentioned earlier, TCP/IP was developed as an open standard. This meant that anyone was free to use TCP/IP. This helped speed up the development of TCP/IP as a standard.

The TCP/IP model has the following four layers:

Application layer
Transport layer
Internet layer
Network access layer

Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly. Most notably, the application layer has different functions in each model.

The designers of TCP/IP felt that the application layer should include the OSI session and presentation layer details. They created an application layer that handles issues of representation, encoding, and dialog control.

The transport layer deals with the quality of service issues of reliability, flow control, and error correction. One of its protocols, the transmission control protocol (TCP), provides excellent and flexible ways to create reliable, well-flowing, low-error network communications.

TCP is a connection-oriented protocol. It maintains a dialogue between source and destination while packaging application layer information into units called segments. Connection-oriented does not mean that a circuit exists between the communicating computers. It does mean that Layer 4 segments travel back and forth between two hosts to acknowledge the connection exists logically for some period.

The purpose of the Internet layer is to divide TCP segments into packets and send them from any network. The packets arrive at the destination network independent of the path they took to get there. The specific protocol that governs this layer is called the Internet Protocol (IP). Best path determination and packet switching occur at this layer.

The relationship between IP and TCP is an important one. IP can be thought to point the way for the packets, while TCP provides a reliable transport.

The name of the network access layer is very broad and somewhat confusing. It is also known as the host-to-network layer. This layer is concerned with all of the components, both physical and logical, that are required to make a physical link. It includes the networking technology details, including all the details in the OSI physical and data link layers.

Figure illustrates some of the common protocols specified by the TCP/IP reference model layers. Some of the most commonly used application layer protocols include the following:

File Transfer Protocol (FTP)
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Domain Name System (DNS)
Trivial File Transfer Protocol (TFTP)

The common transport layer protocols include:

Transport Control Protocol (TCP)
User Datagram Protocol (UDP)

The primary protocol of the Internet layer is:

Internet Protocol (IP)

The network access layer refers to any particular technology used on a specific network.

Regardless of which network application services are provided and which transport protocol is used, there is only one Internet protocol, IP. This is a deliberate design decision. IP serves as a universal protocol that allows any computer anywhere to communicate at any time.

A comparison of the OSI model and the TCP/IP model will point out some similarities and differences.

Similarities include:

Both have layers.
Both have application layers, though they include very different services.
Both have comparable transport and network layers.
Both models need to be known by networking professionals.
Both assume packets are switched. This means that individual packets may take different paths to reach the same destination. This is contrasted with circuit-switched networks where all the packets take the same path.

Differences include:

TCP/IP combines the presentation and session layer issues into its application layer.
TCP/IP combines the OSI data link and physical layers into the network access layer.
TCP/IP appears simpler because it has fewer layers.
TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP model gains credibility just because of its protocols. In contrast, networks are not usually built on the OSI protocol, even though the OSI model is used as a guide.

Although TCP/IP protocols are the standards with which the Internet has grown, this curriculum will use the OSI model for the following reasons:

It is a generic, protocol-independent standard.
It has more details, which make it more helpful for teaching and learning.
It has more details, which can be helpful when troubleshooting.

Networking professionals differ in their opinions on which model to use. Due to the nature of the industry it is necessary to become familiar with both. Both the OSI and TCP/IP models will be referred to throughout the curriculum. The focus will be on the following:

TCP as an OSI Layer 4 protocol
IP as an OSI Layer 3 protocol
Ethernet as a Layer 2 and Layer 1 technology

Remember that there is a difference between a model and an actual protocol that is used in networking. The OSI model will be used to describe TCP/IP protocols.

05-03-2006, 11:29 AM
Detailed encapsulation process

This page describes the process of encapsulation.

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 through a process called encapsulation.

Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the data packet moves down through the layers of the OSI model, it receives headers, trailers, and other information.

To see how encapsulation occurs, examine the manner in which data travels through the layers as illustrated in Figure . Once the data is sent from the source, it travels through the application layer down through the other layers. The packaging and flow of the data that is exchanged goes through changes as the layers perform their services for end users.
As illustrated in Figure , networks must perform the following five conversion steps in order to encapsulate data:

Build the data – As a user sends an e-mail message, its alphanumeric characters are converted to data that can travel across the internetwork.
Package the data for end-to-end transport – The data is packaged for internetwork transport. By using segments, the transport function ensures that the message hosts at both ends of the e-mail system can reliably communicate.
Add the network IP address to the header – The data is put into a packet or datagram that contains a packet header with source and destination logical addresses. These addresses help network devices send the packets across the network along a chosen path.
Add the data link layer header and trailer – Each network device must put the packet into a frame. The frame allows connection to the next directly-connected network device on the link. Each device in the chosen network path requires framing in order for it to connect to the next device.
Convert to bits for transmission – The frame must be converted into a pattern of 1s and 0s (bits) for transmission on the medium. A clocking function enables the devices to distinguish these bits as they travel across the medium. The medium on the physical internetwork can vary along the path used. For example, the e-mail message can originate on a LAN, cross a campus backbone, and go out a WAN link until it reaches its destination on another remote LAN.

05-03-2006, 11:35 AM
لا بقى دى كورس مكثف ولازم اثيته

05-03-2006, 11:36 AM

This page summarizes the topics discussed in this module.

Computer networks developed in response to business and government computing needs. Applying standards to network functions provided a set of guidelines for creating network hardware and software and provided compatibility among equipment from different companies. Information could move within a company and from one business to another.

Network devices, such as repeaters, hubs, bridges, switches and routers connect host devices together to allow them to communicate. Protocols provide a set of rules for communication.

The physical topology of a network is the actual layout of the wire or media. The logical topology defines how host devices access the media. The physical topologies that are commonly used are bus, ring, star, extended star, hierarchical, and mesh. The two most common types of logical topologies are broadcast and token passing.

A local-area network (LAN) is designed to operate within a limited geographical area. LANs allow multi-access to high-bandwidth media, control the network privately under local administration, provide full-time connectivity to local services and connect physically adjacent devices.

A wide-area network (WAN) is designed to operate over a large geographical area. WANs allow access over serial interfaces operating at lower speeds, provide full-time and part-time connectivity and connect devices separated over wide areas.

A metropolitan-area network (MAN) is a network that spans a metropolitan area such as a city or suburban area. A MAN usually consists of two or more LANs in a common geographic area.

A storage-area network (SAN) is a dedicated, high-performance network used to move data between servers and storage resources. A SAN provides enhanced system performance, is scalable, and has disaster tolerance built in.

A virtual private network (VPN) is a private network that is constructed within a public network infrastructure. Three main types of VPNs are access, Intranet, and Extranet VPNs. Access VPNs provide mobile workers or small office/home office (SOHO) users with remote access to an Intranet or Extranet. Intranets are only available to users who have access privileges to the internal network of an organization. Extranets are designed to deliver applications and services that are Intranet based to external users or enterprises.

The amount of information that can flow through a network connection in a given period of time is referred to as bandwidth. Network bandwidth is typically measured in thousands of bits per second (kbps), millions of bits per second (Mbps), billions of bits per second (Gbps) and trillions of bits per second (Tbps). The theoretical bandwidth of a network is an important consideration in network design. If the theoretical bandwidth of a network connection is known, the formula T=S/BW (transfer time = size of file / bandwidth) can be used to calculate potential data transfer time. However the actual bandwidth, referred to as throughput, is affected by multiple factors such as network devices and topology being used, type of data, number of users, hardware and power conditions.

Data can be encoded on analog or digital signals. Analog bandwidth is a measure of how much of the electromagnetic spectrum is occupied by each signal. For instance an analog video signal that requires a wide frequency range for transmission cannot be squeezed into a smaller band. If the necessary analog bandwidth is not available the signal cannot be sent. In digital signaling all information is sent as bits, regardless of the kind of information it is. Unlimited amounts of information can be sent over the smallest digital bandwidth channel.

The concept of layers is used to describe communication from one computer to another. Dividing the network into layers provides the following advantages:

Reduces complexity
Standardizes interfaces
Facilitates modular engineering
Ensures interoperability
Accelerates evolution
Simplifies teaching and learning

Two such layered models are the Open System Interconnection (OSI) and the TCP/IP networking models. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function: application, presentation, session, transport, network, data link, and physical. The TCP/IP model has the following four layers: application, transport, Internet, and network access.

Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly. The TCP/IP application layer is equivalent to the OSI application, presentation, and session layers. The TCP/IP model combines the OSI data link and physical layers into the network access layer.

No matter which model is applied, networks layers perform the following five conversion steps in order to encapsulate and transmit data:

Images and text are converted to data.
The data is packaged into segments.
The data segment is encapsulated in a packet with the source and destination addresses.
The packet is encapsulated in a frame with the MAC address of the next directly connected device.
The frame is converted to a pattern of ones and zeros (bits) for transmission on the media.

05-03-2006, 12:00 PM
لا بقى دى كورس مكثف ولازم اثيته
فعلا يااسمايل هو كورس مكثف وهاتلاقى الديمو بتاعه هنا (http://www.cisco.com/web/learning/netacad/course_catalog/CCNA.html)

30-03-2006, 12:49 PM

Copper cable is used in almost every LAN. Many different types of copper cable are available. Each type has advantages and disadvantages. Proper selection of cabling is key to efficient network operation. Since copper uses electrical currents to transmit information, it is important to understand some basics of electricity.

Optical fiber is the most frequently used medium for the longer, high bandwidth, point-to-point transmissions required on LAN backbones and on WANs. Optical media uses light to transmit data through thin glass or plastic fiber. Electrical signals cause a fiber-optic transmitter to generate the light signals sent down the fiber. The receiving host receives the light signals and converts them to electrical signals at the far end of the fiber. However, there is no electricity in the fiber-optic cable. In fact, the glass used in fiber-optic cable is a very good electrical insulator.

Physical connectivity allows users to share printers, servers, and software, which can increase productivity. Traditional networked systems require the workstations to remain stationary and permit moves only within the limits of the media and office area.

The introduction of wireless technology removes these restraints and brings true portability to computer networks. Currently, wireless technology does not provide the high-speed transfers, security, or uptime reliability of cabled networks. However, flexibility of wireless has justified the trade off.

Administrators often consider wireless when they install or upgrade a network. A simple wireless network could be working just a few minutes after the workstations are turned on. Connectivity to the Internet is provided through a wired connection, router, cable, or DSL modem and a wireless access point that acts as a hub for the wireless nodes. In a residential or small office environment these devices may be combined into a single unit.

Who complete this module should be able to perform the following tasks:

Discuss the electrical properties of matter
Define voltage, resistance, impedance, current, and circuits
Describe the specifications and performances of different types of cable
Describe coaxial cable and its advantages and disadvantages compared to other types of cable
Describe STP cable and its uses
Describe UTP cable and its uses
Discuss the characteristics of straight-through, crossover, and rollover cables and where each is used
Explain the basics of fiber-optic cable
Describe how fiber-optic cables can carry light signals over long distances
Describe multimode and single-mode fiber
Describe how fiber is installed
Describe the type of connectors and equipment used with fiber-optic cable
Explain how fiber is tested to ensure that it will function properly
Discuss safety issues related to fiber optics

03-04-2006, 10:35 AM
اخى الحبيب innerpeace456 شكرا شكرا على موضوعك
انا عاوزا اقولك انى نقلت الموضوع على الجهاز بعد ما قراته سريعا تمهيدا لقرآته بتدقيق
و عاوز اقول ان المعلومات دى اهم من البرامج الجاهزه مائة مرة
فلا تبخل علينا بالمعلومات فى اى مواضيع اخرى و مرحبا بمشاركاتك القيمة فى المنتدى

09-04-2006, 05:38 PM
اخى الحبيب innerpeace456 شكرا شكرا على موضوعك
انا عاوزا اقولك انى نقلت الموضوع على الجهاز بعد ما قراته سريعا تمهيدا لقرآته بتدقيق
و عاوز اقول ان المعلومات دى اهم من البرامج الجاهزه مائة مرة
فلا تبخل علينا بالمعلومات فى اى مواضيع اخرى و مرحبا بمشاركاتك القيمة فى المنتدى

العفو يا constantin
الكورس مفيد جدا وحبيت انقله هنا للافادة ... بس الواضح انه محتاج متخصصين فى الشبكات علشان يفهموه
ربنا يسهل واكملكم الباقى بس الاقى موقع اقدر ارفع عليه فلاشات .. والاقى وقت (sml16)