Networking Basics

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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 200.114.6.51 to its 32-bit binary equivalent.

Convert 10000000 01011101 00001111 10101010 to its dotted decimal equivalent.

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Hexadecimal

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.

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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.

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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:

11111111000000000000000000000000
written in dotted decimal as 255.0.0.0

11111111111111110000000000000000
written in dotted decimal as 255.255.0.0

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 10.34.23.134
in binary form is 00001010.00100010.00010111.10000110.

A Boolean AND of the IP address 10.34.23.134 and the subnet mask 255.0.0.0 produces the network address of this host:

00001010.00100010.00010111.10000110
11111111.00000000.00000000.00000000
00001010.00000000.00000000.00000000

The dotted decimal conversion is 10.0.0.0 which is the network portion of the IP address when the 255.0.0.0 mask is used.

A Boolean AND of the IP address 10.34.23.134 and the subnet mask 255.255.0.0 produces the network address of this host:

00001010.00100010.00010111.10000110
11111111.11111111.00000000.00000000
00001010.00100010.00000000.00000000

The dotted decimal conversion is 10.34.0.0 which is the network portion of the IP address when the 255.255.0.0 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.

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Summary

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.

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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.

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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.

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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.

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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.

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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).

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Local-area networks (LANs)


This page will explain the features and benefits of LANs.

LANs consist of the following components:

Computers
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:

Ethernet
Token Ring
FDDI

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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:

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

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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.

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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.