CCNA :) Be a Good Network Administrator

Summary 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 geog...

Detailed encapsulation process 2.3.7 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 F...

OSI layers 2.3.4 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. In the foll...

Using layers to describe data communication 2.3.2 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. ...

Digital versus analog This page will explain the differences between analog and digital signals. 2.2.7 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 th...

Throughput 2.2.5 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 ...

Importance of bandwidth 2.2.1 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 techno...

Virtual private network (VPN) 2.1.10 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. The next page will explain the benefits of VPNs.   Benefits of VPNs 2.1.11 This page will introduce the three main types of VPNs and explain how they work. Cisco products support the latest in VPN technology. 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...

Network protocols 2.1.5 Protocol suites are collections of protocols that enable network communication between hosts. A protocol is a formal description 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 I...

Network protocols 2.1.5 Protocol suites are collections of protocols that enable network communication between hosts. A protocol is a formal description 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 I...

Network history 2.1.2 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 smalle...

Networking Terminology Data Network 2.1.1 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 introduc...

Overview Bandwidth decisions are among the most important considerations when a network is designed. This module discusses the importance of bandwidth and explains how it is measured. Layered models are used to describe network functions. This module covers the two most important models, which are the Open System Interconnection (OSI) model and the Transmission Control Protocol/Internet Protocol (TCP/IP) model. The module also presents the differences and similarities between the two models. This module also includes a brief history of networking. Students will learn about network devices and different types of physical and logical layouts. This module also defines and compares LANs, MANs, WANs, SANs, and VPNs. Students who complete this module should be able to perform the following tasks: • Explain the importance of bandwidth in networking • Use an analogy to explain bandwidth • Identify bps, kbps, Mbps, and Gbps as units of bandwidth • Explain the difference between ba...

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Summary 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...

IP addresses and network masks 1.2.10 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 i...

Four-octet dotted decimal representation of 32-bit binary numbers 1.2.7 This 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 ...

Bits and Bytes 1.2.2. This 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. The next will describe the Base 10 number system. Base 10 number system 1.2.3 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. T...