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 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:
1. Images and text are converted to data.
2. The data is packaged into segments.
3. The data segment is encapsulated in a packet with the source and destination addresses.
4. The packet is encapsulated in a frame with the MAC address of the next directly connected device.
5. The frame is converted to a pattern of ones and zeros (bits) for transmission on the media.
Thursday, November 19, 2009
Detailed encapsulation process
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 Figure , networks must perform the following five conversion steps in order to encapsulate data:
1. Build the data – As a user sends an e-mail message, its alphanumeric characters are converted to data that can travel across the internet work.
2. Package the data for end-to-end transport – The data is packaged for internet work transport. By using segments, the transport function ensures that the message hosts at both ends of the e-mail system can reliably communicate.
3. 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.
4. 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.
5. 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 internet work 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.
The Lab Activity will provide an in depth review of the OSI model.
The Interactive Media Activity requires students to complete an encapsulation process flowchart.
This page concludes this lesson. The next page will summarize the main points from the module.
OSI layers / Peer-to-peer communications / TCP/IP model
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 following Interactive Media Activity, the student will identify the seven layers of the OSI model.
The next page discusses peer-to-peer communications through the OSI model.
2.3.5This 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 as illustrated in Figure .
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.
The next page describes the TCP/IP reference model.
2.3.6 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.
Students will identify the differences between the OSI model and the TCP/IP model in the Lab Activity.
In the Interactive Media Activity, students will identify the layers of the TCP/IP reference model.
The next page explains the encapsulation process.
Wednesday, November 18, 2009
Using layers / OSI model
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. 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.
The next page explains the OSI model.
2.3.3 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 descriptive 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.
In the Interactive Media Activity, students will identify the benefits of the OSI model.
The next page will describe the layers of the OSI model.
Digital versus analog / Using layers to analyze problems in a flow of materials
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 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.
This page concludes this lesson. The next lesson will discuss networking models. The first page will discuss the concept of layers.
2.3.1 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.
The next page will explain how layers are used to describe data communication.
Throughput / Data transfer calculation
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
• 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.
The next page explains data transfer calculation.
2.2.6 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.
Try to answer the following question, using the formula T=S/BW. Be sure to convert units of measurement as necessary.
Would it take less time to send the contents of a floppy disk full of data (1.44 MB) over an ISDN line, or to send the contents of a ten GB hard drive full of data over an OC-48 line?
The next page will compare analog and digital signals.
Importance of bandwidth / The Desktop / Measurement / Limitations
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 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.
The next page will describe some analogies that can be used to understand bandwidth.
This page will present two analogies that may make it easier to visualize bandwidth in a network.
The desktop
2.2.2 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.
This page will explain how bandwidth is measured.
Measurement
2.2.3 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.
The next page will discuss the limitations of bandwidth.
Limitations
2.2.4 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.
Figure shows some common networking media types along with their distance and bandwidth limitations.
Figure summarizes common WAN services and the bandwidth associated with each service.
The next page will discuss the concept of throughput.
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 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.
The next page will describe some analogies that can be used to understand bandwidth.
This page will present two analogies that may make it easier to visualize bandwidth in a network.The desktop
2.2.2 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.
This page will explain how bandwidth is measured.
Measurement
2.2.3 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.
The next page will discuss the limitations of bandwidth.
Limitations
2.2.4 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.
Figure shows some common networking media types along with their distance and bandwidth limitations.
Figure summarizes common WAN services and the bandwidth associated with each service.
The next page will discuss the concept of throughput.
VPN/Benefits of VPNs/ Intranet and Extranet
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 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.
The next page will introduce intranets and extranets.
This page will teach students about intranets and extranets.Intranets and extranets
2.1.12 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.
This page concludes this lesson. The next lesson will discuss bandwidth. The first page will explain why bandwidth is important.
Network protocols/ LAN / WAN /
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 Industry Association (TIA), Electronic Industries Alliance (EIA) and the International Telecommunications Union (ITU), formerly known as the Comité Consultatif International Téléphonique et Télégraphique (CCITT).
Local-area networks (LANs)
2.1.6 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
Wide-area networks (WANs)
2.1.7 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)
Metropolitan-area networks (MANs)
2.1.8 The next page will introduce metropolitan-area networks (MANs).
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.
Storage-area networks (SANs)
2.1.9 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.
The next page will introduce virtual private networks (VPNs).
Network protocols / Local-area networks (LANs)
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 Industry Association (TIA), Electronic Industries Alliance (EIA) and the International Telecommunications Union (ITU), formerly known as the Comité Consultatif International Téléphonique et Télégraphique (CCITT).
Local-area networks (LANs)
2.1.6 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
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)
The next page will introduce metropolitan-area networks (MANs).
Wednesday, November 11, 2009
Network history / Networking Devices / Network topology
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 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.
Networking devices
2.1.3 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. Network devices provide extension of cable connections, concentration of connections, conversion of data formats, and management of 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 or bridge.
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.
The Interactive Media Activities will allow students to become more familiar with network devices.
The next page will introduce some common types of network topologies.
Network topology
This page will introduce students to the most common physical and logical network topologies.
2.1.4 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.
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 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.
2.1.3 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. Network devices provide extension of cable connections, concentration of connections, conversion of data formats, and management of 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 or bridge.
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.
The Interactive Media Activities will allow students to become more familiar with network devices.
The next page will introduce some common types of network topologies.
This page will introduce students to the most common physical and logical network topologies.
2.1.4 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.
Networking Terminology (Data Network)
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 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. Figure summarizes the relative sizes of LANs and WANs.
Module 2: Networking Fundamentals (Overview)
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 bandwidth and throughput
• Calculate data transfer rates
• Explain why layered models are used to describe data communication
• Explain the development of the OSI model
• List the advantages of a layered approach
• Identify each of the seven layers of the OSI model
• Identify the four layers of the TCP/IP model
• Describe the similarities and differences between the two models
• Briefly outline the history of networking
• Identify devices used in networking
• Understand the role of protocols in networking
• Define LAN, WAN, MAN, and SAN
• Explain VPNs and their advantages
• Describe the differences between intranets and extranets
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 bandwidth and throughput
• Calculate data transfer rates
• Explain why layered models are used to describe data communication
• Explain the development of the OSI model
• List the advantages of a layered approach
• Identify each of the seven layers of the OSI model
• Identify the four layers of the TCP/IP model
• Describe the similarities and differences between the two models
• Briefly outline the history of networking
• Identify devices used in networking
• Understand the role of protocols in networking
• Define LAN, WAN, MAN, and SAN
• Explain VPNs and their advantages
• Describe the differences between intranets and extranets
Sunday, November 8, 2009
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These all materials which have published, this is about first chapter of CCNA first samester chapter. I will publish all material on this my web site. Please do study continue and get more knowledge. In future all person can get presentations related all topics, and keep send yous comments.
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Saturday, November 7, 2009
Summary of First chapter
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 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 ability 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 Cisco 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.
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 ability 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 Cisco 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.
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 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.
This page concludes this lesson. The next page will summarize the main points from the module.
Four-octet dotted decimal representation of 32-bit binary numbers / Hexadecial / Boolean or binary logic
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 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.
The next will introduce the hexadecimal number system.
1.2.8 This page will teach about the hexadecimal number system. Students 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 Cisco routers often requires hexadecimal to binary and binary to hexadecimal conversions. Cisco 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. This would require up to four decimal digits. The use of two decimal digits to represent four bits could cause confusion. For example, the eight bit binary number 01110011 would be 115 if converted to decimal digits. It is unclear if this is 11 and 5 or 1 and 15. If 11-5 is used, the binary number would be 1011 0101, which is not the number originally converted. The hexadecimal conversion is 1F, which always converts back to 00011111.
An eight-bit binary number can be converted to two hexadecimal digits. This 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.
To convert to binary, simply expand each hexadecimal digit into its four-bit binary equivalent.
The next page will discuss Boolean logic.
Boolean or binary logic
1.2.9 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. These functions will be explained in depth later in the curriculum.
The next page will explain how network masks are used.
Network Math (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.
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. 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 = (2x103) + (1x102) + (3x101) + (4x100)
This review of the decimal system will help students understand the Base 2 and Base 16 number systems. These systems use the same methods as the decimal system.
The next will describe the Base 2 number system.
Base 2 number system
1.2.4 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 24 = 16) + (0 x 23 = 0) + (1 x 22 = 4) + (1 x 21 = 2) + (0 x 20 = 0) = 22 (16 + 0 + 4 + 2 + 0)
This example shows that the binary number 10110 is equal to the decimal number 22.
The next will explain the conversion of decimal numbers to binary numbers.
Converting decimal numbers to 8-bit binary numbers
1.2.5 There are several ways to convert decimal numbers to binary numbers. The flowchart in Figure describes one method. This method is one of several methods that can be used. It is best to select one method and practice with it until it always produces the correct answer.
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.
The number converter activity in Figure will allow students to practice decimal to binary conversions.
In the Lab Activity, students will practice the conversion of decimal numbers to binary numbers.
The next page will discuss the conversion of binary numbers to decimal numbers.
Converting 8-bit binary numbers to decimal numbers
1.2.6 How to convert binary numbers to decimal numbers. There are two basic ways to convert binary numbers to decimal numbers. The flowchart in Figure shows one example. Students can also multiply each binary digit by the base number of 2 raised to the exponent of its position.
Here is an example:
Convert the binary number 01110000 to a decimal number.
Note:
Work from right to left. Remember that anything raised to the 0 power is 1.
0 x 20 = 0
0 x 21 = 0
0 x 22 = 0
0 x 23 = 0
1 x 24 = 16
1 x 25 = 32
1 x 26 = 64
0 x 27 = 0
__________
= 112
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