A computer network is simply two or more computers that are connected together via software and hardware so they can communicate. Devices connected to a network are referred to as nodes . A node can be a computer, a peripheral (such as a printer), or a communications device (such as a modem) The main function for most networks is to facilitate information sharing, but networks provide other benefits as well. -they allow users to share peripherals -you can transfer files from one computer to another without using external storage media If you install a device called a router to your network, you can share broadband Internet connections.
The term network architecture refers to the design of a network. Network architectures are classified according to the way in which they are controlled and the distance between their nodes. There are two main ways a network can be controlled: locally or centrally. A peer-to-peer network is the most common example of a locally controlled network. The most common type of centrally controlled network is a client/server network .
In peer-to-peer (P2P) networks , each node connected to the network can communicate directly with every other node on the network, instead of having a separate device exercise central control over the entire network. Thus, all nodes on this type of network are in a sense peers. When printing, for example, a computer on a P2P network doesn’t have to go through the computer that’s connected to the printer. Instead, it can communicate directly with the printer. Because they are simple to set up, P2P networks are the most common type of home network.
Most networks that have 10 or more nodes are client/server networks . A client/server network contains two different types of computers: clients and servers. The client is the computer on which users accomplish specific tasks and make specific requests. The server is the computer that provides information or resources to the client computers on the network. The server on a client/server network also provides central control for functions on the network (such as printing). The Internet is a client/server network. When your computer is connected to the Internet, it is functioning as a client computer . When connecting to the Internet through an ISP, your computer connects to a server computer maintained by the ISP. The server “serves up” resources to your computer so that you can interact with the Internet.
The distance between nodes on a network is another way to describe a network. Local area networks (LANs) are networks in which the nodes are located within a small geographic area. A network in your home or a computer lab at school is an example of a LAN. Wide area networks (WANs) are made up of LANs connected over long distances. Say a school has two campuses located in different towns. Connecting the LAN at the east campus to the LAN at the west campus (by telecommunications lines) allows users on the two LANs to communicate with each other. The two LANs would be described as a single WAN.
In order to move data from one computer to another, four components are required. They are: Transmission media Network adapters that translate the computer’s signal to a network message. Navigation devices that decide how data traffic comes and goes Network software that allows the software to run
All network nodes (computers and peripherals) are connected to each other and to the network by transmission media . A transmission medium establishes a communications channel between the nodes on a network and can take several forms: Networks can use existing wiring (such as phone lines or power lines) to connect nodes. Networks can use additional cable to connect nodes, such as twisted pair cable, coaxial cable, or fiber-optic cable. You have probably seen twisted pair and coaxial cable. Wireless networks use radio waves instead of wires or cable to connect nodes. Data transfer rate (also called bandwidth ) is the maximum speed at which data can be transmitted between two nodes on a network. Throughput is the actual speed of data transfer that is achieved and is usually less than the data transfer rate.
Network adapters are devices connected to or installed in network nodes that enable the nodes to communicate with each other and to access the network. Some network adapters take the form of external devices that plug into an available USB port. Other network adapters are installed inside computers and peripherals as expansion cards. These adapters are referred to as network interface cards (NICs) .
Data is sent over transmission media in bundles called packets . For computers to communicate, these packets of data must be able to flow between computers. Network navigation devices help to make this data flow possible. In simple networks, navigation devices are built right into network adapters. More sophisticated networks need specialized navigation devices. The two most common specialized navigation devices are routers and switches. -Routers transfer packets of data between two or more networks. For example, if a home network is connected to the Internet, a router is required to send data between the two networks. -Switches receive data packets and send them to the node for which they are intended on the same network (not between different networks)
Home networks need OS software that supports peer-to-peer networking. The most common versions of Windows used in the home support P2P networking. You can connect computers running any of these OSs to the same network. The last several versions of the Mac OS also support P2P networking. Client/server networks are controlled by a central server that has specialized network operating system (NOS) software installed on it. This software handles requests for information, Internet access, and the use of peripherals for the rest of the network nodes. Examples of NOS software include Windows XP Professional, Windows Server 2003, and Novell Netware.
Ethernet networks use the Ethernet protocol as the means by which the nodes on the network communicate. An Ethernet network requires that you install or attach network adapters to each computer or peripheral you want to connect to the network. Most computers come with Ethernet adapters preinstalled as network interface cards (NICs). If your computer doesn’t have a NIC, you can buy one and install it, or you can use a USB adapter, which you plug into any open USB port on the system unit. Although you can use USB versions in laptops, PC Card versions of Ethernet NICs are made especially for laptops. The most popular transmission media option for wired Ethernet networks is unshielded twisted-pair (UTP) cable . UTP cable, used in telephone lines, is composed of four pairs of wires that are twisted around each other to reduce electrical interference.
Data is transmitted through the wires of an Ethernet network in packets. Data packets can suffer collisions. If data packets collide, the data in them is damaged or lost. In either case, the network doesn’t function efficiently. A switch in an Ethernet network acts like a traffic signal by enforcing the rules of the data road on the transmission media. The switch keeps track of the data packets and, in conjunction with NICs, helps the data packets find their destination without running into each other.
Routers are devices that transfer packets of data between two or more networks. If a home network is connected to the Internet, you need a router to send data between the home network and the Internet. Because so many people are sharing Internet access in home networks, manufacturers are making devices that combine switches and routers and are specifically designed to connect to DSL or cable modems. These are often referred to as DSL/cable routers .
A wireless network uses radio waves instead of wires or cables as its transmission media. Current wireless networks in the United States are based on the 802.11 standard , which is also known as Wi-Fi (short for Wireless Fidelity). Just like other networks, each node on a wireless network requires a wireless network adapter . These adapters are available as NICs that are inserted into expansion slots on the computer or as USB devices that plug into an open USB port. Wireless network adapters differ from other network adapters in that they contain transceivers . A transceiver is a device that translates the electronic data that needs to be sent along the network into radio waves and then broadcasts these radio waves to other network nodes. Transceivers also receive the signals from other network nodes.
The basic information about the Internet includes its origin, how the web relates to the Internet, how the Internet is based on clients and servers and how to best connect to the Internet.
The Internet was created to respond to two concerns: to establish a safe form of military communications and to create a means by which all computers could communicate. Scientists were asked to come up with a solution to secure communications between large computer centers in case of a nuclear attack. They responded by inventing packet-switching and routers. By taking data messages and breaking them into small packets, each packet could be addressed and sent individually to a destination through a series of routers. The routers, like robot traffic cops, would send each packet along the optimum path to the next router, depending on traffic and availability. This development also gave birth to a network that could be scaled up infinitely. It could be argued that the scientists who quietly built the first packet-switched network in 1969 were more important to the future than the NASA scientists who landed a man on the moon in the same year.
Internet development in the early 1990s gave birth to the Web. One crucial development was the introduction of Hypertext Markup Language (HTML) and Hypertext Transfer Protocol (HTTP): the software technologies that allow Web pages to link to other Web pages, whether they are on the same server or on the other side of the world. The other critical development was the browser, multi-platform software that allows users to see HTML files, called Web pages. Thus, the Web is a subset of the Internet, but because of its tremendous use, it represents the largest amount of Internet traffic.
The Internet is a huge client/server network. Thus, a computer connected to the Internet acts in one of two ways: it is either a client , a computer that asks for data, or a server , a computer that receives the request and returns the data to the client.
To take advantage of the resources the Internet offers, you need a means to connect your computer to it. Home users have several connection options available. The most common is a dial-up connection . A dial-up connection is the least costly method of connecting to the Internet, needing only a standard phone line and a modem. A modem is a device that converts ( mod ulates) the digital signals the computer understands to the analog signals that can travel over phone lines. In turn, the computer on the other end must also have a modem to translate ( dem odulate) the received analog signal back to a digital signal for the receiving computer to understand. Modern desktop computers generally come with internal modems. Laptops use either internal modems or PC cards that are inserted into a special slot on the laptop. Current modems have a maximum data transfer rate of 56 Kbps, usually referred to as 56K
Other connection options, called broadband connections , offer faster means to connect to the Internet. Broadband connections include DSL, cable, and satellite. DSL uses a standard phone line to connect to the Internet . However, the line is split between digital and voice, meaning that the digital signal does not have to be converted into sounds, and greater speeds can be realized. DSL requires a special DSL modem. Although the monthly fee is higher than dial-up, there is no need for a second phone line, and often the end price is comparable, but the Internet speed is at least double. Not all areas of the U.S. have DSL. Also, in order to use DSL, your telephone connection must be within fairly close proximity of a switching station. DSL provider Web sites include interactive tools you can use to determine whether your phone line is capable of including a DSL connection. The more typical DSL transmissions download data from the Internet faster than they can upload data. Such transmissions are referred to as Asymmetrical Digital Subscriber Line (ADSL) . Other DSL transmissions, called Symmetrical Digital Subscriber Line (SDSL) , upload and download data at the same speed.
Another broadband connection is cable Internet. Cable Internet uses coaxial cable and a cable modem. If your cable company has an Internet service, you can receive data at speeds up to 4 Mbps and send data at approximately 500 Kbps. As technology improves, these transfer rates also will improve. This always-on connection can be slowed by the number of users connected at any one time, and it is not available in all areas.
Satellite Internet is another broadband option. You need a satellite dish, which is placed outside your home and connects to your computer with coaxial cable. Therefore, the initial equipment investment is high. Most satellite connections are used by people in rural areas unable to get cable or DSL connections. Even though bandwidth can be high, the signal must travel a long distance from the satellite and back, increasing the delay time. In North America the southern sky has to be free of obstruction, and heavy rain can cause interference in the signal.
Internet connection costs vary widely as does the performance. Generally, dial-up will cost from $10 to $25 per month for an unlimited connection. DSL is being offered for $25 to $40 per month for ADSL. Cable costs about $40 per month if it is coupled with cable television service. Satellite costs between $50 and $90 per month. A thorough investigation is recommended for anyone deciding to obtain Internet access.
The differences between Internet Service Providers and Online Service Providers has to do with content that is exclusively available to the OSP clients. Firms like America Online offer web access but when users log on they must enter through AOL’s site. There they receive information and services unavailable to non-subscribers. Whether these services are worth the premium price is a question each consumer must answer. Generally connection speed is similar and with the enormous amount of information available on the web, many have left the OSP providers in order to save money.
The choice of Internet Service Provider should be based on cost verse service. It is very important that a dial-up provider offer a local access number, so that there are no long distance charges incurred. Many providers will offer multiple e-mail accounts and some will provide space for a personal web page. Local ISPs sometimes maintain sites with local information and web links.
Networks The Great Information Exchange
Networking Fundamentals <ul><li>Computer network: </li></ul><ul><ul><li>Two or more computers connected together </li></ul></ul><ul><ul><ul><li>Each is a Node </li></ul></ul></ul><ul><li>Benefits of a network: </li></ul><ul><ul><li>Sharing resources </li></ul></ul><ul><ul><li>Transferring files </li></ul></ul>
Peer-to-Peer Networks <ul><li>Nodes communicate with each other: </li></ul><ul><ul><li>Peers </li></ul></ul><ul><li>Share peripheral devices: </li></ul><ul><ul><li>Printers </li></ul></ul><ul><ul><li>Scanners </li></ul></ul><ul><li>Home and small office networks </li></ul>
LANs and WANs <ul><li>Local area network (LAN): </li></ul><ul><ul><li>Nodes are within a small geographic region: </li></ul></ul><ul><ul><ul><li>Homes </li></ul></ul></ul><ul><ul><ul><li>Schools </li></ul></ul></ul><ul><ul><ul><li>Small businesses </li></ul></ul></ul><ul><li>Wide area network (WAN): </li></ul><ul><ul><li>LANs connected over long distances: </li></ul></ul><ul><ul><ul><li>A few miles to thousands of miles </li></ul></ul></ul><ul><ul><ul><li>Use telecommunications lines </li></ul></ul></ul>
Transmission Media <ul><li>Provides communications channel between nodes </li></ul><ul><li>Forms of media: </li></ul><ul><ul><li>Telephone wire: </li></ul></ul><ul><ul><ul><li>Twisted pair </li></ul></ul></ul><ul><ul><li>Coaxial cable </li></ul></ul><ul><ul><li>Fiber-optic cable </li></ul></ul><ul><ul><li>Radio waves: </li></ul></ul><ul><ul><ul><li>Wireless </li></ul></ul></ul><ul><li>Bandwidth: </li></ul><ul><ul><li>Data transfer rate </li></ul></ul><ul><ul><li>Throughput </li></ul></ul>
Network Adapters <ul><li>Devices connected to or installed in nodes: </li></ul><ul><ul><li>Network interface cards (NIC) </li></ul></ul><ul><ul><li>External network adapter </li></ul></ul><ul><li>Enable communication between nodes </li></ul>
Network Navigation Devices <ul><li>Devices that help make data flow possible </li></ul><ul><li>Routers: </li></ul><ul><ul><li>Route data between networks </li></ul></ul><ul><li>Switches: </li></ul><ul><ul><li>Receive data and retransmit it to nodes on the network </li></ul></ul>
Networking Software <ul><li>Peer-to-peer Software: </li></ul><ul><ul><ul><li>Built into operating systems that support networking </li></ul></ul></ul><ul><ul><ul><ul><li>Windows </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Mac OS </li></ul></ul></ul></ul><ul><li>Client/server Software </li></ul><ul><ul><ul><li>Network operating system (NOS) software </li></ul></ul></ul><ul><ul><ul><ul><li>Windows XP Professional </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Windows Server 2003 </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Novell Netware </li></ul></ul></ul></ul>
Ethernet Networks <ul><li>Ethernet network adapters are used to connect nodes </li></ul><ul><ul><li>NIC card </li></ul></ul><ul><ul><li>PC Card </li></ul></ul><ul><ul><li>USB adapter </li></ul></ul><ul><li>Computers are connected to each other using unshielded twisted pair cable </li></ul>RJ-45 Phoneline
Ethernet Switches <ul><li>Keep track of data packets </li></ul><ul><li>Amplify and retransmit signals </li></ul><ul><li>Keep the network running efficiently </li></ul>
Ethernet Routers <ul><li>Transfer packets from one network to another </li></ul><ul><li>Home Internet routers transfer data from the Internet to the home network. </li></ul>Router
Wireless Networks <ul><li>Use radio waves to connect nodes </li></ul><ul><li>Basically an Ethernet network that uses radio waves instead of wires </li></ul><ul><li>Each node requires a wireless network adapter: </li></ul><ul><ul><li>Transceiver </li></ul></ul>
The Internet: The Basics <ul><li>Origin of the Internet </li></ul><ul><li>The Web vs. the Internet </li></ul><ul><li>Clients and servers </li></ul><ul><li>Connecting to the Internet </li></ul>
The Origin of the Internet <ul><li>ARPANET: </li></ul><ul><ul><li>Advanced Research Projects Agency Network </li></ul></ul><ul><ul><li>Funded by the US Government in the 1960s </li></ul></ul><ul><ul><li>Allowed computers at leading universities and research organizations to communicate with each other over great distances </li></ul></ul>
The Internet vs. The Web <ul><li>Internet – part of the system that is primarily hardware infrastructure (telecommunications, routers, servers, disk drives, etcetera) </li></ul><ul><li>Web - part of the system that contains intellectual property in many multimedia formats (test files, graphic files, sound files, video files, etcetera) </li></ul>INTERNET WWW
Client and Server <ul><li>Client computer: </li></ul><ul><ul><li>Users connect to the Internet </li></ul></ul><ul><ul><li>Request data and Web pages </li></ul></ul><ul><li>Server computers </li></ul><ul><ul><li>Store Web pages and data </li></ul></ul><ul><ul><li>Return the requested data to the client </li></ul></ul>Server Client
Connecting to the Internet <ul><li>Dial-up connections: </li></ul><ul><ul><li>Uses standard telephone line </li></ul></ul><ul><ul><li>Least costly connection </li></ul></ul><ul><ul><li>Requires a modem </li></ul></ul><ul><ul><ul><li>Converts analog and digital signals </li></ul></ul></ul><ul><ul><li>Slowest connection speed (56kbps) </li></ul></ul>
Broadband Connections <ul><li>Cable: </li></ul><ul><ul><li>Uses TV coaxial cable </li></ul></ul><ul><ul><li>Fast connection speed (300kbps – 4mbps) </li></ul></ul><ul><ul><li>Speed depends on number of users </li></ul></ul><ul><ul><li>Not available in all areas </li></ul></ul><ul><ul><li>Requires a cable modem </li></ul></ul>Coaxial cable
Satellite Connections <ul><li>Uses a satellite dish and coaxial cable </li></ul><ul><ul><li>Download speed 500kbps </li></ul></ul><ul><ul><li>Upload speed 100kbps </li></ul></ul><ul><ul><li>Signal is affected by location and weather </li></ul></ul>
Comparing Internet Connection Options 400kbps 100kbps Satellite 6 mbps 500 kbps Cable 1.5mbps 1.5mbps DSL (SDSL) 1 Mbps 300 kbps DSL (ADSL) 56kbps 56kbps Dial-Up Maximum Download Data Transfer Rate (approximate) Maximum Upload Data Transfer Rate (approximate) Connection Option
Internet Service Providers <ul><li>ISP: </li></ul><ul><ul><li>Internet service provider </li></ul></ul><ul><ul><li>Provide user access to the Internet </li></ul></ul><ul><ul><li>National, regional or local companies </li></ul></ul><ul><li>OSP: </li></ul><ul><ul><li>Online service provider </li></ul></ul><ul><ul><li>Provide online proprietary content as well as Internet access </li></ul></ul><ul><ul><li>AOL, CompuServe, MSN </li></ul></ul>
Choosing an ISP <ul><li>Factors to consider: </li></ul><ul><ul><li>Customer service </li></ul></ul><ul><ul><li>Local access numbers </li></ul></ul><ul><ul><li>E-mail options </li></ul></ul><ul><ul><li>Cost </li></ul></ul><ul><ul><li>Trial period </li></ul></ul>
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