A Standard That Specifies How Two Devices Can Communicate Is Called a
CONTEMPORARY NETWORKING INFRASTRUCTURE
Now that we accept sketched the outlines of the broad concern telecommunications environs, let�southward examine more closely computer networks and networking technologies.
Networks and Corporate Infrastructure
In its simplest course, a network consists of two or more connected computers. Figure 8-iv illustrates the major hardware, software, and transmission components used in a simple network: computers, network interfaces, a connection medium, network operating arrangement software, and either a hub or a switch. Each computer on the network contains a network interface device called a network interface card (NIC). Nearly personal computers today have this menu built into the motherboard. The connexion medium for linking network components can be a telephone wire, coaxial cable, or radio signal in the case of cell phone and wireless local expanse networks (Wi-Fi networks).
FIGURE 8-4 Components of a unproblematic network
Illustrated here is a very elementary network, consisting of computers, network operating system software, cablevision (wiring) to connect the devices, network interface cards, switches, and a router. In this analogy, the network operating arrangement (NOS) resides on a defended server.
Most networks also incorporate a switch or a hub acting as a connexion bespeak between the computers. Hubs are very simple devices that connect network components, sending a packet of data to all other connected devices. A switch has more than intelligence than a hub and can filter and frontwards information to a specified destination. Switches are used within individual networks. To communicate with another network, the network would use a device called a router. A router is a special communications processor used to route packets of data through unlike networks, ensuring that the message sent gets to the correct accost.
Primal Digital Networking Technologies
Contemporary digital networks and the Internet are based on three cardinal technologies: customer/server computing, the apply of packet switching, and the development of widely used communications standards (the nearly of import of which is Transmission Control Protocol/Cyberspace Protocol [TCP/IP]) for linking disparate networks and computers.
CLIENT/SERVER COMPUTING
In Chapter half dozen, nosotros introduce client/server calculating in which client computers are connected in a network with one or more server computers. Client/server calculating is a distributed computing model in which much of the processing power is located inside small, cheap client computers under user control and resides on desktops, laptops, or in handheld devices. These powerful clients are linked to one another through a network that is controlled past a network server computer. The server sets the rules of communication for the network and provides every customer with an address so it tin can exist found by others on the network.
Client/server computing has largely replaced centralized mainframe computing in which nearly or all of the processing takes place on a primal big mainframe computer. Client/server computing has extended calculating to departments, workgroups, manufactory floors, and other parts of the business organization that could non be served by a centralized architecture. The Net is the largest implementation of customer/server computing.
PACKET SWITCHING
Bundle switching is a method of slicing digital messages into parcels called packets, sending the packets along unlike communication paths as they become available, so reassembling the packets in one case they arrive at their destinations (meet Figure eight-5). Prior to the development of packet switching, computer networks used leased, dedicated telephone circuits to communicate with other computers in remote locations. In circuit-switched networks, such as the telephone system, a complete point-to-point circuit is assembled, and so communication can go on. These dedicated circuit-switching techniques were expensive and wasted available communications capacity�the circuit was maintained regardless of whether whatsoever data were beingness sent.
FIGURE 8-5 Packed-switched networks and packet communications
Information are grouped into minor packets, which are transmitted independently over diverse communications channels and reassembled at their last destination.
Data are gathered from many users, divided into small packets, and transmitted over available communications channels using routers. Each packet travels independently through these networks. Packets of information originating at one source can be routed through many different paths and networks earlier being reassembled into the original bulletin when they accomplish their destinations.
Packet switching does not crave a dedicated circuit but can brand utilise of whatsoever spare capacity that is bachelor. If some lines are disabled or too busy, the packets can be sent over any available line that eventually leads to the destination point.
TCP/IP AND CONNECTIVITY
A typical telecommunication network consists of diverse hardware and software components that demand to work together to transmit information. Different components in a network can communicate with each other only past adhering to a mutual set of rules called protocols. A protocol is a set of rules and procedures governing manual of information between two points in a network. In the past many diverse proprietary and incompatible protocols often forced business organization firms to buy calculating and communications equipment from a single vendor. Only today corporate networks are increasingly using a unmarried, common, worldwide standard called Transmission Control Protocol/Internet Protocol (TCP/IP).
TCP/IP provides a universally agreed-on method for breaking up digital letters into packets, routing them to the proper addresses, and then reassembling them into coherent messages. TCP/IP was developed during the early 1970s to support U.S. Section of Defense force Advanced Inquiry Projects Bureau (DARPA) efforts to help scientists transmit data among unlike types of computers over long distances.
TCP/IP uses a suite of protocols, the main ones being TCP and IP. TCP refers to the Transmission Command Protocol (TCP), which handles the movement of data between computers. TCP establishes a connection between the computers, sequences the transfer of packets, and acknowledges the packets sent. IP refers to the Internet Protocol (IP), which is responsible for the delivery of packets and includes the disassembling and reassembling of packets during transmission. Figure 8-6 illustrates the 4-layered Department of Defense reference model for TCP/IP.
FIGURE 8-six The Transmission Control Protocol/Internet Protocol (TCP/IP) reference model
This figure illustrates the iv layers of the TCP/IP reference model for communications.
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Application layer. Enables client awarding programs to access the other layers and defines the protocols that applications employ to exchange data. One of these application protocols is the Hypertext Transfer Protocol (HTTP) that is used to transfer Web page files.
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Ship layer. Responsible for providing the awarding layer with advice and parcel services. This layer includes TCP and other protocols.
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Internet layer. Responsible for addressing, routing, and packaging information packets called IP datagrams. The Internet Protocol (IP) is one of the protocols used in this layer.
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Network interface layer. At the bottom of the reference model, the network interface layer is responsible for placing packets on and receiving them from the physical network medium, which could exist any networking technology.
Open Systems Interconnect (OSI) is some other network connectivity model developed by the International Standards Organization for linking different types of computers and networks. Similar TCP/IP, OSI enables a computer connected to a network to communicate with whatever other computer on the same network or a dissimilar network, regardless of the manufacturer. OSI divides the telecommunications process into seven layers.
Physical Transmission Media
Networks can utilise dissimilar kinds of physical transmission media, including twisted wire, coaxial cable, fiber optics, and media for wireless transmission. Each has advantages and limitations. A wide range of speeds is possible for any given medium depending on the software and hardware configuration.
TWISTED WIRE
Twisted wire consists of strands of copper wire twisted in pairs and is the oldest electronic transmission medium. Most all of the telephone systems in buildings used twisted wires for analog communication, and these same wires can be used for digital communication likewise.
An analog signal is represented by a continuous waveform that passes through a communications medium and has been used for vocalism communication. A digital signal is a discrete, rather than a continuous, waveform. It transmits data coded into ii discrete states: 1 bits and 0 bits, which are represented as on�off electrical pulses. Computers employ digital signals, so if one wants to employ the analog telephone organization to send digital data, a device chosen a modem is required to translate digital signals into analog form (meet Figure viii-7). Modem stands for modulation/demodulation.
FIGURE 8-7 Functions of the modem
A modem is a device that translates digital signals from a computer into analog course so that they can be transmitted over analog phone lines. The modem too is used to translate analog signals back into digital form for the receiving computer.
COAXIAL CABLE
Coaxial cable, like to that used for cable idiot box, consists of thickly insulated and shielded copper wire, which tin transmit a larger book of information than twisted wire. Cable is unremarkably used for local area networks considering it is a faster, more than interference-complimentary manual medium, typically operating at 10 Mbps at the desktop and 100 Mbps and 1 Gbps in network backbones.
Cobweb Optics AND OPTICAL NETWORKS
Fiber-optic cable consists of strands of articulate glass fiber, each the thickness of a human pilus, which are spring into cables. Data are transformed into pulses of light, which are sent through the fiber-optic cable by a laser device at rates varying from 500 kilobits to several trillion bits per 2d in experimental settings. Fiber-optic cable is considerably faster, lighter, and more durable than wire media and is well suited to systems requiring transfers of large volumes of data. All the same, fiber-optic cablevision is more hard to work with, more expensive, and harder to install.
Until recently, fiber-optic cable had been used primarily as the loftier-speed network backbone, whereas twisted wire and coaxial cable were used to connect the backbone to private businesses and households. A backbone is the part of a network that handles the major traffic. It acts as the primary path for traffic flowing to or from other networks. Now, local cable companies and telephone companies are bringing fiber optic cable to homes and small businesses.
These optical networks can transmit all types of traffic�vocalization, information, and video�over fiber cables and provide the massive bandwidth for new types of services and software. Using optical networks, on-demand video, software downloads, and high-quality digital audio can be accessed using set up-top boxes and other information appliances without severe degradation in quality or delays.
Optical networks can boost capacity past using dumbo wavelength division multiplexing (DWDM). Multiplexing enables a unmarried communications channel to carry simultaneous data transmissions from multiple sources. (This tin be accomplished by dividing a highspeed aqueduct into multiple channels of slower speeds or past assigning each manual source a very pocket-size piece of time for using a loftier-speed channel.) DWDM boosts manual capacity by using many dissimilar colors of light, or different wavelengths, to deport separate streams of data over the aforementioned fiber strand at the same time. DWDM combines up to 160 wavelengths per strand and tin transmit up to half-dozen.4 terabits per 2nd (Tbps) over a single fiber. This applied science volition enable communications service providers to add transmission capacity to an existing cobweb-optic network without having to lay more fiberoptic cable. Before wavelength division multiplexing, optical networks could use simply a single wavelength per strand.
WIRELESS TRANSMISSION
Much of the recent growth in communications and networking services is based on wireless technologies that utilise radio frequencies or infrared signals to send data between communications devices without using wires. Mutual technologies for wireless data manual include microwave transmission, communication satellites, pagers, cellular telephones, personal digital assistants (PDAs), and smart phones. Personal computers using wireless Wi-Fi network interface cards can connect to corporate networks and the Internet in locations where a Wi-Fi transmitter has been installed. Wireless transmission has go so important to corporations that we devote the following chapter to this topic.
TRANSMISSION SPEED
The total amount of digital information that can exist transmitted through any telecommunications medium is measured in bits per 2nd (bps). One betoken change, or cycle, is required to transmit 1 or several bits; therefore, the transmission chapters of each type of telecommunications medium is a role of its frequency. The number of cycles per 2d that can exist sent through that medium is measured in hertz�one hertz is equal to ane cycle of the medium.
The range of frequencies that tin be accommodated on a particular telecommunication channel is called its bandwidth. The bandwidth is the difference between the highest and everyman frequencies that tin can be accommodated on a single aqueduct. The greater the range of frequencies, the greater the bandwidth and the greater the channel�s transmission capacity. Table 8-2 compares the transmission speeds of the major types of transmissions media.
Tabular array viii-2 Typical Speeds and Costs of Telecommunications Manual Media
Types of Networks
In that location are many different kinds of networks and ways of classifying them. One way of looking at networks is in terms of their geographic scope (see Table 8-three).
TABLE 8-3 Types of Networks
LOCAL Surface area NETWORKS
The starting time estimator networks appeared in the early 1960s and consisted of brandish terminals linked to a mainframe figurer within the same edifice. Researchers at Xerox Palo Alto Research Center (PARC) invented the first local area network in the early 1970s to connect desktop machines into a coherent computing facility. These networks enabled desktop machines to share printers, communicate with i some other, and store files on a cardinal desktop machine called a server.
Today almost people in corporations connect to other employees and groups using local expanse networks. A local area network (LAN) is designed to connect personal computers and other digital devices within a one-half mile or 500-meter radius. LANs typically connect a few computers in a small-scale office, all the computers in one building, or all the computers in several buildings in close proximity. LANs interconnected inside multiple buildings or a geographic surface area such as a schoolhouse campus or military base create a campus area network (CAN). LANs can link to long-distance wide area networks (WANs, described later on in this section) and other networks around the world by using the Internet.
Review Figure viii-4, which could serve as a model for a small LAN that might be used in an office. One computer is a dedicated network file server, providing users with access to shared calculating resource in the network, including software programs and information files. The server determines who gets access to what and in which sequence. The router connects the LAN to other networks, which could exist the Internet or some other corporate network, then that the LAN tin can exchange information with networks external to it. The about common LAN operating systems are Windows, Linux, and Novell. Each of these network operating systems supports TCP/IP as its default networking protocol.
Ethernet is the ascendant LAN standard at the physical network level, specifying the physical medium to carry signals between computers, access control rules, and a standardized frame, or set of $.25 used to comport data over the system. Originally, Ethernet supported a data transfer rate of 10 Mbps. Newer versions, such as Fast Ethernet and Gigabit Ethernet, support information transfer rates of 100 Mbps and i Gbps, respectively, and are used in network backbones.
The LAN illustrated in Figure viii-iv uses a client/server architecture where the network operating system resides primarily on a single file server and the server provides much of the control and resources for the network. Alternatively, LANs may employ a peer-to-peer architecture. A peer-to-peer network treats all processors equally and is used primarily in pocket-size networks with 10 or fewer users. The various computers on the network can commutation data past direct access and tin share peripheral devices without going through a divide server.
In LANs using the Windows Server 2003 family of operating systems, the peer-to-peer architecture is called the workgroup network model in which a small group of computers can share resources, such as files, folders, and printers over the network without a dedicated server. The Windows domain network model, in contrast, uses a defended server to manage the computers in the network.
Larger LANs take many clients and multiple servers, with separate servers for specific services, such as storing and managing files and databases (file servers or database servers), managing printers (print servers), storing and managing e-mail (mail servers), or storing and managing Web pages (Web servers).
Sometimes LANs are described in terms of the way their components are continued together, or their topology. There are three major LAN topologies: star, bus, and ring (see Figure 8-eight).
FIGURE eight-8 Network topologies
The 3 basic network topologies are the bus, star, and ring.
In a charabanc topology, one station transmits signals, which travel in both directions forth single transmission segment. All of the signals are broadcast in both directions to the entire network. All machines on the network receive the same signals, and software installed on the clients enables each client to listen for letters addressed specifically it. Motorcoach networks are the most mutual Ethernet topology.
A band topology connects network components in a closed loop. Letters pass from reckoner to computer in only one direction around the loop, and simply i station at a time may transmit. Band networks are used primarily in older LANs using Token Ring networking software.
METROPOLITAN AND WIDE Expanse NETWORKS
Wide surface area networks (WANs) bridge broad geographical distances�entire regions, states, continents, or the entire globe. The near universal and powerful WAN is the Net. Computers connect to a WAN through public networks such equally the telephone system, private cable systems, or through leased lines or satellites. A metropolitan area network (Human) is a network that spans a metropolitan area, usually a urban center and its major suburbs. Its geographic telescopic falls between a WAN and a LAN. MANs sometimes provide Cyberspace connectivity for local area networks in a metropolitan region.
Broadband Network Services and Technologies
A number of network services and technologies are available to companies that demand high-speed transmission or access to the Internet.
Frame relay is a shared network service that is faster and less expensive than parcel switching and can achieve transmission speeds ranging from 56 kilobits per second (Kbps) to more than forty Mbps. Frame relay packages data into frames similar to packets merely takes reward of higher-speed, more reliable digital circuits that require less error checking than parcel switching. The major telecommunications carriers provide frame relay services. Many organizations use frame relay services in their international information advice networks.
The Texas Health and Human Services Consolidated Network HHSCN) provides wide-expanse network (WAN) services to Texas state agencies and certain private sector partners.
Integrated Services Digital Network (ISDN) is an international standard for punch-up network access that integrates voice, information, epitome, and video services in a single link. There are two levels of ISDN service: basic charge per unit ISDN (which tin transmit 128 Kbps) and primary rate ISDN (which tin can transmit at one.5 Mbps).
ISDN is being replaced past Digital Subscriber Line (DSL). Similar ISDN, Digital Subscriber Line (DSL) technologies also operate over existing copper telephone lines to comport voice, data, and video, only they have college manual speeds than ISDN. There are several categories of DSL. Asymmetric digital subscriber lines (ADSLs) back up a manual rate of i.five to ix Mbps when receiving data and up to 640 Kbps when sending data. Symmetric digital subscriber lines (SDSLs) support the aforementioned manual charge per unit for sending and receiving data of up to 3Mbps.
Other high-capacity services include cable modems and T lines. Cable modems are modems designed to operate over cablevision Idiot box lines. They tin provide high-speed access to the Web or corporate intranets of up to 4 Mbps. All the same, cablevision modems use a shared line then that transmission slows down if there are a big number of local users sharing the cable line, although this problem can be solved by increasing the capacity of the local cable.
Firms that accept large amounts of information to move beyond the continent, or around the earth, or which have high security or guaranteed service level requirements, ofttimes lease high-speed data lines from communication providers, typically long-altitude phone companies. These lines are designated as T lines, which range from T-1 to T-4. A T-i line offers up to twenty-iv 64-Kbps channels that tin can support a full data transmission charge per unit of i.544 Mbps. Each of these 64-Kbps channels tin can be configured to carry voice or data traffic. A T-3 line offers delivery at 45 Mbps, and a T-4 line (although rarely used) tin deliver up to 274 Gbps. Leasing a T-i line costs about $1,000 to $2,000 per month, whereas a T-3 line costs around $ten,000 to $thirty,000 per month. Table eight-4 summarizes these network services.
TABLE viii-4 Broadband Network Services
Source: https://paginas.fe.up.pt/~acbrito/laudon/ch8/chpt8-2fulltext.htm
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