1、Technology Guide 4,1,Technology Guide 4,Information Technology For Management 4th Edition Turban, McLean, Wetherbe Lecture Slides by A. Lekacos, Stony Brook University John Wiley & Sons, Inc.,Telecommunications,Technology Guide 4,2,Telecommunications,Telecommunications generally refers to all types
2、of long-distance communication that uses common carriers, including telephone, television, and radio. Data communications is the electronic collection, exchange, and processing of data or information, including text, pictures, and voice, that is digitally coded and intelligible to a variety of elect
3、ronic devices.,Technology Guide 4,3,Telecommunications System,The major components are: Hardwareall types of computers (e.g., desktop, server, mainframe) and communications processors (such as a modems or small computers dedicated solely to communications). Communications mediathe physical media thr
4、ough which electronic signals are transferred; includes both wireline and wireless media. Communications networksthe linkages among computers and communications devices. Communications processorsdevices that perform specialized data communication functions; includes front-end processors, controllers
5、, multiplexors, and modems.,A telecommunications system is a collection of compatible hardware and software arranged to communicate information from one location to another.,Technology Guide 4,4,Telecommunications System Continued,Communications softwaresoftware that controls the telecommunications
6、system and the entire transmission process. Data communications providersregulated utilities or private firms that provide data communications services. Communications protocolsthe rules for transferring information across the system. Communications applicationselectronic data interchange (EDI), tel
7、econferencing, videoconferencing, e-mail, facsimile, electronic funds transfer, and others.,Technology Guide 4,5,Electronic Signals,Telecommunications media can carry two basic types of signals: Analog signals are continuous waves that “carry” information by altering the amplitude and frequency of t
8、he waves. Digital signals are discrete on-off pulses that convey information in terms of 1s and 0s, just like the central processing unit in computers.,Technology Guide 4,6,Communications Processors,A modem is a communications device that converts a computers digital signals to analog signals before
9、 they are transmitted over standard telephone lines. A multiplexer is an electronic device that allows a single communications channel to carry data transmissions simultaneously from many sources. A front-end processor, is a specialized computer that manages all routing communications with periphera
10、l devices.,Communications processors are hardware devices that support data transmission and reception across a telecommunications system. These devices include modems, multiplexers, front-end processors, and concentrators.,Modulation Demodulation hence the name modem,Technology Guide 4,7,Communicat
11、ions Media Comparisons,For data to be communicated from one location to another, a physical pathway must be used. These pathways are called communications media (channels) and can be either physical or wireless. The physical transmission use wire, cable, etc.; wireless transmission media send commun
12、ications signals through the air.,Technology Guide 4,8,Communications Media (Channels),Technology Guide 4,9,Satellite Communications Systems,A satellite is a space station that receives microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide
13、area to any number of earth-based stations. Transmission to a satellite is an uplink, whereas downlink is a transmission from a satellite to an earth-based station.,Technology Guide 4,10,“Newer” Wireless Technologies,Bluetooth Fiber optics without the ber Ultrawideband (UWB) Software-Dened Radio Wir
14、eless Personal Area Network Adaptive Radio Mesh Networks HomePlug,Wireless Application Protocol (WAP) is a technology that enables wireless transmissions. Because of the requirements of faster speed and strict security requirements that existing WAP cannot fulfill, newer technologies are being creat
15、ed.,Wireless Network Standards,Technology Guide 4,11,Characteristics of Communications Media,Transmission speed Bandwidth refers to the range of frequencies that can be sent over a communications channel. Frequencies are measured in the number of cycles per second (or Hertz, abbreviated Hz). A baud
16、is a detectable change in a signal. The amount of data that can be transmitted through a channel is known as its baud rate, measured in bits per second (bps). Channel capacity is usually divided into three bandwidths: Narrowband Voice-band Broadband channels,Communications media have several charact
17、eristics that determine their efficiency and capabilities. These characteristics include the speed, direction, mode, and accuracy of transmission.,Technology Guide 4,12,Transmission Rates,Technology Guide 4,13,Transmission Direction and Mode,Simplex data transmission uses one circuit in one directio
18、n only. Half-duplex data transmission uses only one circuit, but it is used in both directions. Full-duplex data transmission uses two circuits simultaneously for communications one for each direction. Asynchronous transmission, only one character is transmitted or received at a time. Synchronous tr
19、ansmission, a group of characters is sent over a communications link in a continuous bit stream while data transfer is controlled by a timing signal initiated by the sending device.,Data transmissions can be described in terms of their direction and their timing. Direction of data transmission can b
20、e a simplex, half-duplex or full-duplex. Timing of data transmissions can be either asynchronous or synchronous.,Technology Guide 4,14,Telecommunications Carriers,Switched lines are telephone lines, provided by common carriers, that a person can access from his or her computer to transmit data to an
21、other computer; the transmission is routed or switched through paths to its destination. Dedicated lines, also called leased lines, provide a constant connection between two devices and require no switching or dialing. These lines are continuously available for transmission.,Telecommunications carri
22、ers are companies that provide the communications technology (e.g., telephone lines, satellites, and communications software) and services needed for data communications.,Technology Guide 4,15,Network Protocols,Token-passing approach, a small data packet, called a token, is sent around the network.
23、Contention, which is part of the Ethernet protocol, a device that wants to send a message checks the communications medium to see if it is in use. Transmission Control Protocol/Internet Protocol (TCP/IP) is a protocol for sending information across sometimes-unreliable networks with the assurance th
24、at it will arrive in uncorrupted form. It is the standard protocol of the Internet and intranets Voice-over IP (VoIP) systems, analog voice signals are digitized and transmitted as a stream of packets over a digital IP data network,Protocol is a set of rules and procedures governing transmission and
25、 communications across a network. Its principal functions are line access, collision avoidance, identification of each device in the communication path, to secure the attention of the other device, to verify correct receipt of the transmitted message, to verify that a message requires retransmission
26、 and to perform recovery when errors occur.,Technology Guide 4,16,Communications Standards,Layer 1: Physical layer. Concerned with transmitting raw bits over a communications channel; provides a physical connection for the transmission of data among network entities and creates the means by which to
27、 activate and deactivate a physical connection.,The protocols required to achieve communication on behalf of an application are actually multiple protocols existing at different levels or layers. Each layer defines a set of functions that are provided as services to upper layers and each layer relie
28、s on services provided by lower layers. At each layer, one or more protocols define how the software programs interact to accomplish the functions for that layer.,The most widely known is the Open Systems Interconnection (OSI) Reference Model developed by the ISO.,Technology Guide 4,17,Communication
29、s Standards Continued,Layer 2: Data link layer. Provides a reliable means of transmitting data across a physical link; breaks up the input data into data frames sequentially and processes the acknowledgment frames sent back by the receiver. Layer 3: Network layer. Routes information from one network
30、 computer to another; computers may be physically located within the same network or within another network that is interconnected in some fashion; accepts messages from source host and sees to it they are directed toward the destination. Layer 4: Transport layer. Provides a network-independent tran
31、sport service to the session layer; accepts data from session layer, splits it up into smaller units as required, passes these to the network layer, and ensures all pieces arrive correctly at the other end.,Open Systems Interconnection (OSI) Reference Model,Technology Guide 4,18,Communications Stand
32、ards Continued,Layer 5: Session layer. Users interface into network; where user must negotiate to establish connection with process on another machine; once connection is established the session layer can manage the dialogue in an orderly manner. Layer 6: Presentation layer. Here messages are transl
33、ated from and to the format used in the network to and from a format used at the application layer. Layer 7: Application layer. Includes activities related to users, such as supporting le transfer, handling messages, and providing security,Open Systems Interconnection (OSI) Reference Model,Technolog
34、y Guide 4,19,Transmission Standards,Fiber distributed data interface (FDDI) like token-ring networks, passes data around a ring Asynchronous transfer mode (ATM) networks are based on switched technologies, allowing for almost unlimited bandwidth on demand. Switched hub technologies are often used to
35、 boost local area networks. A switched hub can turn many small LANs into one big LAN. Synchronous optical network (SONET) is an interface standard for transporting digital signals over fiber-optic links.,A number of network bandwidth boosters address the need for greater bandwidth on networks for ad
36、vanced computing applications.,Technology Guide 4,20,Transmission Standards Continued,T-carrier system is a digital transmission system that defines circuits that operate at different rates, all of which are multiples of the basic 64 Kbps used to transport a single voice call. These circuits include
37、 T1 (1.544 Mbps, equivalent to 24 channels); T2 (6.312 Mbps, equivalent to 96 channels); T3 (44.736 Mbps, equivalent to 672 channels); and T4 (274.176 Mbps, equivalent to 4,032 channels). Integrated services digital network (ISDN) is a high-speed data transmission technology that allows users to sim
38、ultaneously transfer voice, video, image, and data at high speed over standard copper telephone lines, using multiplexing. A Digital Subscriber Line (DSL) provides high-speed, digital data transmission from homes and businesses over existing telephone lines.,Technology Guide 4,21,Transmission Standa
39、rds Continued,Infinite Bandwidth (InniBand) is a new standard designed to dramatically increase the velocity of information by overhauling a key bottlenecktodays general-purpose, shared bus inside the computer. That shared bus, named the Peripheral Component Interconnect (PCI) bus can carry one mess
40、age at a time past many points. The new standard, called a switched fabric network, will able to juggle hundreds or thousands of messages at a time both inside and outside the computer, moving them precisely from origin to destination. Circuit switching is an end-to-end circuit that must be set up b
41、efore the call can begin.,Technology Guide 4,22,Software Standards,Operating systems. A network operating system (NOS) is the system software that controls the hardware devices, software, and communications media and channels across a network. Graphical User Interface standard. X Windows is the stan
42、dard for GUI. It runs on all types of computers. Software application standards. Because of the large number of applications standards are not widespread. The unified standards cover DBMSs, user interfaces, programming languages, electronic data interchange and so on.,Computers and computing devices
43、 from different vendors require an open system to “talk” to each other. Three types of software standards are necessary for an open system:,Technology Guide 4,23,Interfaces,Parallel data transfer, most often used for local communication, employs a communications interface with a series of dedicated
44、wires, each serving one purpose. In parallel communication, both data and control signals are transmitted simultaneously. Serial data transfer, most often used for long-distance communications, is bit by bit rather than many bits in parallel. Most data communications devices transmit in serial fashi
45、on. While much slower than parallel data transfer, serial transfer is simpler and requires much less on the part of the receiving system.,An interface is a physical connection between two communications devices. One important concept of interfacing concerns the types of data transfer parallel or ser
46、ial.,Technology Guide 4,24,Network Topology,There are five basic network topologies: Star Bus Ring Hierarchical Hybrid,The topology of a network is the physical layout and connectivity of a network. Specific protocols or rules of communications, are often used on specific topologies. Note: topology
47、refers to the ways the channels connect the nodes, whereas protocol refers to the rules by which data communications take place over these channels. Neither concept should be confused with the physical cabling of the network.,Technology Guide 4,25,Network Topology - Star,A star network has a central
48、 node that connects to each of the other nodes by a single, point-to-point link. Any communication between one node and another in a star topology must pass through the central node.,Technology Guide 4,26,Network Topology - Bus,In a bus topology, nodes are arranged along a single length of twisted p
49、air wire, coaxial cable, or fiber-optic cable that can be extended at the ends.,Technology Guide 4,27,Network Topology - Ring,In a ring topology, nodes are arranged along the transmission path so that a signal passes through each station one at a time before returning to its originating node.,Techno
50、logy Guide 4,28,Network Topology - Hierarchical,Hierarchical topologies typically connect desktops to minicomputers to a mainframe.,Technology Guide 4,29,Network Topology - Hybrid,Networks that combine more than one type (such as a ring segment connected to a star segment) are considered hybrid topologies.,
