Local Area Networks

1. 1-1 Local Area Networks CS 55 Computer Networks Topic 5

2. 1-2 Loc al Area Networks (LANs)(Study Map) Introduction Review of Data Communications Concepts Review of Basic LAN Concepts Hardware LAN Media Topologies and Media Access Control LAN Hardware Software LAN System Software Client/Server Architecture

3. 1-3 The Ethernet Local Area Network I came to work one day at MIT and the computer had been stolen, so I called DEC to break the news to them that this $30,000 computer that they'd lent me was gone. They thought this was the greatest thing that ever happened, because it turns out that I had in my possession the first computer small enough to be stolen! - Robert Metcalfe on the trials and tribulations of inventing the Ethernet.

4. 1-4 The Ethernet Local Area Network Robert Metcalfe was a member of the research staff for Xerox, at their Palo Alto Research Center (PARC) where some of the first personal computers were being made. Metcalfe was asked to build a networking system for PARC's computers. Xerox's motivation for the computer network was that they were also building the world's first laser printer and wanted all of the PARC's computers to be able to print with this printer.

5. 1-5 The Ethernet Local Area Network Metcalfe had two challenges: the network had to be fast enough to drive the very fast new laser printer; and it had to connect hundreds of computers within the same building. Never before had hundreds of computers been in the same building -- at that time no one had more than one, two or maybe three computers in operation on any one premise.

6. 1-6 The Ethernet Local Area Network The press has often stated that ethernet was invented on May 22, 1973, when Metcalfe wrote a memo to his bosses stating the possibilities of ethernet's potential, but Metcalfe claims ethernet was actually invented very gradually over a period of several years. In 1976, Robert Metcalfe and David Boggs (Metcalfe's assistant) published a paper titled, "Ethernet: Distributed Packet-Switching For Local Computer Networks."

7. 1-7 The Ethernet Local Area Network Metcalfe left Xerox in 1979 to promote the use of personal computers and local area networks (LANs). He successfully convinced Digital Equipment, Intel, and Xerox Corporations to work together to promote ethernet as a standard. Now an international computer industry standard, ethernet is the most widely installed LAN protocol. �

8. 1-8 End of the Story Not yet � we have a �compressed� lecture class today � hmmm ...

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10. 1-10 Section Preview The requirements for communication What constitutes a network The various types of networks in common use today The OSI Reference Model Some of the basic terminology of data communications and networks

11. 1-11 Essential Elements of Communication A message A sender A receiver A medium

12. 1-12 Understanding the Message In computer systems, data can be represented by any of several different codes, the two most common being: the American Standard Code for Information Interchange (ASCII) the Extended Binary Coded Decimal Interchange Code (EBCDIC)

13. 1-13 Security Sensitive data like your credit card number or other secret data should be safeguarded during transmission. The most common mechanism for protecting data during transmission is encryption. Encryption transforms plain text into an (presumably) undecipherable form called cipher-text.

14. 1-14 Two Types of Networks Terminal Network consists of a single host computer with attached terminals the host computer does all or most of the processing, and the terminals imply act as input/output (I/O) devices through which a person gains access to the host�s applications. Network of Computers two or more nodes connected by a data communications medium. individual nodes may have terminals attached to them a single node on this network can look just like the terminal network

15. 1-15 Three Network Subtypes Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN)

16. 1-16 LAN/MAN/WAN Comparison

17. 1-17 The OSI Reference Model The problem of network interconnection is so important that the ISO created the OSI Reference Model that describes the functions a generic network needs to provide. The OSI Reference Model has become the basis for many data communications standards. Because these standards are placed in the public domain, they are called open standards and lead to open systems.

18. 1-18 OSI Peer Layer Communication

19. 1-19 OSI Reference Model Formatting

20. 1-20 The OSI Model at Work Application Layer The application on Node A builds a record with a transaction identifier, the number of the account to be updated, the date and time of the transaction, and the amount to be deducted. Presentation Layer The presentation layer is responsible for translating from one format to another. Session Layer The session layer�s major functions are to set up and perhaps monitor a set of dialogue rules by which the two applications can communicate and to bring a session to an orderly conclusion.

21. 1-21 The OSI Model at Work (cont.) Transport Layer The transport layer is the first of the OSI layers responsible for actually transmitting the data. Network Layer The network layer provides accounting and routing functions. Data Link Layer The data link layer is responsible for data delineation, error detection,and logical control of the link. Physical Layer The physical layer does not append anything to the message. It simply accepts the message from the data link layer and translates the bits into signals on the medium.

22. 1-22 Receiving the Message 1. The message is passed over the link connecting Nodes A and X. 2. The message is passed to the data link layer in Node X. The message is checked for transmission errors, the PDU information applied by A�s data link layer is removed, and the message is sent to X�s network layer. 3. X�s network layer records the accounting information for the message and then strips off the network layer protocol data and examines the destination address. The destination is not Node X in this case, so the network layer consults its network routing table and determines the next link on the path to Node M. X�s network layer affixes the proper network layer protocol data and sends the message to Node X�s data link layer.

23. 1-23 Receiving the Message (cont.) 4. Node X�s data link layer creates its PDU and sends the message to Node M. 5. Node M�s data link layer receives the message, strips off Node X�s data link layer protocol data, checks for transmission errors, and passes the data up to Node M�s network layer. 6. Node M�s network layer gathers accounting data, strips off the network layer protocol data, and fins that the message is destined for an application in this node. 7. The message is passed up to M�s transport layer, where the sequence number is checked to ensure that no messages have been lost. The transport layer protocol data is removed.

24. 1-24 Receiving the Message (cont.) 8. The message arrives at the session layer, where relevant protocol data is examined and remove. 9. The message arrives at Node M�s presentation layer, where appropriate action is taken. 10.The message arrives at the application, where it is acted on.

25. 1-25 General Network Implementations: LANs A LAN services a limited geographic area at high speeds�usually 10 million bits per second or higher. All components of the LAN are commonly owned by the organization that uses it. The nodes in many of today�s LANs are desktop systems like personal computers. Henceforth, we will also use the terms workstations, clients, and servers in referring to LAN nodes. A workstation is used here to represent a LAN user�s computer; other terms used in referring to a workstation are client and node. A server is a network node that is dedicated to providing services to client nodes.

26. 1-26 General Network Implementations: MANs A MAN (metropolitan area network) is a high-speed network covering wider distances than LAN. A MAN spans distances of approximately 100 miles; therefore, it is suitable for connecting devices and LANs in a metropolitan area. MAN speeds are typically 100 Mbps or higher. The most commonly implemented MAN is the fiber distributed data interface (FDDI). It operates at 100 Mbps over fiber optic cable for distances up to 200 kilometers.

27. 1-27 General Network Implementations: WANs A WAN is the oldest type of network. WANs generally span a wide geographic area like a state, province, country, or multiple countries. However, some WANs are confined to a limited geographic area, like a LAN. A WAN in a limited geographic area could be easily extended over a wide area using the same technologies. The same is not true of a LAN.

28. 1-28 General Network Implementations: VANs A VAN is a network owned by a communications utility that sells the services of the network to other companies. A communications utility that owns a VAN provides connectivity to multiple locations. The value added by the communications utility is the maintenance and management of the communications circuits.

29. 1-29 General Network Implementations: Enterprise Networks An enterprise network is an organization�s complete network. With the advent of LANs, many companies installed departmental LANs to improve the productivity of work groups. Soon, these companies realized that there was a benefit to having users on one LAN communicate with users or applications on other LANs or on the WAN, and the various networks were connected together to form one corporate-wide network, the enterprise network.

30. 1-30 General Network Implementations: The Internet An internet (with a lowercase �i�) is the interconnection of two or more networks. An enterprise networks just described is an example of an internet. The Internet (with an uppercase �I�) is a specific instance of an internet. The Internet is a global network of networks. The Internet is made up of hundreds of networks, thousands of nodes, and millions of users throughout most countries of the world.

31. 1-31 General Network Implementations: Intranets An intranet is an organization�s private Web. Companies have found that WWW capabilities can improve the information flow and availability in a company. Companies may use an intranet rather than publishing on the Internet because the information being provided is intended for corporate use only and not for the public at large.

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33. 1-33 Section Preview Reasons organizations use networks Popular network applications Distinguishing features of LANs Situations in which a LAN can be useful Added management responsibilities when using a LAN LAN selection criteria

34. 1-34 Why Use LANs? Resource Sharing The need to share resources is still one of the primary reasons for using a network. Dedicating resources (disk drives, tape drives, printers, data, application programs, scanners, etc.) to each user is expensive. In a network, some or all of these resources may be shared. Communication We use data communications networks for communications, but the objects that are communicating are not always people. A person-to-person communication may be an electronic conversation with the two parties exchanging messages in real time. An application-to-application dialogue may be the transfer of a file from one node to another.

35. 1-35 Why Use LANs? (cont.) Management Control A LAN can help standardize the microcomputer environment. Application standards can be set up more easily in a network because most application programs�for example, word processors and spreadsheet programs�can be installed on one or more network nodes called servers. LANs can also help control computer viruses. A diskless workstation, as the name implies, has no local disk drives. This reduces the ways in which a virus can be introduced.

36. 1-36 Why Use LANs? (cont.) Cost Effectiveness The ability to share resources has a direct impact on an organization�s expenses. If users can share hardware, less hardware is needed. The less obvious cost effectiveness comes from the ability of users to communicate and thus improve their productivity. Downsizing In some companies, LANs have been used to downsize the data processing hardware, software, and personnel requirements.

37. 1-37 Why Use LANs? (cont.) New Application Software One of the newer application technologies associated with networks is called groupware�applications oriented toward improving the productivity of a group of people working together. Groupware automates work functions that require the communication and collaboration of two or more individuals. These tools raise office productivity and make LANs even more cost effective.

38. 1-38 Application Software: Personal Productivity Applications Word Processing and Desktop Publishing It is reasonable to assume that future versions will allow several users to pull out sections of a single document; allow one user to update a document and let others concurrently view but not change it; and allow users to work concurrently on the same document and view or edit the document in concert. Spreadsheets Using spreadsheets on a LAN, users can easily share templates, and multiple users can access, modify, and print completed spreadsheets. A LAN can provide the setting for widespread sharing. At the same time, the LAN can also provide protection against unauthorized changes to spreadsheets.

39. 1-39 Application Software: Personal Productivity Applications (cont.) Database Management A database management system (DBMS) gives you the ability to define, use, and manage data. With LA-oriented databases, users share the database. This reduces the amount of redundant data storage that occurs when individuals maintain their own databases on stand-alone systems. Presentation Services Graphics hardware and software can be rather expensive. A LAN allows these expensive resources to be shared, providing a cost-effective way of distributing graphics capabilities.

40. 1-40 Application Software: Workgroup Applications Electronic Mail Today�s e-mail systems allow correspondents to exchange communications containing text, graphics, and voice images in batch or real-time mode. For many companies, e-mail has become a primary mode of communications. Electronic Appointment Calendars One user can consult other users� appointment calendars to find a time at which each user is available for a meeting. Electronic Filing Cabinets E-mail and other machine-readable documents can be stored in disk folders that are equivalent to file folders in conventional filing cabinets.

41. 1-41 Application Software: Workgroup Applications (cont.) File Exchange Utilities File exchange utilities allow files to be easily copied from one network node to another. Project Management Systems The introduction of LAN implementations has allowed these systems to be integrated more completely into the workgroup. A manager and team member can agree on the parameters of a task, the team member can update his or her progress, and the manager can monitor the progress. Group Decision Support Systems Group decision support systems (GDSSs) assist individuals and groups in the decision-making process and help them set objectives.

42. 1-42 Application Software: Workgroup Applications (cont.) Electronic Meeting Systems The inclusion of networks allow participants to exchange machine-readable information in the form of graphics, text, audio, and full-motion video. Document Management Systems Capabilities include indexing documents, finding documents based on keywords contained in the document, controlling document changes, and allowing several users to collaborate on document editing.

43. 1-43 LAN Characteristics Transparent Use Mixed Hardware and Software Limited Geographical Area High Speed Resource Sharing LAN Media Communication Protocols Local Ownership

44. 1-44 LAN Selection Criteria Cost For most of us, cost is an overriding constraint, an you must choose the best solution within your budget. Usually, cost is the most inflexible constraint under which you must operate, and in the final analysis the LAN must be a cost-effective solution to your problem. Number of Workstations Each LAN is physically capable of supporting some maximum number of workstations. If you exceed that maximum number, you must make some provision for extending the maximum number. Type of Workstations The LAN hardware and software must be compatible with the workstation used and their operating systems.

45. 1-45 LAN Selection Criteria (cont.) Number of Concurrent Users As the number of concurrent users goes up, so does the LAN workload. As the LAN workload increases, you have two basic choices: You can allow system responsiveness to decrease, or you can increase the work potential of the system. Type of Use Many concurrent users may increase the LAN workload. Number and Type of Printers Some LAN operating systems have limits on the number of network printers supported by a server.

46. 1-46 LAN Selection Criteria (cont.) Distance and Medium Attaining high speed over long distances can be very expensive. Thus, each LAN has a maximum distance it can cover. Speed It is important that you select a LAN capable of meeting your performance goals. Common LAN speeds available for microcomputers are 4, 10, 16, 100, and 1,000 Mbps, and the trend is for increasing speeds. Applications If an application uses an interface not supported by a particular LAN, then the application probably will not work on that network. Moreover some software is not LAN compatible.

47. 1-47 LAN Selection Criteria (cont.) Expandability After installing a LAN, you probably will need to add workstations to it or move workstations from one location to another. The ease of doing this varies among implementations. Device connectivity Some organizations need to attach special devices to the LAN, for example, a plotter or scanner. LAN interfaces for such devices may not be available on some LANs or on some LAN file servers. Connectivity to Other Networks A variety of connection capabilities exist, but a given LAN may not support all of them. LAN Software and Hardware You need to select LAN software and hardware that will be compatible with your existing equipment.

48. 1-48 LAN Selection Criteria (cont.) Adherence to Established Standards There are several standards for LAN implementation. Some LANs conform to these standards whereas others do not. There are pros and cons of selecting either a conforming system, or a system that does not conform to standards. Vendor and Support Your vendors ought to be able to help you in times of problems; provide you with maintenance and support; and supply you with spare parts, hardware and software upgrades, and new equipment. Manageability During the selection process, you must ensure that your LAN will have the necessary management tools or that third-party tools are available. Third-party tools are those written by someone other than the LAN vendor.

49. 1-49 LAN Selection Criteria (cont.) Security Data in a LAN is shared. Sharing should not, however, imply that all users should have unlimited access to all data. The LAN software must have the ability to control access to data.

50. 1-50 Immediate and Recurring costs of a LAN

51. 1-51 Basic LAN Management Tasks

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53. 1-53 Section Preview What makes up a LAN system Several of the Leading LAN media Characteristics of LAN media Error sources, detection, and correction

54. 1-54 Three Major LAN Components LAN software Topology The media access control (MAC) protocol

55. 1-55 Things to Consider When Building a LAN A variety of media�twisted-pair wires, coaxial cable, fiber optic cable, and several lesser used wireless media Three basic topologies�ring, bus, and star Two basic media access control protocols�contention and token passing Hardware from many vendors Network operating systems from several vendors Network utilities Application software

56. 1-56 Two Major Classes of LAN Media Conducted Media uses a conductor like a wire or a fiber optic cable to move the signal from sender to receiver includes twisted-pair wires, coaxial cables, and fiber optic cables Wireless Media uses radio waves of different frequencies or infrared light broadcast through space does not need a wire or cable conductor to transmit signals

57. 1-57 Conducted Media Twisted-Pair Wires Twisted-pair wires are classified in several ways by American wire gauge (AWG) rating by shielding, either unshielded twisted-pair (UTP) or shielded twisted-pair (STP) by categories that define the wire�s rated acceptable speed and error characteristics AWG Rating The AWG rating is a measure of the thickness of the copper conductor in the cable. The higher the AWG rating, the smaller the diameter of the wire. Twisted-pair wiring for LANs have an AWG rating of 22-26.

58. 1-58 Conducted Media (cont.) UTP and STP Shielded twisted-pair (STP) These wires have a metal foil or wire mesh wrapped around individual wire pairs with a metal braided shield around the twisted-pair wire bundle itself. Twisting pairs of wires helps eliminate interference from neighboring wires; the metal shielding helps prevent ambient distortion like heavy-duty motors, electrical or magnetic fields, and fluorescent lights. Unshielded twisted-pair (UTP) These wires have no protective metal covering. UTP wires are more susceptible to environmental noise that can disrupt the signal. UTP is used because it is cheaper than STP, and it may safely be used in environments where external disruptions are rare.

59. 1-59 Twisted-Pair Wire Category Summary

60. 1-60 Coaxial Cable Most early microcomputer-based LAN implementations used coaxial cable as the medium. Coaxial cable comes packaged in a variety of ways, but essentially it consists of one or two central data transmission wires surrounded by an insulating layer, a shielding layer, and an outer jacket. Coaxial cable is most commonly used in two types of LANs, ethernet and ARCNET.

61. 1-61 A Single Conductor Coaxial Cable

62. 1-62 Fiber Optic Cable Fiber optic cables come in two varieties, multimode and singlemode, each with a different way of guiding the light pulses from source to destination. Fiber optic links for very short distances cost more than wires, but as distance or the required transmission rate increases, fiber optic cables become cost effective. Fiber optic cables will not corrode, so they can be used in environments unsuited for copper media.

63. 1-63 Views of a Fiber Optic Cable

64. 1-64 Wireless Media Broadcast Radio When broadcast radio is used with local area networks, cables connecting each microcomputer are eliminated. Microwave Radio For networks where installation of conducted media is difficult or too expensive, microwaves provide a high-speed medium alternative. Spread Spectrum Radio Its reliability in environments where signal interference is likely makes SSR well suited for LAN transmissions.

65. 1-65 Wireless Media (cont.) Infrared Transmission Infrared transmission is a line-of-sight technology. It can be used to provide LAN connections between buildings and also is the medium used in some wireless local area networks.

66. 1-66 The Frequencies of Various Wireless Media

67. 1-67 LAN Media Selection Criteria Cost Speed or Capacity Availability Expandability Error Rates

68. 1-68 Media Selection Criteria Cost The costs associated with a given transmission medium include not only the costs of the medium but also ancillary fees, such as the costs for additional hardware like repeaters that might be required. Speed Response time Aggregate data rate Expandability Some LAN media, for example, coaxial cable, are easier to expand than others, for example, fiber optic cables.

69. 1-69 Media Selection Criteria (cont.) Error Rates The propensity for error influences not only the quality of the transmission but also its speed. Security Although most of the hacker incidents reported relate to wide area networks, similar concerns occur on LANs. Distance Before deploying a medium, LAN designers need to determine the distances that need to be covered and ensure that the wiring configuration or wireless configuration does not exceed the distance limitations of the technology being used.

70. 1-70 Media Selection Criteria (cont.) Environment The constraints of environment can eliminate certain types of media. Application In some applications, the characteristics of the required equipment may dictate the type of medium and interfaces to be used.

71. 1-71 Characteristics of Common LAN Media

72. 1-72 Error Sources White Noise White noise, also referred to as thermal noise and Gaussian noise, result from the normal movements of electrons and is present in al transmission media at temperatures above absolute zero. Impulse Noise In LANs, it can be caused by lightning striking the medium, by jarring loose connections, or by transient electrical impulses such as those occurring on a shop floor. Crosstalk Crosstalk occurs when signals from one channel distort or interfere with the signals of a different channel.

73. 1-73 Error Sources (cont.) Echo Echo is essentially the reflection or reversal of the signal being transmitted. Attenuation Attenuation is the weakening of a signal as a result of distance and characteristics of the medium.

74. 1-74 Error Detection Parity Check A parity check (also known as vertical redundancy check [VRC]) involves adding a bit�known as the parity bit�to each character during transmission. Longitudinal Redundancy Check (LRC) With LRC, an additional, redundant character called the block check character (BCC) is appended to a block of transmitted characters, typically at the end of the block. Cyclic Redundancy Check (CRC) A CRC can detect bit errors better than either VRC or LRC or both. The transmitting station generates the CRC and transmits it with the data.

75. 1-75 Error Detection (cont.) Sequence Checks Sequence check numbers can be assigned to each block of data so that the ultimate receiver can determine that all blocks have indeed arrived, and the blocks can be put back into proper sequence. Error Correction Codes Some error-detection schemes allow the receiving station not only to detect errors but also to correct some of them. Such codes are called forward error-correcting codes, the most common of which are called Hamming codes.

76. 1-76 Error Correction Message Acknowledgment The mechanism used to effect retransmission is the positive or negative acknowledgment, often referred to as ACK and NAK, respectively. Retry Limit To cut down on continual retransmission of messages, a retry limit�typically between 3 and 100�can be set. A retry limit of five means that a message received in error will be retransmitted five times; if it is not successfully received by the fifth try, the receiving station either disables the link or disables the sending station itself.

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78. 1-78 Section Preview LAN topologies Media access control protocols Common ways in which topologies and media access control protocols are combined LAN standards Strengths and weaknesses of different LAN configurations

79. 1-79 LAN Topologies The term topology derives from a mathematics field that deals with points and surfaces in space�that is, with the layout of objects in space. The LAN topology is the physical layout of the network. LANs have three basic topologies: ring, bus, and star.

80. 1-80 Ring Topology

81. 1-81 Bus Topology

82. 1-82 Star Topology

83. 1-83 Data Link Protocols In general, a data link protocol establishes the rules for gaining access to the medium and exchanging messages. To do this, the protocol describes several aspects of the message-exchange process. Six of the most important are: Media Access Delineation of Data Error Control Addressing Transparency Code Independence

84. 1-84 Data Link Protocols (cont.) Media Access Media access defines how a node gains the right to transmit data on the medium. Delineation of Data A data link protocol must define or delineate where the data portion of the transmitted message begins and ends. This can be accomplished in two basic ways: by framing the data with certain control characters or by using a standard message format wherein data is identified by its position within the message.

85. 1-85 Data Link Protocols (cont.) Error Control Error control is used to determine whether data has been corrupted during the transmission. Addressing Communication between two network nodes is accomplished through an addressing scheme. Networks use a hierarchical addressing scheme, with the hierarchy being application, network node, and network.

86. 1-86 Data Link Protocols (cont.) Transparency Transparency is the ability of the data link to transmit any bit combination. We like protocols to be transparent because they can be used to transfer binary data such as object programs as well as text data. LAN data link protocols ordinarily provide transparency. Code Independence Code independence means that any data code, such as ASCII or EBCDIC, can be transmitted.

87. 1-87 MAC Protocols LAN technology adheres to two primary MAC protocols: token passing and contention. Contention In a pure contention MAC protocol, each network node has equal access to the medium. Variations of this protocol exist, some of which allow for node priorities. Token Passing Token passing is used on both bus and ring topologies. Token passing is a round-robin protocol in which each node gets an equal opportunity to transmit. With token passing, the right to transmit is granted by a token that is passed from one node to another.

88. 1-88 LAN Standards Standards exist covering most aspects of LAN technology Implementing according to established standards generally results in the availability of components from multiple vendors, competition among vendors, and lower prices. The organizations most active in setting standards for LAN topologies and MAC protocols are the IEEE and ANSI.

89. 1-89 IEEE Standards The 802 Committee established by the IEEE is divided into subcommittees, each of which addresses specific LAN issues and architecture. High-Level Interface Logical Link Control CSMA/CD Token Bus Token Ring MANs Broadband Technical Advisory Group Fiber Optic Technical Advisory Group Integrated Data and Voice Networks LAN Security Wireless LANs Demand Priority Access Method Data Transport over Cable TV Short-Distance Wireless Networks Broadband Wireless Access

90. 1-90 LLC and MAC Sublayers of the OSI Data Link Layer

91. 1-91 ANSI Distributed Queue Dual Bus LAN

92. 1-92 Suggested Broadband Frequency Allocations

93. 1-93 Comparison of Token-Passing and CSMA/CD Media Access Control Protocols

94. 1-94 Topology and Protocol Trade-Offs There are two primary LAN implementations in use, CSMA/CD buses (ethernet) and token-passing rings. Ethernet has the major market share between the two. Ethernet provides fair access for all nodes, but he exact time a node waits before sending a message may vary. Ethernet provides higher speeds and lower costs than token rings.

95. 1-95 Broadband and Baseband Technologies Broadband transmission and baseband transmission are different ways in which you can use a medium. Broadband transmission divides the medium into several channels, thus allowing the medium to be used for distinct transmission needs. Baseband transmission dedicates the entire data-carrying capacity of the medium to the LAN.

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97. 1-97 Section Preview Servers Backup devices Workstation hardware LAN adapters Printers Miscellaneous hardware

98. 1-98 Server Platforms File Services File Servers A file server allows users to share files. Only one copy of application software like word processing, spreadsheet, or database must reside on a file server. Individual clients share these applications. Database Servers The database server was developed to solve problems like passing an entire file over the medium. The most common example of a database server is the SQL server. Structured query language (SQL) is a standard database definition, access, and update language for relational databases.

99. 1-99 Server Platforms (cont.) Print Services When a client shares a printer on the LAN, it can submit jobs to the printer at any time. The print job is collected on disk, and printing is deferred until the printer is available for printing a new job and the print job is the next one eligible to be printed.

100. 1-100 Print Server Technology

101. 1-101 Server Selection Considerations Server Disk Drives When choosing a server, you should carefully select the server�s disk subsystem. There are five factors that are critical when choosing a server�s disk subsystem: Storage Capacity Average Access Time Separation of Function Fault Tolerance Drive Interface

102. 1-102 Server Selection Considerations (cont.) Server Memory In Intel-based servers, there are two classes of memory�Level 1/2 cache and standard random access memory (RAM) Processors and Processor Speed The processing power of the server is also a critical factor. It seldom makes sense to select a server that has fast disks and plenty of memory but a slow CPU. In general, the server ought to be one of the fastest�if not the fastest�computers on the network.

103. 1-103 Server Selection Considerations (cont.) Processor Bus A variety of buses are available. The bus is the path over which data is transferred between the CPU, memory, and peripherals. Expansion and Power A server should have sufficient expansion capability and the power to use the expansion slots effectively. Network server capacity can be expanded by adding hardware to the existing server or by adding additional servers. Compatibility The server platform you choose must be compatible with the topology, MAC protocol, applications, and system software on the network.

104. 1-104 IBM-Compatible System Buses

105. 1-105 Backup Devices Floppy Diskette Drives The major disadvantages of this backup method is the low capacity and speed of the backup media. Removable Disk Drives Manual intervention is necessary for changing disk cartridges, whereas some tape backup system provide tapes with much higher storage capacity and with automatic tape changing. Hard-Disk Drives The arguments for and against this alternative are much the same as those for diskettes. The major difference is that the capacity of hard-disk drives is greater than that of diskettes.

106. 1-106 Backup Devices (cont.) Optical Disk Drives Optical disk drives are gaining popularity as input, output, and backup devices. The reasons for this are their decreasing costs and large storage capacity. Magnetic Tape Drives A magnetic tape drive is the usual choice for a backup device. Magnetic tapes are less expensive than the other options. They hold large volumes of data, are easy to use and store, and generally provide good performance.

107. 1-107 Primary Backup Technologies

108. 1-108 Backup Functions

109. 1-109 Workstations Diskless Workstations A diskless workstation does not have any local disk drives. Instead, a diskless workstation has its boot logic in a read-only memory (ROM) chip located on the LAN adapter. Because diskless workstations have no disk drives, they are inherently less expensive than those with disks. Workstation Memory and Speed The speed of the workstation�s processor must be compatible with the type of work for which it is being used. Basically, it is the application, not the LAN, that determines the power of the workstations.

110. 1-110 LAN Adapters If you have chosen an architecture, medium, and media access control protocol, you have narrowed the options for LAN adapters, also known as a network interface card (NIC). LAN adapters provide the connection between the medium and the bus of the workstation or server. LAN adapters are designed to support a specific protocol using a specific medium, although a few can support two or three different medium types.

111. 1-111 Printers One major factor that affects the success of a LAN is printer support. Some LANs have restrictions regarding the distribution of printers and the number of printers that can be supported by one server. A printer driver is a software module that determines how to format data for proper printing on a specific type of printer. The printers you intend to use must be supported by the software drivers provided by the LAN operating system or printer vendor.

112. 1-112 Hubs and Switches Some LAN architectures use wiring hubs to provide device interconnection. Hubs vary in the number of ports available. A very common configuration is 8 ports, with 12- and 16-port hubs as common alternatives. Hubs may be stand-alone or stackable.

113. 1-113 Making Connections The objective of network connection�that is, connecting a computer to the LAN medium�is to provide a data path between the medium and the computer�s memory. The interface or connection to the medium is called the communications interface unit (CIU), and the interface or connection to the computer�s bus is called the bus interface unit (BIU).

114. 1-114 Details of Node-to-Medium Connection

115. 1-115 Transceiver Located on a LAN Adapter

116. 1-116

117. 1-117 Section Preview The distinction between the different classes of software The generic requirements of workstation software The generic requirements of server software Software requirements for shared access How software can be protected on a LAN Some of the standards covering LAN software The need for and general provisions of software license agreements

118. 1-118 Classes of Software Application Software Operating System Software Memory management The OS manages memory and allocates it among itself and the requesting processes according to a memory management scheme adopted by the OS designers File management The OS provides the ability to organize bits into files, files into directories, and so on User interface Creating user environments is an OS function I/O interfaces The OS and file management system translate the request to access a file into an address the disk can act on

119. 1-119 Classes of Software (cont.) Resource allocation The OS has an algorithm that determines which ready process gets access to the CPU and the conditions under which a running process maintains control of the CPU Accounting CPU usage Lines printed Disk space used Transactions submitted (by type) Data communications medium usage bytes read from and written to disk

120. 1-120 Classes of Software (cont.) Protection/Security The OS provides the base on which security is established. We expect the OS to prevent user programs from crashing the system and to eliminate the intrusion of one program onto the memory occupied by another program�s data. Database Management A database management system (DBS) extends the OS file management capabilities. A DBMS provides software that allows the user or database administrator to: Define records, files, and file relationships Access, update, and delete data in the database Set up security Establish, maintain, and use a data dictionary Use host language interfaces that allow the database to be manipulated by standard programming languages

121. 1-121 Classes of Software (cont.) Utility Software Utilities augment the function of the OS or other subsystem, such as the database management system or the data communications subsystem. Development Software Development software includes text editors, text formatters, compilers, interpreters, link editors, cross-reference programs, testing utilities, and related programs and utilities Network Management Software Network management includes a variety of activities such as backups, problem resolution, capacity planning, and establishing user environments Network Access Software Network access software for a LAN includes the components that allow us to access LAN resources from directly attached workstations and remote workstations

122. 1-122 Generic Functions of LAN System Software LAN system software is essentially an extension of the OS. It carries out hardware-oriented LAN tasks, such as interfacing to the medium, and I/O-oriented tasks such as directing print jobs and disk read/write requests to a server. The purpose of system software is to insulate applications from hardware details such as I/O and memory management. System software provides an interface through which the applications can request hardware services without needing to know the details of how the services are carried out.

123. 1-123 LAN System Software in Server and Workstation

124. 1-124 LAN Redirector Functions

125. 1-125 LAN Server Request Queue

126. 1-126 User Configuration Options

127. 1-127 A Contention Problem

128. 1-128 Exclusive, Protected, and Shared Open Combinations

129. 1-129 Waiting for Lock Release

130. 1-130 Deadlock Situation

131. 1-131 Software Standards Most of the LANs in operation today are called open networks, meaning that they adhere to a set of standards formulated by organizations such as ISO, ANSI, IEEE, and EIA. These standards are placed in the public domain and are called open standards.

132. 1-132 Software Protection Software is protected in seven basic ways: The code is kept secret so other software houses cannot use special algorithms developed by the company to write a competing system. The code is copyrighted to prevent another company from copying the code and writing a competing system. Legislation penalizing those who do not adhere to the copyright and license restrictions is enforced. The software is copy-protected to deter someone from making an illegal copy. License agreements are used to establish the terms of ownership and use. The software requires WAN/Internet verification before it is activated. The software requires a special hardware device to run.

133. 1-133 Software License Agreements The license agreement states the conditions under which you are allowed to use the product. In general, license agreements take one of the following forms: Single-user, single-workstation licenses A single-user, single-workstation license agreement is the most restrictive. It specifies that the software is to be used on one workstation only and by only one person at a time. Single-user, multiple-workstation licenses The constraints of the single-user, single-workstation agreement are relaxed by the single-user, multiple-workstation license agreement. It usually relies on the honor system for enforcement. The purchase of a single copy of the software allows the owner to install it on several systems.

134. 1-134 Software License Agreements (cont.) Restricted number of concurrent users licenses Most LAN-compatible software is designed for multiple users; however, some software vendors limit the number of concurrent users with a restricted number of concurrent users license agreement. The main idea behind this strategy is to charge by the number of users. Server licenses A server license allows an application to be installed on one server. All users attached to that server may use the application. If a company has several servers, say three, and wants to use the application on each of them, the company must purchase three licenses or three copies of the software.,

135. 1-135 Software License Agreements (cont.) Site licenses A site license gives the user unlimited rights to use the software at a given site. The site may be a single LAN or multiple LANs at one location. Corporate licenses A corporate license gives the corporation unlimited use of the software at all locations. Some companies restrict a corporate license to all locations within one country. Sometimes, the right to reproduce documentation is also granted.

136. 1-136 License Agreement Owners� Rights The license agreement is intended primarily to protect the rights of the manufacturer. However, the owner of a license agreement also has certain rights: The owner can transfer or assign the license to another user. The owner can get a refund if the product is defective or does not work as stated. The owner has legal rights granted by certain states or countries regarding the exclusion of liability for losses or damage resulting from the use of the software. The owner can terminate the license by destroying the software and documentation.

137. 1-137

138. 1-138 Section Preview Generic LAN system software functions Workstation system software functions Server system software functions Printer software Backup software

139. 1-139 Server/Workstation Communications The first problem the workstation must address is connecting to a server. Once a client has a server connection, the user at the client can log onto the network. Depending on the LAN OS being used, a user can log onto a single server, a collection of resources called a domain, or the entire corporate network. Regardless of the environment�single server, domain, or network directory�the user�s network software must find a server resource that can authenticate the logon request.

140. 1-140 Server/Workstation Communications (cont.) The address of the server with which the workstation must communicate is essential because the address is part of the data link message header. The network layer protocols determine the format of addresses. Leading transport/network layer protocols include the transmission control protocol/internet protocol (TCP/IP) used on the Internet, and the sequenced packet exchange /internet packet exchange (SPX/IPX) protocol used on many Novell and Microsoft LANs.

141. 1-141 IP and IPX Header Formats

142. 1-142 Services Advertising Protocol In Novell NetWare LAN implementations, the services advertising protocol (SAP) is implemented at the OSI application layer. Inherent in this protocol is the presence of a server table in each server and router. When the server is initiated, one of its startup functions is to broadcast a SAP message. A broadcast message has a distinct destination address that allows it to be accepted by all nodes. The SAP message identifies the server�s name, address, and the types of services it can provide.

143. 1-143 A Generic Server Table

144. 1-144 The Network Directory In a large LAN with hundreds of users, hundreds of e-mail addresses, dozens of printers, and 5 to 10 servers, keeping track of the names and locations of people and equipment is a significant effort. A network directory is fundamentally a database of LAN objects, properties of those objects, and values for properties.

145. 1-145 Possible Contents of a Network Directory

146. 1-146 Client/Server Dialogue Once the client and server have connected, a client/server dialogue can begin. When an application requests a service from the OS, it does so by issuing a signal called an interrupt. The redirector reacts to the interrupt and decides whether it is a LAN request or a local request. The redirector must know which interrupts to intercept. Once the redirector has the request, it must formulate a server message to indicate which service is to be provided. It formats a message with the proper request codes and sends the message to the LANCom process.

147. 1-147 Redirector Implementations

148. 1-148 Redirector Implementations (cont.)

149. 1-149 LAN Operating System Functions Optimized I/O One of the main services provided by a server is disk access. Disk access consists of three components: seek, latency, and transfer. I/O optimization attempts to reduce one or more of these disk access components. Disk Configurations One of the functions of an OS is to implement a file system. This involves allocating and deallocating disk space and keeping track of space allocated to each file. Partitioning sometimes it is beneficial to divide a single disk drive in two or more partitions; each partition can be managed separately

150. 1-150 LAN Operating System Functions (cont.) Single Disk Volume a volume is a logical disk (a partition or collection of partitions) or physical disk that has been formatted and can be used to store data by an OS. Multiple Disk Volumes or Volume Sets Most LAN OSs allow multiple partitions or disks to be combined to form a single logical partition. A volume created from multiple partitions is called a volume set. RAID Level 0�Striping without parity Another capability provided with some LAN OSs is called a Redundant Array of Inexpensive Disks (RAID) Level 0 or striping without parity. Multiple partitions on different disks can be combined to proved a single logical disk; striping with parity differs from a volume just described in that data is written to all partitions simultaneously.

151. 1-151 Fault Tolerance A LAN with fault tolerance allows the server to survive some failures that would ordinarily be disabling. Fault tolerance usually is provided by a combination of backup hardware components and software capable of using the backup hardware. A level of fault tolerance also can be provided by using redundant arrays of inexpensive disks (RAID). There are six levels of RAID, but for fault tolerance we are concerned only with RAID Level 1 and RAID Level 5.

152. 1-152 Mirrored Disk Drives

153. 1-153 Raid Level 5 Technology

154. 1-154 A Fault-Tolerant Duplexed Server

155. 1-155 Logical and Physical Printers In discussing the operation of a printing environment, we need to make a distinction between logical printing and physical printing. The application�s job stream is sent to a logical printer. Logical printers collect print streams from one or more applications. Logical printers are connected to zero, one, or several physical printers that Microsoft call a printing device.

156. 1-156 LAN Printing Configurations Because printing requirements vary among companies using LANs, a wide range of implementation options exist. Among these are: Private printers attached to a user�s computer and not shared Shared printers attached to file servers Shared printers attached to users� workstations Shared printers attached to computers that are dedicated to the printing task Shared printers attached to special-purpose print servers Shared printers attached directly to the LAN via an on-board LAN adapter and print server

157. 1-157 Some Spooler Options

158. 1-158 Backup Software The software used to perform the backups is as important as the hardware. Backup software is responsible for reading the files being backed up and writing them to the backup device. Backup devices often come with a backup/restore program (both capabilities are contained on one program), and most LAN system software includes a backup/restore module. Some LAN administrators choose to purchase a separate, more functional backup system than the LAN or backup device versions.

159. 1-159

160. 1-160 Section Preview What is client/server? Client/server history Client/server advantages and disadvantages Client/server technology Client/server standards Client/server database implementations

161. 1-161 What Is Client/Server? A client is a software module that relies on a server software module for some of an application�s processing requirements. The server performs the work necessary to complete the request and returns the result to the client. Client/server computing is: a modular approach to application design an architecture for software deployment and sharing a hardware-independent approach to application design

162. 1-162 Client/Server Computing: A Modular Approach The client/server approach to application design takes advantage of the fact that applications typically perform a variety of functions. Three of the most common functions are presentation, business, and database logic. If this type of architecture is adopted, changes in one functional area can be isolated from the remainder of the system.

163. 1-163 Single Process Client/Server Configuration

164. 1-164 Client/Server Computing: Software Sharing Client/server computing can take advantage of the fact that some application logic is common to multiple programs. Because most applications use databases, the logic these applications use to access and manipulate data is mostly the same. With client/server computing, these applications can share this logic rather than have it embedded within each program.

165. 1-165 Client/Server Computing: Hardware-Independent Approach Client/server provides a way of crafting application systems for single computers as well as for networks. Therefore, client/server applications can be spread over a wide variety of hardware configurations. The primary requirement is an ability for the client and server to communicate.

166. 1-166 Client/Server on a Network

167. 1-167 Client/Server an Historical Perspective In the early days of computing, a programmer often needed to address the issues of hardware interfaces as well as the issues of business logic. This required more skills from the programmer, and development time was extensive because hardware-oriented logic often had to be duplicated in multiple programs. With the advent of compilers and operating systems, the application programmer�s responsibilities were reduced. Compilers allowed code to be written in high-level languages, like COBOL and C++. ON-line transaction processing (OLTP) provided another step toward client/server computing. The implementation used in leading OLTP systems was the precursor of modern client/server computing environments.

168. 1-168 Client/Server Models

169. 1-169 Local Procedure Call Example

170. 1-170 Remote Procedure Call Example

171. 1-171 SQL Server With SQL server technology, the database processing is done on the server. In file server technology, the database processing is the responsibility of the client. The advantages of the SQL server technology are as follows: Less data is transmitted over the network. Database processing that can be optimized for that task is performed on the server. If database processing demands increase, more powerful SQL servers can be installed to accommodate the increased workload. Processing is distributed over multiple computers, each of which can be optimized for the tasks it performs.

172. 1-172 Relationship Between SQL Server and Client

173. 1-173 The Role of the SQL Server The SQL server�s job is to process the queries it receives from clients. The SQL server must be multithreaded. Because the SQL server specializes in carrying out database requests, it can be highly optimized for tasks it performs. To optimize the SQL server operations, an SQL server computer may be configured with some of the following options: Multiple processors for parallel processing Large amounts of RAM for caching disk images Processor s dedicated for improving the speed of disk access High-speed buses Efficient disk subsystems that allow parallel disk accesses Fault-tolerant disk configurations to reduce the risk of database outages High-speed communications between client and server

174. 1-174 Combined Client/Server Responsibilities Clients and servers have disjoint processing responsibilities. There are some processing responsibilities that may be assigned to either the client or the server or split between them. One example of this is the enforcement of business rules. There are advantages and disadvantages to having the logic for enforcing business rules in the server. When such logic is placed in the server, there is a single point at which the logic is placed. If the business logic changes, the change can be made in the server�s logic, and all clients immediately see the effect of the changes. However, adding application logic to the server increases its workload and can decrease the server�s ability to provide fast responses to requests.

175. 1-175 Client/Server Standards Client/server standards have been formulated to allow open systems and provide a mechanisms for interoperability of clients and servers. The standards being formed include: how clients and servers communicate with each other how clients find the server or servers that perform their needed functions Interfaces between clients and servers have come to be called middleware. Middleware is responsible for making the connection between clients and servers. Examples of middleware and its standardization efforts are: distributed computing environment (DCE) specifications object request broker (ORB) open database connectivity (ODBC)

176. 1-176 A Look to the Future Operating system and application software evolution is placing ever higher demands for disk, memory, and processing. These increasing demands together with a dependence on desktop computing have the following consequences: Newer, higher capacity computers are needed to replace older, lower capacity computers. Existing computers need upgrading to accommodate new software. Installing and supporting distributed applications can be expensive. Managing centralized systems is easier than managing decentralized systems. In an effort to trim the costs associated with software evolution, some companies are adopting the use of thin clients and server clusters.

177. 1-177 A Look to the Future (cont.) A thin client is a stripped-down microcomputer. The function of the thin client is to provide basic input and output much like the terminals in the earlier centralized host computer architectures. A cluster servers consists of two or more servers operating in concert with each other. The benefits of the then client architecture are: Lower costs because the thin clients are less expensive to buy Obsolescence is not as likely for thin clients because they do not need to keep pace with expanding software needs Software distribution and maintenance is simpler when restricted to the servers Management and control of applications and data is easier in a centralized architecture

178. 1-178 Thin Client Architecture

179. Assignment/Exercise 5/6: Local/Wide Area Networks Who is Robert M. Metcalfe? What is/are his contribution/s to the field of local area networks (LANs)? Read Metcalfe and Boggs paper entitled �Ethernet: Distributed Packet Switching for Local Computer Networks�, Communications of the ACM, Vol. 19, pp. 395-404, July 1976 and comment on its relevance or irrelevance as far as local area networking is concerned in the 2000s. (Note: Metcalfe and Boggs �original� Ethernet paper is available for free in some Internet sites [use a search engine and search for the the article title - in quotation marks.])

180. Assignment/Exercise 5/6: Local/Wide Area Networks What is the Institute for Electrical and Electronic Engineers (IEEE) Committee 802? What are its functions and sub-committees? Describe the following (potential) wide area network physical/data link layer connection technologies: plain old telephone system Leased line (64kbps, T1/E1, fractional T1/E1, etc.) Integrated Services Digital Network (ISDN) Digital Subscriber Lines (DSL) Frame Relay Asynchronous Transfer Mode (ATM) What is a repeater, a bridge, a switch, a router and a gateway? In what OSI layer does each of these devices functions? Submit: a 2-4 page write-up of your findings (be brief but concise!) Due: 19/26 Jan. 2002

181. Assignment/Exercise 5/6: Local/Wide Area Networks Familiarize with USENET Newsgroups related to local area networks, that is: comp.dcom.lans.ethernet comp.dcom.lans.fddi comp.dcom.lans.novell comp.dcom.lans.token-ring comp.dcom.lans.misc etc � Tip: For starters, read the Frequently Asked Questions (FAQ) for each area. Where can you access USENET News? A lot of sites in the Internet: Example: http://www.google.com (then click on Groups) Submit: (none) Due: (N.A.)