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MODULE I INTRODUCTION TO DATA COMMUNICATIONS AND NETWORKING Lesson 1 Networking Fundamentals Lesson 2 Network Building Blocks Lesson 3 Types of Networks Lesson 4 The Network Operating System Module I ...

MODULE I INTRODUCTION TO DATA COMMUNICATIONS AND NETWORKING Lesson 1 Networking Fundamentals Lesson 2 Network Building Blocks Lesson 3 Types of Networks Lesson 4 The Network Operating System Module I  2 MODULE I INTRODUCTION TO DATA COMMUNICATIONS AND NETWORKING  INTRODUCTION As you begin your study, it is important that you understand some of the fundamental concepts upon which computer networks are built. This module introduces some basic principles of computer-based networking, discusses advantages of networking, presents the idea of connecting computers together and how the computers in the network are configured and how they share information determine whether the network is peer-to- peer or server based—another important network classification. Without a network operating system of some kind, individual computers cannot share resources, and other users cannot make use of those resources. This module provides a general introduction to network operating systems (NOSs). It describes the basic features and functions of NOS and contrasts these with each other. OBJECTIVES After studying the module, you should be able to: 1. Define a computer network. 2. Discuss advantages of using a network. 3. Identify network services. 4. Identify the network main blocks. 5. Identify a peer-to-peer network and a server-based network. 6. Identify the main functions of network operating systems 7. Identify essential NOS components. 8. Describe the elements and services of client software. 9. Describe the elements and services of server software. 10.Distinguish between network operating types.  DIRECTIONS/ MODULE ORGANIZER There are four lessons in the module. Read each lesson carefully then answer the exercises/activities to find out how much you have benefited from it. Work on these exercises carefully and submit your output to your instructor or to the College of Computer Science office. Module I  3 In case you encounter difficulty, discuss this with your instructor during the face-to-face meeting. If not contact your instructor at the College of Computer Science office. Good luck and happy reading!!! Lesson 1 Module I  4  Networking Fundamentals 1.1 WHAT IS A NETWORK? The information technology has been the driving force in most of the advances witnessed this century. There has been a revolution in the way information is gathered, processed and distributed. This revolution can’t be done without the convergence of computing and communications. Telephones, radio, television, and computers nowadays are the tools for this information revolution. Geographically distributed computers can be hooked up together to permit the exchange of data and information. Computer network can be defined as a collection of devices that can store and manipulate electronic data, interconnected in such a way that network users can store, retrieve, and share information. Commonly connected devices include microcomputers, minicomputers, mainframe computers, terminals, printers, fax machines, pagers, mobiles and various data storage devices as shown in Figure 1.1. In today's business world, a computer network is much more than a collection of interconnected devices. For many businesses, the computer network is the resource that enables them to gather, analyze, organize, and disseminate the information that is essential to their profitability. The rise Module I  5 of Intranets and Extranets is the latest indication of the crucial importance of computer networking to businesses. Intranets and Extranets are private business networks that are based on Internet technology. Intranets, Extranets, and the Internet will be treated in more details later. For now, it is enough to understand that businesses are currently implementing Intranets at a breakneck pace and for one reason only, an Intranet enables a business to collect, manage, and disseminate information more quickly and easily than ever before. Many businesses are implementing Intranets simply to remain competitive; businesses that delay are likely to see their competition outdistance them. 1.2 BENEFITS OF COMPUTER NETWORKING The most obvious benefit of computer networking is that you can store and retrieve virtually any kind of information on a computer network, including textual information such as letters and contracts, audio information such as voice messages, and visual images such as facsimiles, photographs, medical x-rays, and even videos. In addition to information storage and retrieval, there is a host of other important benefits of networking computers. Having a computer network enables us to combine the skills of different people and the power of different equipment, regardless of the physical locations of the people or the equipment. Computer networking enables people to easily share information and hardware, allowing them to take advantage of communication medium such as electronic mail, newsgroups, and video conferencing. It also allows them to work more securely, efficiently, and productively. Nevertheless, the major benefits of computer networking are: 1.2.1 Powerful, Flexible Collaboration To be able to collaborate electronically from widely separate physical locations has significant advantages. It enables people to avoid the considerable time investments and costs connected with traveling. It enables people to communicate instantaneously, regardless of the distance, and to act before their competitors do. It frees people from having to reconcile the differences in multiple information files. Electronic collaboration enables people to minimize the amount of work required to complete projects, it frees them from redoing work they would do correctly in the first place if they had instantaneous access to up-to-date information and instructions. For example, users can engage in real time teleconferencing, talking face to face, while simultaneously viewing and editing the same document, adding and deleting notes and comments, and instantaneously viewing each other’s changes as they are made. They can do this without having to worry about accidentally changing the work of others. 1.2.2 Freedom to Choose the Right Tool Module I  6 Open networking products enable users to work on the type of computer best suited to the job they must do, without placing restrictions on their file-sharing capabilities. The design of any particular computer can make it well suited for some tasks and not suited for others. In an open environment, you can combine many kinds of computers to take advantage of the special strengths of each type of machine. For example, Novel network users can use IBM PCs running any version of Windows or DOS, Macintosh computers running a version of the Macintosh operating system, Sun workstations running the UNIX operating system, and many other types of computers, all on the same network. Scientists, secretaries, doctors, lawyers, writers, editors, artists, engineers, everyone can use the type of computer equipment best suited to the type of work he or she does, yet each can still easily share information with others. 1.2.3 Cost-effective Resource Sharing A network enables users to share any networkable equipment or software and realize the benefits that you would enjoy from resource sharing. On a network, users can share printers, modems; data storage devices, such as hard disks and CD-ROM drives; data backup devices, such as tape drives; E-mail systems; facsimile machines; and all networkable software. When you compare sharing these resources to purchasing them for each computer, the cost savings can be enormous. When we implement an Intranet, we can share network resources with suppliers, consultants, and other outside partners. We will be able to rent applications over the Internet. Businesses have capability to explore Intranet resource sharing. 1.2.4 Worldwide, Instantaneous Access to Information With access to our business's Intranet and Web server, we will be able to easily and inexpensively access any new or updated information, from anywhere in the world, within a few seconds after it is published. The Internet provides the low-cost backbone for global access to your Intranet, and existing Web browsers and other Intranet tools make it easy for even the most novice computer user to access the information and Intranet resources they need. The best networks have extremely powerful security features that enable us to exercise flexible control of who will have access to sensitive data, equipment, and other resources. 1.2.5 Secure Management of Sensitive Information There is another advantage to computer networking that may be even more important than instantaneous, coordinated information and resource sharing. The best networks have extremely powerful Module I  7 security features that enable you to exercise flexible control of who will have access to sensitive data, equipment, and other resources. 1.2.6 Effective Worldwide Communications If you choose a networking company that offers a full suite of products—including robust directory services—and that supports open standards, you will be able to connect heterogeneous computing equipment at distant geographic locations into one cohesive network. As a result, you will be able to disseminate critical information to multiple locations anywhere in the world, almost instantaneously. 1.2.7 Easy, Immediate Information Dissemination When we implement a business Intranet, we can create or update information that will be easily and immediately make it accessible to all company employees. With a World Wide Web server running on our Intranet and with today's powerful Web publishing tools, we can create or change any information using a favorite, familiar application, and we can have that information automatically and instantaneously published on our Web server. This information will then be available to anyone who has the rights to access it, anywhere in the world. 1.3 NETWORK BUILDING BLOCKS Data Communication is a process of exchanging data or information. In case of computer networks this exchange is done between two devices over a transmission medium. This process involves a communication system which is made up of hardware and software. The hardware part involves the sender and receiver devices and the intermediate devices through which the data passes. The software part involves certain rules which specify what is to be communicated, how it is to be communicated and when. It is also called as a Protocol. The following sections describes the fundamental characteristics that are important for the effective working of data communication process and is followed by the components that make up a data communications system.  EXERCISE 1. Discuss Computer Network. 2. What are the services provided by networks? 3. List five advantages of networking. 4. Draw a simple network set-up in your home. Module I  8 Lesson 2  Network Building Blocks 2.1 END SYSTEMS, CLIENTS AND SERVERS In computer networking jargon, we often referred to the computers that we use on a daily basis as "hosts" because they host (run) application- level programs such as a Web browser or server program, or an e-mail program. They are also referred to as "end systems" because they sit at the "edge" of the networks, as shown in Figure 1.2. The computers that end users use to access the resources of the network are Client computers. They are typically located on the users’ desks, while computers that provide shared resources, such as disk storage and printers, as well as network services, such as e-mail and Internet access are known as Server computers. 2.2 NETWORK INTERFACE CARDS (NICS) OR NETWORK ADAPTERS NIC enables the computer to communicate over a network. Every end system must have a network interface card (or a built-in network port) in order to be a part of a network. Module I  9 2.3 PHYSICAL CONNECTING MEDIUM The physical medium can take many shapes and forms, and does not have to be of the same type for each transmitter-receiver pair along the path. Examples of physical medium include twisted-pair copper wire, coaxial cable, multimode Optical fiber cable, terrestrial radio spectrum and satellite radio spectrum. Module I  10 2.4 INTERMEDIATE SWITCHING DEVICES Physical medium usually doesn’t connect computers directly to each other. Instead, each end system is connected to a device that in turn, connects it to the rest of the network. Router, switches, hubs, bridges, and gateways, are examples of connecting and switching devices, we refer to the combination of these devices as a network core. Module I  11 2.5 NETWORK SOFTWARE Although network hardware is essential, what really makes a network work is software. A whole bunch of software has to be set up just right in order to get a network working. Server computers typically use a special network operating system (also known as NOS) in order to function efficiently and client computers need to have their network settings configured properly in order to access the network. A network operating system (NOS) is a specialized operating system for a network device such as a router, switch or firewall. Proprietary network operating systems  Cisco IOS, a family of network operating systems used on Cisco Systems routers and network switches. (Earlier switches ran the Catalyst operating system, or CatOS)  RouterOS by MikroTik  ZyNOS, used in network devices made by ZyXEL FreeBSD, NetBSD, and Linux-based operating systems  Cisco NX-OS, IOS XE, and IOS XR; families of network operating systems used across various Cisco Systems device including the Cisco Nexus and Cisco ASR platforms  Cumulus Linux distribution, which uses the full TCP/IP stack of Linux Module I  12  DD-WRT, a Linux kernel-based firmware for wireless routers and access points as well as low-cost networking device platforms such as the Linksys WRT54G  Dell Networking Operating System; DNOS9 is NetBSD based, while OS10 uses the Linux kernel  Extensible Operating System runs on switches from Arista and uses an unmodified Linux kernel  ExtremeXOS (EXOS), used in network devices made by Extreme Networks  FTOS (Force10 Operating System), the firmware family used on Force10 Ethernet switches  ONOS, an open source SDN operating system (hosted by Linux Foundation) for communications service providers that is designed for scalability, high performance and high availability.  OpenWrt used to route IP packets on embedded devices  pfSense, a fork of M0n0wall, which uses PF  OPNsense, a fork of pfSense  SONiC, a Linux-based network operating system developed by Microsoft  VyOS, an open source fork of the Vyatta routing package  EXERCISE 1. What is Network Operating System? 2. Classify the network main blocks. Module I  13 Lesson 3  Types of Networks 3.1 PEER-TO-PEER NETWORK Not all computers are equal in a network - their status depends on the role they perform. There are three kinds of computers in a network: 1. Client computers: Use network resources. 2. Peer computers: Use and provide network resources. 3. Servers: Only provide network resources. We cannot assume that the role of a computer in a network is tied to the operating system it runs. A Macintosh is not a peer unless it is sharing network resources. And do not be surprised if somebody decides to run Windows NT as merely a client, it would be a tragic waste of resources. The operating system merely determines the networking potential of a computer. Depending on how we assign roles to individual computers in our network, we can classify all networks into three broad categories. Peer-to-peer is a style of networking in which a group of computers communicate directly with each other, rather than through a central server. Every computer in this network functions as both clients and servers to the other computer on the network. Peer nodes may differ in local configuration, processing speed, and network bandwidth and storage quantity. Popular examples of peer-to-peer are file-sharing networks. Peer to peer networks have no role for servers and are thus marked by the total absence of central control. All you have to do is an individual log into workgroups and start working. Everybody shares disk resources and devices like printers in the manner they deem fit. You also need to use a network operating system to recognize the other workstations in the network. In this configuration, each user in the network determines which data Base or resources they wish to share. Figure 1.3 illustrates a peer-to- peer. 3.1.1 Peer-to-Peer Advantages 1. A peer-to-peer network is a simple solution for interconnecting computers. Just add a network interface card (NIC) to each system, connect the systems with cabling and begin sharing information. 2. Peer to peer networks allow economical communication with other users when there is a limited amount of data to exchange. Sharing expensive peripherals becomes easy. Moreover, your productivity will increase with the ability to send files and messages without having to leave your workstation. Module I  14 3. These networks are relatively inexpensive (no server hardware, no administrator) and work quite well for very small operations. 3.1.2 Peer-to-Peer Disadvantages 1. In peer-to-peer networks, all users must be located in the same general area. If you exceed 5-10 users with this type of network, the network management may become very difficult. 2. Because there is no dedicated server to handle the file and print sharing administration, peer to peer networking may not be practical for intensive file transfer/storage or heavy printer sharing applications. 3. Security in these networks is lax, work can be cumbersome if every peer decides to put up a password on his/her machine, and system performance suffers dramatically if there is too much traffic on a particular machine. 4. Plus, the absence of central control means that data is disorganized and very tough to locate over the network. 5. When the numbers of workstations in the network increase, problems will arise due to the cost of administration and security. Module I  15 3.2 CLIENT-SERVER NETWORK Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request. Although the client/server idea can be used by programs within a single computer, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common. For example, to check your bank account from your computer, a client program on your computer forwards your request to a server program at the bank. That program may in turn forward the request to its own client program that sends a request to a data base server at another bank computer to retrieve your account balance. The balance is returned back to the bank data client, which in turn serves it back to the client in your personal computer, which displays the information for you. Servers and clients are usually connected with network interface cards using a cabling system and hub to work with the chosen protocol. Figure 1.4 illustrates a small client/ server network. A dedicated server provides responsive, highly available file storage and backup for all the users; expedited printing capabilities, as well as e-mail or Internet access for the group. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. The client/server model has become one of the central Module I  16 ideas of network computing. Most business applications being written today use the client/server model. In the usual client/server model, one server is activated and awaits client requests. Typically, multiple client programs share the services of a common server program. Both client programs and server programs are often part of a larger program or application. Relative to the Internet, the Web browser is a client program that requests services (the sending of Web pages or files) from a Web server (which technically is called a Hypertext Transport Protocol or HTTP server) in another computer somewhere on the Internet. In the old days, the clients were simply dumb tubes. They had a monitor and a keyboard. This type of system is still common in banks and hotels where storage of data locally at the client is undesired or unnecessary. The trend has been to use smart clients in most new client/server networks. Smart clients will have their own local storage of data and programs that offer far more flexibility. 3.2.1 Client-server Advantages 1. A client-server networking strategy provides powerful and secure communication services for workgroups from 3-4 users up to hundreds of users. 2. The server provides high levels of control over resources shared on the network and makes administrating the network much easier than in a peer-to-peer environment. The Client / Server networking is cost efficient since you can use basic workstations and a fast server. 3. Workstations may be equipped with less memory and smaller hard drives, thus saving on total setup costs. Users will have access to all the power of the server and all the resources on the network with excellent response time, even though hundreds of other users may also be connected. 4. Client-Server networks revolve around powerful machines that take care of the security and administration on the network. 5. Servers normally have very specific roles in the network, therefore they split the support objectives of the network. Module I  17 3.2.2 Client-server Disadvantages Even though the Client-Server type of network has many advantages, there are some disadvantages: 1. The cost of this type of network is relatively high up front. Not only must you purchase the server hardware, but most server software is very expensive, especially for larger networks. This is due to the fact that some software companies charge more for each client computer that requires connection to the main server. 2. Another downside to be considered is the possibility of the main server having problems. How fast must you have the network working again? If you need all time operability, you should allow in your budget a second "redundant" server. Hence if the main server goes down, the redundant server will step in and provide services until the primary server is back up again. An experienced administrator should be able to setup redundant servers that will assume control of failing servers without user intervention. 3.2.3 Comparison between Peer-To-Peer and Client Server Types 3.3 HYBRID NETWORKS Most networks in the world are hybrid networks that run clients, peers and servers together. Users get the best of all worlds - shared resources are located on servers but the users can still directly touch their peers (bypassing the PDC) for shared resources. This has an important implication on security - users can be assigned variable levels of access to the server and peer machines depending on the importance of the data. Hybrid Access Networks refer to a special architecture for broadband access networks where two different network technologies are combined to improve bandwidth. A frequent motivation for such Hybrid Access Networks to combine one xDSL network with a wireless network such as LTE. The technology is generic and can be applied to combine different types of access networks such as DOCSIS, WiMAX, 5G or satellite networks. The Broadband Forum has specified an architecture as a framework for the deployment of such converged networks. Module I  18  EXERCISE 1. List types of networks. 2. Compare between peer-to-peer and server-based networks. Lesson 4  THE NETWORK OPERATING SYSTEM (NOS) 4.1 Network Operating System Definition and Services. Module I  19 A network operating system acts as the command center, enabling all of the network hardware and all other network software to function together as one cohesive, organized system. It is the heart of the network. The term network operating system, however, is generally reserved for software that enhances a basic operating system by adding networking features. NOS, includes special functions for connecting computers and devices into a local-area network (LAN). It is installed onto each PC that requires network access. It is like a traffic warden that monitors the exchange and flow of files, electronic mail, and other network information. NOS is a specialized system software designed to provide networking functionality. It has all the features of a standalone operating system but offers many more facilities in a complex environment. In addition to the usual lower level computing functions, a network operating system is responsible for other functions such as: 1. Directing data traffic through the network 2. Security functions such as authentication, authorization, logon restrictions and access control so it can allow and prevent access to data. 3. Protection and synchronization functions that enable it to prevent access to data files while they are being processed. 4. Managing the flow of information between a variety of workstations 5. Internetworking functions to support data traffic using internetworking device such as switches, routers and other devices. 6. Functions to manage requests for file, print, web services, back- up and replication. 7. Functions to manage connections between the network and remote sites. 8. Functions that provide name and directory services Module I  20 9. User management and support functions for logon and logoff, remote access; system management, administration and auditing tools with graphic interfaces Network Operating System (NOS) is an operating system that includes special functions for connecting computers and devices into a local-area network (LAN) or Inter-networking. You can use NOS to create local area networks (LANs) that function as either peer-to- peer networks or server-based networks, depending on the needs and budget. 4.2 Peer-to-Peer Network Operating Systems Peer-to-peer network operating systems enable networked computers to function as both a server and a workstation. In a peer- to-peer network, the operating system is installed on every networked computer; this enables any networked computer to provide resources and services to all other networked computers. For example, each networked computer can allow other computers to access its files and use connected printers while it is in use as a workstation. Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. Peer-to-peer operating systems have advantages and disadvantages when compared to client-server operating systems. They provide many of the same resources and services as do client- server operating systems, and, under the right circumstances, can provide good performance. They are also easy to install and usually inexpensive. However, peer-to-peer networks provide fewer services than client-server operating systems. The services they provide are less robust than those provided by mature, full-featured client-server operating systems. The performance of peer-to-peer networks commonly decreases significantly under a heavy load. Furthermore, maintenance is often more difficult: Because there is no method of centralized management, there are often many servers to manage (rather than one centralized server), and many people may have access to and the ability to change the configuration of different server computers. Windows XP, Windows Me, Windows 2000 Professional, Windows 98, Windows 95, and Windows for Workgroups offer peer-to- peer networking features. 4.3 Client Server Network Operating System The components of the client server network operating system include: Module I  21 1. Client Software which is the network software installed on the client's machines. They provide the capabilities required for clients to access and use the network resources. 2. Server Software which is the network software that is installed on the servers. They provide the capabilities required for network operation. 4.4 Client Software The network client software actually performs an operation that makes the computer think the network resource is just a local resource. In a network environment when a user initiates a request to use a resource that exists on a server in another part of the network, the request has to be forwarded or redirected to the server that is managing the requested resource. The two component of the client software that does this task are: Redirector may also be referred to as a requester. When a standalone computer accesses a file on the local hard drive or prints to a directly connected local printer, this request for service goes to the computer's processor. The processor then makes this request a reality and either opens the specified file or sends a print job to the printer. All this activity is managed locally. This process is handled by the redirector. If the redirector finds that the user wants to access a remote file on a server or print to a network printer, the request is forwarded to the network server. If the request is for the access of a local file (on the computer's hard drive), the redirector allows the request to proceed to the computer's processor so that the request can be processed locally. Figure 1.6 shows a diagram of how the redirector directs requests to either the local processor or the network server. The client computer is fooled by the redirector into thinking that all the resources it accesses (whether local or remote) are local. Module I  22 Drive Designators may be associated with the shared network resources. They are used by the redirector to locate the network resource. For instance, if you want to access a particular shared directory on a remote computer you can assign a letter of the alphabet say E to it. You can then refer to the shared directory on the remote computer as E and the redirector will locate it. Designators make it unnecessary for users to worry about the actual location of data or peripherals. They can send requests to computers or peripherals. Client workstations can provide business functions using a mixture of personal productivity products in conjunction with a custom application. For example, a document created by a word processor can include input from a spreadsheet program and the invoice data created by the client/server application. The capability to cut and paste input from several different sources is one of the most powerful aspects of a client workstation. It provides the end user with tools to create new applications—without the need to go to professional programmers for assistance. The client almost always provides presentation services. User input and final output, if any, are presented at the client workstation.  Request for Service: Client workstations request services from the attached server. NOS software translates or adds the specifics required by the targeted requester to the application request. The most basic service provided by the NOS is redirection Module I  23  Remote Procedure Call (RPC): Remote procedure calls (RPCs) standardize the way programmers must write calls, so that remote procedures can recognize and respond correctly.  Fax/Print Services: The NOS enables the client to generate print requests even when the printer is busy. The client workstation can view the status of the print queues at any time.  Window Services: The capabilities to activate, view, move, size, or hide a particular window is provided by the window services of the client operating system. These services interact with message services provided to notify the user of events that occur on a server.  Remote Boot Services: Some applications operate well on workstations without any local disk storage; The client workstation must provide sufficient software burned into erasable programmable read-only memory (E-PROM) to start the initial program load (IPL)—that is, boot—process. E-PROM is included in all workstations to hold the Basic Input/Output System (BIOS) services.  Other Remote Services: Software is provided by the NOS to run on the client workstation to initiate some remote applications like Backup services, Business functions such as downloading data from a host or checking a list of stock.  Utility Services: Local functions such as copy, move, edit, compare, and help that execute on the client workstation.  Message Services: Provide the buffering, scheduling, and arbitration services to support this function.  Network Services: Set of services and APIs that create, send, receive, and format network messages. These services provide support for communications protocols, such as NetBIOS, IPX, TCP/IP, APPC, Ethernet, Token Ring, FDDI, and X.25.  Application Services: Custom applications use APIs embedded in an RPC to invoke specialized services from a remote server.  Data base Services: Data base requests are made using the SQL syntax. SQL is an industry standard language supported by many vendors.  Network Management Services-Alerts: Most network interface cards (NICs) can alerts to signify detected errors and perhaps to signify messages sent and received. These alerts are generated by Module I  24 (NICs) and are valuable in remote LAN management to enable early detection of failures.  Dynamic Data Exchange (DDE): DDE is a feature that enables users to pass data between applications from different vendors through support for common APIs.  Object Linking and Embedding (OLE): This is an extension to DDE that enables objects to be created with the object components software aware, which automatically launches the appropriate software to manipulate the data. OLE focuses on data sharing between applications on a single desktop.  Common Object Request Broker Architecture (CORBA): CORBA addresses cross-platform data transfer and the process of moving objects over networks. CORBA support enables Windows and UNIX clients to share objects. 4.5 Server Software The server software makes it possible for users on machines to share the server's data and peripherals including shared directories, printers, plotters and disks. The server software not only allows the sharing of resources but also determines the degree of sharing. The degree of sharing includes: 1. Allowing different users different levels of access to the resources. For example, a file server could give Read, Write or Read and Write permissions to different users. 2. Coordinating access to the resources to make sure that two users do not use the same resource at the same time. The sever software is used to: 1. Create user privileges which indicates who will be using the various resources on the network 2. Validate user names and passwords at the time of logging on 3. Grant or deny user privileges on the network 4. Add and remove users. Module I  25 Servers are designed for nearly every purpose imaginable, from simple email servers to more complicated application servers. Every application will have specific server requirements, and is typically designed to run on Windows NT/2000/2003, Novell Netware, or Linux. Many servers can run multiple applications to serve a variety of needs. The following is just a brief of the most common types of server applications... File and Print Servers File servers store files created by application programs. In some configurations, the file servers might also hold the application programs themselves. A file server is a computer that has a hard disk drive large enough to share. File servers provide the ability to simultaneously access the same file. Print servers accept print jobs sent by anyone across the network. The print-server software also reports the status of jobs waiting for printing and recognizes the priorities assigned to specific users. Mail Servers: Mail servers manage local (within your network) and global (Internet-wide) electronic messaging. The mail server you choose should support the Internet standards such as POP3, and SMTP. Fax Servers: Fax servers manage fax traffic in and out of the network, allowing multiple users to send and receive faxes without a fax machine. Web Servers: Web servers allow Internet users to attach to your server to view and maintain web pages. The two most popular web servers are Apache and Microsoft Internet Information Services (IIS). Data base Servers or Data base Management Systems (DBMS): Though not exactly a server, DBMS systems allow multiple users to access the same data base at the same time. While this functionality is typically built into data base software (ex. Microsoft Access allows concurrent connections to its databases), a larger data base or a data base with many users may need a dedicated DBMS to serve all the requests. Application Servers: Application servers have undergone many changes and have grown in both quantity and variety with the growth of the Internet. An application server acts as an intermediary to information. In many usages, the application server works with a Web server and is called a Web application server. The web application server receives requests from a web page then returns the information in a new web page based on the results and uniquely created. Module I  26 Terminal Servers or Communication Server: Generally, a terminal server refers to a piece of hardware that allows devices to be attached to the network without a need for network cards. PCs, "dumb" terminals supporting just a mouse and monitor, or printers can all be attached via standard ports, and can then be managed by the network administrator. Proxy Servers: Proxy servers act as interne diaries between your network users and the wide world of the Internet. Proxy servers perform a number of functions: 1. Masks network users IP addresses 2. Strengthens security by only allowing certain requests to come through and by providing virus protection 3. Caches web page data for a given period to allow for more rapid access Wi Windows NT Server, Windows 2002 Server, Windows 2003 Server, Linux and the Macintosh OS/X Server are good examples of Server NOS. 4.6 Hybrid Network Operating System Some NOS producers build peer-to-peer networking into their operating systems from the ground up. The two systems essentially run on top of each other. Users can share files on their workstations in addition to the resources available to them on the network. The focus of the network however, remains on the fileserver and users are normally discouraged from using the peer-to-peer functionality available to them. Windows NT networks are a perfect example of a hybrid network operating system.  EXERCISE 1. What are the services provided by NOS? 2. What is client software? 3. What is server software? 4. What is redirector? 5. What is client/server system’s primary function? 6. List the most common server types you know. Module I  27 7. List the most common presentation services provided by client software. Module I