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Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

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Most traditional applications are hosted centrally on mainframe computers, and users access these applications via dumb terminals or PCs running terminal emulation software. In this case, the application runs entirely on the mainframe computer. The user interfaces tend to be character-oriented instead of graphical, making them somewhat user unfriendly. Another problem is that they are costly and time-consuming to change. For example, a programmer normally must alter the program to accommodate simple changes to a report format. Some products, though, are starting to appear on the market that convert terminal updates to graphical formats. For example, Client/Server Technologies Inc.’s GUISys/3270 file format conversion software enables users to migrate from IBM’s 3270 screens to GUI applications. GUISys/3270 is a Microsoft Windows application that reads 3270 screen information from a PC’s 3270 emulator buffer and sends the data through a pattern-matching knowledge base to create GUI formats for the 3270 screen. This product enables users to change screens without complex programming techniques. All-in-all, however, mainframes are generally more expensive to maintain.

Today, many companies are beginning to deploy client-server applications based on the model shown in figure 8.3. The user interfaces to the application located on the server via a client program that performs some of the processing. The server software is generally a database, such as Sybase.


Figure 8.3  The concept of a client-server system.

There are several benefits of developing applications based on client-server principles. For one, the interfaces are graphical (generally based on Microsoft Windows) and are very simple to use and relatively easy to develop and modify. For example, Powersoft’s Powerbuilder and Microsoft’s Visual Basic are common tools for developing client-server applications that interface with various databases.

Many applications are available off-the-shelf, especially common office software such as Microsoft’s Word for word processing, PowerPoint for presentations, and Excel for spreadsheets. In some cases, though, it might be necessary to develop a specific application. This process is beyond the scope of this book, but would include a software engineering process similar to deploying a wireless network—that is, to analyze requirements, design the software, implement the code, and install. The main difference between an application and network implementation project is the level of detail required in the analysis phase. Generally, you must determine much more specific requirements for applications than for the networks that support them.

Network Operating System

The network operating system (NOS) provides a platform for applications, printing, and file sharing. The NOS, combined with a hardware platform such as a PC, is referred to as a server. Most NOSs require the installation of client software on a user’s PC to act as an interface to the server. As shown in figure 8.4, some NOSs are server-oriented, meaning a dedicated hardware platform supports the NOS software and users generally access network services directly from the server. Generally the server-oriented NOSs offer the greatest performance and functionality. Other NOSs are peer-to-peer, which distribute network applications and services among the users’ workstations. Novell’s NetwareLite and Artisoft’s Lantastic are examples of peer-to-peer NOSs.


Figure 8.4  Server-oriented versus peer-to-peer network operating systems.

Through the NOS software, a system administrator can open accounts for users by assigning user names, passwords, and access rights to resources located on the server. The NOS supports the remote storage of applications and files, and users can access these via the network. If a user runs an application, such as Microsoft Word, located on a server, the user opens the drive mapped to a directory on the server where the application resides, then runs the application. The server sends the application to the user’s workstation where the application will run. As users create documents, they can store the files on the server.

In some cases, such as the interfacing of wireless terminals to a database, you probably do not need an NOS—all the networking you need can be handled by wireless products performing physical and data link functions, along with software to interface with the database. If you’re going to host client-server applications for others to access, you need to choose an NOS. Two prominent NOSs on the market today are Microsoft’s NT Server 3.51 and Novell Netware 4.1. Novell’s Netware supports access to all enterprise network resources via a single-point login and leads the industry in market share for NOSs. Most people agree Netware is an excellent choice for file and print services; however, many feel Netware doesn’t support applications as well as NT Server. NT Server is a 32-bit multithreaded, multitasking operating system and is scaleable in terms of processors. NT Server also includes a preemptive multitasking operating system that dedicates time slots to application processes. This means that the failure of one process does not affect the processing time of another process; thus NT Server is unlikely to crash because of a single bad application. This is analogous to the operation of a multicylinder automobile engine. If one of the spark plug wires breaks, the other spark plugs keep the car running.

Desktop Operating System

Whether the wireless network implementation includes either portable or desktop PCs, you probably need to select an appropriate desktop operating system. This operating system runs on the PC and supports the client piece of the NOS and client-server application. Desktop operating systems have undergone a dramatic evolution in the past fifteen years. Initially for PCs, Microsoft developed the Disk Operating System (DOS), which is character-based and requires users to understand DOS commands in order to copy and edit files and run applications. Later, of course, Microsoft introduced Windows, offering a graphical interface for users to manage their files and execute applications.


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