50-20-42 DATA COMMUNICATIONS MANAGEMENT ACCESSING WINDOWS APPLICATIONS FROM UNIX AND VICE VERSA Raj Rajagopal INSIDE Accessing Windows Applications from an X-Station, Coexistence Options, Windows in an X-Station, Accessing Windows Applications, Accessing UNIX Applications from Windows Desktops, Emulators Migrating from one environment to another takes planning, resources and, most importantly, time (except in very trivial cases). This implies that even if eventually migrating to another environment, one still has to deal with coexistence among environments in the interim. In many com- panies it would make good business sense not to migrate legacy systems at all. Instead, it may be better to develop new systems in the desired en- vironment and phase out the legacy applications. The data created by the legacy applications is important and one must ensure that data can be ac- cessed from a new environment. Coexistence considerations are very im- portant in this case. Coexistence between Windows PAYOFF IDEA NT, UNIX, and NetWare deals with a Some users want applications they develop in number of related issues. One may one environment to execute in other environ- need to access Windows applications ments with very little change. With this approach, they can continue to develop applications with from a UNIX machine or need to ac- the confidence that they will execute in another cess UNIX applications from Win- environment even if the environments change in dows desktops. One may prefer to the future. In applications that can run in both have the same type of desktop (Òan Windows NT and UNIX, this can be accomplished enterprise desktopÓ) for all users and in several ways: be able to access different environ- •use APIs — there are three flavors of this ap- ments. One may also need to emulate proach one environment within another. •layered APIs that reside on top of native APIs It may also be necessary to access •layered APIs plus extensions •emulated APIs services such as file and print servic- •use Win32 and port to UNIX es in heterogeneous environments. A •use POSIX and port to Win32 Auerbach Publications © 1999 CRC Press LLC EXHIBIT 1 — Heterogeneous Client Interconnectivity It may also be necessary to access services such as file and print ser- vices in heterogeneous environments. A set of interoperability products exists to enable clients attached to one type of server (e.g., UNIX, Net- Ware, and Windows NT) to have transparent access to services from oth- er servers and mainframes, as shown in Exhibit 1. As mentioned earlier, access to the data available in another environ- ment is very important and heterogeneous file access is needed. ACCESSING WINDOWS APPLICATIONS FROM AN X-STATION The previous article discussed the different options for porting or migrat- ing applications between environments. There are situations where port- ing would make good business sense. There are other situations where the best business option would be to leave applications running in one environment and access these applications from other environments. There are many organizations that have existing UNIX applications that are satisfactory. They are also using Windows desktops, primarily for of- fice needs. An important requirement is to access the Windows office ap- plications from the same X-stations that are already accessing the UNIX applications. An X-station includes X-terminals, UNIX workstations, and any device capable of performing a similar function. Organizations can provide access to different environments and appli- cations by providing separate systems on users’ desks or arrange a shared pool of machines. There are other options that provide access to applications executing in different environments from the same desktop. These are called coex- istence options. Using coexistence options, different applications are ac- cessed in multiple windows on the same desktop, transparently, to the user. Coexistence options may avoid the necessity to port applications, but keep in mind that there are subtle end-user differences between the user interface used in UNIX and that used in Windows. These differences could become an annoying factor for a user to deal with, particularly if the user has to switch back and forth between Windows and UNIX ap- plications often. Another potential problem is the lack of some Windows functionality, such as OLE and Clipboard, when these functions are not supported by the coexistence solution provider. COEXISTENCE OPTIONS There are several ways in which applications in different heterogeneous environments can coexist. These include: • In an environment where X-stations or X-terminals are already con- nected to different applications, Windows applications can be added to the X-station. Examples of this coexistence approach include WinDD from Tektronix, X Connection from ConnectSoft, and Win- Center from Network Computing Devices. Adding Windows applica- tions to an X-station is covered in this article. • Just as Windows can be added to an existing X-station, an X-server can be added to a PC that may already be running Windows applica- tions to access non-Windows applications. Examples of this coexist- ence approach include DESQview/X from Quarterdeck, and eXceed from Hummingbird Communications. X-server on Windows is cov- ered later in this article. • To cater to the needs of desktops capable of working in heteroge- neous environments, some vendors have developed machines with features useful for operating in heterogeneous environments. Such features include different connectivity options to connect to different networks. Examples of this coexistence approach include Personal Workstations from Digital, which are multi-client desktops. • There are emulation solutions that permit an executable developed in one environment to run on another through emulation. The emu- lation solutions interface between the application executable and the operating environment. Examples of emulation solutions include Windows Binary Application Interface (WABI), SoftWindows from In- signia, and MERGE from Locus Computing. • In some instances, the applications and users’ access are fine, but an individual may want to access the data across environments. There are solutions that permit applications to have file access in heteroge- neous networked environments. Examples of networked file access EXHIBIT 2 — Windows in an X-Station solutions include BW-Connect NFS, Chameleon 32 NFS, and PC-In- terface, and PC-NFS from Intergraph. WINDOWS IN AN X-STATION An overview of how a Windows application can be added to an existing X-station is shown in Exhibit 2. The X-station may already be attached to an IBM mainframe applica- tion using a 3270 emulation window, to a VAX application, and to a UNIX application as an X-server. The Windows application is enabled as another window on the X-station and the new window is controlled by an application server running the Windows application. How Do X-Stations Support Windows Applications? A simplified, conceptual view of how X-stations support Windows Appli- cations is shown in Exhibit 3. The Windows application performs its application processing and in- vokes the operating system for end-user display services. Typically, the display is physically attached to the same machine on which the applica- tion runs but that need not always be the case. The X-station vendors provide a server piece and a client piece that comes in between the Windows application and the display and interfac- es between the two. The client passes user responses, such as keystrokes and mouse clicks, to the server which passes them to the Windows ap- EXHIBIT 3 — X-Station Support for Windows Applications plication. The Windows application responds to the user input just as it normally would. The application server sends the output from the Windows application back to the client. The user sees the regular Windows application screens. The protocols used for the exchange between the application server and the client is the X Windows protocol or the intelligent console architecture (ICA) protocol. The connection between the application server and the client could be LANs (if it local), intranets, or even the Internet. Do not confuse the X-station approach with keeping applications on a file server and loading them locally for execution. With X-stations, the Windows applications run on an NT server which has been modified to add multi-user support, and not locally. Note on protocols: the X Windows protocol is the industry standard protocol for communication between a client and an X-server. Use of X protocol permits the use of any device that follows the protocol. The ICA is similar to the X Window protocol. ICA is a proprietary protocol devel- oped by Citrix Systems. Citrix has licensed this protocol to some vendors (e.g., Tektronix and Network Computing Devices). Microsoft recently announced that it will include ICA support in future versions of Windows 95 and NT, and, potentially, in Internet Explorer. By using the ICA protocol, vendors have been able to provide more func- tionality and faster responses than the X Window protocol. The ICA pro- tocol transmits less data. However, some graphics-rich and multimedia applications do not run well with ICA. ICA supports only 256 colors. X- stations vendors typically offer a choice of protocols between which the user can alternate. Considerations in Using the X-Station Approach If one is a manager trying to decide if an X-station approach is right for your business, here are some advantages and disadvantages to consider. Advantages of the X-Station Approach. • Using an X-station approach may be able to provide access to Win- dows applications, such as office applications and e-mail, without having to buy a PC and Windows for every user. • It is easier to administer Windows applications usage since the actual Windows application is installed only on one machine (the applica- tion server). It is also easier to control usage and availability of the Windows applications.