Many companies today have heterogeneous networks, that is, networks with components by many different manufacturers and with different operating systems. Terminal servers are often integrated in these networks, most of which are not based on pure Microsoft platforms. Integrating third-party systems is very important in these environments but is not of central importance in this book. Third-party integration is covered by more general publications about Windows Server 2003. That is why we provide only a quick overview of this topic here.
In heterogeneous terminal server environments, Novell or UNIX servers are especially popular. Mixed operation requires a connection through gateways, directory services, network-based file system, and the special implementation of Server Message Blocks. In some cases, the Network Information System (NIS) is also required as a name service.
For years, Novell NetWare has been an established and powerful network operating system in the PC world, competing with Windows 2000 and Windows Server 2003. With the growing use of Windows environments, many companies and institutions have been considering how to integrate an existing Novell network. Both Microsoft and Novell offer suitable solutions. Whereas the solutions supplied by Microsoft mostly focus on converting an existing NetWare environment to a Windows 2000 or Windows Server 2003 environment, Novell, of course, targets the integration of Windows systems in a NetWare centric environment. Particularly on terminal servers, it is possible to replace the existing authentication component (GINA-DLL) with an alternative that allows logon using Novell servers.
UNIX is a widely used operating system, albeit with no common standard. Various manufacturers, such as IBM, Sun, Hewlett-Packard, Silicon Graphics, and Apple offer their own UNIX derivates. These, however, are mostly bundled with hardware. Another option is to use the open-source UNIX variant named Linux that is supplied by different distributors. Linux is not owned by a commercial company but is developed by a global independent software community. Most traditional UNIX manufacturers also support the Linux software community and are increasingly adapting their products to Linux.
Most UNIX derivatives come with a graphical user interface based on the X11 standard. For terminal servers to access UNIX server file and print services, either Samba, the Network File System or the remote line printer (LPR) mechanism can be used. In principle, it is possible to start and use UNIX and Windows-based applications from a suitable client. This is, in fact, practiced by many companies that have Linux on the client platforms but terminal servers and ICA clients for a number of applications.
An interesting alternative to X11 for transmitting UNIX desktops and applications to remote clients is the Citrix MetaFrame XP Presentation Server for UNIX. This system replaces the X11 protocol with the ICA protocol, which is done by modifying the UNIX operating system. The advantage of this solution for transmitting screen content is that the bandwidth required by ICA is significantly lower than that needed by X11.
As in the client/server landscape, it is possible to connect mainframes to a terminal server by installing emulation tools for direct mainframe access. Another option is a gateway for the implementation of TCP/IP access methods for mainframe-specific communication protocols. A third option is middleware products that allow direct communication between the two rather contradictory computer worlds. Integrating terminal servers and mainframes can therefore be a very complex task that might even require specific adjustments to some software components. It is, for instance, very possible that, for Windows to access a mainframe, the middleware first needs to be adjusted for multiple-user operation before it can be used on terminal servers.
Now, we are again at a point where we started in the Preface of the book: looking at Mainframes and terminal server as central execution platforms for applications. The last 11 chapters showed, however, why terminal servers are not just another incarnation of mainframes but comprise many advanced concepts related to modern, centrally managed Windows-based applications. The next two chapters will show another, even more spectacular aspect of server-based computing: the combination of terminal servers and Web technologies. If mainframe computing represents the past, and pure terminal server environments stand for the present use of centrally managed Windows-based applications, the advantages of combining terminal servers and Web technologies might well be seen as a preferred enterprise application providing option in the near future. Microsoft Windows Server 2003, including the .NET Framework, Terminal Services and Internet Information Services, is a perfect platform for this option.