Figure 4.4 The Windows networking stack consists of several components that work together to provide client access to network resources.
A client is a software component that enables a computer to access the resources provided by a server. Clients can take many forms, and can either be included as part of an operating system or distributed as a separate product. In its simplest form, a client can be a standalone program that sends requests to and receives replies from a server. Your Web browser, for example, is a client that communicates with Web servers on your local network or the Internet. In the same way, FTP, e-mail, and news reader programs are all clients. These clients function at the application layer of the OSI reference model and are highly specialized; they only communicate with one type of server. Application-layer clients contain no lower-layer protocols of their own, relying instead on protocols such as TCP/IP and Ethernet, which are already installed on the computer, to provide network communication services.
The other main type of client on a workstation is the one that enables you to access shared resources on the local network, such as files and printers. This type of client is more tightly integrated with the operating system; you don't have to launch a special program and you can access files and printers through your regular applications, just as though they were part of your local computer environment. This type of client is specific to the platform used by the server. There are clients for Windows networks, clients for NetWare, and clients for UNIX systems. In some cases, the client is supplied as part of the operating system, while in others you must install a separate client software package. The following sections examine the different LAN client platforms.
Almost all versions of Windows (including Windows for Workgroups, Windows 95, Windows 98, Windows Me, as well as Windows NT and Windows 2000, in both Server and Workstation versions) include both client and server capabilities with the operating system. This means that you can share the files and printers on any of these Windows systems and also use the client capabilities to access shared files and printers on other systems. Note that Windows 3.1 and earlier ship with no network client at all.
In the case of Windows 95, Windows 98, Windows Me, Windows NT, and Windows 2000, the operating system includes everything you need to connect to a Windows network, including a complete client networking stack. The stack (shown in Figure 4.4) consists of the following major components:
Together with the network interface adapter, these software components provide the functions of all seven layers of the OSI model. A system can have more than one of each component installed, providing alternative paths through the networking stack for different applications. Most of the Windows operating systems include two redirectors. For example, there might be one for Windows networking and one for connecting to NetWare servers. The operating systems include multiple protocol drivers for the same purpose. NetWare connectivity traditionally requires the IPX protocol (although the latest versions of NetWare do support TCP/IP), and a Windows network can use TCP/IP or NetBEUI. Windows and NetWare systems usually share the same network medium, but it's also possible to install two network interface adapters, each with its own driver, and connect the computer to two networks, one for Windows and one for NetWare.
The protocols at the various layers specify the path up or down through the OSI model. For example, when a packet arrives at a workstation from the network, the Ethernet frame contains a code that specifies the network layer protocol that it should use. The network layer protocol header then specifies a transport layer protocol, and the transport layer header contains a port number that identifies the application that should receive the data. For packets generated by the workstation, the process works in reverse. The redirector specifies a transport layer protocol, the transport layer specifies the network layer protocol, and the network layer specifies the data-link layer protocol.
While technologies like Plug and Play now automate the installation of the Windows networking components in most cases, you may still find yourself having to install a client or a protocol manually. The process of installing a protocol module on a Windows 2000 Professional system is described below. The procedure is virtually identical in Windows 95, Windows 98, and Windows Me. Windows NT uses a slightly different user interface, but the networking architecture is essentially the same.
When Microsoft first introduced its own network operating systems (Windows for Workgroups and Windows NT) in 1993, Novell NetWare ruled the local area networking industry. In order to successfully compete with Novell, Microsoft knew that their operating systems had to be able to access NetWare resources, but early attempts to have Novell supply a NetWare client for the Windows operating systems failed. As a result, Microsoft developed the NetWare clients for Windows, and Novell subsequently released clients of their own. Both have continued to update their software, and to this day you can choose between the Microsoft client for NetWare that ships with Windows or download Novell's client from their Web site.
The NetWare clients provided in the Windows operating systems by Microsoft fit into the same networking architecture as the client for Microsoft networking. In order to access NetWare resources in Windows 2000 Professional, you must install the Client Service for NetWare (CSNW) and the NWLink IPX/SPX/NetBIOS Compatible Transport Protocol modules using the same procedure described earlier in this lesson under "Installing Windows Networking Components." In Windows 95, Windows 98, or Windows Me, the names of the modules are slightly different; you must install the Client for NetWare Networks and the IPX/SPX-compatible Protocol.
The CSNW module is a second redirector that you can use along with—or instead of—the Microsoft networking client. When an application requests access to a network resource, the system determines whether the request is for a Windows or NetWare file and sends it to the appropriate redirector. The NWLink protocol module is a reverse-engineered version of Novell's IPX protocols. In most cases, Windows systems use the IPX protocols only to access NetWare servers. The NetWare redirector is connected to the NWLink protocol module, while the Microsoft redirector uses TCP/IP or NetBEUI. Both protocols' modules are then connected to the same network interface adapter driver, as shown in Figure 4.6.
The CSNW included with Windows 2000 Professional and Windows NT Workstation provides basic NetWare connectivity, but Windows 2000 Server and Windows NT Server include the Gateway Service for NetWare (GSNW), which expands this functionality. In addition to providing client access to NetWare servers, GSNW also enables Windows systems without a NetWare client installed to access NetWare resources. Once you've installed GSNW, the service's client capabilities enable it to connect to NetWare servers. You can then configure GSNW to share those NetWare resources using the system's Microsoft networking capabilities. When a Windows client accesses the share on the Windows NT or Windows 2000 server, the server accesses the files on the NetWare server and relays them to the client.
Novell continues to maintain its own client software packages for NetWare, which you can use instead of those included with the Windows operating systems. The Microsoft and Novell clients both provide the same basic functionality, such as access to NetWare volumes and printers and access to Novell Directory Services, but Novell's clients also provide additional capabilities that are helpful to administrators and power users.
The primary difference between the Microsoft and Novell clients is that the Novell clients include the NetWare Administrator application, which is the tool that administrators use to create and maintain objects in the NDS database. This is a critical part of NetWare administration, and it's the main reason for using Novell clients instead of Microsoft clients. Apart from including NetWare Administrator, Novell clients provide additional file management functions and utilities accessible from shortcut menus and the Taskbar tray, but they also tend to be noticeably slower than Microsoft clients.
Novell maintains the following three NetWare clients for Windows:
The Windows 95, Windows 98, Windows NT, and Windows 2000 clients all consist of modules that fit into the existing Windows networking architecture. Each client includes its own redirector—which is a genuine Novell IPX protocol module, rather than Microsoft's compatible version—and network interface adapter drivers that conform to the Open Data-Link Interface (ODI) standard used by Novell. However, the client can use the NDIS drivers supplied with Windows, if one is already installed.
Though Novell has not added Windows Me to the list of supported clients, they claim that the client for Windows 95 and Windows 98 will fully support Windows Me, as well.
The client for DOS and Windows 3.1x is different, because these operating systems don't have their own networking capabilities. The client provides a complete networking architecture in itself, which can also work alongside the Windows client included in Windows for Workgroups.
