Platform-Specific Information

Windows 95 out of the box supports the Winsock 1.1 specification. Microsoft has made freely available a Winsock 2 update that can be downloaded from its Web site (http://www.microsoft.com/windows95/downloads/). Also, a Winsock 2 SDK is available that includes the necessary headers and libraries to compile a Winsock 2 application. Windows 98, Windows NT 4, and Windows 2000 all support Winsock 2 natively without any necessary add-ons. Windows CE supports only the Winsock 1.1 specification.

As far as support for various transport providers goes, a few limitations should be mentioned. Windows CE supports only TCP/IP and Infrared Sockets. For Windows 95 and Windows 98, the NetBIOS transport providers (transports with the address family AF_NETBIOS) are not exposed to the Winsock API. If you perform a WSAEnumProtocols, none of the NetBIOS providers will be listed, even though they are installed on the machine. However, NetBIOS is still available by using the native NetBIOS interface, as described in Chapter 1. Last, the RSVP (which offers QOS) and ATM providers listed are natively available on Windows 98 and Windows 2000.

The Winsock API and the OSI Model

Let's look at how some of the concepts presented in this chapter relate to the OSI model (see Figure 1-1). The transport providers in the Winsock catalog that are enumerated by WSAEnumProtocols are at the Transport layer of the OSI model. That is, each of these transports provides a method of transferring data; however, each is a member of a protocol, and a network protocol is at the Network layer because it is the protocol that provides a method of addressing each node on a network. For example, UDP and TCP are transports, but both belong to the Internet Protocol.

The Winsock API fits between the Session and Transport layers. Winsock provides the ability to open, manipulate, and close data sessions for a given transport. Under Windows, the top three layers (Application, Presentation, and Session) relate for the most part to your Winsock application. In other words, your Winsock application controls all aspects of the session and if necessary formats the data for the purpose of your program.