We've focused on TCP/IP for most of this article, but we promised to describe how an application can use Windows Sockets other transport protocols in Windows NT and Chicago. We'll focus on the highlights and the key features that differentiate different transport protocols, and on the mechanisms for opening sockets for use with different transport protocols.
Although these are not explicitly addressed in the Windows Sockets specification, the fact that the fundamental job of a transport protocol is data transfer, along with the fact that Windows Sockets provides a rich interface for low-level data transfer in applications, make the interface to Windows Sockets over different transport protocols quite feasible. In fact, having a common, well-known API interface allows applications to be ported quickly between different transport protocols, and there are several successful examples of this.
Because of the architecture of the Windows Sockets components of Windows NT and Chicago, all supported transports are accessed through the same DLL, WSOCK32.DLL. In fact, a single application may simultaneously use sockets of different transport protocols.
An application uses the parameters to the socket() API to specify the protocol it desires. For example, a TCP socket is opened with
s_tcp = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );
while an SPX socket is opened with
s_spx = socket( AF_IPX, SOCK_SEQPACKET, NSPROTO_SPX );
After opening a socket for a specific protocol, all actions performed on the socket go through the specified protocol. In the above example, if the application did a listen() on the s_tcp socket but not on the s_spx socket, it would receive incoming connects through TCP but not receive incoming connects through SPX.