4 - Server Message Block Protocol

Abstract

The redirector and server functions of the IBM PC LAN Program implement the Server Message Block (SMB) protocol developed by Microsoft, Intel, and IBM. SMB operates at the application level, and the IBM version requires NETBIOS for proper operation. SMB is designed to be machine- and operating-system-independent, although the IBM implementation is closely tied to PC-DOS. The IBM PC LAN program is broken up into four major functions: redirector, receiver, messenger, and server. The redirector intercepts DOS 21H function calls and determines whether the request is for a local device or a remote device. If the device is local, the redirector simply passes the request to the local operating system. If the request is for a remote device, then the redirector must translate it into SMB protocols. The receiver listens for SMB protocols passed from another PC on the network, and then removes a message portion that is human-readable and passes it to a local device such as the screen, a file, or a printer. The messenger is a superset of the receiver; besides handling messages, it can also send messages the other way. It can translate messages from the user into SMB to be sent off over the network to another PC. The server is the most complex function of the program in that it implements the full set of SMB protocols and manages local devices for shared use by other PCs on the network. The types of requests that it must handle from the other PCs include requests to access files and print spooling.