The Server Message Block Protocol (SMB), is an application level protocol see the appendix called Open Systems Interconnection (OSI) Reference Model

SMB is used to implement network session control, network file and print sharing and messaging. SMB is used to provide functionality that is broadly analogous to the AppleTalk Session Protocol, AppleTalk Filing Protocol and Printer Access Protocol etc in the AppleTalk suite of protocols. SMB is also broadly analogous with Novell's NetWare Core Protocol (NCP). It is difficult to find a non-proprietary protocol or protocols with in the TCP/IP suite which can be compared to SMB; file sharing via FTP or NFS and network printing via LPR are examples of similar functionality.

SMB requires a transport /session protocol and the early versions of IBM's implementation were closely linked with NetBIOS. In general SMB runs either over the NetBIOS Frames Protocol (NBF), NetBIOS over TCP/IP, or NetBIOS over IPX; the most recent versions of CIFS can run directly over TCP/IP.

Server Message Block (SMB) / CIFS
/   /   \   \
NetBIOS Frames Protocol (NBF) i.e. NetBEUI i.e. NetBIOS or NetBIOS over TCP/IP RFC 1001 RFC 1002 or NetBIOS over IPX or directly over TCP/IP

See the appendix called Open Systems Interconnection (OSI) Reference Model for details of the relationship between the various protocols.

SMB has inherited some of the advantages and disadvantages of NetBIOS, in particular, prior to the latest versions of CIFS it was directly linked with the NetBIOS addressing scheme.