There is a suite or family of protocols which includes the NetBIOS Frames Protocol, NBF, (often referred to as NetBEUI or sometimes as NetBIOS), the Server Message Block protocol, SMB, and Common Internet File System, CIFS. These protocols are associated with the original NetBIOS implementation with which they have a historical link. Many systems use SMB including Microsoft's Windows for Workgroups, Windows 95 / 98 / ME, LAN Manager, Windows NT, Windows 2000 and IBM's OS/2 and LAN Server, NetWare 6 and the SAMBA implementation. SAMBA is freely available for a wide range of systems and further information can be found at the SAMBA web site. http://www.samba.org This document begins by describing NetBIOS (Network Basic Input / Output System) also known as NetBEUI (NetBIOS Extended User Interface) or NBF (NetBIOS Frames protocol) in terms of an original suite of protocols which includes the Name Management Protocol (NMP), Diagnostic and Monitoring Protocol (DMP), User Datagram Protocol (UDP) and the Session Management Protocol (SMP) that were used in the original implementation. Following a brief description of supporting technologies such as Ethernet and Token Ring, encapsulation of these protocols is considered as well as using these protocols to encapsulate other protocols. There is no formal standard that defines the protocol(s) used with NetBIOS; in practice the IBM LAN Technical Reference IEEE 802.2 and NetBIOS Application Program Interface is used as a reference (see ). There are many implementations of NetBIOS networking and these implementations are generally incompatible. It is because of the diversity and lack of a formal standard that makes understanding NetBIOS networking difficult. It is not clear whether there is only one protocol or several protocols involved in NetBIOS networking. The original implementation for the PC Network certainly seemed to have the above-mentioned protocols (NMP, DMP, UDP and SMP) however the distinction is less clear with NetBIOS on Token-Ring and other implementations. Given that at least network layer and session layer functions are involved, the various packets used will be discussed in terms of the original protocols for convenience, even if the distinctions are somewhat arbitrary. Following descriptions of the lower level protocols and encapsulation, important higher level protocols (such as SMB, CIFS and the browser service) that run over these lower protocols are described. The situation with respect to the higher level protocols is also complicated; the protocols (SMB and CIFS) were developed as proprietary protocols and information has been difficult to obtain. Although information has been released from time to time, it is not always easy to obtain information on the latest version. Currently Microsoft continues to develop CIFS for it's range of operating systems. Teams of developers such as the SAMBA group reverse engineer the technology. This documentation presents information that is publicly available.

The NetBIOS interface was developed for International Business Machines Corporation (IBM) in 1983 by Sytec Inc. (which became Hughes LAN Systems, then Whittaker Communications). This operated over proprietary Sytec protocols on IBM's PC Network which is a broadband local area network. The broadband PC Network is a bus-attached LAN, which can accommodate up to 72 connecting devices. The baseband PC Network is also a bus-attached LAN which can accommodate up to 80 connecting devices; It is important to note the scale of LAN which NetBIOS was designed for. NetBIOS was not designed for large networks. When IBM announced the Token-Ring, an emulator for NetBIOS was produced allowing applications developed for the PC Network to operate on Token-Ring. The NetBIOS Extended User Interface (NetBEUI) was introduced in 1985. The Token-Ring network can accommodate up to 260 devices on one ring and multiple rings can be connected by Bridges. In 1986 Novell released Advanced NetWare version 2.0. With version 2.0 and all subsequent packages a NetBIOS interface has been included; Novell implemented NetBIOS encapsulated in IPX/SPX. Later Microsoft reverse- engineered the technology to provide encapsulation of NetBIOS in IPX/SPX that is compatible with the Novell implementation. With the Personal System /2 computer (PS/2) in 1987, IBM announced the PC LAN Support Program which included a NetBIOS driver. In March 1987, RFC 1001 was published which described a "Protocol Standard for a NetBIOS Service on a TCP/UDP Transport". Prior to the IBM Lan Support Program, versions of NetBIOS were named with version numbers 1.X. With the LAN Support Program the following NetBIOS versions were used: LAN Support Program version NetBIOS version 1.00 2.0 1.01 2.1 1.02 2.2 Version 2.x of NetBIOS has been superseded by NetBIOS version 3.0 and version 4.0. In 1987 Microsoft announced the LAN Manager which runs natively over NetBIOS frames. Microsoft and Intel introduced the SMB Core Protocol in 1988 (SMB-CORE.PS). SMB has been developed during subsequent years and is widely used be many systems. The protocol began life as a proprietary protocol and documentation was very difficult to find. A Version of the protocol (version 2) was published by the Open Group X/Open 1992. However since that time subsequent versions have been developed by Microsoft which re-named the protocol Common Internet File System (CIFS). The history of SMB and CIFS is further discussed in:

The protocols considered here are mainly proprietary and documentation is often poor and hard to find. A high level view is presented here that attempts to describe how the protocols relate to each other. The original NetBIOS protocol was developed to become the NetBIOS Frames Protocol (NFB) often referred to as NetBEUI or just NetBIOS. This protocol is still used today, but is not popular because it is not routable or scalable. NBF or NetBEUI provides a datagram delivery and session service that can be used for a variety of network applications. The above protocol is often encapsulated in other (routable) protocols such as IPX/SPX (which Microsoft refers to as NBIPX) or TCP/IP (which Microsoft refers to as NBT). The use of NetBIOS over TCP/IP is still one of the most popular network protocol configurations. Although NBF (either in encapsulated form or "on the wire") can be used for a variety of applications it is often used as a foundation for the Server Message Block (SMB) protocol. One of the most widely used network configurations is SMB running over NetBIOS over TCP/IP. SMB has been developed to become the Common Internet File System (CIFS). Recently CIFS has been implemented directly on TCP/IP without requiring the NetBIOS over TCP/IP layer. The relationship between the various protocols with respect to the OSI model is illustrated in:

NetBIOS is often described as a "Session Layer" protocol and a variety of transport systems have been used in different implementations. Some of these implementations are described in . The protocols used to encapsulate NetBIOS are generally well understood and well documented; what is often not well understood are implementations of NetBIOS "on the wire" in a "raw" un-encapsulated form. Two implementations of NetBIOS "on the wire" are considered here: The original NetBIOS in IBM PC Networks (See ) and NetBIOS Frames Protocol on 802.2 networks. Although the IBM PC Network version was developed first, the current NetBIOS Frames Protocol on 802.2 networks is emphasized in this document as being the more relevant. It should be noted that the frames in NetBIOS in IBM PC Networks are more complex and seem less consistent than frames in the NetBIOS Frames Protocol on 802.2 networks. The IBM PC Networks implementation separates in to the protocols mentioned above, where as all the frames in NetBIOS Frames Protocol on 802.2 networks are more consistent in their format.

Because of the history of the protocols being discussed here (See ) and lack of standards, there is often confusion in the use of some of the terms; it is not uncommon to hear statements of the form "NetBIOS is not a protocol" or "NetBEUI is a protocol". NetBIOS is not a protocol As described in the history above, NetBIOS was designed as an interface. NetBIOS was designed to be an extension to the BIOS (Basic Input/Output System) of PCs to provide networking services. At the risk of being pedantic, NetBIOS was designed as an application programming interface (API). It is interesting (and the source of some confusion) that it was the API which was the standard. NetBIOS is a protocol The term "protocol" is often used as a shorthand reference to a suite of protocols (a well-known example is the use of the term "TCP/IP protocol" to refer to a collection of protocols). The informal use of the term "protocol" is well-understood and accepted practice. It has become standard practice to use the term "NetBIOS protocol" to refer to the original set of protocols in use with the NetBIOS API and the protocols which followed. The current official term used by IBM is "NetBIOS Frames Protocol" (NBF) and it is not unreasonable to shorten this to "NetBIOS". NetBEUI is not a protocol If NetBIOS is not a protocol, but is an API, then an "Extended User Interface" to this API is also not a protocol. As mentioned above, and described in the history, when IBM developed Token Ring it was continuity of the API to ensure applications would continue to function which was important. The NetBIOS API was preserved and extended in the NetBIOS Extended user Interface, NetBEUI. NetBEUI is a protocol With the development of NetBEUI, a set of protocols was developed, now known as the NetBIOS Frames Protocol. Since the NetBIOS Frames Protocol was used with the NetBEUI API it became accepted practice to refer to these protocols as the "NetBEUI protocol". It is still common to find documentation which refers to the "NetBEUI protocol".