To begin, let's step back in time. In 1984, IBM authored a simple application programming interface (API) for networking its computers called the
Network Basic Input/Output System (NetBIOS). The NetBIOS API provided a rudimentary design for an application to connect and share data with other computers.
It's helpful to think of the NetBIOS API as networking extensions to the standard BIOS API calls. With BIOS, each low-level call is confined to the hardware of the local machine and doesn't need any help traveling to its destination. NetBIOS, however, originally had to exchange instructions with computers across IBM PC or Token Ring networks. It therefore required a low-level transport protocol to carry its requests from one computer to the next.
In late 1985, IBM released one such protocol, which it merged with the NetBIOS API to become the
NetBIOS Extended User Interface (
NetBEUI). NetBEUI was designed for small local area networks (LANs), and it let each machine claim a name (up to 15 characters) that wasn't already in use on the network. By a "small LAN," we mean fewer than 255 nodes on the network - which was considered a practical restriction in 1985!
The NetBEUI protocol was very popular with networking applications, including those running under Windows for Workgroups. Later, implementations of NetBIOS over Novell's IPX networking protocols also emerged, which competed with NetBEUI. However, the networking protocols of choice for the burgeoning Internet community were TCP/IP and UDP/IP, and implementing the NetBIOS APIs over those protocols soon became a necessity.
Recall that TCP/IP uses numbers to represent computer addresses, such as 192.168.220.100, while NetBIOS uses only names. This was a major issue when trying to mesh the two protocols together. In 1987, the Internet Engineering Task Force (IETF) published a series of standardization documents, titled RFC 1001 and 1002, that outlined how NetBIOS would work over a TCP/UDP network. This set of documents still governs each of the implementations that exist today, including those provided by Microsoft with their Windows operating systems as well as the Samba suite.
Since then, the standard this document governs has become known as
NetBIOS over TCP/IP, or NBT for short. The NBT standard (RFC 1001/1002) currently outlines a trio of services on a network:
The name service solves the name-to-address problem mentioned earlier; it allows each computer to declare a specific name on the network that can be translated to a machine-readable IP address, much like today's DNS on the Internet. The datagram and session services are both secondary communication protocols used to transmit data back and forth from NetBIOS machines across the network.
