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NetBIOS (abbreviation for English Net work B asic I nput O utput S ystem ) is a programming interface (API) for communication between two programs over a local network.


NetBIOS was developed in 1983 on behalf of IBM by Sytek for IBM's PC network as a proprietary hardware solution for networking small workgroups.

The functions made available by NetBIOS, however, went beyond the pure hardware abstraction, such as that provided by the system BIOS , for example . In contrast to today's network drivers, whose function is the delivery of data packets by the respective hardware ( layer 2 ), NetBIOS implements functions for name resolution, packet-oriented and connection-oriented communication. Direct access at the package level was not provided for in the PC network.

The first network functions in PC-DOS and MS-DOS were based on NetBIOS.

With the transition to standardized networks such as Token Ring and Ethernet from around 1985, the need arose to be able to use existing software over the new networks. For this purpose, the NetBIOS functions were implemented in an emulation program, which in turn accesses the new, packet-oriented network drivers. The protocol used was commonly referred to as NetBIOS, which led to the confusion that still exists today about whether or not NetBIOS is a protocol. The protocol, i.e. the implementation of NetBIOS directly on layer 2, was later referred to as NetBEUI . In the absence of appropriate provisions in the protocol, it cannot be routed , and due to the concept of the NetBIOS functions, it uses a relatively large number of broadcasts and is therefore commonly regarded as a "chatty" protocol.

In 1986, the Novell company implemented a NetBIOS emulation based on the IPX / SPX protocol. In 1987 IBM followed with the implementation of NetBIOS on the TCP / IP protocol, which is now known as NetBIOS over TCP / IP (NBT), as defined in RFC 1001 (Protocol Standard for a NetBIOS Service on a TCP / UDP Transport ). Both IPX and IP are routable protocols, which means that NetBIOS-based applications can be used beyond the boundaries of small local networks.

The use of alternative name resolution mechanisms ( WINS , DNS ) also solves the problem of high broadcast volumes.

Functions of NetBIOS

Name resolution
NetBIOS allows an application to register a 16-character name across the network. Originally the assignments of names to network addresses were announced to all participants by broadcast. Each NetBIOS name is configured as either a unique name (exclusive) or a group name (non-exclusive).
In Microsoft networks, 15 of the 16 possible characters are used for names; the 16th character is used as a suffix to address various services such as server, RAS, messenger, etc.
Computer name + 00h exclusive Workstation Service
Computer name + 03h exclusive Intelligence service
Computer name + 20h exclusive Server service
Username + 03h exclusive Name of the logged in user
Domain name + 1Bh not exclusive Name of the domain of which the computer is a member
(If the name is less than 15 characters, it will be padded with spaces.)
Connectionless data exchange (datagram service)
The corresponding functions implement unsecured, packet-wise communication between two end points, similar to UDP in the Internet. The connectionless datagram mode supports some broadcast functions and offers the possibility of establishing virtual transport connections as well as the management of symbolic names for end addresses. The application is responsible for maintaining the session.
Connection-oriented data exchange (session service)
Analogous to TCP , NetBIOS offers secure, serialized point-to-point connections, i.e. This means that messages can be transmitted that are larger than the maximum length of an individual data packet, and packets that have arrived incorrectly or that have been lost are requested again. Error detection and error correction are therefore carried out in this mode.

Individual evidence

  1. NetBIOS - Network Basic Input / Output System. Retrieved December 18, 2018 .