NetBEUI

From Free net encyclopedia

NetBIOS Extended User Interface (NetBEUI, pronounced net-booey, also known as NetBIOS Frame, or NBF) is an unrouted network- and transport-level data protocol most commonly used as one of the layers of Microsoft Windows networking. NetBIOS over NetBEUI is used by a number of network operating systems released in the 1990s, such as LAN Manager, LAN Server, Windows for Workgroups, Windows 95 and Windows NT.

The protocol is commonly confused with NetBIOS itself; NetBIOS is best thought of as a set of services provided to applications, with NetBEUI being a protocol that implements those services. NetBEUI can be seen as implementing NetBIOS over IEEE 802.2 LLC. Other protocols, such as NetBIOS-over-IPX/SPX and NetBIOS-over-TCP/IP (NBT), also implement the NetBIOS services over other protocol suites.

NetBEUI uses 802.2 type 1 mode to provide the NetBIOS name service and datagram service, and 802.2 type 2 mode to provide the NetBIOS session service (virtual circuit). NetBEUI makes wide use of broadcast messages, which accounts for its reputation as a chatty interface.

Sytek developed NetBIOS for IBM for the PC-Network program and was used by Microsoft for MS-NET in 1985. In 1987, Microsoft and Novell utilised it for their network operating systems LAN Manager and Netware.

Because NetBEUI is an unrouted protocol, It can only be used to communicate with devices on the same network segment or segments that are connected to that segment via bridges. This means that it is only well-suited for small to medium-sized networks; it must be encapsulated within another protocol in order to be of use in a wide area network.

The use of NetBEUI has decreased quickly since the development of NetBIOS-over-TCP/IP.

1 Services
2 External links

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Services

NetBIOS provides three distinct services:

Name service for name registration and resolution
Session service for connection-oriented communication
Datagram distribution service for connectionless communication

NetBEUI implements all of those services.

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Name service

In order to start Sessions or distribute Datagrams, an application must register its NetBIOS name using the Name service. To do so, an "Add Name Query" or "Add Group Name Query" packet is broadcast on the network. If the NetBIOS name is already in use, the Name service, running on the host that owns the name, broadcasts a "Node Conflict" message on the network.

In addition, to start a session or to send a datagram to a particular host rather than to broadcast the datagram, NetBEUI will have to determine the MAC address of the host with a given NetBIOS name; this is done by sending a "Name Query" packet, the response to which will have the MAC address of the host sending the response, i.e. the host with that name.

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Session service

Session mode lets two computers establish a connection for a "conversation," allows larger messages to be handled, and provides error detection and recovery.

Sessions are established by exchanging packets. The computer establishing the session sends a "Name Query" request, specifying that a session should be initialized. The computer with which the session is to be established will respond with a "Name Recognized" response indicating either that no session can be established (either because that computer isn't listening for sessions being established to that name or because no resources are available to establish a session to that name) or that a session can be established (in which case the response will include a local session number to be used in subsequent packets). The computer that's starting the session will then send a "Session Initialize" request which will prompt a "Session Confirm" response.

Data is transmitted during an established session by data packets. IEEE 802.2 handles flow control and retransmission of data packets. Because NetBIOS allows packets to be sent that are larger than the largest packet that could be transmitted on a particular MAC layer, a NetBIOS packet might have to be transmitted as a sequence of "Data First Middle" packets and a "Data Only Last" packet; packets that don't need to be segmented in that fashion will be sent as a single "Data Only Last" packet. An acknowledgment will be sent for all "Data Only Last" packets that are successfully received; this will also acknowledge all preceding "Data First Middle" packets. Sessions are closed by sending a "Session End" request.

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Datagram distribution service

Datagram mode is "connectionless". A datagram is sent with a "Datagram" packet if it's being sent to a particular NetBIOS name, or a "Datagram Broadcast" packet if it's being sent to all NetBIOS names on the network.

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