Document revision date: 30 March 2001

The NetBIOS Extended User Interface (NetBEUI) was first introduced by IBM in 1985. NetBIOS, an integral part of the NetBEUI protocol driver, is a programming interface that implements many session layer functions. NetBEUI is a small, efficient, and fast protocol with low overhead.

One reason for NetBEUI's lower overhead is that NetBEUI does not require an explicit acknowledgment (ACK) of each frame before it sends the next. Instead, the computer packages up several ACKs and sends them all at once. Requiring an ACK for every packet wastes network resources. NetBEUI dynamically determines the number of frames the sender can transmit before receiving an ACK, based on the network's current conditions.

NetBEUI was developed for LANs segmented into workgroups of 20 to 200 computers, with gateways connecting LAN segments to one another or to mainframes. NetBEUI is optimized for very high performance when used in departmental LANs or LAN segments. For traffic within a LAN segment, NetBEUI typically is the fastest protocol.

While NetBEUI is fast on small LANs, it is not so effective on large networks because it has a poor addressing scheme. NetBEUI does not allow duplicate computer names on the same network. This prevents a network from having two computers with the same name---something difficult to eliminate on a large network.

Table B-3, NetBEUI Protocol, summarizes the advantages and disadvantages of the NetBEUI protocol.

Table B-3 NetBEUI Protocol

Advantages	Disadvantages
Tuned for small LAN communication, and therefore is very fast on LANs.	Not routable.
Good error protection.	Performance across WANs is poor.
Small memory usage.	Requires each network computer to have a unique name.

B.3.3 DECnet-Plus Protocol

DECnet-Plus is a proprietary protocol; it is a collection of many layered protocols offered together as a major data communications network. Developed as a distributed network, it supports a wide range of applications and programs.

One of the DECnet protocol's major advantages is flexibility in network configuration and applications functionality. DECnet-Plus includes the Local Area Transport (LAT) protocol that terminal servers use to communicate with hosts.

Table B-4, DECnet-Plus Protocol, lists the advantages and disadvantages of the DECnet-Plus protocol:

Table B-4 DECnet-Plus Protocol

Advantages	Disadvantages
Major flexibility in network configuration.	Complex network architecture.
Routable.	Proprietary.
Maintains a high level of availability, even in the event of node or link failure.
Supports a wide range of communications facilities, such as Ethernet and X.25.

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