Connectionless Network Communications

With unreliable connectionless communications, NBF transmits the message once or a specified number of times and is responsible only for ensuring that the frame is properly transmitted on the network medium. The message can only be a single frame. The SSAP, DSAP, and the network adapter address of the destination client are all that is needed for unreliable connectionless communications, and no acknowledgment from the destination client is required.

Note

Connectionless communications can be either unreliable or reliable. NBF provides only unreliable connectionless communications. Reliable connectionless communication is like a registered letter whose sender is notified that the letter arrived. If reliable connectionless communication is required, NBF can be configured for certain communication commands to send a number of frames that allow time for the destination computer to respond to the message. The number is based on setting a retry value for the registry entry NameQueryRetries . The time between sending each frame is determined by time-out registry entry NameQueryTimeout .

Three types of NetBIOS commands generate connectionless communications:

• Name claim and resolution

• Datagrams

• Miscellaneous commands

These commands are sent as Unnumbered Information frames at the LLC layer.

To understand how Windows 2000 uses retry and time-out values, consider what happens when a Windows 2000–based computer running NBF registers its NetBIOS computer name. The Windows 2000–based computer sends a multicast message containing an ADD_NAME_QUERY frame on the network. Other computers on the network running NBF can retrieve and process the ADD_NAME_QUERY message. The multicast frames are sent as many times as is specified by AddNameQueryRetries at time intervals specified by  AddNameQueryTimeout. This allows computers on the network enough time to inform the sending computer if the name is already registered as a unique computer name or as a group name on the network.

All registry values discussed in this chapter are found under the following registry path:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Nbf

Warning

Do not use a registry editor to edit the registry directly unless you have no alternative. The registry editors bypass the standard safeguards provided by administrative tools. These safeguards prevent you from entering conflicting settings, or settings that are likely to degrade performance or damage your system. Editing the registry directly can have serious, unexpected consequences that can prevent the system from starting, and require that you reinstall Windows 2000. To configure or customize Windows 2000, use the programs in the Microsoft Management Console (MMC) or Control Panel whenever possible.