TCP/IP-32 Waits on Synchronous NCBs

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There are two types of NetBIOS commands; asynchronous and synchronous. All NetBIOS capable transports, such as TCP/IP-32, return immediately to the calling application for any asynchronous commands. The NetBIOS driver in TCP/IP-32 sets the NCB_RETCODE field to FFH to indicate that the command has been queued. When the command completes, the NCB_RETCODE field, as well as NCB_CMD_CPLT, are set to the final return code.

In the case of synchronous commands, the TCP/IP-32 NetBIOS driver waits and return only when the command has been satisfied or if the application submits a NetBIOS CANCEL or RESET. As a result, all NetBIOS commands submitted or received by the workstation are blocked until the outstanding command is processed.

To avoid blocking other NetBIOS related activity, applications should be written to submit asynchronous NCBs when possible.