NCB

The NCB structure describes a network control block. A pointer to this structure is passed to the Netbios function.

typedef struct _NCB { // ncb

UCHAR ncb_command;

UCHAR ncb_retcode;

UCHAR ncb_lsn;

UCHAR ncb_num;

PUCHAR ncb_buffer;

WORD ncb_length;

UCHAR ncb_callname[NCBNAMSZ];

UCHAR ncb_name[NCBNAMSZ];

UCHAR ncb_rto;

UCHAR ncb_sto;

void (*ncb_post) (struct _NCB *);

UCHAR ncb_lana_num;

UCHAR ncb_cmd_cplt;

UCHAR ncb_reserve[10];

HANDLE ncb_event;

} NCB;

Members

ncb_command

Specifies the command code and a flag that indicates whether the NCB structure is processed asynchronously. The most significant bit contains the flag. If the ASYNCH constant is combined with a command code (by using the OR operator), the NCB structure is processed asynchronously. The following command codes are supported:

Code	Meaning
NCBACTION	Enables extensions to the transport interface. NCBACTION commands are mapped to TdiAction. When this code is specified, the ncb_buffer member points to a buffer to be filled with an ACTION_HEADER structure, which is optionally followed by data. NCBACTION commands cannot be canceled by using NCBCANCEL.
NCBADDGRNAME	Adds a group name to the local name table.
NCBADDNAME	Adds a unique name to the local name table.
NCBASTAT	Retrieves the status of the adapter. When this code is specified, the ncb_buffer member points to a buffer to be filled with an ADAPTER_STATUS structure, followed by an array of NAME_BUFFER structures.
NCBCALL	Opens a session with another name.
NCBCANCEL	Cancels a previous command.
NCBCHAINSEND	Sends the contents of two data buffers to the specified session partner.
NCBCHAINSENDNA	Sends the contents of two data buffers to the specified session partner and does not wait for acknowledgment.
NCBDELNAME	Deletes a name from the local name table.
NCBDGRECV	Receives a datagram from any name.
NCBDGRECVBC	Receives broadcast datagram from any host.
NCBDGSEND	Sends datagram to a specified name.
NCBDGSENDBC	Sends a broadcast datagram to every host on the local area network (LAN).
NCBENUM	Enumerates LAN adapter (LANA) numbers. When this code is specified, the ncb_buffer member points to a buffer to be filled with a LANA_ENUM structure.
NCBFINDNAME	Determines the location of a name on the network. When this code is specified, the ncb_buffer member points to a buffer to be filled with a FIND_NAME_HEADER structure followed by one or more FIND_NAME_BUFFER structures.
NCBHANGUP	Closes a specified session.
NCBLANSTALERT	Notifies the user of LAN failures that last for more than one minute.
NCBLISTEN	Enables a session to be opened with another name.
NCBRECV	Receives data from the specified session partner.
NCBRECVANY	Receives data from any session corresponding to a specified name.
NCBRESET	Resets a LAN adapter. An adapter must be reset before any other NCB command that specifies the same number in the ncb_lana_num member will be accepted.
	The IBM NetBIOS 3.0 specification documents several NCB_RESET NCB's. Win32 implements the NCB.RESET using the dynamic link routine interface. Particular values can be passed in specific bytes of the NCB, more specifically:
	If ncb_lsn is not 0x00, all resources associated with ncb_lana_num are to be freed.
	If ncb_lsn is 0x00, all resources associated with ncb_lana_num are to be freed, and new resources are to be allocated. The ncb_callname[0] byte specifies the maximum number of sessions, and the ncb_callname[2] byte specifies the maximum number of names. A nonzero value for the ncb_callname[3] byte requests that the application use NAME_NUMBER_1.
NCBSEND	Sends data to the specified session partner.
NCBSENDNA	Sends data to specified session partner and does not wait for an acknowledgment.
NCBSSTAT	Retrieves the status of the session. When this value is specified, the ncb_buffer member points to a buffer to be filled with a SESSION_HEADER structure, followed by one or more SESSION_BUFFER structures.
NCBTRACE	Activates or deactivates NCB tracing. Support for this command in the system is optional and system-specific.
NCBUNLINK	Unlinks the adapter.

ncb_retcode

Specifies the return code. This value is set to NRC_PENDING while an asynchronous operation is in progress. One of the following return code values can be specified:

Value	Meaning
NRC_GOODRET	The operation succeeded.
NRC_BUFLEN	An illegal buffer length was supplied.
NRC_ILLCMD	An illegal command was supplied.
NRC_CMDTMO	The command was timed out.
NRC_INCOMP	The message was incomplete. The application is to issue another command.
NRC_BADDR	The buffer address was illegal.
NRC_SNUMOUT	The session number was out of range.
NRC_NORES	No resource was available.
NRC_SCLOSED	The session was closed.
NRC_CMDCAN	The command was canceled.
NRC_DUPNAME	A duplicate name existed in the local name table.
NRC_NAMTFUL	The name table was full.
NRC_ACTSES	The command finished; the name has active sessions and is no longer registered.
NRC_LOCTFUL	The local session table was full.
NRC_REMTFUL	The remote session table was full. The request to open a session was rejected.
NRC_ILLNN	An illegal name number was specified.
NRC_NOCALL	The system did not find the name that was called.
NRC_NOWILD	Wildcards are not permitted in the ncb_name member.
NRC_INUSE	The name was already in use on the remote adapter.
NRC_NAMERR	The name was deleted.
NRC_SABORT	The session ended abnormally.
NRC_NAMCONF	A name conflict was detected.
NRC_IFBUSY	The interface was busy.
NRC_TOOMANY	Too many commands were outstanding; the application can retry the command later.
NRC_BRIDGE	The ncb_lana_num member did not specify a valid network number.
NRC_CANOCCR	The command finished while a cancel operation was occurring.
NRC_CANCEL	The NCBCANCEL command was not valid; the command was not canceled.
NRC_DUPENV	The name was defined by another local process.
NRC_ENVNOTDEF	The environment was not defined. A reset command must be issued.
NRC_OSRESNOTAV	Operating system resources were exhausted. The application can retry the command later.
NRC_MAXAPPS	The maximum number of applications was exceeded.
NRC_NOSAPS	No service access points (SAPs) were available for NetBIOS.
NRC_NORESOURCES	The requested resources were not available.
NRC_INVADDRESS	The NCB address was not valid.
	This return code is not part of the IBM NetBIOS 3.0 specification and is not returned in the NCB structure. Instead, it is returned by the Netbios function.
NRC_INVDDID	The NCB DDID was invalid.
NRC_LOCKFAIL	The attempt to lock the user area failed.
NRC_OPENERR	An error occurred during an open operation being performed by the device driver. This return code is not part of the IBM NetBIOS 3.0 specification.
NRC_SYSTEM	A system error occurred.
NRC_PENDING	An asynchronous operation is not yet finished.

ncb_lsn

Specifies the local session number. This number uniquely identifies a session within an environment.

ncb_num

Specifies the number for the local network name. This number is returned by Netbios after a successful NCBADDNAME or NCBADDGRNAME command. This number, not the name, must be used with all datagram commands and for NCBRECVANY commands.

The number for NAME_NUMBER_1 (see NCBRESET) is always 0x01. Netbios assigns values in the range 0x02 to 0xFE for the remaining names.

ncb_buffer

Points to the message buffer.

ncb_length

Specifies the size, in bytes, of the message buffer.

ncb_callname

Specifies the string that contains the remote name. Trailing space characters should be supplied to make the length of the string equal to NCBNAMSZ.

ncb_name

Specifies the string that contains the local name. Trailing space characters should be supplied to make the length of the string equal to NCBNAMSZ.

ncb_rto

Specifies the receive time-out period, in 500-millisecond units, for the session. A value of zero implies no time-out. Specified with the NCBCALL or NCBLISTEN command. Affects subsequent NCBRECV commands.

ncb_sto

Specifies the send time-out period, in 500-millisecond units, for the session. A value of zero implies no time-out. Specified with the NCBCALL or NCBLISTEN command. Affects subsequent NCBSEND and NCBCHAINSEND commands.

ncb_post

Specifies the address of the routine to call when the asynchronous NCB finishes. The completion routine is passed a pointer to the completed network control block.

ncb_lana_num

Specifies the LAN adapter number. This zero-based number corresponds to a particular transport provider using a particular LAN adapter board.

ncb_cmd_cplt

Specifies the command complete flag. This value is the same as the ncb_retcode member.

ncb_reserve

Reserved; must be zero.

ncb_event

Specifies a handle to a Windows event that is set to the signaled state when the asynchronous network control block finishes. The event is signaled if the Netbios function returns a nonzero value.

The ncb_event member must be zero if the ncb_command member does not have the ASYNCH value set or if ncb_post is nonzero. Otherwise, NRC_ILLCMD is returned.

The event specified by ncb_event is set to the nonsignaled state by the system when an asynchronous NetBIOS command is accepted, and it is set to the signaled state when the asynchronous NetBIOS command finishes.

Using ncb_event to submit asynchronous requests requires fewer system resources than using ncb_post. Also, when ncb_event is nonzero, the pending request is canceled if the thread terminates before the request is processed. This is not true for requests sent by using ncb_post.

Only manual reset events should be used with Netbios. A given event should not be associated with more than one active asynchronous NetBIOS command.

See Also

ACTION_HEADER, ADAPTER_STATUS, FIND_NAME_BUFFER, FIND_NAME_HEADER, LANA_ENUM, NAME_BUFFER, Netbios, SESSION_BUFFER, SESSION_HEADER

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