NetIPC 3000/XL Programmer's Reference Manual (5958-8600)

110 Chapter3
NetIPC Intrinsics
IPCRECVCN
— calling node address available (bit 16,
output). (X.25 only.) This flag indicates that the
calling node X.25 address was present.
• Facility field (code=145, length=n, n bytes)
(output). (X.25 only.) This option provides a buffer
for the return of the facility field. If the facility field
is present, but this buffer is not supplied, then the
discarded flag (bit 25) is set.
If the buffer is not long enough to contain all of the
data, then the data is truncated and the discarded
flag (bit 25) is set. This buffer should be at least
109 bytes long to ensure receipt of the facility field.
The received buffer contains the facilities exactly as
they were received from the network.
result (output)
32-bit integer, by reference. The error code
returned; zero if no error.
Description
The IPCRECVCN intrinsic allows a process to receive a connection
request and establish a connection (virtual circuit). The connection is
identified by the returned VC socket descriptor. The calling process can
then employ the IPCSEND and IPCRECV intrinsics to send and receive
data on the connection. A maximum of one unreceived connection
request may be queued to a call socket.
If the calling process sets the defer reply to connection request flag
(
flags [18]), this intrinsic will complete when a connection request is
received, but the virtual circuit will not be established. The calling
process must use IPCCONTROL to either accept or reject the request.
This feature is useful if an application must defer replying to the
connection request and then, depending upon the identity of the
requestor, decide to reject or accept the request.
The calling process may also specify whether TCP checksumming is to
be enabled. Checksumming is usually disabled unless it is included by
the remote protocol module or if the TCP checksumming flag
(
flags [21]) is set. When checksumming is enabled, performance is
usually degraded because of increased overhead.
If this intrinsic is called in nowait mode, the data structures for the
connection are created when the call to IOWAIT completes. They are not
created with the initial call to IPCRECVCN. Therefore the address of the
VC socket descriptor parameter is retained by NetIPC, and the
descriptor’s value is returned to that location when IOWAIT completes.
The VC socket descriptor parameter must be global to both the