12.7.5 Call Acceptance by User

Normally Incoming Call packets are examined and responded to by X.25. If the call is accepted, a Call Accepted packet is sent by X.25 directly. In the event a user process wants to have additional checks before sending a Call Accepted packet, an X25_CALL_ACPT_APPROVAL ioctl may be used.

int approved_by_user, s, error;
 error = ioctl(s, X25_CALL_ACPT_APPROVAL, &approved_by_user);

where approved_by_user = 0 means the approval is done by X.25, and approved_by_user = 1 means approval is done by the user process. By default (that is, if this call is not issued), approval is done by X.25. Note that if a user wants to do call approval, the X25_CALL_ACPT_APPROVAL ioctl must be issued before the listen call is issued.

Regardless of the value of approved_by_user, X.25 always performs address matching and facilities negotiation before notifying accept. If a user process assumes the final incoming call approval, accept will return without sending a Call Accepted packet. At this time, the user process should reply as soon as possible to avoid the Call Request timeout on the remote calling side. To accept the call, use:

int news, error;
 error = ioctl(news, X25_SEND_CALL_ACPT);

Here, news is the socket descriptor returned by accept.

The X25_SEND_CALL_ACPT ioctl call is also needed for fast select calls, as described in an earlier section. To reject the call, simply close the socket:

int news;
 close(news); 

where news is the socket descriptor returned by accept.