12.7.2.2 Fast Select

There are three possible values for this facility. FAST_OFF indicates that fast select is not in effect. FAST_CLR_ONLY indicates fast select with restriction on response, and FAST_ACPT_CLR indicates fast select with no restriction on response.

This is set as follows:

u_char fast_select_type;
 fast_select_type = FAST_CLR_ONLY;
 f.type = T_FAST_SELECT_TYPE;
 f.f_fast_select_type = fast_select_type;
 error = ioctl(s, X25_SET_FACILITY, &f); 

This is read as follows:

f.type = T_FAST_SELECT_TYPE;
 error = ioctl(s, X25_GET_FACILITY, &f);
 fast_select_type = f.f_fast_select_type;

If this facility is set before making the connect call, the Call Request packet is sent out with this facility. If this facility is set before making the listen call, the behavior that follows will depend on whether or not restriction on response was indicated, and on whether the Incoming Call has this facility. In order for an Incoming Call bearing the fast select facility to be acceptable, the listener should have specified fast select (with or without restriction). However, an Incoming Call not bearing the fast select facility will still be acceptable to a listener who has specified fast select with no restriction on response. The type of fast select in effect will be either the type of fast select in the Incoming Call, or fast select with restriction on response if either end of the connection has specified fast select with restriction on response. If the Incoming Call does not specify fast select, and is accepted by a listener who has specified fast select with no restriction on response, fast select will not be in effect for the duration of the call.

A listener that has specified fast select (with or without restriction) must use the X25_SEND_CALL_ACPT ioctl to accept the call or use close to clear the call, after successful completion of the accept call, regardless of whether fast select is in effect for the call. If the type of fast select in effect after accept is either FAST_OFF or FAST_ACPT_CLR, the user may either accept or clear the call. If the type of fast select in effect is FAST_CLR_ONLY, the user cannot accept the call (it can only be cleared). The handling of user data in conjunction with fast select is described later.