12.7.3.2 Called Side

To receive a fast select incoming call, the called side must specify either FAST_ACPT_CLR or FAST_CLR_ONLY as the value for fast_select_type using the X25_SET_FACILITY ioctl, before issuing the listen call.

If the Incoming Call has the fast select facility, it will be accepted only if the listener has specified fast select. The incoming call will also be accepted if it does not have the fast select facility and the listener has specified FAST_ACPT_CLR.

The call will be rejected if there are more than 16 bytes of user data, and the called side has either not specified the fast select facility at all, or has specified FAST_OFF (which is equivalent to not specifying fast select).

After accept returns, the called side may use the X25_GET_FACILITY ioctl to determine the type of fast select in effect. For example, if the called side has specified FAST_ACPT_CLR and the calling side has specified FAST_CLR_ONLY, after accept returns, the type of fast select in effect will be FAST_CLR_ONLY. If fast select is indicated, the called side can read the user data that was received in the Call Request by looking at the CONN_DB structure returned by accept. If more than 102 bytes of user data were received, the extra bytes can be read with the X25_RD_USER_DATA ioctl.

The X25_WR_USER_DATA ioctl can be used to specify user data to be sent back in the response to the fast select Call Request. To write more than MAX_USER_DATA bytes of user data, a second X25_WR_USER_DATA ioctl can be used to append the additional data after that from the first X25_WR_USER_DATA ioctl (total length of all user data may not exceed 128 bytes).

If the type of fast select in effect is FAST_CLR_ONLY, the called side can only clear the fast select call by closing the socket (which causes the user data specified by X25_WR_USER_DATA to be sent in the Clear Request). If the type of fast select in effect after accept returns is FAST_ACPT_CLR, the called side has the option, after writing the reply message with the X25_WR_USER_DATA ioctl, of either sending a Clear Request packet with close or sending a Call Accepted packet with the X25_SEND_CALL_ACPT ioctl and thereby entering the normal data transfer state.

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

When the value in effect is FAST_CLR_ONLY, the called side can only close the socket with the close system call after writing the reply message.

FAST_OFF is the type of fast select that will be in effect when the listener has specified FAST_ACPT_CLR and the incoming call does not have the fast select facility. Even in this case, the listener must use the X25_SEND_CALL_ACPT ioctl to put the connection into normal data transfer state.

In the current release (and not in SunNet X.25 7.0), the listen socket should not be closed until after the incoming fast select call has been either cleared (with close) or accepted (with X25_SEND_CALL_ACPT).