HDLC-Frame Protocol User's Guide (February 2004)

Using the SS7 Mode Feature
Transmitting Frames
Appendix B38
Transmitting Frames
When enabled HDLC.FRAME begins sending flags. The application can
then send a MSU, LSSU or FISU to HDLC.FRAME for transmission.
Note that an LSSU may have one or two bytes of status information.
Following the transmission of the frame, HDLC.FRAME enters one of
two states. The two states are the FISU transmission mode or the LSSU
transmission mode and they are set according to the following rules:
• If an MSU or FISU is transmitted first, HDLC.FRAME enters the
FISU transmission mode. In this mode HDLC.FRAME continues to
send FISUs, until the application sends a new frame for
transmission.
• If an LSSU is transmitted first, HDLC.FRAME enters the LSSU
transmission mode. In this mode HDLC.FRAME continues to send
LSSUs, until the application sends a new frame for transmission.
During the ensuing operation, the transmission mode may change as
follows:
• When a FISU is sent by the application for transmission, and
HDLC.FRAME is currently in LSSU transmission mode,
HDLC.FRAME changes to FISU transmission mode.
• When an LSSU is sent by the application for transmission, and
HDLC.FRAME is currently in FISU transmission mode,
HDLC.FRAME changes to LSSU transmission mode.
• When an MSU is sent by the application for transmission, the
HDLC.FRAME transmission mode is unchanged.