HP UX 11.x Operating Systems 46

Using the SS7 Mode Feature

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.

46	Appendix B