AP1.2 Message & Signal Transfer
AP1-11
Ship-to-shore Message Transfer Steps
1. The MES normally receives the NCS common channel and decodes the information
which is included in the NCS common channel to know the LES TDM channel.
2. The MES tunes to the LES TDM channel for the required LES.
3. The MES sends an “Assignment Request” packet on a signaling channel informed
by the BB (Bulletin Board) and SCD (Signaling Channel Descriptor).
4. In response to the “Assignment Request” packet, the LES informs the NCS that it is
communicating with the MES.
5. The LES sends the MES an “Assignment” packet. This establishes the link between
LES and MES.
6. The MES sends the message on the assigned message channel and the slot timing.
7. After the LES receives all messages it sends "Acknowledgement" to the MES.
8. This “Acknowledgement” packet contains a list of any packets that were missed or
received in error. Reception of an "Acknowledgement" packet prompts the MES to
retransmit any messages in error.
9. When all messages are received error free, the LES sends “Clear” to the MES and
tells the NCS that the MES is idle.
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