🔍 Key Concepts

• ARQ (Automatic Repeat reQuest) procedures in narrow-band direct-printing (NBDP) communications • Typical sequence of operations after link establishment with a coast radio station • Common command or control signals exchanged between ship and coast station (e.g., GA+?, WRU, AAB, DIRTLX+, OBS+, AMV+)

💭 Think About

• Once ARQ communication is established, think about what the next logical step is in setting up or conducting the actual traffic. Are you still identifying parties, choosing services, or already sending the full message? • Look at which answer choices describe initial identification and setup, which describe service selection, and which assume that traffic is already in progress on a working channel. • Consider what type of signal a coast radio station would send to invite the ship to choose a specific service or action rather than immediately sending the full text of the message.

✅ Before You Answer

• Verify which of the options correctly matches known NBDP control/command codes (WRU, AAB, GA+?, DIRTLX+, OBS+, AMV+) and their function. • Check which answer choice assumes that you are already on a working channel; compare that to what actually happens right after ARQ link establishment. • Confirm which process involves the coast radio station giving the ship a choice of services or actions before the detailed text of the message is sent.