🔍 Key Concepts

• ARQ (Automatic Repeat reQuest) purpose in digital communications • Role of parity checks in error detection • What the ISS (Information Sending Station) must do when an error is detected

💭 Think About

• Ask yourself: If the parity check fails, what does that tell the system about the integrity of the last data block that was sent? • Think about the automatic part of ARQ: what action is built into the protocol to handle detected errors? • Consider what the ISS logically needs to do to ensure the receiving station ends up with a correct copy of the data block.

✅ Before You Answer

• Verify how error detection (parity check) differs from link failure (loss of communication). • Confirm whether a failed parity check would cause the system to move on to new data, or to address the problem with the last data block. • Check your GMDSS/communications notes on ARQ sequences: what happens after a NAK (negative acknowledgment) or error indication?