In ARQ, when the information sending station (ISS) receives a signal that the parity check failed what happens?
• 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
• 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.
• 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?
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