🔍 Key Concepts

• GMDSS (Global Maritime Distress and Safety System) digital selective calling (DSC) messages need built-in error detection and correction because they may be received under poor radio conditions. • How data bits and error-checking bits (parity or error-correction) are arranged in a code word (e.g., data first then check bits, or check bits first then data). • The typical bit-length and structure of a DSC character (how many total bits, how many are for data, how many for checking).

💭 Think About

• Look at each choice and ask: does this sound like a realistic way to structure a single digital character for a safety-critical system like GMDSS-DSC? Consider total length and whether it includes both data and protection bits. • Think about the difference between simple parity (just detects some errors) and error-correcting codes (can detect and often correct multiple-bit errors). Which would be more appropriate for distress and safety calls? • Consider which options describe a structure that cleanly separates information bits from check bits in a way that is easy for equipment to encode and decode.

✅ Before You Answer

• Identify which answers use parity only versus a longer error-correcting code and decide which is more suitable for critical distress signaling. • Check which options have a clear count of data bits vs error-correction bits that add up logically to the total code length given in the option. • Eliminate any option whose structure seems too weak or too simple for reliable emergency communications over noisy HF/VHF channels.