🔍 Key Concepts

• SITOR (NBDP) has two main modes: ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) • Difference between BFEC (Broadcast FEC) / HF MSI vs SFEC (Simple FEC) / NAVTEX • What parity bits actually do in digital communications (detect or correct errors?)

💭 Think About

• First, recall which services (NAVTEX, HF MSI, ARQ) use FEC versus ARQ in SITOR. • Think about whether parity is used the same way in all SITOR modes, or if its role is specific to certain combinations of FEC/ARQ. • Consider which answer choices mix up BFEC vs SFEC, and which pair correctly with NAVTEX and HF MSI services.

✅ Before You Answer

• Verify which mode NAVTEX uses: SFEC or BFEC? • Verify which mode HF MSI broadcasts use: BFEC or SFEC? • Confirm that two-way exchanges use ARQ and one-way broadcasts use FEC, then match this to the choices.