What protection method is used in 4F BLSR networks?（）

• A、Each fiber has half of its SONET capacity reserved for protection.
• B、Two fibers in the span carry working traffic, while the other two fibers in the span are reserved for protection.
• C、The signal is sent simultaneously in both directions around the ring. The receiver determines which fiber to listen to based on signal quality.
• D、The signal is sent simultaneously in both directions around the ring. The transmitter determines which fiber has the working bit set for the receiver to acknowledge.