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單項選擇題

UPSR protection switching is initiated by (), while BLSR is initiated by ().

A. the K1 SONET byte; the K2 SONET byte
B. the K2 SONET byte;the K1 SONET byte
C. transmitter switching;receiver detection
D. Line Overhead bytes;Path Overhead bytes
E. Path Overhead bytes;Line Overhead bytes

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