單項選擇題Scrambling of SONET signals is done to （）.

A. prevent the leakage of external fiber emissions
B. provide the optical network with the highest level of security possible
C. assure an even distribution of 1's and 0's for extended transmitter life
D. assure an adequate number of transitions for clock recovery at the receiver
E. prevent the receiver from assuming AIS inadvertently when all 0's are received


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1.單項選擇題A Channel ID mismatch occurs when （）.

A. fibers are terminated incorrectly on a node
B. the channel number in the received K1 byte is not identical to the channel number transmitted in the K2 byte
C. the channel number in the received C1 byte is not identical to the channel number transmitted in the C2 byte
D. the channel number in the received C2 byte is not identical to the channel number transmitted in the C1 byte
E. the channel number in the received K2 byte is not identical to the channel number transmitted in the K1 byte

3.單項選擇題Which timing mode is most appropriate for an ONS 15454 that has lost its BITS-1 and optical references?（）

A.line timing
B.loop timing
C.internal timing
D.through timing
E.external timing

5.單項選擇題A customer has 2 DS1s to add between adjacent nodes in a UPSR ring. What type of circuit should you recommend?（）

A. VT circuits
B. STS circuits
C. VT tunnel circuits
D. 1:1 protection circuits
E. 1:N protection circuits