Quadrature Phase-shift Keying
A Converts digital data to analog signal
B The baud rate is twice the bit rate
C Allows 64 different combinations
D The phase shifted is 180 degree
(2)单选题PSTN (public switched telephone network) consists:
A Local loop, toll connecting trunk, and inter-toll trunk
B Telephone and central office
C Local loop, trunks, and switching office
D Telephone, end office, and trunks
(3)单选题For Multiplexing,
A FDM divides frequency spectrum into frequency bands
B TDM allows mutilple signals to be transmitted on
C the channel at the same time
D TDM has higher efficiency than FDM
(4)单选题For switching
A Packet swiching is more reliable than circuit swiching
B Circuit swiching requires path setup in advance
C Packet swich is more likely to waste bandwidth
D Packet swiching is less efficient than circuit swiching
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