光纤通信中使用的复用方式是(20)。E1载波把32个信道按(21)方式复用在一条2.048Mbit/s的高速信道上，每条话音信道的数据速率是(22)。
-
(65)
- A．half duplex
- B．full duplex
- C．half or full duplex
- D．half and full duplex
-
(64)
- A．a primary station
- B．one or more primary stations
- C．a secondary station
- D．one or more secondary stations
-
(63)
- A．a primary station
- B．one or more primary stations
- C．a secondary station
- D．one or more secondary stations
-
SDLC was invented by IBM to replace the older Bisynchronous protocol for wide area connections between IBM equipment . A varietion of the (71) protocol called NRM is essentially the same as SDLC. SDLC is (72) protocol like HDLC, Frame. Relay or X.25. An SDLC network is made up of (73) that controls all communications, and (74) . It is capable of (75) operation, but almost all practical applications are strictly half duplex.
- A．HDLC
- B．Frame. Relay
- C．X.25
- D．X.21
-
(62)
- A．a peer to peer
- B．a point-to-point
- C．not a peer to peer
- D．a peer to peers
-
(59)
- A．bits
- B．frequencies
- C．packets
- D．messages
-
(60)
- A．rate
- B．velocity
- C．bandwidth
- D．period
-
(57)
- A．direct-sequence
- B．discrete-sequence
- C．duplicate-sequence
- D．dedicate-sequence
-
(58)
- A．data
- B．byte
- C．packet
- D．bit
-
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
Spread spectrum simply means that data is sent in(66)pieces over a number of the discrete frequencies available for use at any time in the specified range. Devices using(67) spread spectrum (DSSS)communicate by splitting each(68)of data into several parts and sending them concurrently on different (69), DSSS uses a lot of the available(70), about 22 megahertz (MHz).
- A．small
- B．high
- C．low
- D．long
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