单选题Which test checks the transmitter and receiver of a local modem？（）A data parityB analog loop backC local digital loop backD remote digital loop back

第一组

An automatic system usually consists of a control system and an information system. A control system is a system which measures the condition of some entity and, with the information, governs the state of a variable; i.e., speed, temperature, pressure, position, etc. The open-loop system is the simplest form. a control system may assume. It is distinguished from the closed-loop system by the lack of an input which measures the state of the controlled variable; such an input is called a feedback. In modern ships the open-loop system has practically disappeared and the closed-loop system which operates with a feed-back is extensively used. An information system serves the parallel function of monitoring system or plant performance. The monitoring function may serve a number of purposes; specifically it may indicate values of controlled variables to guide remote control operations, warn of off-limit conditions and provide record of performance. In many cases a visual and audible alarm may be provided to warn of off-limit conditions on board ship and, associated with this, the important variables will be recorded on demand. The automatic control system can be more sophisticated by incorporating digital-processing equipment, that is, a computer. This computer is usually fed with signals from all sensors. It scans the values of the sensors and generates alarm signals for off-limit conditions, acting as a super-supervisor. Sometimes, it can even make necessary and take the necessary action to optimize performance without human intervention.

The closed-loop system differs from the open-loop system by

A.the lack of a feedback

B.the presence of a feed back

C.the lack of a computer

D.the presence of a computer

The network administrator must complete the connection between the RTA of the XYZ Company and the service provider. To accomplish this task, which two devices could be installed at the customer site to provide a connection through the local loop to the central office of the provider (Choose two.)（）。

A.WAN switch

B.PVC

C.ATM switch

D.multiplexer

E.CSU/DSU

F.modem

As a network administrator, you will need to decide on the appropriate network devices to use. Which of the following correctly describes the roles of devices in a WAN? (Choose three)

A. A CSU/DSU terminates a digital local loop.

B. A router is commonly considered a DCE device.

C. A modem terminates an analog local loop.

D. A router is commonly considered a DTE device.

E. A modem terminates a digital local loop.

F. A CSU/DSU terminates an analog local loop.

G. A modem is used to terminate a T1

A.Set the encapsulation of the interface to HDLC

B.Place the CSU/DSU in local-loop mode

C.Enable local-loop mode on the DCE Frame Relay router

D.Verify that the encapsulation is set to Frame Relay

A.A CSU/DSU terminates a digital local loop

B.A modem terminates a digital local loop

C.A CSU/DSU terminates an analog local loop

D.A modem terminates an analog local loop

E.A router is commonly considered a DTE device

F.A router is commonly considered a DCE device

A.A CSU/DSU terminates a digital local loop.

B.A modem terminates a digital local loop.

C.A CSU/DSU terminates an analog local loop.

D.A modem terminates an analog local loop.

E.A router is commonly considered a DTE device.

F.A router is commonly considered a DCE device.

_______control system is one in which the control action is independent of the output.

A.Feed back

B.Negative feed back

C.Close loop

D.Open loop

A.loop back interface是CISCO路由器上缺省端口

B.loop back interface一个永远不会DOWN的逻辑端口

C.loop back interface是一个做自环测试的端口

D.loop back interface是对端使用LOOPBACK命令测试链路后本端的端口状态