【单选题】In HDLC, frame acknowledgment, flow and error control are the functions of .

【单选题】以下流程图的基本元素中，表示程序中的输入输出框是( )。

【单选题】Two coding schemes, B8ZS and HDB3 are commonly used in long-distance transmission, which are based on the use of .

【填空题】R256是内部“字”继电器WR25的( )号位。

【多选题】变量必须先定义后使用。定义变量需要确定变量()

【单选题】In ARQ，if a NAK frame is received，only the lost or damaged frame is retransmitted.

【单选题】下列关于局部变量和用户变量的描述中，错误的是()

【多选题】表示逻辑与的运算符有()

【单选题】Delay distortion and attenuation are .

【单选题】E1 carrier link multiplexes channels according to TDM. The original analog voice signal is digitized using PCM at a rate of 8000 samples. So,the data rate of E1 is .

【填空题】The least expensive and most widely used guided transmission medium is

【填空题】填写完整，表示职称duty为副教授或教授、年龄age小于40岁的关系表达式：age<40 (duty=="副教授" or duty=="教授")

【单选题】以下程序：a=input("please input a：")if a=="A": print(ord(a))print("OK")运行时输入：A程序的执行结果是( )。

【填空题】The guided transmission media include twisted pair, coaxial and ( )

【单选题】Full-duplex transmission means two stations can simultaneously send and receive data from each other. This requires .

【单选题】For a noise-free channel with a bandwidth of 3kHz, assuming the possible voltage levels of each symbol signal in the channel is 16, the maximum data transmission rate that the channel can support is ( ).

【单选题】以下程序：x=eval(input())if x%2==0: print(2,end=',')if x%3==0: print(3,end=',')if x%5==0: print(5,end=',')运行时输入：30程序的执行结果是( )。

【单选题】The procedure is used in HDLC frame to avoid confusion with data containing Flag Fiel bits.

【单选题】2. 下列说法错误的是( )

【单选题】 is generally only a minor annoyance for analog signals, but it is the primary source of error in digital data communication.

【单选题】The purpose of twisting for twisted pair is .

【单选题】Which one of the following elements does not affect the data rate of channel.

【单选题】The multiplexing mode ( ) used in CDMA system.

【判断题】局部变量必须在存储程序中定义和使用。

【判断题】运算符+和-可以用来计算日期

【单选题】If the predetermined generation polynomial is P(X) = X4 + X3 + 1, the number of CRC bit derived by this P(X) is ( )

【单选题】MySQL语言中不可使用的逻辑运算符是()

【多选题】用单引号括起来的常量有()

【单选题】14) HDLC is a kind of data link control protocol.

【填空题】R256是内部“字”继电器()的其中一位。

【多选题】表示逻辑或的运算符有()

【判断题】In general, the bandwidth is wasted largest in FDM system.

【单选题】In Sliding-Window flow control protocol, the frames located on the left side of the receiver’s window are .

【单选题】A file is transmitted from A to B .The data rate is 9600bit/s .After one hour of continuous transmission, 150 error bits are received by B . What is the bit error ratio(BER) of the channel?

【判断题】A broad-band data link has higher data propagation volicity than narrow-band link.

【单选题】 is caused by the fact that the velocity of propagation of a signal through a guided medium varies with frequency.

【填空题】关系表达式 "abc" >= "ad"的运算结果是( )。

【判断题】A telephone channel with a 3000-Hz bandwidth and a signal-to-noise ratio of 20dB, this channel can provided reliable voice transmission with data rate 56kb/s.

【单选题】When the input data streams with different data rates are multiplexed on a TDM link, the various sources is synchronized by technique.

【单选题】结构化程序的三种基本控制结构是()

【单选题】The type of HDLC frame is determined by .

【单选题】下列选项中，不属于MySQL合法常量的是()’

【多选题】以下表达式结果相同的是()

【填空题】The common multiplexing technique used in communcation system are 、TDM、WDM and CDM.

【单选题】 is the most inefficient error-control mechanism.

【判断题】5<>5与5!=5结果相同

【单选题】与表达式35%3值相同的表达式是

【单选题】The data rate of the multiplexed line in STDM is .

【单选题】In TDM system，if the data of one channel is error, how to apply error control technique?

【判断题】case语句能根据不同条件选择执行不同的语句或语句块