C．full-duplex point-to-point D．full-duplex point-to-points

(3)A．Physical Layer B．Link Layer

C．Network Layer D．Transport Layer

(4)A．X.21 B．X.25 C．X.28 D．X.29

(5)A．ITU B．IEEE C．OSI D．ANSI

答案:1:A,2:C,3:B,4:B,5:A

                第5套

     Data communications equipment(DEC) (1) the serial data stream from the DTE and converts it to some form of (2) suitable of transmission on voice grade lines. At the (3),the DCE performs the reverse function of convering the received analog signal to serial digital data stream .The simplest form of DCE is a (4) or data set . At the transmit end, the modem can be considered a form of (5),while at the receive end, it can be considered a form of analog to digital converter. The most common forms of modulation by modems are frequency shift keying(FSK),phase shift keying(PSK) ,and quadrature amplitude modulation(QAM). If the cables and signal levels used to interconnect the DTE and DCE were left unregulated,the variations generated would probably be proporation to the number of manufactures. Electronics Industries Association(EIA) ,an organization of manufactuuers concerned with establishing industry standards,have agreed on the RS-232C as the standard interface between the DTE and the modem .This is a 25 pin cable pins have designated funtons and specified signal levels.

(1) A. accepts B.sends C.delivers D.receives

(2) A. digital signal B.analog signal C.light signal D.sound signal

(3) A. back end B.front end C.sending end D.receive end

(4) A. modem B.cpu C.demodulator D.modulator.

(5) A. host computer B.digital to analog converter

C. analog to digital converter D.secondaries

答案:

1:A,2:B,3:D,4:A,5:B

               第6套

    In ATM,cells serve as universal units for all information types:data,voice,video,etc,Since switches know beforehand the size and format of each information unit sent through the network,switch architectures can be 1),Futhermore ,since the CMS determines the connection path during connection setup,switches do not have to make complex routing decisions on a (2) basis.Communiciation paths can be “hard wired” into the switch’s circuits to enable fast,simple decisions. Hardware techniques,using VLSI based state machines and ,in the future,optical switching techniques,can be applied to switches.Hardware Based switch matrices take advantage of all these (3) characteristics.The matrix approach to implementing cell switching greatly increases the scalability of ATM based solutions,One fundamental advantage of matrix based switches is that,as more ports are added to the switching complex,the aggregate switching capacity of the switch increases. In other words, as(4) are added to a switched network, they tap into an increasing band width pool-the complete opposite of shared media networks,where user are forced to share smaller and smaller slices of a fixed amount of (5).Simply put,cell switching based on ATM enables extremely fast,massively scalable networdks.