第4套

LAPB is a (1) protocol that provides complete data transparency in  a (2)operation. It supports a peer-to-peer link in that neither end  of the link plays the role of the permanent master station.  HDLC LAPB is the (3)that is usually used by(4), the (5)standard for  Packet Switched Networks.

(1)A．bit-oriented synchronous    B．byte-oriented synchronous
   C．bit-oriented asynchronous      D．byte-oriented asynchronous
(2)A．half-duplex point-to-point     B．half-duplex point-to-points
   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. 

 (1) A.optimized    B.increased       C.decreased  D.fixed
 (2) A.cell by cell B.object oriented C.bit-by-bit D.LAN
 (3) A.VLSI         B.OSI             C.CMS        D.ATM
 (4) A.cells        B.switches        C.users      D.approaches
 (5) A.data         B.media           C.bandwidth  D.information

答案:1:A,2:A,3:D,4:C,5:C

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