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ISDN,which stands for Integrated Services Digital Network, is a system of digital phone connections, which has been available for over a decade.This system allows data to be transmitted simultaneously across the world using (1) digital connectivity.With ISDN,voice and data are carried by bearer channels occupying a  bandwith of  (2) (bits per second).Some switches limit B channels to  capacity of 56 Kbps.A data channel (3) handles signaling at 16Kbps  or 64Kbps,depending on (4) .Note that,in ISDN terminology,¡±k¡±  means (5),and not 1024(2^10) as in many computer  applications;therefore,a 64Kbps channel carries data at a rate of  64000bps. A new set of standard prefixes has recently been created  to handle this. Under this scheme,¡±K¡±(Kilo) means 1000(10^3),¡±M¡± (Mega) means 1000000(10^6),and soon ,and ¡°Ki¡±(Kibi) means 1024 (2^10),¡±Mi¡± (Mebi) means 1048576(2^20).and soon¡£ 
(1). A.Multi-ends  B.circle    C.indirect    D.end-to-end 
(2). A.34 Kbps    B. 84 Kbps  C. 64 Kbps  D. 54 Kbps 
(3). A.D channel    B.A channel  C.B channel  D.C channel 
(4). A.the method  B.the number    C.the service type    D.the user type 
(5). A.100000(10^5)  B.1000(10^3)    C.10000(10^4)    D.100(10^2) 
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1:D,2:C,3:A,4:C,5:B