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