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

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　　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...[查看详情]