In the Ethernet frame structure, the Data field carries the ( ).
A. IP datagram
B. segment
C. frame
D. message
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In the following four descriptions, which one is not correct? ( )
A. Ethernet uses baseband transmission.
B. All of the Ethernet technologies provide connection-oriented reliable service to the network layer.
C. The Ethernet 10Base2 technology uses a thin coaxial cable for the bus.
D. The Ethernet 10BaseT technology uses a star topology.
Ethernet’s multiple access protocol is ( ).
A. CDMA
B. CSMA/CD
C. slotted ALOHA
D. token-passing protocol
In the following four descriptions about CSMA/CD, which one is not correct? ( )
An adapter may begin to transmit at any time.
B. An adapter never transmits a frame when it senses that some other adapter is transmitting.
C. A transmitting adapter aborts its transmission as soon as it detects that another adapter is also transmitting.
D. An adapter retransmits when it detects a collision.
A hub（集线器）is a ( )device that acts on individual bits rather than on frames.
A. physical-layer
B. link-layer
C. network-layer
D. ransport-layer
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