足球守门员观察点球射门运动员的踢球动作,这是一个( )的过程
A. 主动获取外界信息
B. 被动获取外界信息
C. 思考扑球动作
D. 简单反应
In the following four descriptions about random access protocol, which one is NOT correct?
A. In slotted ALOHA, nodes can not transmit at random time.
B. In pure ALOHA, if a frame experiences a collision, the node will retransmit it immediately with probability p.
C. The maximum efficiency of a slotted ALOHA is higher than a pure ALOH
D. In slotted ALOHA, no node listens to the channel before transmitting.
In the CSMA/CD protocol, what condition on the transmission delay T1 and the propagation delay T2 has to be satisfied to guarantee that a node always detects a collision?
A. T1 > T2
B. T1 > 2*T2
C. T1 < T2
D. 2*T1 < T2
FDM can be very efficient under certain circumstances