2. 计算机
  3. The usual way to ensure reliable delivery is to provide the(11)with some feedback about what is happening at the other end of th

The usual way to ensure reliable delivery is to provide the(11)with some feedback about what is happening at the other end of th

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问题 The usual way to ensure reliable delivery is to provide the(11)with some feedback about what is happening at the other end of the line．Typically，the protocol calls for the receiver to send back special  (12)flame bearing positive or negative  (13)about the incoming flames．If the sender receives a positive．Acknowledgement about a flame，it knows the flame has arrived safely．On the other hand，a negative acknowledgement means that something has gone wrong，and the frame must be transmitted again．An additional complication comes from the possibility that hardware troubles may cause a flame to(14)completely．In this case，the receiver will not react at all，since it has no any reason to react．It should be clear that a protocol in which the sender transmits a frame and then waits for an acknowledgement，positive or negative，will hang forever if a flame is ever lost due to，for example，(15)handware．(2008年下半年试题)
(15)
选项 A、acting
B、working
C、malfunctioning
D、functioning
答案C
解析 译文：保证可靠提交的常用方法是向发送端提供一些反馈信息，使它知道在线路的另一端发生了什么情况。典型的情况是：协议要求接收端回送一个承载有关输入帧的肯定或否定应答的特殊控制帧。如果发送端收到了有关帧的肯定应答，它就知道发送的帧已经安全到达。另外，否定应答则意味着出现了某种错误，应该重新发送出错的帧。还有一些复杂的情况可能发生，硬件故障可能引起帧完全消失。在这种情况下，接收端完全没有反应，因为它根本无法反应。显然，如果一个帧由于硬件失效而丢失了，那么这样的协议——发送端发出一个帧然后等待肯定或否定应答，就会被永远地挂起了。
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