四川大学林峰计算机网络第三次作业.docVIP

Chapter 3 Review Questions R3.Describe why an application developer might choose to run an application over UDP rather than TCP? 答:An application developer may not want its application to use TCP’s congestion control, which can throttle the application’s sending rate at times of congestion. Often, designers of IP telephony and IP videoconference applications choose to run their applications over UDP because they want to avoid TCP’s congestion control. Also, some applications do not need the reliable data transfer provided by TCP. R5.Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP? If so, how? 答:是的，在UDP的协议上添加验证的数据，例如给每个包传输时加个头，并且设置返回值。 R6.Consider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source port number x and destination port number y. What are the source and destination port numbers for the segments traveling from Host B to Host A? 答:The source port number is y, the destination port number is x. R7.Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B each sends a UDP segment to Host C with destination port number 6789. Will both of these segments be directed to the same socket at Host C? If so, how will the process at Host C know that these two segments originated from two different hosts? 答:正确,两个部分将针对同一接口。在套接字接口，对于每个收到的片段，操作系统将提供过程与IP地址确定各段的起源。 R8.Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B. Are all of the requests being sent through the same socket at Host C? If they are being passed through different sockets, do both of the sockets have port 80? Discuss and explain. 答:对于每个坚持的连接，web服务器会创建一个连接套接字，每个连接套接字由4个数组定义。当主机C收到一个请求的时候，它会检查数据报和段中的4个区域，以此决定用哪个区域来接收TCP段。因此，A和B传输的套接字是不一样的。每一个套接字的标识符都使用80端口作为目的的，但是不同的资源有不同的IP地址。和UDP不同的是，当传输层传输一个TCP段