计网-第三章作业(2)

h. 在第1个传输周期内，报文段1被传送；在第2个传输周期发送报文段2-3；在第3

个传输周期发送报文段4-7，在第4个传输周期发送8-15；在第5个传输周期发送16-31；在第6个传输周期发送32-63；在第7个传输周期发送64-96；因此，报文段70在第7个传送周期内发送。

i. 当丢失出现时拥塞窗口和threshold的值被设置为目前拥塞窗口长度8的一半。因此

新的拥塞窗口和threshold的值为4.

11. (P38)Host A is sending an enormous file to Host B over a TCP connection. Overthis

connection there is never any packet loss and the timers never expire.Denote the transmission rate of the link connecting Host A to the Internet byR bps. Suppose that the process in Host A is capable of sending data into itsTCP socket at a rateS bps, where S = 10*R. Further suppose that the TCPreceive buffer is large enough to hold the entire file, and the send buffer canhold only one percent of the file. What would prevent the process in HostAfrom continuously passing data to its TCP socket at rate S bps? TCP flowcontrol? TCP congestion control? Or something else? Elaborate. 答：

在这个问题中，接收机没有溢出的危险，因为接收机的接收缓冲区可以承载整个文件。同样的，因为在计时器计时完毕前，没有丢失和回复确认，TCP不会限制发送方。但是，在端系统A上的进程不会一直传输数据给套接字，因为发送缓冲区会很快被填满，一旦发送缓冲区满，那么进程就会以平均速率传输数据。

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