计算机网络作业.doc

精品文档Computer Network 2015fallHomework 1作业提交地址： /zhgf/ComputerNetwork2015/1. What is the difference between a host and an end system? List several different types of end systems. Is a Web server an end system?答：(1) 基本相同，经常互换。(2) web服务器、PC机、手机、平板电脑。(3) 是的。2. What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers?答：(1) 应用层、运输层、网络层、链路层和物理层。(2) 应用层是网络应用程序及其应用层协议存留的地方；运输层提供了在应用程序端点之间传送应用层报文的服务；网络层将称为数据报的网络层分组从一台主机移动到另一台主机；链路层将分组从一个节点(主机或路由器)移动到路径上的下一个节点；物理层将该帧中的一个一个比特从一个节点移动到下一个节点。3. What is an application-layer message? A transport-layer segment? A network layer datagram? A link-layer frame?答：(1) 应用层报文是位于应用层的信息分组。(2) 运输层报文段由应用层报文和运输层首部信息构成。(3) 网络层数据报由运输层报文段和网络层首部信息构成。(4) 链路层帧由网络层数据报和链路层首部信息构成。4. Suppose Host A wants to send a large file to Host B. The path from Host A to Host B has three links, of rates R1 = 500 kbps, R2 = 2 Mbps, and R3 = 1 Mbps.a. Assuming no other traffic in the network, what is the throughput for the file transfer?答：R1=0.5MbpsR3 4*104 bits，所以最大字节量应为4*104。c) Provide an interpretation of the bandwidth-delay product.答：the maximum number of bitsthat will be in the link at any given time。即在给定时刻，链路中字节数的最大值。d) What is the width (in meters) of a bit in the link? Is it longer than a football field?答：。是。e) Derive a general expression for the width of a bit in terms of the propagation speed s, the transmission rate R, and the length of the link m.答：7. Referring to problem 6, suppose we can modify R. For what value of R is the width of a bit as long as the length of the link?答：设一个bit的长度为m，由6(e)知，。8. Refer again to problem 6.a) How long does it take to send the file, assuming it is sent continuously?答：，b) Suppose now the file is broken up into 10 packets with each packet containing 40,000 bits. Suppose that each packet is acknowledged by the receiver and the transmission time of an acknowledgment packet is negligible. Finally, assume that the sender cannot send a packet until the preceding one is acknowledged. How long does it take to send the file?答：。因为