Chapter I 1. What is the difference between a host and an end system List the types of end systems. Is a Web server an end system 2. What is a client program What is a server program Does a server program request and receive services from a client program 3. List six access technologies. Classify each one as residential access, company access, or mobile access. 4. Dial-up modems, HFC, and DSL are all used for residential access. For each of these access technologies, provide a range of transmission rates and comment on whether the transmission rate is shared or dedicated. 5. Describe the most popular wireless Internet access technologies today. Compare and contrast them. 6. What advantage does a circuit-switched network have over a packet-switched network What advantages does TDM have over FDM in a circuit-switched network 7. Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable 8. How long does it take a packet of length 2,000 bytes to propagate over a link of distance
2,000 km, propagation speed 8102 m/s, and transmission rate 2 Mbps More generally, how long does it take a packet of length L to propagate over a link of distance d, propagation speed s, and transmission rate R bps Does this delay depend on packet length Does this delay depend on transmission rate 9. What are the five layers in the Internet protocol stack What are the principal responsibilities of each of these layers 10. Which layers in the Internet protocol stack does a router process Which layers does a link-layer switch process Which layers does a host process 11. What is an application-layer message A transport-layer segment A network-layer datagram A link-layer frame 12. This elementary problem begins to explore propagation delay and transmission delay, two central concepts in data networking. Consider two hosts, A and B, connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters, and suppose the propagation speed along the link is s meters/sec. Host A is to send a packet of size L bits to Host B.
a. Express the propagation delay, propd, in terms of m and s.
b. Determine the transmission time of the packet,transd, in terms of L and R. c. Ignoring processing and queuing delays, obtain an expression for the end-to-end delay. d. Suppose Host A begins to transmit the packet at time t = 0. At time transdt,where is the last bit of the packet e. Suppose propd is greater than transd. At time t = transd,where is the first bit of the packet f. Suppose propd is less than transd. At time t = transd, where is the first bit of the packet
g. Suppose 8105.2s, L = 100bits, and R = 28 kbps. Find the distance m so that propd equals transd. 13. In modern packet-switched networks, the source host segments long, application-layer messages (for example, an image or a music file) into smaller packets and sends the packets into the network. The receiver then reassembles the packets back into the original message. We refer to this process as message segmentation. Figure 1.24 illustrates the end-to-end transport of a message with and without message segmentation. Consider a message that is
6108 bits long that is to be sent from source to destination in Figure 1.24. Suppose each
link in the figure is 2 Mbps. Ignore propagation, queuing, and processing delays. a. Consider sending the message from source to destination without message segmentation. How long does it take to move the message from the source host to the first packet switch Keeping in mind that each switch uses store-and-forward packet switching, what is the total time to move the message from source host to destination host b. Now suppose that the message is segmented into 4,000 packets, with each packet being 2,000 bits long. How long does it take to move the first packet from source host to the first switch When the first packet is being sent from the first switch to the second switch, the second packet is being sent from the source host to the first switch. At what time will the second packet be fully received at the first switch c. How long does it take to move the file from source host to destination host when message segmentation is used Compare this result with your answer in part (a) and comment. d. Discuss the drawbacks of message segmentation. 14. 下列说法中,正确的是( )。 A.在较小范围内布置的一定是局域网,币在较大范围内布置的一定是广域网 B.城域网是连接广域网而覆盖园区的网络 C.城域网是为淘汰局域网和广域网而提出的一种网络技术 D.局域网是基于广播技术发展起来的网络,广域网是基于交换技术发展起来的向络 解答:D。 通常而言,局域网的覆盖范围较小,而广域网的覆盖范围较大,但这并不绝对。有时候在一个不大的范围内采用广域网,这取决于应用的需要和是否采用单一网络等多种因素。特别是局域网技术的进步,使得其覆盖范围越来越大,达到几十千米的范围。 城域网是利用广域网技术、满足一定区域需求的一种网络,事实上,城域网的范围弹性非常大。 最初的局域网采用广播技术,这种技术一直被沿用,而广域网最初使用的是交换技术,也一直被沿用。 ? 15. 相对于o⒏的7层参考模型的低4层,TCP/IP协议集内对应的层次有( )。 A.传输层、互联网层、网络接口层和物理层 B.传输层、互联网层、网络接口层 C.传输层、互联网层、ATM层和物理层