計(jì)算機(jī)網(wǎng)絡(luò)第一周作業(yè)-文庫(kù)吧
2025-06-03 00:12 本頁(yè)面
【正文】 k of distance 2,500 km, propagation speed 108 m/s...答：10 ^ 5 s。 L/s。 否；否 end system A wants to send a large file to end system B. At a very high level, describe how end system A creates packets from the file. When one of these packets arrives to a packet switch, what information in the packet does the switch use to determine the link onto which the packet is forwarded? Why is packet switching in the Internet analogous to driving from one city to another and asking directions along the way?答：將文件拆成多個(gè)小塊。并為每個(gè)塊添加標(biāo)頭，從而從文件生成多個(gè)數(shù)據(jù)包。每個(gè)數(shù)據(jù)包中的標(biāo)頭包括目的地址的IP。分組交換機(jī)使用該IP地址確定輸出鏈路。在給定數(shù)據(jù)包的目的地址情況下，詢(xún)問(wèn)哪條路要類(lèi)似于這個(gè)的數(shù)據(jù)包，詢(xún)問(wèn)它應(yīng)該轉(zhuǎn)發(fā)哪個(gè)輸出鏈路。22. Which layers in the Internet protocol stack does a router process? Which layers does a linklayer switch process? Which layers does a host process?答: 路由器處理第1層到第3層。23. List five tasks that a layer can perform. Is it possible that one (or more) of these tasks could be performed by two (or more) layers?答： 五個(gè)通用任務(wù)是錯(cuò)誤控制、流控制、分段和重組、多路復(fù)用和連接設(shè)置。這些任務(wù)可以在不同的層重復(fù)。 25. What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers? 答： 應(yīng)用層：應(yīng)用層是網(wǎng)絡(luò)應(yīng)用層協(xié)議存留的地方；運(yùn)輸層：因特網(wǎng)的運(yùn)輸層在應(yīng)用程序端點(diǎn)之間傳輸報(bào)文；網(wǎng)絡(luò)層：因特網(wǎng)的網(wǎng)絡(luò)層負(fù)責(zé)將成為數(shù)據(jù)報(bào)的網(wǎng)絡(luò)層分組從一臺(tái)主機(jī)移動(dòng)到另一臺(tái)主機(jī)；鏈路層：因特網(wǎng)的網(wǎng)絡(luò)層通過(guò)源和目的地之間的一系列路由器路由數(shù)據(jù)報(bào)；物理層：將幀的一個(gè)個(gè)比特從一個(gè)結(jié)點(diǎn)轉(zhuǎn)移到另一個(gè)結(jié)點(diǎn)。 Problem1 Consider the circuitswitched network in Figure . Recall that there are n circuits on each link 答 a：4n；b：2n。2．Consider an application that transmits data at a steady rate (for example, the sender generates an Nbit unit of data every k time units, where k is small and fixed). Also, when such an application starts, it will continue running for a relatively long period of time. Answer the following questions, briefly justifying your answer: 答：a：電路交換非常適合這個(gè)應(yīng)用，因?yàn)閭鬏斔俾室阎⑶視?huì)話(huà)為長(zhǎng)會(huì)話(huà)，不會(huì)造成帶寬的大量浪費(fèi)。b：在最壞的情況下，所有應(yīng)用程序都通過(guò)一條鏈路傳輸數(shù)據(jù)，因?yàn)檫€未達(dá)到鏈路最大帶寬所以不會(huì)發(fā)生擁堵，所以網(wǎng)絡(luò)不需要擁塞控制機(jī)制。3. Review the carcaravan analogy in Section . Assume a propagation speed of 100 km/hour. a. Suppose the caravan travels 150 km, beginning in front of one tollbooth, passing through a second tollbooth, and finishing just after a third tollbooth. What is the endtoend delay? b. Repeat (a), now assuming that there are eight cars in the caravan instead of ten.答： 2min+60min+2min+60min=124min；+60min++60min=4. (未留) 5. 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.答：dprop=m/s；dtrans=L/R；endtoend delay = m/s+L/R；剛剛離開(kāi)host A；還在鏈路上，未到達(dá)host B；已經(jīng)到達(dá)了host B；m=L/R*s = 6. Suppose users share a 1 Mbps link. Also suppose each user requires 100 kbps when transmitting, but each user transmits only 10 percent of the time. (See the discussion of packet switching versus circuit switching in Section .) 答：a：1Mbps/100kbps = 10；b：p=；c：(C40,n)\*(p)\^n\*(1p)\^(40n)；d：P(11人或以上人使用)=7. In this problem, we consider sending realtime voic
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