网络原理课后作业

1、 网络课后作业Chap.23.Televisionchannelsare6MHzwide.Howmanybits/seccanbesentif four-leveldigitalsignalsareused?Assumeanoiselesschannel.电视频道的带宽是6MHz。如果使用4级数字信号，则每秒钟可以发送多少位？假设电视频道为无噪声信道。4.Ifabinarysignalissentovera3-kHzchannelwhosesignal-to-noiseratiois20dB,whatisthemaximumachievabledatarate?如果在一条3kHz信道上发送一个

2、二进制信号，该信道的信噪比为20dB，则最大可达到的数据传输率为多少？28.Tensignals,eachrequiring4000Hz,aremultiplexedontoasinglechannelusingFDM.Howmuchminimumbandwidthisrequiredforthemultiplexedchannel?Assumethattheguardbandsare400Hzwide.有10个信号，每个都要求4000Hz，现在用FDM将它们复用在一条信道上。对于被复用的信道，最小要求多少带宽？假设防护频段为400Hz宽。43.Supposethatxbitsofuserda

3、taaretobetransmittedoverak-hoppathinapacket-switchednetworkasaseriesofpackets,eachcontainingpdatabitsandhheaderbits,withxp+h.Thebitrateofthelinesisbbpsandthepropagationdelayisnegligible.Whatvalueofpminimizesthetotaldelay?假定x位用户数据将以一系列分组的形式，在一个分组交换网络中沿着一条共有k跳到路径向前传输，每个分组包含p位数据和h位的头，这里xp+h。线路的传输率为bbps

4、，传播延迟忽略不计。请问什么样的p值使总延迟最小？Chap.33.Thefollowingdatafragmentoccursinthemiddleofadatastreamforwhichthebyte-stuffingalgorithmdescribedinthetextisused:ABESCCESCFLAGFLAGD.Whatistheoutputafterstuffing?下面的数据片段发生数据流用于文本中所述的梯段字节填充算法BESCCESCFLAG FLAGD.在填料后的输出是什么？5.Abitstring,needstobetransmittedatthedatalink la

5、yer.Whatisthestringactuallytransmittedafterbitstuffing?位串需要在数据链路层上被发送，请问，经过位填充之后实际被发送出去的是什么？8.To provide more reliability than a single parity bit can give,an error-detecting coding schema uses one parity bit for checking all the odd-number bits and a second parity bit for all the even-numbered bits

6、.What is the Hamming distance of this code?提供比单奇偶校验位可以给更高的可靠性，错误检测的编码架构为所有偶数位使用一个奇偶校验位为检查所有奇数位和第二的奇偶校验位。此代码的汉明距离是什么？17.Achannelhasabitrateof4kbpsandapropagationdelayof20msec.For whatrangeofframesizesdoesstop-and-waitgiveanefficiencyofatleast50 percent?一个信道的位速率为4kbps，传输延迟为20ms。请问帧的大小在什么范围内，停-等协议才可以获得

7、至少50的效率？29.Framesof1000bitsaresentovera1-Mbpschannelusingageostationarysatellitewhosepropagationtimefromtheearthis270msec.Acknowledgementsarealwayspiggybackedontodataframes.Theheadersareveryshort.Three-bit sequencenumbersareused.Whatisthemaximumachievablechannelutilization for (a)Stop-and-wait.(b)Pr

8、otocol5.(c)Protocol6.利用地球同步卫星在一个1Mbps的信道上发送1000位的帧，该信道离开地球的传输延迟为270ms。确认信息总是被捎带在数据帧傻姑娘。头部非常短，并且使用3位序列号。在下面的协议中，最大可获得的信道利用率是多少？(a)停-等协议(b)协议5(c)协议637. What is the minimum overhead to send an IP packet using PPP?Count only the over-head introduced by PPP itself ,not the IP header overhead.什么是开销最少要发送IP

9、数据包使用PPP的？数只介绍了PPP本身，不IP标头开销过度头。Chap.42. A group of N stations share a 56-kbps pure ALOHA channel.Each station outputs a 1000-bit frame on an average of once every 100 sec,even if the previous one has not yet been sent (e.g.,the stations can buffer outgoing frames). What is the maximum value of N?N个

10、站共享一个56kbps的纯ALOHA信道？每个站平均每100秒输出一个1000位帧，即使前面的帧还没有被送出，它也这样进行（比如这些站可以将送出的帧缓存起来）。请问N的最大值是多少？3. Consider the delay of pure ALOHA versus slotted ALOHA at low load. Which one is less? Explain your answer.考虑在底载荷情况下纯的ALOHA和分槽的ALOHA的延迟。哪一个延迟更小？请说明你的理由。5. A large population of ALOHA users manages to generat

11、e 50 request/sec, including both originals and retransmissions. Time is slotted in units of 40 mesc.一大群ALOHA用户每秒钟产生50个请求，包括原始的请求和重传的请求。时槽单位为40ms。(a) What is the chance of success on the first attempt?首次发送成功的几率是多少？(b)恰好k次冲突之后成功的概率是多少?What is the probability of exactly k collisions and then a success?

12、(c)所需传送次数的期望值是多少？What is the excepted number of transmission attempts needed? 44. To make VLANs work,configuration tables are needed in the switches and bridges. What if the VLANs of Fig.4-49(a) use hubs rather than multidrop cables?Do the hubs need configurations tables,too?Why or why not?为了使Vlan工作

13、，配置表需要在交换机和桥梁。如果Fig.4-49(a)Vlan使用集线器，而不是多点电缆？集线器太需要配置表了吗？为什么或为什么不？Chap.510. Ifdelaysarerecordedas8-bitnumbersina50-routernetwork,anddelayvectorsareexchangedtwiceasecond,howmuchbandwidthper(full-duplex)lineischewedupbythedistributedroutingalgorithm?Assumethateachrouterhasthreelinestootherrouters.假设在一

14、个50台路由器的网络中，用8位数值记录延迟信息，并且每秒钟交换延迟矢量两次，请问，分布式路由算法需要在每条（全双工）线路上消耗多少宽带？假设每台路由器有三条线路连接到其他的路由器。22. Adatagramsubnetallowsrouterstodroppacketswhenevertheyneedto.Theprobabilityofarouterdiscardingapacketisp.Considerthecaseofasourcehostconnectedtothesourcerouter,whichisconnectedtothedestinationrouter,andthent

15、othedestinationhost.Ifeitheroftheroutersdiscardsapacket,thesourcehosteventuallytimesoutandtriesagain.Ifbothhost-routerandrouter-routerlinesarecountedashops,whatisthemeannumberof(a)hopsapacketmakespertransmission?(b)transmissionsapacketmakes?(c)hopsrequiredperreceivedpacket?一个数据报子网允许路由器在必要的时候丢弃分组。一台路

16、由器丢弃一个分组的概率为p。请考虑这样的情形：源主机连接到路由器，源路由器连接到目标路由器，然后目标路由器连接到目标主机。如果任一台路由器丢掉了一个分组，则源主机最终会超时，然后再重试发送。如果主机至路由器以及路由器之间的线路都计为一跳，那么：（a） 一个分组每次传输中的平均跳数是多少？（b） 一个分组的平均传输次数是多少？（c） 每个接收到的分组平均要求多少跳？39. A network on the Internet has a subnet mask of 255.255.240.0. What is the maximum number of hosts it can handle?一

17、个网络在互联网上有255.255.240.0的子网掩码。它可以处理的主机的最大数目是什么？53. When the IPv6 protocol is introduced,does the ARP protocol have to be changed?IF so,are the changes conceptual or technical?介绍IPv6协议时，ARP协议必须改变吗？如果变化，是概念变化还是技术变化？Chap.614. Why does UDP exists? Would it not have been enough to just let user processes s

18、end raw IP packets?UDP为什么有必要存在？难道只让用户进程发送原始的IP分组还不够吗？16. A client sends a 128-byte request to a server located 100 km away over a 1-gigabit optical fiber.What is the efficiency of the line during the remote procedure call?一个客户端发送128 字节的请求到服务器位于1 千兆位光纤100公里。在远程过程调用过程中的效率是线的什么？20. Datagram fragmentation and reassembly are handled by IP and are invisible to TCP.Does this meant that TCP does not have to worry about data arriving in the wrong order?数据报的分段和重组机制是由IP来处理的，对于TCP是