网络原理课后作业

1、网络课后作业 Chap.2 3. Televisi on cha nn els are 6 MHz wide. How many bits/sec can be sent if four-level digital sig nals are used? Assume a no iseless cha nn el. 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. If a binary sig nal is sent over a 3-kHz cha nnel whose sig nal-to-no ise ratio is 20dB,

2、 what is the maximum achievable data rate? 如果在一条3kHz信道上发送一个二进制信号，该信道的信噪比为20dB，贝愎大 可达到的数据传输率为多少？ 28. Te n sig nals, each requiri ng 4000 Hz, are multiplexed on to a sin gle cha nnel using FDM. How much minimum ban dwidth is required for the multiplexed cha nn el? Assume that the guard bands are 400 H

3、z wide. 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.Suppose that x bits of user data are to be tran smitted over a k-hop path in a packet-switched n etwork as a series of packets, each containing p data bits and h header bits, with x p + h. The bit rate of the lines is

4、b bps and the propagati on delay is n egligible. What value of p mi ni mizes the total delay? 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b bps，传播延迟忽略不计。请问什么样的p值使总延迟最小？ Chap.3 3.The followi ng data fragme nt occurs in the middle of a data stream for whichthe byt e-st

5、uffi ng algorithm described in the text is used: A B ESC C ESC FLAGFLAG D. What is the output after stuffi ng? 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：B ESC C ESC FLAG FLA在填料后的输出是什么？ 5. A bit stri ng, 0111101111101111110, needs to be tran smitted at the data link layer. What is the stri ng actually tran smitt

6、ed after bit stuffi ng? 位串0111101111101111110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 cod ing schema uses one parity bit for check ing all the odd-nu mber bits and a sec ond parity bit for all the eve n-nu mbered bits.Wha

7、t is the Hamming dista nee 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.A eha nnel has a bit rate of 4 kbps and a propagati on delay of 20 msec. For what range of frame sizes does stop-a nd-wait give an effieie ncy of at least 50 peree nt? 一个信道的位速率为4kb

8、ps，传输延迟为20ms。请问帧的大小在什么范围内，停 -等协议才可以获得至少50%的效率？ 29. Frames of 1000 bits are sent over a 1-Mbps cha nnel using a geostati onary satellit e whose propagati on time from the earth is 270 msec. Ack no wledgeme nts are alway s piggybacked onto data frames. The headers are very short. Three-bit seque nee n

9、u mbers are used. What is the maximum achievable cha nnel utilizatiorfor (a) Stop-a nd-wait. (b) Protocol 5. (c) Protocol 6. 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6 37.What is the minimum overhead to send an IP

10、 packet using PPP?Count only the over-head in troduced by PPP itself , not the IP header overhead. 什么是开销最少要发送IP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.4 2. A group of N stati ons share a 56-kbps pure ALOHA cha nn el.Each stati on outputs a 1000-bit frame on an average of once every 100 sec,eve n if

11、 the previous one has not yet bee n sent (e.g.,the stati ons can buffer outgo ing frames). What is the maximum value of N? N个站共享一个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. Co nsider the delay of pure ALOHA versus slotted ALOHA at low load. Which one

12、 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 populatio n of ALOHA users man ages to gen erate 50 request/sec, in cludi ng both origi nals and retra nsmissi ons. Time is slotted in un its 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

13、the chanee of successon 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 collisi ons and the n a success? (c) 所需传送次数的期望值是多少？What is the excepted number of transmission attempts n eeded? 44. To make VLANs work,configuration tables are needed in the switches

14、 and bridges. What if the VLANs of Fig.4-49(a) use hubs rather than multidrop cables?Do the hubs n eed con figuratio ns tables,too?Why or why not? 为了使Vian工作，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.5 1O.lf delays are recorded as 8-bit nu mbers in a 50-router n etwork,

15、 and delay vectors are excha nged twice a sec ond, how much ban dwidth per (full-duplex) line is chewed up by the distributed routi ng algorithm? Assume that each router has three lines to o ther routers. 假设在一个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

16、。 22. A datagram sub net allows routers to drop packets whe never they n eed to. The pr obability of a router discard ing a packet is p. Con sider the case of a source host conn ected to the source router, which is conn ected to the desti nati on router, and the n to the desti nati on host. If eithe

17、r of the routers discards a packet, the source host eve ntu ally times out and tries aga in. If both host-router and router-router lines are coun ted as hops, what is the mean nu mber of (a) hops a packet makes per tran smissi on? (b) tran smissi ons a packet makes? (c) hops required per received pa

18、cket? 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) 个分组每次传输中的平均跳数是多少？ (b) 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 In ternet has a sub net mask of 255.255.240.0. What is the

19、maximum nu mber of hosts it can han dle? 一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 cha nged?IF so,are the cha nges con ceptual or tech ni cal? 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.6 14.Why does UDP exists? Would it not have bee n eno ugh to just let user processes send 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 clie nt sends a 128-byte request to a server located 100 km away over a 1