Homework Chapter 5

1、Computer Networks and InternetHomework Chapter 51. How big is the LAN address space? The IPv4 address space? The IPv6 address space?248，232，21282. Suppose four active nodesnodes A, B, C and Dare competing for access to a channel using slotted ALOHA. Assume each node has an infinite number of packets

2、 to send. Each node attempts to transmit in each slot with probability p. The first slot is numbered slot 1, the second slot is numbered slot 2, and so on.假设四个活动节点，节点A，B，C和D-正在争夺访问使用时隙ALOHA的通道。假设每个节点有分组的无限号码发送。每个节点将尝试在每个时隙的概率为p传输。第一时隙编号为时隙1，第二时隙编号为2的插槽，并依此类推。a. What is the probability that node A su

3、cceeds for the first time in slot 5?b. What is the probability that some node (either A, B, C or D) succeeds in slot 4?c. What is the probability that the first success occurs in slot 3?d. What is the efficiency of this four-node system?1.节点A首次就成功插在插槽5的概率是多少？2.某些节点（或A，B，C或D）成功插在插槽4的概率是多少？3.第一次成功发生在槽

4、3的概率是多少？4.这四个节点系统的效率？ 3. Calculate the efficiency of slotted ALOHA and pure ALOHA as a function of p (p=0, 0.1, 0.2, 0.3, 0.4, 0.5, , 1.0) for the following values of N:a. N=15. b. N=20. c. N=30.Answer: Equationpure ALOHAp=00.10.20.30.40.50.60.70.80.91.0N=15N=20N=30slotted ALOHAp=00.10.20.30.40.50.6

5、0.70.80.91.0N=15N=20N=30 4. Consider three LANs interconnected by two routers, as shown in Figure 1.考虑由两个路由器相互连接3个网，如图1。Figure 1a. Assign IP addresses to all of the interfaces. For Subnet 1 use addresses of the form 192.168.1.xxx; for Subnet 2 uses addresses of the form 192.168.2.xxx; and for Subnet

6、 3 use addresses of the form 192.168.3.xxx.b. Assign MAC addresses to all of the adapters.c. Consider sending an IP datagram from Host E to Host B. Suppose all of the ARP tables are up to date. Enumerate all the steps, as done for the single-router example in ARP.d. Repeat (c), now assuming that the

7、 ARP table in the sending host is empty (and the other tables are up to date).1.将IP地址分配给所有的接口。对于子网1使用形如192.168.1.xxx的地址;子网2使用的形式192.168.2.xxx地址;而对于子网3使用形式192.168.3.xxx地址。2.指定MAC地址的所有适配器。3.考虑发送IP数据报从主机E至主机B.假设所有的ARP表是最新的。枚举所有的步骤，可用于在ARP单路由器为例。4.重复（c）中，现在假定在发送主机ARP表是空的（和其他表是最新的）。1。在E转发表确定数据包应该被路由接口192

8、.168.3.002。2。在E的适配器创建和以太网目的地址88-88-88-88-88-88以太网数据包。3。路由器2接收该分组，并提取该数据报。在该路由器的转发表指示数据报路由到198.162.2.002。4。路由器2然后通过与198.162.2.003的IP地址，端口发送带有的55-55-55-55-55-5533-33-33-33-33-33和源地址到达目的地址的以太网数据包。5。该过程继续，直至该分组到达主机B5. Consider Figure 1 in above problem 4. Provide MAC addresses and IP addresses for the i

9、nterfaces at Host A, both routers, and Host F. Suppose Host A sends a datagram to Host F. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (i) from A to the left router, (ii) from the left router to the right router, (iii) from the

10、 right router to F. Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.考虑图1中的上述问题4.提供MAC地址，并在主机A上，两个路由器的接口的IP地址和主机F.假设主机A发送数据报给主机F.提供的源和目的MAC地址的帧封装这IP数据报作为帧被发送（）从A到左侧路由器，（）从左侧路由器到合适的路由器，（）从右侧路由器至F也给在IP源和目的地IP地址在时间框架的每一个点

11、的范围内数据报封装。 6. Suppose now that the leftmost router in Figure 1 is replaced by a switch. Hosts A, B, C, and D and the right router are all star-connected into this switch. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (i) from A

12、to the switch, (ii) from the switch to the right router, (iii) from the right router to F. Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.现在假定最左边的路由器在图1中被替换为一个开关。主机A，B，C和D和正确的路由器都是星型连接到该交换机。给在帧的封装的源和目的地MAC地址此IP数据报作为帧

13、被发送（）从A到交换机上，（）从交换机到合适的路由器，（）从右侧路由器至F也给在IP数据报中的时间帧内包封在每个这些点的源和目的地IP地址。7. Recall that with the CSMA/CD protocol, the adapter waits K 512 bit times after a collision, where K is drawn randomly. For K = 100, how long does the adapter wait until returning to Step 2 for a 10 Mbps Ethernet? For a 100 Mbps

14、 Ethernet?回想一下CSMA / CD协议，适配器等待512比特时间的碰撞，其中K是随机抽取。对于K =100，时间适配器等多长时间能回到步骤2，对于10 Mbps以太网？对于100 Mbps以太网？8. Suppose nodes A and B are on the same 10 Mbps Ethernet bus, and the propagation delay between the two nodes is 325 bit times. Suppose node A begins transmitting a frame and, before it finishes,

15、 node B begins transmitting a frame. Can A finish transmitting before it detects that B has transmitted? Why or why not? If the answer is yes, then A incorrectly believes that its frame was successfully transmitted without a collision. Hint: Suppose at time t = 0 bit times, A begins transmitting a f

16、rame. In the worst case, A transmits a minimum-sized frame of 512 + 64 bit times. So A would finish transmitting the frame at t = 512 + 64 bit times. Thus, the answer is no, if Bs signal reaches A before bit time t = 512 + 64 bits. In the worst case, when does Bs signal reach A?假设节点A和B是相同的10 Mbps以太网总线,两个节点之间的传播延迟是325倍。假设节点开始发送一帧,在它结束之前,B节点传输一帧开始。能完成传输之前检测到B传播么?为什么或为什么不呢?如果答案是肯定的,那么一个错误地认为其框架没有碰撞的成功传播。提示:假设在时间t = 0倍,开始传送一帧