Homework Chapter 4

《Computer Networks and Internet》 Homework Chapter 4 1.In the text we have used the term connection-oriented service to describe a transport-layer service and connection service for a network-layer service. Why the subtle shades in terminology? 在文中,我们所用的术语面向连接的服务来描述传输层服务和连接服务为网络层的服务。为什么术语中细微的色调? In a virtual circuit network, there is an end-to-end connection in the sense that each router along the path must maintain state for the connection; hence the terminology connection service. In a connection-oriented transport service over a connectionless network layer, such as TCP over IP, the end systems maintain connection state; however the routers have no notion of any connections; hence the terminology connection-oriented service. 在一个虚电路网络,有在这个意义上,沿路径的每个路由器必须维护状态为连接端至端连接;即术语连接服务。在通过无连接网络层,例如TCP到IP上一个面向连接的传输服务,所述终端系统保持连接状态;但是,路由器没有任何连接的概念;因此术语面向连接的服务。 2.Consider a datagram network using 32-bit host addresses. Suppose a router has four links, numbered 0 through 3, and packets are to be forwarded to the link interfaces as follows: 考虑使用32位主机地址的数据包网络。假设路由器具有四个链接,编号为0到3,并且分组将被转发到链路接口如下: Destination Address Range Link Interface 11100000 00000000 00000000 00000000 through 0 11100000 00111111 11111111 11111111 11100000 01000000 00000000 00000000 through 1 11100000 01000000 11111111 11111111 11100000 01000001 00000000 00000000 through 2 11100001 01111111 11111111 11111111 otherwise 3 a. Provide a forwarding table that has four entries, uses longest prefix matching, and forwards packets to the correct link interfaces. b. Describe how your forwarding table determines the appropriate link interface for datagrams with destination addresses: 11001000 10010001 01010001 01010101 11100001 01000000 11000011 00111100 11100001 10000000 00010001 01110111 1.提供一个转发,有四个条目,使用最长前缀匹配,并且报文转发到正确的链路接口。 2.描述你如何根据转发表,决定了数据报的目的地址相应的链路接口: 1 3.Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has the following forwarding table: 考虑使用8位主机地址的数据包网络。假设一台路由器使用最长前缀匹配,并具有下列转发表: For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range. 对于每4个接口,给目的地的主机地址相关联的范围,并在范围内的地址的数目。 4.Consider sending a 2400-byte datagram into a link that has an MTU of 700 bytes. Suppose the original datagram is stamped with the identification number 422. How many fragments are generated? What are the values in the various fields in the IP datagram(s) generated related to fragmentation? 考虑派遣一个2400字节的数据包到具有700字节的MTU的链接。假设原始数据包上印有识别号码422。产生多少碎片?什么是在IP数据报(多个)的各个领域中的值产生相关碎片? 5.Suppose datagrams are limited to 1500 bytes (including header) between source Host A and destination Host B. Assuming a 20-byte IP header, how many datagrams would be required to send an MP3 consisting of 5 million bytes? Explain how you computed your answer. 假设数据报被限制在1500字节(包括字头)在源主机A和目标主机B之间.假设一个20字节的IP报头,有多少数据包将被要求送往一个有5亿字节的MP3?解释你如何计算你的答案。 6.Consider the network setup in following Figure. Suppose that the ISP instead assigns the router the address 24.34.112.235 and that the network address of the home network is 192.168.1/24. 考虑下图中的网络设置。假设在ISP代替分配路由器的地址24.34.112.235和所述家庭网络的网络地址为192.168.1/ 24。 a. Assign addresses to all interfaces in the home network. b. Suppose each host has two ongoing TCP connections, all to port 80 at host 128.119.40.86. Provide the six corresponding entries in the NAT translation table. 1.指定地址在家庭网络中的所有接口。 2.假定每个主机有两个正在进行的TCP连接,所有80端口的主机128.119.40.86。提供NAT 转换表的六个相应的条目。 7.Consider the following networ k. With the indicated link costs, use Dijkstra’s shortest-path algorithm to compute the shortest path from x to all network nodes. And compute the shortest path from t to all network nodes. Show how the algorithm works by computing a table. 考虑下面的网络。用所示链路成本,使用Dijkstra的最短路径算法来从x到所有的网络节点计 算最短路径。并从t到所有的网络节点计算最短路径。显示如何算法通过计算表。 Answer: Step N’D(t),p(t) D(u),p(u) D(v),p(v) D(w),p(w) D(y),p(y) D(z),p(z) 0 x 1 2 3 4 5 6 Step N’D(x), p(x) D(u),p(u) D(v),p(v) D(w),p(w) D(y),p(y) D(z),p(z) 0 t 1 2 3 4 5 6 8.Consider the network shown below, and assume that each node initially knows the costs to each of its neighbors. Consider the distance-vector algorithm and show the distance table entries at node z. 考虑如下所示的网络中,并且假设每个节点知道与相邻节点之间的初始距离。考虑距离向量算法,并显示在节点Z的距离表项。 《Computer Networks and Internet 》 6