计算机网络试题.doc

精品文档1. Explain Client-Server model for distributed computing by example.l Client-server model can make computing faster than just use the server to computing and the client just be a browser.For example ,the data stored in a powerful server machine ,and the cilent connected with the server by internet,it maniplation data at local cilent ,so the server can handle more request from other clients,and the client can make full use of it hardware resource.So the distributed computing can be very fast. 2. Explain Peer-to-Peer model for distributed computing by examplePeer-to-Peer model means individuals who form a loose group can communicate with others in the group,everyone in this group can communicate with one or more other people ,and everone can be clients and servers.For example ,if we use BitTorrent to download a film,we download it from other people who also have this software and the resource, not just from one or two server.At the same time ,our resources also be shared and downloaded by other people , it makes the speed of the transmission more faster than before.3. Compare concepts of Broadcasting, Multicasting, Unicasting.Broadcasting: Broadcast systems usually allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network.Multicasting:If borad cast systems also support taransmission to a subset of the machine,it called multicasting. Unicasting:Point-to-point transmission with exactly one sender and exactly one receiver is sometimes called unicasting.4. What are the two generally acceptedangles by which computer networks can be classified? It can be classified from Network node distribution and Network Topology.5. Describe some characteristics of the Ethernet. Ethernet often used in local area networks, is the most common type of wired LAN. it use copper wires, optical fibers.and it frame in IEEE802.36. How is a WAN organized? explain packet-switched principle.WAN spans a large geographical area,often a country or continent,and less lines,In WAN,the hosts and subnet are owned and operated by different people.And before the message be sended,it will be cut into packets,every packetss header be inserted some message about the target address ,and then post them ,be received at each intermediate router .7. What are two reasons for using layered protocols?It can reduce the design complexity,every layer just need to concern about its own fuction.if the protocols changes,the other layers protocols dont need to change.8. What is the principal difference between connectionless communication and connection-oriented communication?Connection-oriented service need to establish a connection and until the connection establish success ,it starts the data transmission.if the transmission stop ,it close the connection,and the data transmission is ordered.Connectionless service :each message carries the full destination address and each one is routed through the intermediate nodes inside the system independent of all the subsequent messages.and the receiver get the messages unordered. 9. Explain the relationship between services and protocols.The service defines what operations the layer is prepared perform on its users ,but doesnt say how these operations are implemented.and its on a low level.The protocol is a set of rules governing the format and meaning of the packets,ormessages that are exchanged by the peer entities within a layer(同一层上的对象)entities use protocols to implement(实施) their serevice definitions.10. Which of the OSI layers handles each of the following:(a)Dividing the transmitted bit stream into frames. Data Link Layer(b)Determining which route through the subnet to use. Network Layer11. If the unit exchanged at the data link level is called a frame and the unit exchanged at the network level is called a packet, do frames encapsulate packets or do packets encapsulate frames? Explain your answer.Do frames encapsulate packets, because the data link level is lower than network level,the packet which from network level neet to be encapsulated in frames data header,and the sent to physical layer.12. A system has an n-layer protocol hierarchy(分层协定). Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers? h*n /(M+h*n)13. Suppose the algorithm used to implement the operations at layer k is changed, how does this impact operations at layers k-1 and k+1?It doesnt influence the layer k+1 and k-1;14. Suppose there is a change in the service (set of operations) provided by layer k, how does this impact services at layers k-1 and k+1? It doesnt influence the layer k+1 and k-1;15. List two ways in which the OSI reference model and the TCP/IP reference model are the same. Now list two ways in which they differ.Samethey all need layer for each different level of abstarctioneach layer performs a function.Difference :OSI reference model have seven level,and tcp/ip just has four level .OSI supports both in the network layer ,tcp/ip supports only connectionless mode in the network layer.16. Please draw a diagram showing the OSI reference model.sorry17. What is the main difference between TCP and UDP.Tcp is connection-oriented protocol.UDP is connectionless protocol.Tcps transmitted message is ordered ,and UDPs not18. When a file is transferred between two computers, two acknowledgement strategies are possible. In the first one, the file is chopped up into packets, which are individually acknowledged by the receiver, but the file transfer as a whole is not acknowledged. In the second one, the packets are not acknowledged individually, but the entire file is acknowledged when it arrives. Discuss these two approaches.First one :if one packge has error,it dont need to send all the file again,but the size of all transferred message is larger than the second one.Second one:if one packet has error,the whole file need to retransfer again.19. Assume you post a regular letter to a friend, do you think the postal service is a reliable service? if you want to make sure that the letter will arrive at your friends mail box, think of a protocol based on the regular letter postal service.Postal service is not a reliable service ,I will send two letters ,one is the message which be encrypted,the other is the key,and each ones header has the message that tell the friend if he just get one letter,then reply me ,and I will send it again,thats all.if he get all,reply ok to me.else ,I will send two messages again.2