計算機網(wǎng)絡試卷B理科班

1、2003年理科班計算機網(wǎng)絡試卷B 補考用一、填空題（每空0.5分，共10分）1網(wǎng)絡互連設備的作用是_1_。在不同層次上的網(wǎng)絡互連，名稱分別為數(shù)據(jù)鏈路層的互連設備叫_2_。網(wǎng)絡層的互連設備叫_3_；傳輸層的互連設備叫_4_；傳輸層上的設備叫_5_。網(wǎng)絡互連設備統(tǒng)稱為_6_。2TCP/IP協(xié)議參考模型由_7_、_8_、_9_、_10_。3在海明碼中，信息比特的位數(shù)與校驗比特位數(shù)之間的關系為_11_。4IP地址是_12_比特的二進制數(shù)。5互連網(wǎng)絡內部的路由選擇分二個層次_13_和_14_。 6Internet上的每個接口必須有一個_15_。7距離矢量路由選擇算法存在收斂慢的問題，為了克服此問題，AR

2、PANET采用了_16_。8ARP協(xié)議用于 17 。RARP用于 18 9DNS是_19_的簡稱。10TCP/IP網(wǎng)絡標準的傳輸服務原語是 20 。二、名詞解釋（5´2¢）1. 網(wǎng)橋2. 多路分解技術3. TCP協(xié)議與UDP協(xié)議4. 流量控制5. 差錯控制Question 3: Quickies'' (20 points)a. What is meant by the term statistical multiplexing?b. Consider an http client that wants to retrieve a WWW document a

3、t a given URL. The IP address of the http server is initially unknown. The WWW object at the URL has one embedded GIF image that resides at the same server as the original object. . What transport and application layer protocols besides http are needed in this scenario? . Suppose that the time neede

4、d to contact and receive a reply from any server (for any protocol) is RTT. How many RTTs are needed from when the user first enters the URL until the complete document is displayed? Assume that non-persistent http is used. Consider the delays of all protocols in your answer, not just those of http.

5、 c. How are ports numbers used by UDP in demultiplexing incoming segments? d. Which protocol Go-Back-N or Selective-Repeat - makes more efficient use of network bandwidth? Why?二、請描述Ethernet的CSMA/CD協(xié)議的工作原理。（5分）三、請說明橋接器（Bridges）的工作原理，與交換機(Switches)比較各有什么優(yōu)缺點。（5分）四、傳輸層的數(shù)據(jù)可靠傳輸機制是采用那些措施保證的？（5分）五、（5分）請根據(jù)如圖

6、1所示的網(wǎng)絡，說明ARP協(xié)議的工作原理。 HOST1 HOST2 HOST3IP= MAC=08005A7A7ED1 IP= MAC=08005A7A7ED2 IP= MAC=08005A7A7ED1 圖1六、（10分）考慮建立一個CSMA/CD網(wǎng)，電纜長1公里，不使用重發(fā)器，運行速率為1Gbps。電纜中的信號速度是200000公里/秒。問最小幀長度是多少？七、（10分）以太網(wǎng)幀必須至少64字節(jié)長，才能保證在線纜的遠端發(fā)生碰撞的情況下發(fā)送方仍然在發(fā)送?？焖僖蕴W(wǎng)同樣有一個64字節(jié)的最小幀長規(guī)范，但位速率提高到了10倍。它是

7、如何使得最小幀長規(guī)范能夠維持不變的？八、（10分）在下列情況下，計算傳送1000KB文件所需要的總時間，即從開始傳送時起直到文件的最后一位到達目的地為止的時間。假定往返時間RTT是100毫秒，一個分組是1KB（即1024字節(jié)）的數(shù)據(jù)，在開始傳送整個的文件數(shù)據(jù)之前進行的起始握手過程需要2×RTT的時間。1 帶寬是1.5Mbps，數(shù)據(jù)分組可連續(xù)發(fā)送。(2¢)2 帶寬是1.5Mbps，但在結束發(fā)送每一個數(shù)據(jù)分組之后，必須等待一個RTT才能發(fā)送下一個數(shù)據(jù)分組。(3¢)3 帶寬是無限大的值，即我們取發(fā)送時間為0，并且在等待每個RTT后可發(fā)送多達20個分組。(2¢)

8、4 帶寬是無限大的值，在緊接起始握手后我們可以發(fā)送一個分組，此后，在第一次等待RTT后可發(fā)送21個分組，在第二次等待RTT后可發(fā)送22個分組，在第n次等待RTT后可發(fā)送2n個分組。(3¢)Question 9: Addressing, and following the data (10 points)Consider the simple network shown below:AEWrite down an IP address for all interfaces at all hosts and routers in the network. The IP addresses

9、 for A and E are as given. You should assign IP addresses so that interfaces on the same network have the same network-part of their IP address. Indicate the number of bits in the network-part of this address.a) Choose physical addresses (LAN addresses) for only those interfaces on the path from A t

10、o E. Can these addresses be the same as in part a)? Why?b) Now focus on the actions taken at both the network and data link layers at sender A, the intervening router, and destination E in moving an IP datagram from A to E:1. How do A, E and the router determine the IP addresses needed for the IP da

11、tagram? 2. What, specifically, are the addresses in the IP datagram that flows from A to the router. What, specifically, are the addresses in the IP datagram that flows from the router to E.3. What are three other fields found in an IP datagram?4. How do A, E and the router determine the physical (LAN) addresses needed for the data link layer frame?d) Suppose that the router in the figure below is replaced by a bridge.1. How would the IP addresses change in this case?2. Ho