【命題要點(diǎn)】英語(yǔ)詞語(yǔ)是最基礎(chǔ)的部分，由于網(wǎng)絡(luò)技術(shù)是不斷更新的領(lǐng)域，不斷有新的思想涌現(xiàn)，也伴隨著新的詞匯出現(xiàn)。由于新出現(xiàn)的詞匯和網(wǎng)絡(luò)技術(shù)的專業(yè)性，往往造成理解上的偏差，因此需要應(yīng)試者在基本了解網(wǎng)絡(luò)技術(shù)中英語(yǔ)專業(yè)詞匯的基礎(chǔ)上，將英語(yǔ)詞匯和漢語(yǔ)詞匯在功能和語(yǔ)義上相對(duì)應(yīng)形成正確的理解。應(yīng)試者需要準(zhǔn)確掌握詞語(yǔ)的意義，區(qū)分同義詞在意義和使用上的差別；準(zhǔn)確掌握名詞單、復(fù)數(shù)形式，以及由單、復(fù)數(shù)形式帶來(lái)不同語(yǔ)義的解釋；準(zhǔn)確掌握關(guān)系代詞、關(guān)系副詞、聯(lián)系詞在語(yǔ)句乃至整個(gè)語(yǔ)篇中的邏輯意義。在詞匯復(fù)習(xí)中，尤其還需要注意專業(yè)詞匯的縮寫，這些縮寫往往是某些技術(shù)、設(shè)備或協(xié)議的代稱，在整個(gè)試題中是核心詞匯。復(fù)習(xí)時(shí)應(yīng)多讀一些計(jì)算機(jī)網(wǎng)絡(luò)方面的英語(yǔ)時(shí)文。解題時(shí)，一般先考慮語(yǔ)義，后考慮語(yǔ)法。一、考題格式上午科目的71?75題一般是完形填空的形式。主要考查應(yīng)試者結(jié)合計(jì)算機(jī)專業(yè)技術(shù)知識(shí)對(duì)全文綜合理解的程度，和聯(lián)系上下文的能力；應(yīng)試者語(yǔ)法知識(shí)和對(duì)句法結(jié)構(gòu)的辨識(shí)能力；應(yīng)試者的詞匯量和詞匯運(yùn)用能力。具體而言，完形填空主要考查應(yīng)試者對(duì)語(yǔ)篇中句法、詞語(yǔ)和短語(yǔ)的把握能力，具有較強(qiáng)的測(cè)試性。每一個(gè)空處都要通過(guò)上下文進(jìn)行綜合考慮，僅僅依靠一個(gè)單句往往無(wú)法確立正確選項(xiàng)。語(yǔ)篇的內(nèi)容往往是對(duì)網(wǎng)絡(luò)技術(shù)中協(xié)議、通信過(guò)程、設(shè)備、最新技術(shù)等相關(guān)知識(shí)的描述，需要應(yīng)試者對(duì)于這些內(nèi)容有一定的了解。二、答題要領(lǐng)首先，通過(guò)首句或出現(xiàn)的核心詞匯來(lái)推斷全文的信息。短文的首句往往是主題句，或出現(xiàn)了核心詞匯，能為理解文章的大意和主要內(nèi)容提供必要線索。一般首句還提供背景資料，因此要特別注意首句，抓住整個(gè)段落的綱要。其次，把握文章發(fā)展的基本線索。文章總是按照一定思路發(fā)展起來(lái)的，而不同的邏輯關(guān)系主要依靠使用邏輯連接詞來(lái)表達(dá)的，文章如果沒有出現(xiàn)內(nèi)在的邏輯關(guān)系，就會(huì)出現(xiàn)語(yǔ)義不清，邏輯混亂。所以通過(guò)表示邏輯關(guān)系的詞匯把握文章發(fā)展的基本線索是至關(guān)重要的。借助語(yǔ)法知識(shí)和專業(yè)背景知識(shí)確定正確的詞匯選項(xiàng)。計(jì)算機(jī)專業(yè)英語(yǔ)詞匯的考查在試題中占一定比例，詞匯選項(xiàng)的設(shè)計(jì)和文章難度的制定與語(yǔ)法都息息相關(guān)。應(yīng)試者務(wù)必借助語(yǔ)法知識(shí)和專業(yè)背景知識(shí)來(lái)確定正確的詞匯選項(xiàng)。同時(shí)注意填入的詞匯和文中句子的結(jié)構(gòu)要求相一致。三、答題步驟第一步，通讀全文。完形填空是考查全面理解內(nèi)容的基礎(chǔ)上運(yùn)用語(yǔ)言的能力，由于試題篇幅較短，完全有時(shí)間利用通讀對(duì)全文內(nèi)容有一個(gè)基本的了解。應(yīng)試者要快速閱讀段落，把握基本觀點(diǎn)，通讀時(shí)以瀏覽為主，可以忽略細(xì)節(jié)。第二步，復(fù)讀答題。在通讀的基礎(chǔ)上，應(yīng)試者最好能立即復(fù)讀，并結(jié)合選項(xiàng)，從語(yǔ)法結(jié)構(gòu)、語(yǔ)義、詞義、固定搭配等方面結(jié)合專業(yè)知識(shí)來(lái)考慮選項(xiàng)。選定之后，還需要回讀。在整個(gè)答題過(guò)程中，切記全文的整體意義，保持思路的連貫性，從而做出最合適的正確選擇。第三步，重讀檢查。在確定了所有選項(xiàng)以后，一定還要重讀全文，檢查并核實(shí)每個(gè)選項(xiàng)在正篇文章中沒有造成語(yǔ)義、結(jié)構(gòu)、邏輯等方面的差錯(cuò)，確保短文是一個(gè)內(nèi)容連貫、層次清晰、中心思想突出的整體。四、常用詞匯下面列出常用的計(jì)算機(jī)網(wǎng)絡(luò)技術(shù)基本術(shù)語(yǔ)，供考生復(fù)習(xí)時(shí)參考。accept 接受 access control 訪問控制acknowledgement (ACK)確認(rèn)adaptive routing 自適應(yīng)路由address field 地址字段amplitude 振幅analog signal 模擬信號(hào)anonymous FTP 匿名 FTPapplication layer 應(yīng)用層asynchronous 異步backbone 主干bandwidth 帶寬baseband mode 基帶模式baud rate波特率binary exponential backoff algorithm 二進(jìn)制指數(shù)退避算法bit-oriented protocol 面向比特的協(xié)議 block check character 塊校驗(yàn)字符Border Gateway Protocol 邊界網(wǎng)關(guān)協(xié)議bridge網(wǎng)橋bridge protocol data unit 網(wǎng)橋協(xié)議數(shù)據(jù)單元broadcast address 廣播地址 Brouter橋路器buffering 緩沖cable modem電纜調(diào)制解調(diào)器Caesar cipher凱撒密碼 call confirmation 呼叫證實(shí)call request呼叫請(qǐng)求Carrier Sense Multiple Access (CSMA)載波偵聽多路訪問Carrier Sense Multiple Access with Collision Detection (CSMA/CD)帶沖突檢測(cè)的載波幀聽多路訪問carrier signal載波信號(hào) Cell信元channel 信道 Checksum校驗(yàn)和Choke packet抑制分組 ciphertext 密文circuit switching 電路交換 client客戶client/server model客戶端/服務(wù)器模式 coaxial cable 同軸電纜code編碼 common bus topology 公共總線拓?fù)浣Y(jié)構(gòu)Common Gateway公共網(wǎng)關(guān)接口 Common Management Information Protocol通用管理信息協(xié)議communications subnet 通信子網(wǎng) compact disc 光盤compression 壓縮 congestion 擁塞connection 連接contention 競(jìng)爭(zhēng)contention protocol 競(jìng)爭(zhēng)協(xié)議control bits 控制位control character 控制字符Data Circuit-Terminating Equipement (DCE)數(shù)據(jù)電路端接設(shè)備Data Encryption Standard (DES)數(shù)據(jù)加密標(biāo)準(zhǔn)data link layer數(shù)據(jù)鏈路層 datagram數(shù)據(jù)報(bào)decryption 解密 demodulation 解調(diào)destination address 目的地址 differential encoding 差分編碼digital signal 數(shù)字信號(hào) digital signature 數(shù)字簽名directory service 目錄服務(wù) domain 域Domain Name System 域名系統(tǒng) echo reply回送響應(yīng)echo request回送請(qǐng)求 electronic mail (email)電子郵件encryption 加密 encryption key 密鑰error control 差錯(cuò)控制 error correction 差錯(cuò)校正error detection 差錯(cuò)檢測(cè)Ethernet以太網(wǎng)even parity 偶校驗(yàn) exterior gateway protocol 外部網(wǎng)關(guān)協(xié)議fiber distributed data interface 光纖分布式數(shù)據(jù)接口file server文件服務(wù)器file transfer protocol 文件傳輸協(xié)議filter濾波器flow control流量控制fragment 段fragmentation 分段frame 幀 frequency 頻率frequency-division multiplexing 頻分多路復(fù)用full duplex 全雙工 gateway 網(wǎng)關(guān)graded-index multimode fiber 級(jí)率多模光纖hacker黑客half duplex 半雙工Hamming code 海明碼handshaking 握手High-level Data Link Control (HDLC)高級(jí)數(shù)據(jù)鏈路控制協(xié)議host主機(jī)hypertext transfer protocol (HTTP)超文本傳送infrared light 紅外線 Internet因特網(wǎng)Internet Control Message Protocol (ICMP) 網(wǎng)際控制報(bào)文協(xié)議Internet Protocol 網(wǎng)際協(xié)議 Internet worm因特網(wǎng)蠕蟲key exchange密鑰交換 laser激光local area network (LAN)局域網(wǎng)local exchange本地交換局local loop本地回路Manchester code曼徹斯特編碼medium access control (MAC)媒體訪問控制message handling 報(bào)文處理message transfer protocol 報(bào)文傳送協(xié)議modem 調(diào)制解調(diào)器modulation 調(diào)制multiplexer 多路復(fù)用器 network 網(wǎng)絡(luò)Network Control Protocol 網(wǎng)絡(luò)控制協(xié)議 network interface card (NIC)網(wǎng)絡(luò)接口卡network layer protocol 網(wǎng)絡(luò)層協(xié)議 network topology網(wǎng)絡(luò)拓?fù)浣Y(jié)構(gòu)network virtual terminal 網(wǎng)絡(luò)虛擬終端 Non-persistent CSMA 非堅(jiān)持CSMANyquist theorem 奈奎斯特定理 octet字節(jié)odd parity奇校驗(yàn) Open Systems Interconnect (OSI)開放系統(tǒng)互連packet分組packet header 分組頭packet-switched network分組交換網(wǎng)絡(luò)parity bit奇偶校驗(yàn)位path通路path control通路控制physical layer 物理層 pixels像素plaintext 明文 prefix前綴presentation layer 表示層 protocol 協(xié)議pulse amplitude modulation 脈沖幅度調(diào)制pulse code modulation 脈碼調(diào)制radio 無(wú)線電收發(fā)機(jī)receiving window 接收窗口remote logins 遠(yuǎn)程登錄 repeater 中繼器reply 應(yīng)答root bridge 根網(wǎng)橋root port 根端口route 路由router 路由器 routing algorithm 路由算法Routing Information Protocol路由信息協(xié)議routing table 路由表sampling frequency 采樣率satellite人造衛(wèi)星script腳本 security 安全 segment 段sequence number 序列號(hào) serial transmission 串行傳輸server服務(wù)器 session 會(huì)話session control 會(huì)話控 session layer 會(huì)話層signal-to-noise ratio 信噪比 simplex 單工Simple Mail Transfer Protocol (SMTP)簡(jiǎn)單 郵件傳輸協(xié)議single-mode fiber 單模光纖sliding window 滑動(dòng)窗口協(xié)議socket套接字source address 源地址source quench 源抑制spanning tree algorithm 生成樹算法start bit起始位start of frame delimiter 幀起始定界符static routing 靜態(tài)路由stop bit 停止位subnet子網(wǎng) successor 后繼switch交換機(jī)SYN character同步字符Synchronous 同步Synchronous Optical Network (SONET)同步光纖網(wǎng)telegraph 電報(bào) terminal adapter終端適配器three-way handshake 三次握手 time exceeded 超時(shí)time to live 生存期 time-division 時(shí)分multiplexing 多路復(fù)用 timestamp reply 時(shí)戳應(yīng)答timestamp request 時(shí)戳請(qǐng)求 token令牌 transceiver 收發(fā)器transmission rate 傳輸速率transparent bridge 透明網(wǎng)橋transport layer 運(yùn)輸層 twisted pair 雙絞線tunneling 隧道Uniform Resource Locator (URL)統(tǒng)一資源定位器User Datagram Protocol (UDP)用戶數(shù)據(jù)報(bào)協(xié)議 verification 驗(yàn)證virutalcircuit (route) 虛電路（路由） virus病毒wide area network (WAN)廣域網(wǎng) window 窗口World Wide Web 萬(wàn)維網(wǎng) worm蠕蟲【試題14-1】 2013年5月真題71~75Traditional IP packet forwarding analyzes the (71) IP address contained in the network layer header of each packet as the packet travels from its source to its final destination. A router analyzes the destination IP address independently at each hop in the network. Dynamic (72) protocols or static configuration builds the database needed to analyze the destination IP address (the routing table). The process of implementing traditional IP routing also is called hop-by-hop destination-based (73) routing. Although successful , and obviously widely deployed, certain restrictions, which have been realized for some time, exist for this method of packet forwarding that diminish its (74) .New techniques are therefore required to address and expand liie functionality of an IP-based network infrastructure. This first chapter concentrate on identifying these restrictions and presents a new architecture, known as multipleprotocol (75) switching, that provides solutions to some of these restrictions.(71) A.datagram B.destinationC.connectionD.service(72)A.routing B.forwarding C.transmissionD.management(73)A.anycast B.multicast C.broadcast D.unicast(74)A.reliabilityB.flexibilityC.stability D.capability(75)A.const B.cast C.mark D.label解析：當(dāng)數(shù)據(jù)包從其來(lái)源到其最終目的地址時(shí)，傳統(tǒng)的IP報(bào)文轉(zhuǎn)發(fā)分析包含在每一個(gè)數(shù)據(jù)包的網(wǎng)絡(luò)層 報(bào)頭的目的IP地址。路由器獨(dú)立地分析網(wǎng)絡(luò)中的每一跳目標(biāo)IP地址。動(dòng)態(tài)路由協(xié)議或靜態(tài)配置生成所需的數(shù) 據(jù)庫(kù)來(lái)分析目標(biāo)IP地址（路由表）。傳統(tǒng)的IP路由實(shí)現(xiàn)的過(guò)程也被稱為基于逐跳目的地的單播路由。雖然成功地廣泛釆用，但是一些已經(jīng)實(shí)現(xiàn)一段時(shí)間的限制仍存在，此方法存在報(bào)文的轉(zhuǎn)發(fā)減少其靈活性。因此，需要新的技術(shù)，以處理和擴(kuò)展一個(gè)基于IP的網(wǎng)絡(luò)基礎(chǔ)設(shè)施的功能。第一章著重識(shí)別這些限制，并提出了一種新的架構(gòu)，被稱為多協(xié)議標(biāo)簽交換，來(lái)提供解決這些限制的方法。【答案：（71) B、(72) A、(73) D、（74) B、(75) D】【試題14-2】 2013年11月真題71~75The de facto standard application program interface (API) for TCP/IP applications is the "sockets" interface. Although this API was developed for (71) in the early 1980s. it has also been implemented on a wide variety of non-Unix systems. TCP/EP (72) written using the sockets API have in the past enjoyed a high degree of portability and we would like the same (73) with IPv6 applications. But changes are required to the sockets API to support IPv6 and this memo describes these changes. These include a new socket address structure to carry IPv6 (74) ，new address conversion functions, and some new socket options. These extensions are designed to provide Access to the basic IPv6 features required by TCP and UDP applications, including multicasting,while introducing a minimum of change into the system and providing complete (75) for existing IPv4.(71) A.Windows B.Linux C.Unix D.DoS(72) A.applications B.networks C.protocols D.systems(73) A.portabilityB.availabilityC.capabilityD.reliability(74) A.connections B.protocols C.networks D.addresses(75) A.availability B.compatibility C.capability D.reliability解析：事實(shí)上的標(biāo)準(zhǔn)應(yīng)用程序接口（API),用于TCP/ IP應(yīng)用程序是“套接字”界面。雖然這個(gè)API 是在80年代初為Unix開發(fā)的。它也被在各種各樣的非Unix系統(tǒng)的實(shí)施。使用套接字API編寫的TCP/. IP應(yīng)用程 序在過(guò)去享有的可移植性程度高，我們想同樣的便攜性與IPv6應(yīng)用。但改變是必需的套接字API,支持IPv6和 本備忘錄描述了這些變化。這包括一個(gè)新的套接字地址結(jié)構(gòu)來(lái)進(jìn)行IPv6地址，新地址轉(zhuǎn)換功能，和一些新的套接字選項(xiàng)。這些擴(kuò)展的目的是提供訪問IPv6基本功能由TCP和UDP應(yīng)用程序，包括多播要求，同時(shí)引入一個(gè) 最小變化到系統(tǒng)中，并提供給現(xiàn)有的IPv4應(yīng)用程序完全兼容?！敬鸢福海?1) C、(72) A、(73) A、(74) D、(75) B】【試題14-3】 2012年5月真題71~75The TCP protocolis a (71) layer protocol. Each connection connects two TCPs that may be just one physical network apart or located on opposite sides of the globe. In other words, each connection creates a (72) witha length that may be totally different from another path created by another connection. This means that TCP cannot use the same retransmission time for all connections. Selecting a fixed retransmission time for all connections can result in serious consequences. If the retransmission time does not allow enough time for a (73) to reach the destination and an acknowledgment to reach the source, it can result in retransmission of segments that are still on the way. Conversely, if the retransmission time is longer than necessary for a short path, it may result in delay for the application programs .Even for one single connection, the retransmission time should not be fixed.A connection may be able to send segments and receive (74) faster during nontraffic period than during congested periods. TCP uses the dynamic retransmission time,a transmission time is different for each connection and which may be changed during the same connection. Retransmission time can be made (75) by basing it on the round-trip time (RTT). Several formulas are used for this purpose.(71) A.physical B.network C.transport D.application(72) A.path B.window C. response D.process(73) A.process B.segment C.program D.user(74) A.connectionsB.requestsC. acknowledgmentsD.datagrams(75) A.long B.short C.fixed D.dynamic解析：TCP是一種傳輸層協(xié)議，每個(gè)TCP連接都連接著兩個(gè)TCP,這兩個(gè)TCP可能是在一個(gè)物理網(wǎng)絡(luò)里， 但是是分開的或者位于全局網(wǎng)絡(luò)的對(duì)立面。換句話說(shuō)，每個(gè)連接創(chuàng)建一個(gè)路徑的長(zhǎng)度可能完全不同于由另外一個(gè)連接創(chuàng)建的路徑。這意味著TCP不能為所有的連接使用相同的轉(zhuǎn)發(fā)時(shí)間。為所有的連接選擇一個(gè)固定的 轉(zhuǎn)發(fā)時(shí)間可能會(huì)導(dǎo)致嚴(yán)重的后果。如果這個(gè)轉(zhuǎn)發(fā)時(shí)間并不為一個(gè)段提供足夠的時(shí)間去到達(dá)目的地以確認(rèn)獲取 來(lái)源，將導(dǎo)致段轉(zhuǎn)發(fā)的部分仍在路上。相反，如果轉(zhuǎn)發(fā)時(shí)間超過(guò)了必要的短路徑，它可能會(huì)導(dǎo)致延遲的應(yīng)用程序，甚至一個(gè)單獨(dú)的連接，轉(zhuǎn)發(fā)時(shí)間也應(yīng)該是不固定的，相比于擁擠的時(shí)期，一個(gè)連接在不擁擠的時(shí)期可 能能夠更快地發(fā)送和接收確認(rèn)。TCP使用動(dòng)態(tài)轉(zhuǎn)發(fā)時(shí)間，每個(gè)連接的傳輸時(shí)間是不同的，而且可能在相同的連接中變化。轉(zhuǎn)發(fā)時(shí)間可能是動(dòng)態(tài)的基于往返時(shí)間，有幾個(gè)準(zhǔn)則用于這一目的。【答案：（71) C； (72) A； (73) B； (74) C； (75) D】【試題14-4】 2012年11月真題71~75Let us now see how randomization is done when a collision occurs.After a (71) , time is divided into discrete slots whose length is equal to the worst-case round-trip propagation time on the ether (2t) .To accommodate the longest path allowed by Ethernet, the slot tome has been set tO 512 bit times,or 51.2(isec.After the first collision,each station waits either 0 or 1 (72) times before trying again.If two stations collide and each one picks the same random number,they will collide again.After the second collision,each one picks either 0，l，2,or3 at random and waits that number of slot times.If a third collision occurs (the probability of this happening is 0.25) ,then the next time the number of slots to wait is chosen at (73) from the interval 0 to 23-l.In general,after i collisions,a random number between 0 and 2*-l is chosen,and that number of slots is skipped.However, after ten collisions have been reached,the randomization (74) is frozen at a maximum of 1023 slots.After 16 collisions,the controller throws in the towel and reports failure back to the computer.Further recovery is up to (75) layers.(71) A.datagramB.collisionC.connectionD.service(72)A.slot B.switch C.process D.fire(73)A.rest B.randomC.once D.odds(74)A.unicastB.multicastC.broadcastD.interval(75)A.local B.next C.higher D.lower解析：現(xiàn)在讓我們觀察沖突發(fā)生時(shí)如何做隨機(jī)處理。沖突發(fā)生后，時(shí)間被劃分成離散的長(zhǎng)度，等于最壞的往返傳播時(shí)間的時(shí)槽。為了容納以太網(wǎng)允許的最長(zhǎng)路徑，沖突時(shí)槽縮小為5.12μs。第一次沖突后，每個(gè)站在再次嘗試前需要等待0或1時(shí)槽。如果每一站發(fā)生沖突，且每一個(gè)挑選相同的隨機(jī)數(shù)，它們將再次發(fā)生沖突,第2次沖突之后，每一站隨機(jī)選擇0、1、2或3，即等待時(shí)槽的個(gè)數(shù)。如果第3次沖突發(fā)生（發(fā)生的概率為0.25)，則下次時(shí)槽的等待數(shù)量都是在0?23-1之間隨機(jī)挑選的?？傮w來(lái)說(shuō)，第i次沖突后，將在0~2i-1:之間挑選隨機(jī)數(shù)，而且那個(gè)時(shí)槽數(shù)是被略過(guò)的。然而，當(dāng)沖突次數(shù)達(dá)到10次，隨機(jī)間隔被鎖定在最高1023時(shí)槽。當(dāng)發(fā)生16次沖突后，控制器丟棄報(bào)告而不再返回計(jì)算機(jī)。進(jìn)一步恢復(fù)已經(jīng)達(dá)到更高的層次?！敬鸢福海?1) B； (72) A； (73) B； (74) D； (75) C】【試題14-5】 2011年5月真題71-75Border Gateway Protocol(BGP) is inter-autonomous system (71) protocol. BGP is based on a routing method called path vector routing. Distance vector routing is not a good candidate for inter-autonomous system routing because there are occasions on which the route with the smallest (72) count is not the preferred route. For example, we may not want a packet through an autonomous system that is not secure even though it is shortest route. Also, distance vector routing is unstable due to the fact that the routers announce only the number of hop counts to the destination without defining the path that leads to that (73) . A router that receives a distance vector advertisement packet may be fooled if the shortest path is actually calculated through the receiving router itself. Link (74) routing is also not a good candidate for inner-autonomous system routing because an internet is usually too big for this routing method. To use link state routing for the whole internet would require each router to have a huge link state database. It would also take a long time for each router to calculate its routing (75) using the Dijkstra algorism.(71) A.routingB.switchingC.transmittingD.receiving(72) A.path B.hop C.route D.packet(73) A.connection B.window C.source D.destination(74) A.status B.search C.state D.research(75) A.table B.state C.metric D.cost參考譯文：邊界網(wǎng)關(guān)協(xié)議（BGP)是自治系統(tǒng)間的路由協(xié)議。BGP是基于路由的方法稱為距離矢量路 由。距離矢量路由是自己系統(tǒng)路由的很好的候選者，因?yàn)榭缱灾蜗到y(tǒng)路由場(chǎng)合上最小的跳數(shù)的路由不一定是最合適的路由。例如，我們可能不希望通過(guò)一個(gè)自治系統(tǒng)不安全的數(shù)據(jù)包，即使它是最短的路線。此外，距離矢量路由是不穩(wěn)定的，路由器只宣布到目的地的跳數(shù)，但不指出到達(dá)目的地的路徑。實(shí)際上，如果是通過(guò)接收路由器本身計(jì)算的最短路徑，接收距離矢量通告報(bào)文的路由器可能被愚弄。鏈路狀態(tài)路由在跨自治系統(tǒng)中也不是一個(gè)好的候選者，因?yàn)閷?duì)于這種方法互聯(lián)網(wǎng)是通常過(guò)大。要對(duì)整個(gè)互聯(lián)網(wǎng)使用鏈接狀態(tài)路由，就需要每個(gè)路由器有一個(gè)巨大的鏈路狀態(tài)數(shù)據(jù)庫(kù)。它也需要每個(gè)路由器用很長(zhǎng)的時(shí)間來(lái)使用的Dijkstra算法計(jì)算自己的路由表。【答案:(71) A； (72) B； (73) D； (74) C； (75) A】【試題14-6】 2011年11月真題71~75A transport layer protocol usually has several responsibilties.One is to create a process-to-process communication UDP uses (71) numbers to accomplish this.Another responsibility is to provide control mechanisms at the transport level UDP does this task at a very minimal level.There is no flow control mechanism and there is no (72)for received packet.UDP,however,does provide error control to some extent.If UDP detects an error in the received packet,it will silently drop it.The transport layer also provides a connection mechanism for the processes.The (73) must be able to send streams of data to the transport layer.It is the responsibility of the transport layer at (74) station to make the connection with the receiver chop the stream into transportable units,number them，and send them one by one.it is the responsibility of the transport layer at the receiving end to wait until all the different units belonging to the same process have arrived,check and pass those that are (75) freehand deliver them to the receiving process as a stream.(71) A.hop B.port C.route D.packet(72) A.connectionB.windowC.acknowledgementD.destination(73) A.jobs B.processes C.programs D.users(74) A.sending B.routing C.switching D.receiving(75) A.call B.state C.cost D.error參考譯文：傳輸層協(xié)議通常有多種責(zé)任。一個(gè)是創(chuàng)建進(jìn)程間通信，UDP使用端口數(shù)來(lái)完成這項(xiàng)工作。另一個(gè)是在傳輸層提供控制機(jī)制。UDP以一個(gè)最低的級(jí)別完成這項(xiàng)工作，無(wú)流控制機(jī)制和接收包的應(yīng)答機(jī)制。但是，UDP在一些范圍上提供了差錯(cuò)控制。如果UDP在接收包中檢測(cè)到了錯(cuò)誤，它將靜靜地丟棄它。傳輸層同樣為進(jìn)程提供了一個(gè)連接機(jī)制。這個(gè)進(jìn)程必須能發(fā)送數(shù)據(jù)流到傳輸層。而在發(fā)送站傳輸層的責(zé)任就是與接收站建立連接，將流放入傳輸單元，并編號(hào)，然后一個(gè)接一個(gè)地發(fā)送。接收站傳輸層的責(zé)任是等待一個(gè)相同進(jìn)程中的不同的數(shù)據(jù)單元的到達(dá)，并且檢查它們，將錯(cuò)誤單元丟棄，并且以流的形式傳遞到接收進(jìn)程中?！敬鸢福海?1) B； (72) C； (73) B； (74) A； (75) D】【試題14-7】 2010年5月真題71~75Although a given waveform may contain frequencies over a very broad range, as a practical matter any transmission system will be able to accommodate only a limited band of (71) . This, in turn, limits the data rate that can be carried on the transmission (72) . A square wave has an infinite number of frequency components andhence an infinite (73) . However, the peak amplitude of the kth frequency component, kf, is only 1/k, so most of the (74) in this waveform is in the first few frequency components. In general, any digital waveform will have (75) bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted.(71) A.frequencies B.connections C.diagrams D.resources(72) A.procedures B.function C.route D.medium(73) A.source B.bandwidth C.energy D.cost(74) A.frequency B.nergy C.amplitude D.phase(75) A.small B.limited C.infinite D.finite參考譯文：雖然一個(gè)給定的波形包含了很寬的頻率范圍，但任何實(shí)際的傳輸系統(tǒng)只能通過(guò)有限的頻率。這樣，就限制了傳輸介質(zhì)可以承載的數(shù)據(jù)速率。一個(gè)方波包含了無(wú)限多的頻率成分，因而也具有無(wú)限的帶寬。然而，第k個(gè)頻率成分的峰值幅kf只是1/k，所以波形的大部分能量只是包含在前面的少數(shù)頻率成分中。一般來(lái)說(shuō)，任何數(shù)字波形都有無(wú)限帶寬。如果我們?cè)噲D在某種介質(zhì)上傳輸這種波形信號(hào)，則傳輸系統(tǒng)實(shí)際上會(huì)限制可以發(fā)送的帶寬?！敬鸢福?71) A； (72) D； (73) B； (74) B； (75) C】【試題14-8】 2010年11月真題71~75The metric assigned to each network depends on the type of protocol.Some simple protocol, like RIP, treats each network as equals.The (71) of passing through each network is the same;it is one (72) count.So if a packet passes through 10 network to reach the destination, the total cost is 10 hop counts.Other protocols, such as OSPF, allow the administrator to assign a cost for passing through a network based on the type of service required.A (73)through a network can have different costs (metrics) .For example, if maximum (74) is the desired type of service, a satellite link has 狂 lower metric than a fiber-optic line.On the other hand, if minimum (75) is the desired type of service, a fiber-optic line has a lower metric than a satellite line.OSPF allow each router to have several routing table based on the required type of service.(71) A.numberB.connectionC.diagramD.cost(72) A.processB.hop C.route D.flow(73) A.flow B.window C.route D.cost(74) A.packet B.throughput C.error D.number(75) A.delay B.stream C.packet D.cost參考譯文；每個(gè)網(wǎng)絡(luò)釆用的度量標(biāo)準(zhǔn)依賴于協(xié)議類型。對(duì)于簡(jiǎn)單的協(xié)議，如RIP，將每個(gè)網(wǎng)絡(luò)同等對(duì)待。 通過(guò)每個(gè)網(wǎng)絡(luò)的代價(jià)都是一跳。因此，如果一個(gè)分組通過(guò)10個(gè)網(wǎng)絡(luò)后到達(dá)目的地，則總的代價(jià)為10個(gè)其他協(xié)議，如OSPF，允許網(wǎng)絡(luò)管理員基于服務(wù)為通過(guò)的網(wǎng)絡(luò)設(shè)置代價(jià)。因此，通過(guò)一個(gè)網(wǎng)絡(luò)的路由可能有不同的代價(jià)（度量標(biāo)準(zhǔn)）。例如，若期望服務(wù)類型是最大吞吐量，則衛(wèi)星鏈路比光纖線路的度量小。如果期望的服務(wù)類型是最小時(shí)延，則光纖線路的度量小于衛(wèi)星鏈路。OSPF允許每個(gè)路由器有幾張基于服務(wù)類型的路由表?！敬鸢福海?1) D; (72) B； (73) C； (74) B； (75) A】