互聯(lián)網(wǎng)絡(luò)聯(lián)網(wǎng)的基本原理-3_WAN(zslcn周生烈編譯摘注評)

1、啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊 (fm.DocWiki CISCO / zslcn編譯注)三Introduction to WAN Technologies介紹廣域網(wǎng)技術(shù)聯(lián)網(wǎng)技術(shù)手冊 指導(dǎo)目錄 Contents Part 1 Internetworking Basics 互聯(lián)網(wǎng)絡(luò)聯(lián)網(wǎng)基本原理 Part 2 LAN Technologies局域網(wǎng)技術(shù) part 3 WAN Technologies 廣域網(wǎng)技術(shù) part 4 Internet Protocols 互聯(lián)網(wǎng)協(xié)議 part 5 Bridging and Switching 橋接和交換 part 6 Ro

2、uting 路由 part 7 Network Management 網(wǎng)絡(luò)管理 part 8 Voice/Data Integration Technologies 聲音/數(shù)據(jù)集成技術(shù) part 9 Wireless Technologies 無線技術(shù) part 10 Cable Access Technologies 有線接入技術(shù) part 11 Dial-up Technology 撥號技術(shù) part 12 Security Technologies 安全技術(shù) part 13 Quality of Service Networking 聯(lián)網(wǎng)服務(wù)質(zhì)量 part 14 Network Cach

3、ing Technologies 網(wǎng)絡(luò)緩存技術(shù) part 15 IBM Network Management IBM網(wǎng)絡(luò)管理 part 16 Multiservice Access Technologies 多業(yè)務(wù)接入技術(shù)This page was last modified on 17 December 2009, at 21:54三Introduction to WAN Technologies介紹WAN技術(shù)From DocWikiJump to: navigation, searchThis article introduces the various protocols and tec

4、hnologies used in wide-area network (WAN) environments. Topics summarized here include point-to-point links, circuit switching, packet switching, virtual circuits, dialup services, and WAN devices. Chapters in Part 3, “WAN Protocols,” address specific technologies in more detail. 本章介紹了用于WAN(廣域網(wǎng))環(huán)境的各

5、種協(xié)議和技術(shù)。在這里概述的題目包括點對點鏈路，電路交換，分組包交換，虛電路，撥號服務(wù)，和WAN設(shè)備。在手冊第3部分,WAN協(xié)議,的各章里將更詳細(xì)地講述專門技術(shù)。Contentshide1 What Is a WAN? 什么是廣域網(wǎng)？1.1 Figure: WAN Technologies Operate at the Lowest Levels of the OSI Model 圖1.1：廣域網(wǎng)技術(shù)運行在OSI模型的最低三層2 Point-to-Point Links 點對點鏈路2.1 Figure: A Typical Point-to-Point Link Operates Through

6、 a WAN to a Remote Network 圖2.1：一個通過廣域網(wǎng)到遠(yuǎn)程網(wǎng)的,典型的點對點鏈路的運行3 Circuit Switching 電路交換3.1 Figure: A Circuit-Switched WAN Undergoes a Process Similar to That Used for a Telephone Call 圖3.1：一個電路交換的廣域網(wǎng)經(jīng)歷了類似于用于電話呼叫的過程4 Packet Switching 分組交換4.1 Figure: Packet Switching Transfers Packets Across a Carrier Networ

7、k圖4.1：分組交換將數(shù)據(jù)包傳輸通越一個承載網(wǎng)絡(luò) 5 WAN Virtual Circuits 廣域網(wǎng)虛電路6 WAN Dialup Services 廣域網(wǎng)撥號電路7 WAN Devices 廣域網(wǎng)設(shè)備7.1 WAN Switch 廣域網(wǎng)交換機7.1.1 Figure: Two Routers at Remote Ends of a WAN Can Be Connected by WAN Switches 圖7.1.1廣域網(wǎng)遠(yuǎn)程兩端的兩個路由器可以通過廣域網(wǎng)交換機連接起來7.2 Access Server 接入服務(wù)器7.2.1 Figure: An Access Server Concent

8、rates Dial-Out Connections into a WAN 圖7.2.1：一個接入服務(wù)器將各撥出連接連到一個廣域網(wǎng)內(nèi)7.3 Modem 調(diào)制解調(diào)器7.3.1 Figure: A Modem Connection Through a WAN Handles Analog and Digital Signals 圖7.3.1：一個通過廣域網(wǎng)的調(diào)制解調(diào)器連接,處理模擬和數(shù)字信號7.4 CSU/DSU通道服務(wù)單元/數(shù)字服務(wù)單元7.4.1 Figure: The CSU/DSU Stands Between the Switch and the Terminal圖7.4.1：CSU/DS

9、U置于交換機和終端之間 7.5 ISDN Terminal Adapter ISDN終端適配器7.5.1 Figure: The Terminal Adapter Connects the ISDN Terminal Adapter to Other Interfaces 圖7.5.1：終端適配器將ISDN終端適配器連接到其他接口8 Review Questions復(fù)習(xí)問答9 For More Information提供更多的信息1. What Is a WAN? 什么是WAN(廣域網(wǎng))?A WAN is a data communications network that covers a

10、relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Figure: WAN

11、 Technologies Operate at the Lowest Levels of the OSI Model illustrates the relationship between the common WAN technologies and the OSI model. WAN(廣域網(wǎng))是一種數(shù)據(jù)通信網(wǎng)絡(luò),覆蓋了一個相對廣闊的地理區(qū)域,并通常使用由公共承運商,如電話公司,提供的傳送設(shè)施。WAN技術(shù)通常在OSI參考模型的低三層起作用：物理層,數(shù)據(jù)鏈路層,和網(wǎng)絡(luò)層。圖1.1舉例說明了常用WAN技術(shù)和OAI模型之間的關(guān)系。（本章講述了一大堆的術(shù)語和具體設(shè)備的名字，應(yīng)該是互聯(lián)網(wǎng)絡(luò)聯(lián)網(wǎng)長

12、期進(jìn)展的歷史過程中形成的產(chǎn)物。似乎予人以堆積、少章、雜亂的感覺。既然基本原理是一種概念性的思路，可否這樣來歸納一下：）1.1 Figure: WAN Technologies Operate at the Lowest Levels of the OSI Model 圖1.1：廣域網(wǎng)技術(shù)在OSI模型的最低三層上起作用2. Point-to-Point Links 點對點鏈路A point-to-point link provides a single, pre-established WAN communications path from the customer premises thro

13、ugh a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only. These circuits are generally

14、 priced based on bandwidth required and distance between the two connected points. Point-to-point links are generally more expensive than shared services such as Frame Relay. Figure: A Typical Point-to-Point Link Operates Through a WAN to a Remote Network illustrates a typical point-to-point link th

15、rough a WAN. 點對點鏈路提供了單一的預(yù)建的WAN通信通路,從用戶附加的設(shè)備,通過一個承運商網(wǎng)絡(luò),如電話公司,到一個遠(yuǎn)端網(wǎng)絡(luò)。點對點線路通常從一個承運商處租借而來,因而通常稱為租借線路。對于一個租借線路,承運商只給你分配線對和設(shè)施硬件。這些電路,通常是基于所需要的帶寬和兩個連接點間的距離來計價。點對點鏈路s通常要比共享服務(wù),如幀中繼,更貴。圖2.1舉例說明了一個典型的通過一個WAN的點對點鏈路。2.1 Figure: A Typical Point-to-Point Link Operates Through a WAN to a Remote Network 3. Circuit

16、Switching 電路交換Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete. This works much like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When

17、a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network. In the case of ISDN circuits, the device actually places a call to the telephone number of the remote ISDN circuit. When the two networks are connected and authenticated, they can tr

18、ansfer data. When the data transmission is complete, the call can be terminated. Figure: A Circuit-Switched WAN Undergoes a Process Similar to That Used for a Telephone Call illustrates an example of this type of circuit. 交換式電路允許數(shù)據(jù)連接在需要時啟動(接通連接),通信完成后終止(斷開連接)。這十分像用于聲音通信的正常電話。ISDN(綜合業(yè)務(wù)數(shù)字網(wǎng))是電路交換的一個很好的

19、例子。當(dāng)一個路由器有用于遠(yuǎn)處的數(shù)據(jù)時,交換電路就被啟動,并使用遠(yuǎn)方網(wǎng)絡(luò)的電路號碼。在ISDN電路的情況下,設(shè)備實際上對遠(yuǎn)方ISDN電路的電話號碼安排一次呼叫。當(dāng)兩個網(wǎng)絡(luò)連接并生效時,它們就可以傳輸數(shù)據(jù)。當(dāng)數(shù)據(jù)傳送完成了,呼叫就可以結(jié)束。圖3.1舉例說明了這類電路的一個例子。3.1 Figure: A Circuit-Switched WAN Undergoes a Process Similar to That Used for a Telephone Call4. Packet Switching 分組包交換Packet switching is a WAN technology in wh

20、ich users share common carrier resources. Because this allows the carrier to make more efficient use of its infrastructure, the cost to the customer is generally much better than with point-to-point lines. In a packet switching setup, networks have connections into the carriers network, and many cus

21、tomers share the carriers network. The carrier can then create virtual circuits between customers sites by which packets of data are delivered from one to the other through the network. The section of the carriers network that is shared is often referred to as a cloud. 分組包交換是一種WAN技術(shù),在那里用戶共享公共的承運商資源。

22、由于這能使承運商更有效地使用其基礎(chǔ)結(jié)構(gòu),用戶所付出的代價會優(yōu)于點對點線路。在分組交換建立中,網(wǎng)絡(luò)已經(jīng)連入承運商網(wǎng)絡(luò),并且許多用戶共享了承運商的網(wǎng)絡(luò)。承運商于是可以在用戶所在地之間創(chuàng)建虛電路,從而分組包數(shù)據(jù)就可以通過網(wǎng)絡(luò)從一處被交付到到另一處。承運商的被共享的那部分網(wǎng)絡(luò)通常被稱之為一片云。Some examples of packet-switching networks include Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multimegabit Data Services (SMDS), and X.25. Figu

23、re: Packet Switching Transfers Packets Across a Carrier Network shows an example packet-switched circuit. 分組交換網(wǎng)絡(luò)的一些例子包括ATM(異步傳輸模式),FR(幀中繼),SMDS(交換式多兆位數(shù)據(jù)服務(wù)),和X.25。圖4.1示明了分組交換電路的一個例子。4.1 Figure: Packet Switching Transfers Packets Across a Carrier Network圖4.1 分組交換傳輸數(shù)據(jù)包通過承運商網(wǎng)絡(luò)5. WAN Virtual Circuits WAN

24、虛電路 The virtual connections between customer sites are often referred to as a virtual circuit. 用戶所在地之間的虛連接通常稱之為一個虛電路。A virtual circuit is a logical circuit created within a shared network between two network devices. Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent

25、 virtual circuits (PVCs). 一個虛電路是一個在共享的網(wǎng)絡(luò)內(nèi)兩個網(wǎng)絡(luò)設(shè)備之間產(chǎn)生的邏輯電路。有兩類虛電路：SVC(交換式虛電路)和PVC(永久性虛電路)。 SVCs are virtual circuits that are dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and ci

26、rcuit termination. The establishment phase involves creating the virtual circuit between the source and destination devices. Data transfer involves transmitting data between the devices over the virtual circuit, and the circuit termination phase involves tearing down the virtual circuit between the

27、source and destination devices. SVCs are used in situations in which data transmission between devices is sporadic, largely because SVCs increase bandwidth used due to the circuit establishment and termination phases, but they decrease the cost associated with constant virtual circuit availability.S

28、VC是在需要時動態(tài)建立的,而在傳送完成后被終止。在一個SVC上承載的通信由三個階段組成：電路建立,數(shù)據(jù)傳輸,和電路終止。電路建立階段涉及在源設(shè)備和目的設(shè)備之間創(chuàng)建虛電路。數(shù)據(jù)傳輸涉及在虛電路上的兩個設(shè)備間傳送數(shù)據(jù),而電路終止階段則涉及在源和目的設(shè)備間關(guān)閉虛電路。 SVCs用于設(shè)備間偶有數(shù)據(jù)傳輸?shù)那闆r。PVC is a permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations in which data transfer between

29、 devices is constant. PVCs decrease the bandwidth use associated with the establishment and termination of virtual circuits, but they increase costs due to constant virtual circuit availability. PVCs are generally configured by the service provider when an order is placed for service.PVC是一種永久建立的電路,它

30、只有一種模式：數(shù)據(jù)傳輸模式,而且保持設(shè)備間進(jìn)行傳輸?shù)那闆r不變。PVCs減少了SVCs的使用帶寬,卻由于PVCs保持不變的可用性而增加了用戶的代價。PVCs通常是由服務(wù)提供商根據(jù)用戶要求服務(wù)的訂單配置的。6. WAN Dialup Services WAN撥號服務(wù)Dialup services offer cost-effective methods for connectivity across WANs. Two popular dialup implementations are dial-on-demand routing (DDR) and dial backup. 撥號服務(wù)提供了一類

31、用于WANs范圍內(nèi)有效連接計價的方法。撥號有兩種流行的實現(xiàn)：DDR(需要時撥號路由)和撥號后備。DDR is a technique whereby a router can dynamically initiate a call on a switched circuit when it needs to send data. In a DDR setup, the router is configured to initiate the call when certain criteria are met, such as a particular type of network traf

32、fic needing to be transmitted. When the connection is made, traffic passes over the line. The router configuration specifies an idle timer that tells the router to drop the connection when the circuit has remained idle for a certain period. DDR是一種技術(shù),當(dāng)需要發(fā)送數(shù)據(jù)時,路由器可以動態(tài)地在一個交換電路上發(fā)起一個呼叫。在DDR建立期間,當(dāng)某種條件滿足時,

33、例如需要發(fā)送一種具體類型的網(wǎng)絡(luò)信流,就配置路由器,以發(fā)起呼叫。連接完成后,信流就在線路上傳遞。如果呼叫時線路空置,在超過指定時間后路由器就放棄連接。,Dial backup is another way of configuring DDR. However, in dial backup, the switched circuit is used to provide backup service for another type of circuit, such as point-to-point or packet switching. The router is configured

34、so that when a failure is detected on the primary circuit, the dial backup line is initiated. The dial backup line then supports the WAN connection until the primary circuit is restored. When this occurs, the dial backup connection is terminated. 撥號后備是另外一種配置DDR的方法,通常作為交換電路的后備,如點對點或分組交換。當(dāng)發(fā)現(xiàn)交換電路失效時,路由

35、器就啟動撥號備用線路,以支持WAN連接,直至交換電路恢復(fù)。于是撥號后備連接終止。7. WAN Devices WAN設(shè)備WANs use numerous types of devices that are specific to WAN environments. WAN switches, access servers, modems, CSU/DSUs, and ISDN terminal adapters are discussed in the following sections. Other devices found in WAN environments that are u

36、sed in WAN implementations include routers, ATM switches, and multiplexers. 有很多種用于WAN環(huán)境的設(shè)備。WAN交換機,接入服務(wù)器,調(diào)制解調(diào)器,CSU/DSU,和ISDN終端適配器，將在以下各節(jié)中討論。其它WAN中用于WAN實現(xiàn)的設(shè)備,還包括路由器,ATM交換機,和復(fù)用器。7.1 WAN Switch WAN交換機A WAN switch is a multiport internetworking device used in carrier networks. These devices typically swi

37、tch such traffic as Frame Relay, X.25, and SMDS, and operate at the data link layer of the OSI reference model. Figure: Two Routers at Remote Ends of a WAN Can Be Connected by WAN Switches illustrates two routers at remote ends of a WAN that are connected by WAN switches. WAN交換機是一個用于承運商網(wǎng)絡(luò)的多口網(wǎng)絡(luò)互聯(lián)設(shè)備。這

38、些設(shè)備,通常用來交換如幀中繼,X.25,和SMDS等的信流,它們運行在OSI參考模型的數(shù)據(jù)鏈路層上。圖7.1.1舉例說明了兩個相距很遠(yuǎn)的WAN路由器用WAN交換機連接起來。7.1.1 Figure: Two Routers at Remote Ends of a WAN Can Be Connected by WAN Switches7.2 Access Server 接入服務(wù)器An access server acts as a concentration point for dial-in and dial-out connections. Figure: An Access Server

39、 Concentrates Dial-Out Connections into a WAN illustrates an access server concentrating dial-out connections into a WAN. 一個接入服務(wù)器作為用于撥入撥出連接的一個集中點。圖7.2.1舉例說明了一個接入服務(wù)器是如何將撥出連接集中進(jìn)入WAN的。7.2.1 Figure: An Access Server Concentrates Dial-Out Connections into a WAN 圖7.2.1 一個接入服務(wù)器將撥出連接集中進(jìn)入WAN 7.3 Modem 調(diào)制解調(diào)器A

40、 modem is a device that interprets digital and analog signals, enabling data to be transmitted over voice-grade telephone lines. At the source, digital signals are converted to a form suitable for transmission over analog communication facilities. At the destination, these analog signals are returne

41、d to their digital form. Figure: A Modem Connection Through a WAN Handles Analog and Digital Signals illustrates a simple modem-to-modem connection through a WAN. 調(diào)制解調(diào)器是一種設(shè)備,用來轉(zhuǎn)換數(shù)字和模擬信號,使能在聲音級電話線上傳送數(shù)據(jù)。在源端,數(shù)字信號轉(zhuǎn)換成適合于模擬通信設(shè)施上傳送的形式;而在目的端,則將模擬信號轉(zhuǎn)回數(shù)字信號。圖7.3.1舉例說明了一個調(diào)制解調(diào)器,通過一個WAN,連接到另一個調(diào)制解調(diào)器上。7.3.1 Figure:

42、 A Modem Connection Through a WAN Handles Analog and Digital Signals 7.4 CSU/DSU A channel service unit/digital service unit (CSU/DSU) is a digital-interface device used to connect a router to a digital circuit like a T1. The CSU/DSU also provides signal timing for communication between these device

43、s. Figure: The CSU/DSU Stands Between the Switch and the Terminal illustrates the placement of the CSU/DSU in a WAN implementation. CSU/DSU(通道服務(wù)單元/數(shù)字服務(wù)單元)是一種數(shù)字接口單元,用于路由器和數(shù)字電路,如T1,相連。CSU/DSU也提供信號同步用于設(shè)備間的通信。圖7.4.1舉例說明了在一個WAN實現(xiàn)中CSU/DSU的位置。7.4.1 Figure: The CSU/DSU Stands Between the Switch and the Term

44、inal圖7.4.1 在交換機和終端間CSU/DSU的位置7.5 ISDN Terminal Adapter ISDN終端適配器An ISDN terminal adapter is a device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces, such as EIA/TIA-232 on a router. A terminal adapter is essentially an ISDN modem, although it is called a terminal ada

45、pter because it does not actually convert analog to digital signals. Figure: The Terminal Adapter Connects the ISDN Terminal Adapter to Other Interfaces illustrates the placement of the terminal adapter in an ISDN environment. ISDN終端適配器是一種用于將ISDN的BRI(基本速率接口)連接到其它的接口上,如路由器上的EIA/TIA-232。一個終端適配器本質(zhì)上是一個ISDN調(diào)制解調(diào)器,但它不屬于A/D-D/A