202080316_李大壯_中英文資料翻譯.doc

附錄一：英文技術(shù)資料翻譯英文原文ROUTING AND SWITCHING1. LOCAL AREA NETWORKS(LANS)Organizations often need networks to connect geographically close resources, such as PCs located in the same college classroom or business office. Such networks are known as local area networks or LANs. Most LANs are of the client-server or peer-to-peer variety.The most widespread topology for LANs designed to function as data communication for the interconnection of local computer-based equipment is star topology, in which the major equipment used to connect a variety of computer-based devices are hubs or switches. Typical LAN product of using the star topology is the most famous Ethernet which dominates the LAN world today.EthernetIEEE802.3 supports a LAN standard originally developed by Xerox and later extended by a joint venture between Digital Equipment Corporation, Intel Corporation, Intel Corporation, and Xerox. This was called Ethernet.2. SwitchSwitches are basically multi-port bridges, but share some characteristics with routers.Like routers, switches work by dividing up the network into a number of segments. Switching is performed at layer 2 of the sever-layer model-the same as bridging. Since it performed at layer 2, the MAC address is used, which is independent of protocol address. Like a bridge, a switch learns which address reside on each of its ports and then switches data appropriately. A switch can be designed using conventional microprocessors or dedicated ASIC (Application-Specific Integrated Circuit) technology.3. Router Routers have been known by several names. Back in ancient times when what is now Internet was called APPANET, routers were called IMPs, for internet message processors. More recently, router called gateways, remnants of this nomenclature still be found in terms such as Border Gateway Protocol(BGP) and Interior Gateway Routing Protocol(IGRP). In the Open System Interconnection (OSI) world, routers are known as Intermediate System (IS).Router, as a name, is probably the most descriptive of what the modern version of these devices do. A router sends information along a route-a path between two networks. This path may traverse a single router or many routers. Furthermore, in inter-networks that have multiple best route. Should that route become less than optimal or entirely unusable, the router selects the next-best path. The procedures used by the router to determine and select the best route and to share information about network reachability and status with other routers are referred to collectively as a routing protocol.Just as a data link may directly connect two devices, a router also cleats a connection between two devices. The difference is that, as Fig. 4-6 shows, whereas the communication path between two devices sharing a common data link is a physical path, the communication path provided by routers between two devices on different network is a higher-level, logical path.This concept is vitally important understanding a routers function. Notice that the logic path, or route, between the devices in Fig. 4-6 traverses types of data links: an Ethernet, an FDDI ring, a serial link, and a Token Ring. As noted earlier, to be delivered on the physical path of a data link, data must be encapsulated within a frame, a sort of digital envelope. Likewise, to be delivered across the logical path of a routed-inter-network, data must also be encapsulated; the digital envelope used by routers is packet.4. Three routing technologyExchange network routing technology, there are three, the first of which is the most conservative approach, the method of combining of the third layer routers with Layer 2 switches. Layer 2 switches strict restrictions on the bridge structure for data exchange between different nodes within the same virtual network, virtual LAN features in the second layer of the OSI reference model, the data link layer, the third layer function left to the router to achieve data transfer between the virtual network connection with the establishment of LAN and corporate backbone router.The second method uses a distributed routing technology. Its characteristics is that it uses multi-layer switch, combined with a second layer of the bridge with the third layer routing, some literature also called multi-layer switch to the third layer switch. It has routing capabilities to support virtual LANs, and supports most of the same virtual network or virtual network node communication, and reduce the number of routers between work groups and departments. But it is still not completely free from the use of traditional routers, this is because the multi-layer switches can only provide high-end router can provide the protocol, security, traffic management and WAN connectivity, a subset of. CISCOs 7000 series routers can handle 12 kinds of agreements and supports point-to-point, circuit switching and cell switching, wide area network, the the Alantec production Powerhub multilayer switch can only handle three protocols: DECnet, IP and IPX, and There is no WAN interface. Therefore, the multilayer switch network need to use the router as the gateway of the WAN, and to create more complex routing functions.The third in the switching network routing technology with a new structure: the combination of routing server and the boundary switch. We know that a traditional router packet forwarding and routing the two tasks. Routing server-based networks from two separate devices of these two functions: the boundary switch to complete the packet forwarding, routing information is identified by the more expensive routing server. Boundary switch only to not find the address of the destination node when the access route server in the address table, the router on the response to a correct address, the switch and then the cache standby. Should be noted that the communication protocol between the routing server and the switch is not uniform, not compatible with products from different manufacturers.5. Comparison and EvaluationHave their own characteristics of the three routing technology, network design can be selected according to the actual situation. To make them a better understanding of the following four to compare them.(1) network sizeThe size of the network is the decisive factor in the choice of routing technology network. The second layer switches and router combination of approaches for smaller networks, which is characterized by economic and practical. But when the backbone is extended into a larger network, the overhead of the second layer of the virtual LAN will be significantly increased.With the expansion of the backbone, intelligent multilayer switch advantages into full play, it is only forwarded to those who belong to a particular subnet segment broadcasting, thus reducing the number of backbone broadcast traffic. Virtual network of multi-layer switch with filtering capabilities, and can save the bandwidth of the backbone and the side site of the clock, virtual network security is better. In addition, it is compared with the first method, the switch can work within the scope of the work group and department is also responsible for switching and routing selected diameter, therefore saving the number of traditional routers use. Distributed router method and routing server is also more applicable to large-scale distributed network.2 DelayThe increase in network delay will lead to a decline in network performance, the size of the network delay is generally proportional to the size and operating equipment must be addressed before forwarding traffic. In terms of the second layer of the Ethernet switch, use the bridge due to the nature of the second layer of virtual network without using a router, so the relative speed, when to perform a simple MAC address to find an information packet (64 bytes) delay of less than 100 microseconds. The use of layer 3 router head and the subject of looking for and the implementation of the algorithm, thus greatly increasing the packet delay, the delay time of up to 5 ms.Visible, when the flow of traffic through the router from a switch to another switch for Layer 2 switches and layer 3 routers, combined with a network has a very good performance when the traffic through the switch; poor performance.Almost all of the Layer 2 switches and software used in conjunction with all the nodes to form a virtual network (broadcast domain), and improve network performance. Exchange between nodes within the same virtual network traffic at the MAC layer delay smaller. Nodes to exchange information between the different virtual network, the packets pass to go through the router, then the network latency.Distribution of routing technology allows the switch to the virtual gateway of the subnet ID of the third layer protocol to transmit information to be able to overcome the bottleneck formed by the above router.Boundary switch routing server method to use to make the choice of the path. Occasionally in the boundary switches do not know to send the destination address to the routing server asking for information packets to appear routing delay. Under normal circumstances, the switches can be directly in the cache address table to find the address, then packets can be forwarded directly delay in this case the delay is basically the same with MAC layer switches.3 ManagementThe routing information stored at each router in the network, each protocol has a corresponding table column. Network management personnel must be individually configured on the router, including the settings of the filter, add, modify routing table. Combined with man-machine interface is text-based interface, when the enterprise network is extended to large-scale, management and configuration of the router is very time consuming.Distributed routing technology, the downside is its management overhead and routing, and increase the number of switching table exponential increase trend. To overcome this shortcoming, the production businesses will adopt the following measures: the development of traffic control strategies in the center console, and automatically propagated through the network, thus avoiding one by one configuration for each device, and increase the graphical man-machine interface.The characteristics of the routing server is easy to administer, just a routing server configuration can provide high quality services and management of virtual network. Management procedures such as Cabletron company Securefast allows administrators to take advantage of the screen, assign access privileges to different groups of users access rights through the implementation of the software will notify all of the switches.Another advantage of the routing server method allows administrators to transparently develop traffic management strategies, do not care about the type of the users end station. For example, network management personnel will be too on the switch node and ATM server is assigned to a virtual local area network, without having to enter the Ethernet nodes MAC or IP address do not have to enter the ATM node the VPI / VCI. 4 PriceThe price is another major factor to consider people networking. Following the author gives the production of several companies 50,250,500 port three routing products per port price comparison (see Table 1-2). The price of each port is to remove the port number of the total price of the results of network equipment, network devices including Ethernet switches, ATM switches, routing server and router.Routing server networking Newbridge only company given the price, the average price of its 50,250,500-port devices per port for 1920,1520 and 1435 U.S. dollars.Can be seen from the data given above, the cheapest price-based Layer 2 switching network with the router the way the program, distributed routing network price, while the moderate price of network routing server approach. From which we can find, the use of Layer 2 switches and layer 3 router network, with the expansion of the network size, the average price for each port getting smaller and smaller, similar routing server networking. Distributed router networking per-port price of the network size has little effect.路由與交換技術(shù)1. 局域網(wǎng)技術(shù)各單位通常把位置上比較靠近的資源，如放在學(xué)院的教室中或企業(yè)的辦公室中的PC連在一起而構(gòu)成網(wǎng)絡(luò)。這類網(wǎng)絡(luò)就被稱為局域網(wǎng)（LAN）。大多數(shù)局域網(wǎng)是客戶-服務(wù)器或?qū)Φ确绞?。?yīng)用最廣的、用于本地計算機設(shè)備互連，以進行數(shù)據(jù)通信的局域網(wǎng)拓撲是星型結(jié)構(gòu)，在這種結(jié)構(gòu)中以集線器或交換機作為主要的聯(lián)網(wǎng)設(shè)備，連接各種計算機設(shè)備。使用這種拓撲結(jié)構(gòu)的局域網(wǎng)的典型產(chǎn)品是著名的以太網(wǎng)，先進它在全世界局域網(wǎng)中占統(tǒng)治地位。以太網(wǎng)IEEE802.3支持最初由施樂公司，后來由數(shù)據(jù)設(shè)備公司、英特爾和施樂公司聯(lián)合開發(fā)的局域網(wǎng)標(biāo)準(zhǔn)，被稱為以太網(wǎng)。2. 交換機交換機基本上是多端口網(wǎng)橋，但是具有某些路由器的特性。像路由器那樣，交換機是把網(wǎng)絡(luò)分成很多段，每段的本地業(yè)務(wù)都不會對其他網(wǎng)段產(chǎn)生干擾。交換技術(shù)是在七層模型的第二層上實現(xiàn)的與網(wǎng)橋技術(shù)相同。因為它在第二層上實現(xiàn)，要使用MAC地址，與協(xié)議地址無關(guān)。像網(wǎng)橋一樣，交換機記住了常駐在每個端口的那些地址，并且對數(shù)據(jù)進行相應(yīng)的交換。交換可以使用常規(guī)的微處理器或?qū)Ｓ肁SIC技術(shù)進行設(shè)計。3. 路由器路由器已經(jīng)有幾個名字了。回到過去稱為ARPANET的那個時代，路由器稱為互聯(lián)網(wǎng)報文處理機（IMP）。最近路由器又被稱為網(wǎng)關(guān)；這個術(shù)語的痕跡仍可在邊界網(wǎng)關(guān)協(xié)議（BGP）和內(nèi)部網(wǎng)關(guān)路由協(xié)議（IGRP）中見到。在開放式系統(tǒng)互聯(lián)領(lǐng)域被稱為中間系統(tǒng)。路由器最能表達設(shè)備的功能。路由器沿兩個網(wǎng)絡(luò)之間的路由路徑傳送信息。這條路徑可以經(jīng)過一個路由或或者更多個路由器。進而，在有很多條路徑指向同一目的地的互聯(lián)網(wǎng)中，現(xiàn)代路由器用一組程序去決定并使用最佳路徑。如果這一路有不再是最佳或完全不可用，路由器會選擇下一條最佳路徑。由路由器使用的，用于確定和選擇最佳路徑，并與其他路由器共享網(wǎng)絡(luò)可達性和狀態(tài)信息的程序，稱為路由選擇協(xié)議。正如數(shù)據(jù)鏈路可以直接連接兩個設(shè)備一樣，路由器也在兩個設(shè)備之間建立一個連接。不同的是，如果共享一條公共數(shù)據(jù)鏈路的兩個設(shè)備之間通信路徑是一條物理路徑，而由路由器提供在不同的網(wǎng)絡(luò)上的兩個設(shè)備之間的通信路徑是高層邏輯路徑。一個以太網(wǎng)，一個FDDI環(huán)網(wǎng)，一個串行鏈路和一個令牌網(wǎng)，如前所說，數(shù)據(jù)在數(shù)據(jù)鏈路上傳送，必須封裝成一個幀。同樣，數(shù)據(jù)要在通過路由的、跨網(wǎng)絡(luò)邏輯路徑上傳送，也必須封裝，路由器使用數(shù)字封裝是分組。4.三種路由技術(shù)目前交換網(wǎng)絡(luò)中的路由技術(shù)有三種，其中第一種是最為保守的方法，即第三層的路由器與第二層交換機相結(jié)合的方法。第二層交換機嚴格限制于橋結(jié)構(gòu)，用于同一虛擬網(wǎng)內(nèi)的不同節(jié)點之間的數(shù)據(jù)交換，在OSI參考模型的第二層，即數(shù)據(jù)鏈路層實現(xiàn)虛擬LAN的功能，將第三層的功能留給路由器實現(xiàn)，由路由器完成虛擬網(wǎng)絡(luò)之間的數(shù)據(jù)傳輸與建立LAN與企業(yè)主干網(wǎng)連接的工作。第二種方法采用分布式路由技術(shù)。其特點是它使用多層交換機，將第二層的橋與第三層的路由結(jié)合在一起，有的文獻也將多層交換機稱之為第三層交換機。它本身所具有的路由功能支持虛擬LAN，并支持大多數(shù)同一虛擬網(wǎng)內(nèi)或不同虛擬網(wǎng)之間節(jié)點的通信，減少了工作組與部門之間所使用的路由器的數(shù)目。但它仍然不能完全擺脫使用傳統(tǒng)路由器，這是因為多層交換機只能提供高檔路由器所能提供的協(xié)議、安全、交通管理及與WAN連接功能的子集。如CISCO公司7000系列路由器能夠處理12種協(xié)議并支持點對點、電路交換與信元交換的廣域網(wǎng)通信，而Alantec公司生產(chǎn)的Powerhub多層交換機卻只能處理三種協(xié)議:DECnet、IP與IPX，并且沒有WAN接口。因此，多層交換機網(wǎng)絡(luò)中需要使用路由器作為廣域網(wǎng)的網(wǎng)關(guān)，并完成較為復(fù)雜的路由功能。交換網(wǎng)中的第三種路由技術(shù)則采用了一種全新的結(jié)構(gòu):路由服務(wù)器與邊界交換機相結(jié)合。我們知道，傳統(tǒng)的路由器完成信息包的轉(zhuǎn)發(fā)與路由選擇兩項工作。而基于路由服務(wù)器的網(wǎng)絡(luò)則由兩個獨立的設(shè)備分別完成上述兩項功能:邊界交換機完成信息包的轉(zhuǎn)發(fā)，而路由信息的確定由價格較為昂貴的路由服務(wù)器完成。邊界交換機只有在自己的地址表中找不到目標(biāo)節(jié)點的地址時才訪問路由服務(wù)器，此時路由器對之響應(yīng)一個正確的地址，交換機再將該信息緩存?zhèn)溆?。需要指出的是，目前路由服?wù)器與交換機之間的通信協(xié)議還不統(tǒng)一，不同廠家的產(chǎn)品還不兼容。 5.比較與評價 上述三種路由技術(shù)各有特色，網(wǎng)絡(luò)設(shè)計人員可根據(jù)實際情況加以選用。為使人們對它們有更好的了解，我們分以下四個方面對它們進行比較。 1.組網(wǎng)規(guī)模 網(wǎng)絡(luò)的大小是選擇何種路由技術(shù)組網(wǎng)的決定性因素。第二層交換機與傳統(tǒng)路由器相結(jié)合的辦法適用于較小規(guī)模的網(wǎng)絡(luò)，其特點是經(jīng)濟實用。但當(dāng)主干網(wǎng)擴展成比較大的網(wǎng)絡(luò)時，第二層虛擬LAN的開銷將明顯增大。 隨著主干網(wǎng)的擴展，多層交換機的智能優(yōu)勢得到充分發(fā)揮，由于它僅向那些屬于某一特定子