202080316_李大壮_中英文资料翻译.doc

附录一：英文技术资料翻译英文原文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.路由与交换技术1. 局域网技术各单位通常把位置上比较靠近的资源，如放在学院的教室中或企业的办公室中的PC连在一起而构成网络。这类网络就被称为局域网（LAN）。大多数局域网是客户-服务器或对等方式。应用最广的、用于本地计算机设备互连，以进行数据通信的局域网拓扑是星型结构，在这种结构中以集线器或交换机作为主要的联网设备，连接各种计算机设备。使用这种拓扑结构的局域网的典型产品是著名的以太网，先进它在全世界局域网中占统治地位。以太网IEEE802.3支持最初由施乐公司，后来由数据设备公司、英特尔和施乐公司联合开发的局域网标准，被称为以太网。2. 交换机交换机基本上是多端口网桥，但是具有某些路由器的特性。像路由器那样，交换机是把网络分成很多段，每段的本地业务都不会对其他网段产生干扰。交换技术是在七层模型的第二层上实现的与网桥技术相同。因为它在第二层上实现，要使用MAC地址，与协议地址无关。像网桥一样，交换机记住了常驻在每个端口的那些地址，并且对数据进行相应的交换。交换可以使用常规的微处理器或专用ASIC技术进行设计。3. 路由器路由器已经有几个名字了。回到过去称为ARPANET的那个时代，路由器称为互联网报文处理机（IMP）。最近路由器又被称为网关；这个术语的痕迹仍可在边界网关协议（BGP）和内部网关路由协议（IGRP）中见到。在开放式系统互联领域被称为中间系统。路由器最能表达设备的功能。路由器沿两个网络之间的路由路径传送信息。这条路径可以经过一个路由或或者更多个路由器。进而，在有很多条路径指向同一目的地的互联网中，现代路由器用一组程序去决定并使用最佳路径。如果这一路有不再是最佳或完全不可用，路由器会选择下一条最佳路径。由路由器使用的，用于确定和选择最佳路径，并与其他路由器共享网络可达性和状态信息的程序，称为路由选择协议。正如数据链路可以直接连接两个设备一样，路由器也在两个设备之间建立一个连接。不同的是，如果共享一条公共数据链路的两个设备之间通信路径是一条物理路径，而由路由器提供在不同的网络上的两个设备之间的通信路径是高层逻辑路径。一个以太网，一个FDDI环网，一个串行链路和一个令牌网，如前所说，数据在数据链路上传送，必须封装成一个帧。同样，数据要在通过路由的、跨网络逻辑路径上传送，也必须封装，路由器使用数字封装是分组。4.三种路由技术目前交换网络中的路由技术有三种，其中第一种是最为保守的方法，即第三层的路由器与第二层交换机相结合的方法。第二层交换机严格限制于桥结构，用于同一虚拟网内的不同节点之间的数据交换，在OSI参考模型的第二层，即数据链路层实现虚拟LAN的功能，将第三层的功能留给路由器实现，由路由器完成虚拟网络之间的数据传输与建立LAN与企业主干网连接的工作。第二种方法采用分布式路由技术。其特点是它使用多层交换机，将第二层的桥与第三层的路由结合在一起，有的文献也将多层交换机称之为第三层交换机。它本身所具有的路由功能支持虚拟LAN，并支持大多数同一虚拟网内或不同虚拟网之间节点的通信，减少了工作组与部门之间所使用的路由器的数目。但它仍然不能完全摆脱使用传统路由器，这是因为多层交换机只能提供高档路由器所能提供的协议、安全、交通管理及与WAN连接功能的子集。如CISCO公司7000系列路由器能够处理12种协议并支持点对点、电路交换与信元交换的广域网通信，而Alantec公司生产的Powerhub多层交换机却只能处理三种协议:DECnet、IP与IPX，并且没有WAN接口。因此，多层交换机网络中需要使用路由器作为广域网的网关，并完成较为复杂的路由功能。交换网中的第三种路由技术则采用了一种全新的结构:路由服务器与边界交换机相结合。我们知道，传统的路由器完成信息包的转发与路由选择两项工作。而基于路由服务器的网络则由两个独立的设备分别完成上述两项功能:边界交换机完成信息包的转发，而路由信息的确定由价格较为昂贵的路由服务器完成。边界交换机只有在自己的地址表中找不到目标节点的地址时才访问路由服务器，此时路由器对之响应一个正确的地址，交换机再将该信息缓存备用。需要指出的是，目前路由服务器与交换机之间的通信协议还不统一，不同厂家的产品还不兼容。 5.比较与评价 上述三种路由技术各有特色，网络设计人员可根据实际情况加以选用。为使人们对它们有更好的了解，我们分以下四个方面对它们进行比较。 1.组网规模 网络的大小是选择何种路由技术组网的决定性因素。第二层交换机与传统路由器相结合的办法适用于较小规模的网络，其特点是经济实用。但当主干网扩展成比较大的网络时，第二层虚拟LAN的开销将明显增大。 随着主干网的扩展，多层交换机的智能优势得到充分发挥，由于它仅向那些属于某一特定子