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Volume 4 The Dragon Heads Up Chapter 30 Multiprotocol Router

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    Fu Xin is even more aware of multi-protocol routers. In December 1984, Cisco_Systems, Inc. was established in the United States. The founders were a couple of teachers from Stanford University and the director of the Computer Center of the Department of Computer Science, Leonard.  Leonard_Bosack and Sandy_Lerner, director of the Business School's Computer Center.  The couple designed a networking device called a "multiprotocol router" for the Stanford Campus Network (SUNet) to integrate incompatible computer LANs on campus into a unified network.  This Internet-connected device is considered to be a sign of the true arrival of the Internet era.  ¡°You say, how could someone like Fu Xin, the reincarnation of a great scientist, not know this?  Routers can be divided into first-generation single-bus single-CPU structure routers, second-generation single-bus master-slave CPU structure routers, third-generation single-bus symmetrical multi-CPU structure routers; fourth-generation multi-bus multi-CPU structure routers, and fifth-generation routers.  There are many types of shared memory architecture routers, sixth-generation crossbar architecture routers and cluster-based system routers.  A router has four elements: input ports, output ports, switching switches, route processors and other ports.  An input port is the physical link and entry point for input packets.  Ports are usually provided by line cards. A line card generally supports 4, 8 or 16 ports. An input port has many functions.  The first function is to encapsulate and decapsulate the data link layer.  The second function is to find the destination address of the incoming packet in the forwarding table to determine the destination port (called route lookup). Route lookup can be implemented using general hardware, or by embedding a microprocessor on each line card.  .  Third, in order to improve QoS (Quality of Service), the port must divide the received packets into several predefined service levels.  Fourth, the port may need to run data link-level protocols such as SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol) or network-level protocols such as PPTP (Point-to-Point Tunneling Protocol).  Once the route lookup is complete, the switch must be used to send the packet to its output port.  If the router is input-queued, several inputs share the same switch.  The final function of such an input port is to participate in an arbitration agreement on a common resource such as a switch. ? Switches can be implemented using a number of different technologies.  The most commonly used switch technologies are bus, crossbar switch and shared memory.  The simplest switch uses a bus to connect all input and output ports. The disadvantage of a bus switch is that its switching capacity is limited by the capacity of the bus and the additional overhead caused by shared bus arbitration.  The crossbar switch provides multiple data paths through the switch. A crossbar switch with N¡ÁN crosspoints can be considered to have 2N buses.  If a cross is closed, the data on the input bus is available on the output bus, otherwise it is not available.  The closing and opening of the crosspoints is controlled by the scheduler, which therefore limits the speed of the switch.  In a shared memory router, incoming packets are stored in the shared memory, and only the packet pointers are exchanged. This increases the switching capacity, but the switching speed is limited by memory access.  speed.  Although memory capacity can double every 18 months, memory access time only decreases by 5 per year, an inherent limitation of shared memory switches.  The output port stores packets before they are sent to the output link and can implement complex scheduling algorithms to support priority and other requirements.  Like input ports, output ports must also support data link layer encapsulation and decapsulation, as well as many higher-level protocols.  The route processor calculates the forwarding table to implement the routing protocol, and runs the software that configures and manages the router.  At the same time, it also handles packets whose destination addresses are not in the line card forwarding table.  Other ports generally refer to control ports. Since the router itself does not have input and terminal display devices, it requires necessary configuration before it can be used normally. Therefore, general routers have a control port 'Console', which is used to communicate with a computer or computer.  The terminal device is connected and the router is configured through specific software.  All routers are equipped with a console port, allowing users or administrators to use a terminal to communicate with the router and complete router configuration.  This port provides an EIA/TIA-232 asynchronous serial interface for local configuration of the router (first-time configuration must be done through the console port).  The Console port is directly connected to the computer serial port using a dedicated configuration cable, and a terminal emulation program (such as ¡®HyperTerminal¡¯ under Windows) is used for local configuration of the router.  The console port of the router is mostly an RJ-45 port.  Routers play an important role in computer networks and are the bridge of computer networks.  Not only can it connectDifferent networks can also select the data transmission path and block illegal access.  As a node of the backbone network, the multi-protocol router runs a certain Ad_Hoc network routing protocol to realize the routing and addressing function of the backbone network.  Ad_Hoc originates from Latin, meaning "for_this" and extended to "for_this_purpose_only", which means "set up for a certain purpose, special", that is, the Adhoc network is a network with a special purpose.  The Ad_Hoc structure is a peer-to-peer network structure that eliminates the wireless intermediary device AP. As long as a wireless network card is installed, computers can achieve wireless interconnection with each other; the principle is that a computer host in the network establishes a point-to-point  Point connection is equivalent to a virtual AP, and other computers can directly connect and share the network through this point-to-point connection.  Ad_Hoc network, also known as mobile self-organizing network and multi-hop network, has the characteristics of flexible and fast networking, and is not affected by wired networks. It can be widely used in military and rescue situations where it is impossible or inconvenient to lay network facilities in advance.  Ad_Hoc wireless network has its own particularity. When establishing an actual wireless working network, the application scale and scalability of the network, as well as the reliability and real-time requirements of the application must be fully considered to select an appropriate network topology.  At present, Ad_Hoc wireless network is developing in a large-scale direction, gradually showing a hierarchical trend, represented by a two-level network.  In a two-level network, the network is divided into two levels: backbone network and subnet.  At the subnet level, each subnet can form an independent Ad_Hoc network and can use different routing protocols.  The backbone network is composed of multi-protocol router nodes and ordinary nodes. The ordinary nodes mainly complete the distribution of data and control information in the backbone network; while the multi-protocol routers, in addition to having the functions of ordinary nodes, are also responsible for managing the subnet and  Control and data interaction are the core equipment of the backbone network.  In a hierarchical Ad_Hoc network, multi-protocol routers manage subnets through data exchange with subnet gateways.  Communication within a subnet is similar to a general Ad_Hoc network; while communication between subnets needs to be relayed through subnet gateway nodes and backbone network nodes, which can be divided into two situations - between homogeneous/heterogeneous subnets under the same router  communication and communication between homogeneous/heterogeneous subnets under different routers.  In order to achieve effective communication between subnets, routers need to complete mutual conversion between multiple protocols.  The demand for Internet access requires the existence of an access point AP (Access_Point) in the hierarchical AdHoc network.  Considering the network environment, this function needs to be implemented by a multi-protocol router.  Therefore, multi-protocol routers mainly implement the three major functions of backbone network routing addressing, protocol conversion, and Internet access AP.  Generally speaking, routers in AdHoc networks are vehicle-mounted or backpack-mounted, so multi-protocol routers must have high integration and mobility.  The hardware structure of the multi-protocol router is divided into two parts: one is the core module (MCF5272) part, which is composed of a microcontroller module and a memory module (including SDRAM and Flash); the other part is the communication interface module part, which is composed of asynchronous serial control and  It is composed of transceiver module, Ethernet control and transceiver module and universal serial bus USB (UniversalSerialBus) interface module.  In the core module part, the microprocessor module is mainly responsible for processing data.  The memory module is divided into two parts: one part is Flash (composed of two pieces of Flash, totaling 4MB), which is used as program memory to store the operating system kernel, various routing protocols and routing table constants; the other part is SDRAM, which is used as data memory.  Used as a running space for the operating system and various routing programs.  In the communication interface module, the asynchronous serial control and transceiver module is used to wirelessly connect to multiple backbone network nodes and connect multiple subnet gateways PRU (ie, packet wireless control unit).  The Ethernet control and transceiver module can realize Internet access function.  The USB interface module is used to connect to the network device control terminal and implement the router's storage control of USB devices (such as USB standard mobile hard disks, used to store important routing information).  "Mr. Zhou, this is great stuff!" Fu Xin read the information roughly and said with a cheerful smile.  Zhou Zhengming nodded and ordered: "I won't tell you where this thing came from. You can guess it yourself! But I can tell you that this came from Stanford University. It is not easy to get this information.  Don¡¯t leak it out, keep it away after reading it, show it to others, be sure to give it to someone you trust, and be sure to remember it!¡± ¡°Minister Zhou, don¡¯t worry, I know the importance of this thing, please negotiate more.  The router was made by Cisco in December 1984, so it is an advanced technology. I know its importance and will definitely keep it safe!" Fu Xin said seriously. Zhou Zhengming didn't need to say anything else, he also knew this.  What happened to the thing? Perhaps, this is still a piece of information stained with blood. He must cherish it!  "By the way, Fu Xin, JingCity Component Factory No. 3, just teach their leaders a lesson. Don¡¯t be too harsh. After all, they cooperate with the Commission of Science, Technology and Industry for National Defense, which affects their production. It won¡¯t be easy for us to explain at that time!  "Zhou Zhengming warned again. "Okay.  "Fu Xin nodded thoughtfully! He Fu Xin likes to kill everyone, but at the same time, he also likes to play with slaps in the face. (To be continued. Please search Piao Tian Literature, the novel is better and updated faster!)
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