Cellular Router is a network device that connects multiple networks or network segments. It can "translate" the data information between different networks or network segments, so that they can "read" each other's data, thus forming a larger network. Cellular Router has two typical functions, namely data channel function and control function.Data channel functions include forwarding decisions, backplane forwarding, and output link scheduling, which are generally performed by specific hardware. Control functions are generally implemented by software, including information exchange with adjacent Cellular Routers, system configuration, system management, etc.

  Cellular Router plays an important role in the computer network. It is the bridge of the computer network. It can not only connect different networks, but also choose the path of data transmission, and prevent illegal access. As the core equipment of IP network, Cellular Router technology has become the key technology of the current information industry, and its equipment itself plays an increasingly important role in data communication.

  Performance and business play a key role in the evolution of Cellular Router technology. On the one hand, the growth of bandwidth and network scale promotes the performance and capacity of Cellular Router. On the other hand, the development of service drives Cellular Router to be more intelligent and have stronger service delivery capability.Among these two key factors, the performance factor plays a leading role in the early stage of the development of Cellular Router. With the rapid development of IP networks and services, the service factor or the value of service performance in the network will play an increasingly important role.

  Cellular Router has had its ups and downs over the years. In the mid-1990s, the traditional Cellular Router became the bottleneck of the development of the Internet. Instead, the ATM switch becomes the core of the IP backbone, and the Cellular Router becomes a supporting role.At the end of the 1990s, the scale of the Internet was further expanded, the traffic doubled every six months, and the ATM network became the bottleneck. Cellular Router made a comeback. After the appearance of GBPS routing switch in 1997, people began to replace ATM switch with GBPS routing switch. A backbone network with Cellular Router as the core.Today, Cellular Router is in its fifth era. Let's take a look at the application development of Cellular Router technology and its typical products.

  First Generation Cellular Router: Centralized Forwarding, Bus Switching

  The original IP network was not large, and the devices that needed to be connected to the gateway and the load that needed to be processed were also very small. At this time, the gateway (Cellular Router) can basically be implemented by inserting multiple network interface cards into a computer. The interface card is connected with the central processing unit (CPU) through an internal bus, and the CPU is responsible for all transaction processing, including route collection, forwarding processing, device management, and the like. After receiving the message, the network interface transmits it to the CPU through the internal bus, and the CPU completes all the processing and transmits it out from another network interface.

  Second-generation Cellular Router: Centralized + distributed forwarding, interface modularization, bus switching and other technologies

  Because each message is sent to the CPU through the bus, with the increase of network users, the network traffic is increasing, and the bottleneck effect of the number of interfaces, bus bandwidth and CPU is becoming more and more prominent. So it is natural to think: how to increase the number of network interfaces, how to reduce the burden of CPU, bus?In order to solve this problem, the second-generation Cellular Router performs some intelligent processing on the network interface card. Because network users usually only visit a few places, it can be considered to keep a few commonly used routing information on the service interface card by using Cache technology. In this way, most of the packets can be forwarded directly through the routing table of the service board Cache to reduce the demand on the bus and CPU.

  Third Generation Cellular Router: Distributed Forwarding, Bus Switching

  The Web technology that appeared in the 1990s has made the IP network develop rapidly, the user's access area has been greatly broadened, and the access place is no longer as fixed as in the past, so it often appears that the router can not be found from the Cache, and the bottleneck effect of the bus and CPU appears again. In addition, the problems caused by the increase of users and the insufficient number of Cellular Router interfaces have been exposed again.In order to solve these problems, the third generation of Cellular Router came into being. The third generation of Cellular Router adopts a fully distributed structure, i.e. The technology of separating routing and forwarding. The main control board is responsible for the management of the entire equipment and the collection and calculation of routing, and sends the forwarding table formed by calculation to each service board. Each service board can independently perform route forwarding according to the stored route forwarding table.In addition, the bus technology has also been greatly developed. Through the data forwarding between the bus and the service board, which is completely independent of the main control board, the parallel high-speed processing is realized, and the processing performance of Cellular Router is doubled.

  Fourth Generation Cellular Router: ASIC Distributed Forwarding, Network Switching

  In the late 1990s, with the commercialization of IP network and the emergence of Web technology, Internet technology has developed unprecedentedly, and Internet users have increased rapidly. The network traffic, especially the core network traffic, is growing exponentially, and the traditional software-based IP Cellular Router has been unable to meet the needs of network development. With common backbone nodes 2.Taking 5G POS port as an example, the line-speed traffic of 2.5g POS port is about 6.5Mpps according to the minimum IP message of 40 bytes. Moreover, the packet processing needs to include complex operations such as QoS guarantee, routing lookup, stripping/adding of the layer 2 frame header, and the like, which are impossible to be realized by the traditional method. Therefore, some manufacturers have proposed ASIC implementations, which implement all the details of the forwarding process in hardware.In addition, Crossbar or shared memory is used to solve the problem of internal exchange. In this way, the performance of Cellular Router reaches gigabit, which is the early Gigabit Switch Router (GSR).

  Fifth Generation Cellular Router Technology: Network Processor Distributed Forwarding, Network Switching

  The fourth generation Cellular Router adopts the hardware forwarding mode, which solves the bottleneck problem of insufficient bandwidth capacity and performance, but also leaves a hidden danger: the hardware forwarding based on ASIC sacrifices the service flexibility while obtaining high performance.This is related to the implementation of ASIC technology. When designing the ASIC chip, a lot of optimization has been done to the forwarding process, so that IP forwarding can be implemented in a simple and fixed way, thus solidifying it and achieving hardware. If you have to do some complex additional processing in IP forwarding, ASIC can't do anything. Moreover, the design cycle of ASIC is very long, and it usually takes two to three years to design a stable ASIC chip.In the field of IP Internet, the business is developing very rapidly. On average, a new business will emerge every six months, and these businesses may have an impact on the forwarding process, which requires appropriate adjustment of the forwarding program to obtain high-quality support.Recently, MPLS VPN technology has gradually become popular. Operators need to develop MPLS VPN services in backbone networks and metropolitan area networks. At this time, they find that the fourth generation Cellular Router originally used in backbone networks can not provide high-performance VPN services, so they need to upgrade or build a special VPN bearer network.In the current operating environment where bandwidth is no longer the main contradiction and service application is the king, the inherent problems of poor flexibility and insufficient service support of ASIC have become the main contradiction in the development of Cellular Router. New needs bring about new contradictions, which will lead to new development. The rise of network processor technology has led to the emergence of the fifth generation Cellular Router.

  From the first generation to today's fifth Cellular Router technology is not the same, the development of technology is with the rapid development of network technology applications.