In recent years, abnormal development of the Internet rapidly growing commercial applications, the development of the Internet users is difficult to predict. In addition, more and more users need high-speed access. The data indicate that in China, Internet users complain about slow is the first of many problems. Therefore, improving the network bandwidth, network quality of service, router, network management system becomes increasingly important. Ensuring the quality of the premise, to maximize land use of bandwidth, early detection and Zhenduanshebei Gu Zhang, quick and easy to Genju need to change installed Deng network management functions, Cheng Wei directly affect the network users and network operators the interests of important factors. Generally speaking, the structure of the router is moving faster, better and easier to service quality integrated management of three directions.
Two functions of the router
Data path functions: For each arrival packet router, without losing the case, for wayfinding. This feature includes: forwarding the decision by the backplane output link queue scheduling. Forwarding is implemented through dedicated hardware, each packet through the router package should perform this operation. Data path functions for improving the performance of the router is very important.
Control functions: including routing table management and system configuration and management, as well as with neighboring routers to exchange routing table information, such as through software. These features are not for each packet, so the use of relatively lower frequency.
The key technical problems router
The design of the current router of some key technologies, some problems have yielded results, some have only just begun. Be noted that this area is developing very fast. To facilitate a systematic understanding of these key technologies, we develop according to the three major trends in the router, these problems generally fall into three categories. One with high speed-related issues, such as the routing table to quickly find the bus back and exchange structure. Second, QoS issues, such as data flow and packet classification, traffic engineering and congestion control. Third, and software-related issues, such as software stability, configuration and management. Be noted that this classification is not strict, some problems could belong to two categories.
1. And speed-related technology
Fast routing table lookup techniques
In order to solve the address shortage of resources, reduce routing table size, reduced management difficulties, the Internet using CIDR (Classless Inter-Doma in Routing). Thus, the routing table is not stored in one by one specific IP address, but the variable length network prefixes. Routers in the IP packet addressing, the use of the longest prefix match (LPM-Longest Prefix Matching). For example, suppose the routing table has two entries "202.168.XX, output port 1" and "202.168.16.X, output port 2" (X, said any), if there is an IP packet's destination address is 202.168.16.5 , then the packet should be output from port 2. The traditional implementation of the longest prefix match the router is a long time, so the routing table to find a router speed bottleneck. The last two years there have been some fast lookup table algorithm, able to support gigabit link. These algorithms include improved precision matching, trie-based method, parallel hardware method, the agreement to change the routing tables simplify the query and buffer law. These algorithms, some easily implemented in hardware, some suitable software. Multicast address for addressing, IP packet according to the source address and multicast address look-up table, using the source address of the longest prefix matching method, the destination address using the exact matching.
Switch architecture and scheduling algorithm
Exchange structure Crossbar, shared memory and bus ways. Crossbar structures determine the speed of the scheduler, shared memory structure, the speed of the decision by the memory read and write speeds, the speed of shared bus architecture and arbitration by the bus, the cost of the capacity of the decision. Crossbar switch fabric scheduler is the core of it within a time slot in each scheduling of collecting the relevant data packet queue input information received after a certain scheduling algorithm between input and output ports of a match, to provide input to the output port pathway. Non-blocking mode using input buffer Crossbar, with ESLIP scheduling algorithm has been adopted by some manufacturers. Scheduler design is difficult, it is necessary to achieve 100% throughput to meet the system requirements, but also support the CoS (Classes of Service). Scheduling algorithm, weighted fair queuing algorithm (WFQ-Weighted Fair Queuing) and through the improved flow weighted fair queuing algorithm (WF2Q-Weighted Fair Flow Queuing) relatively easy to implement, but performance is not bad. In short, make the Internet truly integrated multi-service, as a network router connecting the core equipment, must enhance the port rate and exchange capacity, to provide QoS guarantees and traffic engineering (TE-Traffic Engineering) function.