Research On Graceful Convergence Of Inter-Domain Routing Protocol

As the rapid development of Internet, the role of the network has been transformed from the pure scientific research communication infrastructure for national defense or the applications into the most important information infrastructure of modern social, economic development, social progress and technological innovation. Therefore, it is mostly important to enhance the networks's ability of providing continuous service. As relates with economic stability, national security and human life. In recent years, network technology and types of services develops rapidly, but failures of system components and unexpected accidents may fail at any time. It depends on the current routing protocol to resume the forward path to avoid failure point. The characteristic of slow convergence and conflicting route information destroy the forwarding path and influence the reachability of networks. The serviceability of network is decreased.This work relies on the 973 project on "Integrated Network Architecture Model and Switch, Routing Theory and Technology", focusing on ensuring the reachability of the network during link failures. Firstly, protocol convergence model is built and factors of affecting network reachability is analyzed and discovered. Then, a graceful convergence protocol framework is presented and three key issues are given. Secondly, it is presented that the rapid re-routing technology based on the protection tunnel, the smooth convergence technology based on ordered update and session reliability enhancing technology based on timer retransmission and burst detection mechanism. Finally, integration of the three key technologies of the graceful convergence protocol are summarized to form a comprehensive routing system which ensures all networks to be continuously reached. Main research results and innovations of this paper are as follows:1. A state convergence model of inter-domain routing protocol is constructed, the graceful convergence protocol framework is presented. The influence of forwarding loop or blackhole on the network reachability is analyzed. The formation causes of forwarding loop or blackhole is discovered. Based on the analysis results on loop and blackhole states, the graceful convergence framework of the inter-domain routing protocol is presented and three key issues are summarized.2. A protection tunnel based rerouting technology is presented to ensure the reachability during the period of link failures. A protection tunnel has established between the nodes whose best path including or not including the failed link. When the link failed, the upstream node of failed link could immediately reroute the traffic to corresponding tunnel egress node. The egress node succeeds to forward rerouted traffic to the destination with normal path. So, the destination is continuously reached during the link failures. The existence and effectiveness of the protection tunnel is analytically proved. The corresponding implement technologies are presented under the network environment of multi-homed networks or general networks. Simulation results show that the tunnel mechanism can ensure the continuously reachability during link failures, while not significantly increase the number of protocol messages and the number of routing table entries. It is also a good approach to be deployed incrementally. 3. An ordered route update based smooth convergence technology is presented to ensure the reachability during the period of convergence. During the convergence, the node forwarding table should be updated in an order which is in accordance with the distance from current node to the failed link. If the order is follows, those influenced node will continuously use the former path to forward traffic until obtained a valid path. So, the reachability is continuously during the protocol convergence. The correctness and completeness of ordered updated technology is proved and the protocol message contents and algorithm are designed. The simulation results show that the method can ensure the reachability during the period of convergence, while the convergence performance has also been improved.4. The timing retransmission of TCP and keepalive message burst transmission mechanism is presented to enhance the reliability of peer session. Firstly, the distribution of the duration of link failure is assumed so as to establish session failure probability model. By modifying the TCP retransmission mechanism, the session reliability is improved. Then, by modifying the sending mechanism of keep-alive message to sudden delivery mechanism, the session reliability can be improved further. At this time, peer session could tolerance the duration of link failure in the maximum. The session keeping mechanism is a connector between the protection tunnel mechanism and ordered route update mechanism. The enhancement of peer session reliability could not only increase the used efficiency of protection tunnel but also avoid unnecessary ordering update messages triggered during convergence process. It reduces the frequent route calculation and route oscillations incurring by convergence. The route stability is also improved.