Server Selection Policy in Active Anycast

In active anycast where accesses from the clients are distributed among the servers by an active router, the information used for selecting the adequate server from the viewpoint of improvement of response time for clients is important. Response time perceived by clients consists of processing delay at the server and network delay. To realize good selection of servers, both of server processing delay and network delay should be taken into account. Furthermore, the way of collecting that information is an important technical problem for an active router. In this paper, we propose the server selection policy using RTT information measured at an active router. By means of the server selection based on this RTT, the selection of the server considering not only the server load but also network congestion and distance from the active router to the server can be achieved. Active anycast using this server selection policy is designed to select the server for the purpose of reducing pure latency—server load balancing is secondary. We evaluate performance of active anycast applying this server selection policy and show that proposed scheme achieves good selection of servers from the viewpoint of both server load and network latency. 1.Introduction In the Internet, several types of services use replicated servers which are geographically dispersed across the whole network. One typical example is replicated server technology in the Web, e.g. mirroring and CgR[1]. The aim of this approach is to prevent too many accesses from concentrating to a particular server, which causes degradation of the response time of a server itself and congestion in the network around that server. We have proposed a new network paradigm, ''active anycast'', which enables a network to select an adequate server to achieve improvement of average user response time from the viewpoint of load balancing among candidate servers[2]. Active anycast makes use of anycast[3][4][5] and active network technology[6]-[10]. At a router equipped with the active network technology, an individual operation for each application or for each user can be accomplished. This means that an active router can operate additional intelligent processing as well as conventional routing in the network layer. In active anycast proposed in [2], a new function of selecting an adequate server from the viewpoint of load balancing is injected to an active router. We evaluated efficiency of the proposed active anycast with the assumption that all active routers have the load information of all servers …