Showing papers on "Anycast published in 2000"

Application-layer anycasting: a server selection architecture and use in a replicated Web service

Abstract: Server replication improves the ability of a service to handle a large number of clients. One of the important factors in the efficient utilization of replicated servers is the ability to direct client requests to the "best" server, according to some optimality criteria. In the anycasting communication paradigm, a sender communicates with a receiver chosen from an anycast group of equivalent receivers. As such, anycasting is well suited to the problem of directing clients to replicated servers. This paper examines the definition and support of the anycasting paradigm at the application-layer, providing a service that uses an anycast resolver to map an anycast domain name and a selection criteria into an IP address. By realizing anycasting in the application-layer, we achieve flexibility in the optimization criteria and ease the deployment of the service. As a case study, we examine the performance of our system for a key service: replicated Web servers. To this end, we develop an approach for estimating the response time that a client will experience when accessing given servers. Such information is maintained in the anycast resolver that clients query to obtain the identity of the server with the best estimated response time. Our performance collection technique combines server push with resolver probes to estimate the expected response time without undue overhead. Our experiments show that selecting a server using our architecture and estimation technique can improve the client response time by a factor of two over nearest server selection and by a factor of four over random server selection.

A framework for scalable global IP-anycast (GIA)

Abstract: This paper proposes GIA, a scalable architecture for global IP-anycast. Existing designs for providing IP-anycast must either globally distribute routes to individual anycast groups, or confine each anycast group to a pre-configured topological region. The first approach does not scale because of excessive growth in the routing tables, whereas the second one severely limits the utility of the service. Our design scales by dividing inter-domain anycast routing into two components. The first component builds inexpensive default anycast routes that consume no bandwidth or storage space. The second component, controlled by the edge domains, generates enhanced anycast routes that are customized according to the beneficiary domain's interests. We evaluate the performance of our design using simulation, and prove its practicality by implementing it in the Multi-threaded Routing Toolkit.

A routing protocol for anycast messages

Abstract: An anycast packet is one that should be delivered to one member in a group of designated recipients. Using anycast services may considerably simplify some applications. Little work has been done on routing anycast packets. In this paper, we propose and analyze a routing protocol for anycast message. It is composed of two subprotocols: the routing table establishment subprotocol and the packet forwarding subprotocol. In the routing table establishment subprotocol, we propose four methods (SSP, MIN-D, SET, and GET) for enforcing an order among routers for the purpose of loop prevention. These methods differ from each other on information used to maintain orders, the impact on QoS, and the compatibility to the existing routing protocols. In the packet forwarding subprotocol, we propose a Weighted-Random Selection (WRS) approach for multiple path selection in order to balance network traffic. In particular, the fixed and adaptive methods are proposed to determine the weights. Both of them explicitly take into account the characteristics of distribution of anycast recipient group while the adaptive method uses the dynamic information of the anycast traffic as well. Correctness property of the protocol is formally proven. Extensive simulation is performed to evaluate our newly designed protocol. Performance data shows that the loop-prevention methods and the WRS approaches have great impact on the performance in terms of average end-to-end packet delay. In particular, the protocol using the SET or CBT loop-prevention methods and the adaptive WRS approach performs very close to a dynamic optimal routing protocol in most cases.

Integrated routing algorithms for anycast messages

Abstract: The use of anycast service can considerably simplify many communication applications. Two approaches can be used for routing anycast packets. Single-path routing always uses the same path for anycast packets from a source, while multipath routing splits anycast traffic into several different paths. The former is simple and easy to implement, while the latter may potentially reduce congestion, improving delay and throughput performance. However, multipath routing may require additional cost to maintain multipath information. To take advantage of both approaches and overcome their shortcomings, we develop a set of integrated routing algorithms that can adaptively select a subset of routers in the network to carry out multipath routing for anycast messages. We demonstrate that systems using our integrated routing algorithms perform substantially better than those where either the single-path or multipath approach is used alone.

Server Load Balancing with Network Support: Active Anycast

Abstract: In server load balancing where replicated servers are dispersed geographically and accesses from clients are distributed to replicated servers, a way of distributing the accesses from clients to an adequate server plays an important role from the viewpoint of load balancing. In the paper, we propose a new network paradigm for server load balancing using active any cast. In active anycast, an end user only sends its request to group of servers using an anycast address. When this request arrives at an active router, it selects an adequate server from the viewpoint of load balancing and changes the anycast address of a packet to the unicast address of the selected server. Thus, the decision which server is the best one from the viewpoint of server load balancing is made by an active router rather than an end user, so active any cast is a network-initiated method. Simulation results show that active any cast can accomplish efficient server load balancing, even when a small part of routers are equipped with active network technology.

Load-balanced anycast routing in computer networks

Abstract: We present a practical approach to routing and anycasting with near-optimum delays taking into account the processing loads at routers and processing elements of a computer network. To accomplish this, the minimum-delay routing problem formulated by Gallager (1977) is generalized into the problem of minimum-delay routing with load-balancing to account for processing delays in network nodes (servers and routers). Gallager's theorem for necessary and sufficient conditions for minimum-delay routing is modified to include processing delays and changes of traffic levels at network nodes. The first distributed algorithm for load-balanced anycasting and routing in computer networks is presented. This algorithm, named MIDAS, provides approximate solutions to the modified necessary and sufficient conditions for minimum-delay routing. Simulations are use to compare the performance of the new algorithm with the performance of a traditional approach to sever load balancing.

Integrated fault-tolerant multicast and anycast routing algorithms

Abstract: Anycast is a new communication service defined in IPv6 (Internet Protocol Version 6 for the next generation). An anycast message is the one that should be delivered to the 'nearest' member in a group of designated recipients. Anycast and multicast mechanisms may be integrated to provide better services. A group of replicated (or mirrored) servers that provides anycast service may also provide multicast services and needs multicast to consistently update, whereas anycast routing may help a multicast request to reach the 'nearest' member in a multicast group. A novel integration routing protocol is presented for both multicast and anycast messages communications in the Internet. The protocol is composed of four algorithms: (1) dynamic anycast routing algorithm for efficient transmission of anycast messages over the Internet to a group of servers. (2) integrated anycast routing with core-based tree technique based on multicast routing algorithms taking advantage of short delay, high throughput and load sharing. (3) Fault-tolerant algorithms for both anycast and multicast routing using backup paths restoring techniques. The performance figures have demonstrated the benefits of anycast routing in reducing end-to-end packet delay, and attaining load balance and fault-tolerance for multicast.

Optimal request routing by exploiting packet routers topology information

Abstract: A technique for redirecting client computer requests for content files to the closest replica of the requested content, by using anycast messaging. The request to resolve a domain name is forwarded as an anycast message to a name service provided by a group of name servers distributed in the network. The closest name server then responds to the anycast message by returning a unique network address for an associated content server that contains a replica of the requested content file. This scheme permits a client computer to subsequently establish higher level protocol access method, such as a Hyper Text Transfer Protocol (HTTP) request, to open a connection and deliver the content file replica, from a content server that is topologically close to the client, using only standard network protocols.