(Georgia Institute of Technology, 1997)
Bhattacharjee, Samrat; Zegura, Ellen W.; Ammar, Mostafa H.; Fei, Zongming
Server replication is an approach often used to improve 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 this paper we target an environment
in which servers are distributed across the Internet, and clients
identify servers using our application-layer anycasting service.
Our goal is to allocate servers to clients in a way that minimizes
a client's response time. To that end, we develop an approach for
estimating the performance that a client would experience when
accessing particular servers. Such information is maintained in a
resolver that clients can query to obtain the identity of the server
with the best response time. Our performance collection technique
combines server push with client probes to estimate the expected
response time. A set of experiments is used to demonstrate the
properties of our performance determination approach and to show its
advantages when used within the application-layer anycasting architecture.
(Georgia Institute of Technology, 1996)
Ammar, Mostafa H.; Zegura, Ellen W.; Shah, Viren; Fei, Zongming; Bhattacharjee, Samrat
Server replication is a key approach for maintaining user-perceived quality
of service within a geographically wide-spread network. The anycasting
communication paradigm is designed to support server replication by allowing
applications to easily select and communicate with the "best" server,
according to some performance or policy criteria, in a group of content-
equivalent servers. We examine the definition and support of the anycasting
paradigm at the application layer, providing a service that maps anycast
domain names into one or more IP addresses using anycast resolvers. In
addition to being independent from network-layer support, our definition
includes the notion of filters, functions that are applied to groups of
addresses to affect the selection process. We consider both metric-based
filters (e.g., server response time) and policy-based filters; we further
allow filtering both at the anycast resolver and local to the anycast
client. A key input to the filtering process is metric information
describing the relative performance of replicated servers. We examine the
use of various techniques for maintaining this information at anycast
resolvers.