A General Purpose Proxy Filtering

A General Purpose Proxy Filtering - A General Purpose Proxy...

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A General Purpose Proxy Filtering Mechanism Applied to the Mobile Environment* Bruce Zenel Dan Duchamp Juno Online Services, L.l? baz@staff.juno.com AT&T Labs - Research duchamp@research.att.com Abstract 1.1 Our proxy In recent years, proxies have become more prevalent. Generally, these systems are used to process data tlowing between two end- points using an intermediary. More specifically, they can be used to filter or process traffic flowing to and from a network-limited host. Benefits include more efficient use of network resources, re- duced cost, and increased security. In this paper, we describe the design and capabilities of such a system, how it has been applied to the mobile environment, and provide an evaluation of the work. The environment for which our work is intended is shown in figure 1. In this figure a pair of mobile hosts are communicating with a number of fixed hosts. To simplify the discussion, we assume that an application (or “client”) runs on the mobile host and communi- cates with a server on a fixed host, but the proxy mechanism can work with any two communicating endpoints located anywhere, including two mobile hosts. In our model of the environment, we assume the “last link” to the mobile host is the likely problem area. Currently and in the foreseeable future, this link will typically be slower, more costly, less reliable, and perhaps less secure than typical WANs or LANs. Accordingly, a proxy is placed somewhere on the opposite side of this link from the mobile host, and the two work together to overcome or attenuate the link’s limitations. The proxy need not be physically attached to this last link. 1 Introduction Proxy based systems can be considered commonplace in today’s heterogenous network environment. In general, a proxy takes the form of an intermediary placed between two communicating end- points such as a client and server. The purpose of the intermedi- ary is to improve the quality of the network as perceived by the client along some dimension which is constrained (e.g., connec- tivity, cost, security). Examples include firewalls [12], protocol specific proxies [lo], programmable routers [26], and gateways that reduce traffic over low bandwidth or heterogeneous network links [3, 181. As part of our research on mobile computing, we have spent two years building a general purpose proxy system. Our work is general purpose in’that it provides a mechanism for downloading and executing proxy programs (called “filters”), interposing filters into the middle of client-server connections, and dynamically con- trolling filter behavior. The filters are often application specific, and usually act under control of an application running on a mo- bile host. They may drop, delay, or transform data moving to and from the mobile host. This paper provides a detailed analysis of this system, how it
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A General Purpose Proxy Filtering - A General Purpose Proxy...

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