TCD-CS-1999-60.pdf (PDF) 298.2Kb
One of the important issues that are quite often a challenge in modern distributed systems is the issue of adaptability. The need for adaptability rises from the fact that these systems are very much open, heterogeneous environments encompassing a wide range of hardware/software products from an ever-increasing number of vendors. Therefore, mechanisms are needed that allow these products to live and interact dynamically in a way that satisfies the different performance and functionality requirements of their heterogeneous environments. The Mobile Proxies (MP) project provides one such mechanism for client/server systems that are integrated using the Common Object Request Broker Architecture (CORBA) technology. The system achieves adaptability by exposing the low-level data traffic, exchanged between clients and servers, to different functionality-manipulating programs, each capable of modifying the data traffic in such a way that adaptability is achieved between client and server environments. The system design relies on two major principles: The first is the well-known proxy principle, defined by Shapiro in 1986, and implemented in a number of middleware technologies including CORBA. The other is the concept of interceptors defined by the Object Management Group (OMG) as part of the CORBA v2.3 specification. These interceptors allow the above-mentioned exposure of the low-level data. The system combines these two principles such that a client is allowed to specialize the proxy it has by downloading from the server, another proxy that performs some extra functionality. The MP system then informs the server of the downloaded proxy, allowing it in turn to specialize itself with the same type of functionality. Two aspects of adaptability were taken into consideration when developing the system and the functionality extensions it offers. The first is performance, which aims at minimizing the communication overhead using performance-enhancement techniques like compression. The second is security, where the issues of confidentiality, message integrity, and trust of downloaded code were all taken into consideration using digital signatures and encryption (both symmetric and asymmetric).
Author: Aziz, Benjamin
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