France Telecom - CNET

CNET is involved in the design of many algorithms to be used in a distributed environment. During 1997, CNET participated to two meetings (Bologna and Amsterdam) and two experiments related to CONFER-2 have been made.

The first one consists of adapting a theorem prover (Coq) for specifying and proving safety and liveness properties of protocols and distributed algorithms in a modular way. This works implements results obtained in 1996 by P. Crégut and B. Heyd on the theory of Unity. In order to apply Coq-Unity to real-world protocol, a translation from SDL is used. This method is currently applied on an ATM protocol.

Our second experiment is with join-calculus language (P. Brisset). The release of an implementation of the join-calculus by INRIA in 1997 allowed us to begin evaluating its usefulness for real-world applications.

We took advantage of the features of the join-calculus to design a very primitive distributed search engine that indexes text files residing on a network of workstations. Each workstation runs an autonomous agent which first builds an indexed database of the local files, then answers keyword-based queries while continuously updating the database. The only central element is a name-server whose function is mainly to transmit queries and answers between these agents and client processes.

Compared to popular WWW search engines like AltaVista, which fetch files from servers through the Internet and process them in a high-performance, centralized database server, this distributed architecture yields lower network usage (assuming low query rates) and allows the database to be kept consistent with the original files at a much lower cost.

Future work on this application might include:

• designing a generic mechanism that would allow agents to be upgraded without interrupting the system;
• testing a hybrid architecture in which local databases are transmitted incrementally to a central server; this would allow high query rates while still yielding good consistency with low usage of network resources;
• implementation of fault-tolerance, which is expected to be easy with upcoming releases of the join-calculus.