The TACOMA Project 

 Dag Johansen
 University of Tromso                            
 Dept. of Computer Science                         
 N-9037 Tromso, NORWAY    

 Robbert van Renesse, Fred B. Schneider 
 Cornell University
 Dept. of Computer Science                  
 Ithaca, NY, USA 
                                             

  The TACOMA (Tromso And COrnell Moving Agents) project focuses on
operating-system support for "agents", programs that traverse the
hosts of a network in accomplishing some task.  We are investigating
efficient implementations of abstractions and services for
agent-computing in a heterogeneous network having malicious hosts.

  Over the last three years, we have built a series of TACOMA system
prototypes [JRS 95], which are publicly accessible (see
http://www.cs.uit.no/DOS/Tacoma/).  TACOMA is in daily use as a
production platform and runs under HP-UX, Solaris, BSD Unix, and
Linux.  In contrast to other agent based approaches, TACOMA supports
agents written in a variety of languages.  Currently, these languages
include C, Java, Perl, Scheme, Python, and Tcl/Tk.  Also, we have
developed schemes in which TACOMA agents can be launched from hosts
that do not implement local TACOMA support but instead just have web
browsers or regular mailers [JRS 96].

  Surprisingly, just a few abstractions are sufficient to implement
our basic computational metaphor: agents, folders (sets of
uninterpreted data elements), and groups of folders (either as
stationary file cabinets or movable briefcases).  Services for
agents -- communication, synchronization, and so on -- are provided
directly by other agents.  For example, an agent moves from one host
to another by meeting with the "tac_firewall" agent on the destination
host.  The TACOMA "tac_firewall" agent logs the incoming briefcase to
disk, performs security checks, and activates the appropriate compiler
or interpreter to run the agent(s) found in the briefcase.

  We have already used TACOMA to implement distributed applications to
gather and visualize Arctic weather data (see
http://www.cs.uit.no/DOS/StormCast/), to provide matching between
service providers and potential clients, to communicate and interact
with users (i.e. active documents), and to manage software
installation in a network.  We find that agents are an attractive way
to describe and implement network-wide computations.

  Currently, we are also investigating host-integrity issues,
including the use of wrappers, whereby the TACOMA run-time system
provides a firewall around an executing agent.  Also, we are studying
methods for replicating agents transparently to implement agent
integrity [MRSS 96].

References

[JRS 95] Johansen, D., R. van Renesse, and F.B. Schneider. Operating
system support for mobile agents. Proc. Fifth Workshop on Hot Topics
in Operating Systems (HOTOS-V), IEEE Press (May 1995), 42-45.

[JRS 96] Johansen, D., R. van Renesse, and F.B. Schneider.  Supporting
Broad Internet Access to TACOMA.  To appear, Proc. Seventh ACM SIGOPS
European Workshop (September 1996).

[MRSS] Minsky, Y., R. van Renesse, F.B. Schneider, and
S.D. Stoller. Cryptographic Support for Fault-Tolerant Computing. To
appear, Proc. Seventh ACM SIGOPS European Workshop (September 1996).