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Introduction:
The Communicator
The Communicator
is the part of the RETSINA agent architecture that provides
for and handles communication with other agents or entities.
The Communicator has been designed as a self-contained component
that can be configured as part of a RETSINA agent or can be
used as the communication component in other agent systems
or application programs.
The Communicator
provides an abstraction that supports peer-to-peer communication
between agents based on the names of the agents. The communication
is in the form of ASCII messages transmitted on TCP/IP sockets.
The Communicator provides an API specification for establishing
connections to external agents and for several forms of asynchronous
IO for the sending and receiving of messages with options
for blocking or non-blocking IO. There is also a synchronous
interface. Connection setup and management is handled transparently
within the Communicator. The Communicator does the mapping
of agent names to their host and port addresses through our
Agent NameServer (ANS). The ANS provides
for a distributed agent name registration and lookup facility.
(See subsequent section.
The Communicator
does not support any complex message protocols or specific
message formats. It simply transmits messages, leaving message
protocols to the higher level modules in the agent. With respect
to message formats, the Communicator sets forth minimal requirements
by defining an interface that provides the abstraction it
needs to handle messages that come in from external agents
and a separate interface for the messages that the agent,
in which the Communicator is incorporated, wishes to send
out. These interfaces, ExternalMsg and InternalMsg respectively,
define a small number of basic message fields deemed essential
for inter-agent communication along with accessor methods
for extracting and setting message fields.
We define two different
interfaces since the Communicator has slightly different needs
at each end of communication management and also for greater
flexibility and portability of agents into different agent
communities. For example an agent developed in a community
that uses KQML-based communication can be easily ported to
a FIPA-based community by supplying a new module that implements
the ExternalMsg interface to support FIPA formats. The Communicator
deals with messages using only the abstractions of InternalMsg
and ExternalMsg and thus is divorced from particular formats.
The original implementation
of the Communicator is in Java. Besides our RETSINA agents,
we have incorporated it into two other agent interface applications
and a server. We have implementations of InternalMsg and ExternalMsg
for KQML formats. This also explains why our set of basic
message fields-performative, sender, receiver, content, reply-with,
in-reply-to-have names suggestive of KQML. The performative
field is not tied to any KQML semantics, rather the suggestion
from KQML that messages have a category seems a good one.
The replywith and in- reply-to fields more directly borrow
from KQML as a means to tie a series of message exchanges
into a single thread of conversation. The Communicator can
make use of this to provide some specialized forms of message
routing that the agent can engage. The Communicator also supports
multiple open connections between two agents which, on the
other hand, somewhat diminishes the need for the replywith/inreply
threading.
The Communicator
also provides an interface for performing logging of message
traffic to abstract message-logging facilities. The logging
facility could be a file or another agent that might graphically
display the agent communication activity in the agent community
or simply serve as a debugging tool. We may extend the logging
facility to permit arbitrary logging of agent activity beyond
just communicative activity. We also have plans to develop
an abstraction of the use of the ANS so that some other agent
name service facility could be substituted if desired. For
some agents, such as pure servers, a name service would not
strictly be necessary. We have also developed a C/C++ implementation
of the Communicator.
Start here: Download the Guide to Java Libraries for RETSINA
Agent Communications:
- in
.PDF
- in
Postscript
- In
Html
Communicator FAQ
Java
Libraries for RETSINA Agent Communications: Download Page
: See
instructions for access, below:
Instructions
for access to Communications Library:
To receive access to the Java Libraries for RETSINA Agent
Communications (Communicator), please print the
CMU License Agreement:
- Read
carefully and if you agree to the terms, complete the bottom
portion of the Agreement. Include your name, institutional
affiliation and address, a url for the website that describes
your group's or your own research activities, your email
address, and, if you are a student, the name, position,
url and email address of your advisor. Please
sign and date the agreement.
- Send
the completed agreement to us by mail at:
Katia Sycara
The Robotics Institute
5000 Forbes Avenue
PIttsburgh, PA 15213
- We
will send qualified users a user name and password via email,
so that you can access the executable by downloading Communicator
Library v1.4.1_Apr2003 (Jar) from the downloads page, here.
- If
you have any questions regarding access, use, or programming,
send email to the following:
retsina-request at cs dot cmu dot edu. Please
first see the Communicator FAQ (forthcoming).
Communicator
Internal Site (Restricted Access).
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