1. Inter-agent communication in a distributed mobile agent system Ching-Feng Li

2. Outline  Introduction  Different inter-agent communication mechanism  Implementation plan and future works  References

3. Introduction  A mobile agent is able to move autonomously around the network during its execution.  In various situations mobile agents need to communicate with each other.  Remote inter-agent communication is thus a fundamental facility in mobile agent systems.

4. Challenges in design inter-agent communication mechanisms for mobile agent system  Location Transparency  An agent can send messages to other agents without knowing where they reside physically.  Reliability  No matter how frequently the target agent migrates, messages can be routed to it in a bounded number of hops.  Asynchrony  Asynchronous migration and asynchronous execution of mobile agents  Efficiency  Adaptability

5. Different inter-agent communication mechanisms  Home-based approach  Mailbox-based approach  Multicast-based approaches

6. Home-based approach (1/2)  Agent should update the new location to its home context when it migrates.  Messages to the receiver agent is sent to the home context of the receiver agent.  The home context of the receiver agent should forward the messages to the receiver agent.  The sender should know the home context of the receiver agent by some ways.  Caching  Discovery on demand

7. Home-based approach (2/2) Sender ContextHome Context Context Receiver (2’) Push messages (1)Send messages (2”) Pull messages

8. Mailbox-based approach (1/2)  Similar to home-based approach.  Each receiver agent has a registered mailbox  Difference to home-base approach  The location of home context will not change even if the receiver agent migrates to other context.  The location of the mailbox maybe migrate to other context or stay at the current context when the receiver agent migrates.

9. Mailbox-based approach (2/2) Context Sender Context MB Context Receiver (2’) Push messages (1)Send messages (2”) Pull messages

10. Multicast-based approaches  Group communication and coordination  Well-known approaches  IP multicast-based ä There is a multicast tree formed by mobilet contexts where agents execute the task.  Application-level multicast-based ä There is a multicast tree formed by mobile agents in the same group.  The construction and maintenance of the multicast will be an important issue.

11. IP multicast between mobile agents Context agent multicast Context agent Context agent Context agent

12. Application-level multicast between mobile agents agent

13. Comparison of different inter-agent communication mechanisms  Home-based approach  Location Transparency  Asynchrony  Mailbox-based approach  Location Transparency  Asynchrony  Multicast-based approaches  Asynchrony

14. Adaptive and reliable protocol for inter-agent communication (1/4)  Adaptive and reliable protocol (ARP) is applied on mailbox-based communication  Agent is able to move autonomously during its execution.  The advertisement claims the existence or the current location of the receiver agent may provide outdated information.  Adv. claims receiver agent is at the host A, but actually at the host B.  Adv. claims receiver agent is alive, but actually it is dead or offline.

15. Adaptive and reliable protocol for inter-agent communication (2/4)  Definition 1  The migration path of a mobile agent A, denoted Path a (A), is an ordered list of hosts (h a0, h a1, …, h an )  The set of hosts on the path is denoted S a (A) = {h ak | h ak is on Path a (A)}.  Definition 2  The migration path of the mailbox of a mobile agent A, denoted Path m (A), is an ordered list of hosts (h m0, h m1, …, h mn )  The set of hosts on the path is denoted S m (A) = {h mk | h mk is on Path m (A)}.  S m (A) ⊆ S a (A) and h m0 =h a0  Definition 3  The function f A : S a (A) → S m (A) maps the location of a mobile agent A to that of its mailbox such that for every h ak ∈ S a (A)

16. Adaptive and reliable protocol for inter-agent communication (3/4)  In the ARP each host on Path m (A) maintains the current address of the mailbox M A in an address table  Attributes in a entry of the address table ä the ID of M A ä the current address of M A ä a valid tag ä the number of messages mNum that have been forwarded to M A ä a message block queue for M A.  Defines the operations for two processes  Migrating  Message-forwarding

17. Migrating Receiver MB Receiver (1)MVMB (2)DEREGISTER(3)REPLY MB (4)REGISTER

18. Message-forwarding MB Sender Receiver MB (2) forward the message To M A ’s current address (2’) send back a “UPDATE” message to the sender to refresh its cache about M A ’s current location (1)send message

19. Adaptive and reliable protocol for inter-agent communication (4/4)  In the ARP the mailbox MA of an agent A has to first deregister and then register with all the hosts on Path m (A) for each migration.  The migration overhead will increase continuously without an upper bound as Path m (A) becomes longer and longer.  A PATH PRUNING ALGORITHM is designed to reduce the overhead caused by long term agent migration.  The cache maintained by the sender is updated whenever it sends a message to an outdated address of M A.

20. Patterns to design ARP for different applications  Mailbox Migration Frequency  No Migration (NM)  Full Migration (FM)  Jump Migration (JM)  Mailbox-to-Agent Message Delivery  Push (PS)  Pull (PL)  Migration-Delivery Synchronization  SHM/SMA  Synchronizing the Host ’ s message forwarding and the Mailbox ’ s migration  Synchronizing the Mailbox ’ s message forwarding and the Agent ’ s migration  Full Synchronization (FS)  No Synchronization (NS)  A string of the format XX-YY-ZZ expresses a protocol  XX : Mailbox Migration Frequency pattern  YY : Mailbox-to-Agent Message Delivery pattern  ZZ : Migration-Delivery Synchronization pattern

21. Efficiency of communication mechanism  The cost of a protocol is characterized by  The number of messages sent  The size of the messages  The distance traveled by the messages

22. Implementation plan and future works  Different applications, different decisions.  Use mailbox-based approach for inter-agent communication.  How the mailbox migrates and when the mailbox decide to migrate?  Use application-level multicast approach to improve the performance of group communication and coordination.  How to maintain the multicast tree more efficiently

23. References (1/2)  C. Ragusa, A. Liotta, G. Pavlou: "A Scalable Application-level Multicast Approach based on Mobile Agents". Proceedings of IEEE International Conference on Networks (ICON'03), Sydney, Australia, 28th Sept - 1st October 2003.  S. W. Shah, P. Nixon, and R. I. Ferguson: "On the Use of IP Multicast to Facilitate Group Communication between Mobile Agents". IEEE/WIC/ACM International conference on Intelligent Agent Technology. 2004. pp. 487- 490.  Flávio M. Assis Silva, Raimundo J. A. Macêdo. "Reliable Communication for Mobile Agents with Mobile Groups". In the Proceedings of the Workshop on Software Engineering and Mobility (co-located with IEEE/ACM ICSE 2001). Toronto, Ontario, Canada. May 13-14, 2001.  Jorn Hartroth und Markus Hofmann: "Using IP multicast to improve communication in large scale mobile agent systems". In Proceedings of the 31st Hawaiian International Conference on System Sciences (HICSS'31), Kohala Coast, Hawaii, Jan. 6-9, 1998, Januar 1998.

24. References (2/2)  Jiannong Cao, Liang Zhang, Xinyu Feng, Sajal K. Das: "Path Pruning in Mailbox-based Mobile Agent Communications". J. Inf. Sci. Eng. 20(3): 405-424 (2004)  Jiannong Cao, Xinyu Feng, Jian Lu, Henry Chan, Sajal K. Das: "Reliable Message Delivery for Mobile Agents: Push or Pull". ICPADS 2002: 314-320  Jiannong Cao, Xinyu Feng, Jian Lu, Sajal K. Das: "Mailbox-"Based Scheme for Designing Mobile Agent Communication Protocols". IEEE Computer 35(9): 54-60 (2002)