Inter-agent communication in a distributed mobile agent system

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

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

10. Multicast-based approaches • Group communication and coordination • Well-known approaches • IP multicast-based • There is a multicast tree formed by mobilet contexts where agents execute the task. • Application-level multicast-based • 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. agent multicast Context Context Context agent agent agent IP multicast between mobile agents Context

12. agent agent agent agent agent agent agent Application-level multicast between mobile agents

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 Patha(A), is an ordered list of hosts (ha0, ha1,…, han) • The set of hosts on the path is denoted Sa(A) = {hak | hakis on Patha(A)}. • Definition 2 • The migration path of the mailbox of a mobile agent A, denoted Pathm(A), is an ordered list of hosts (hm0, hm1,…, hmn) • The set of hosts on the path is denoted Sm(A) = {hmk | hmkis on Pathm(A)}. • Sm(A) ⊆ Sa(A) and hm0=ha0 • Definition 3 • The function fA: Sa(A) → Sm(A) maps the location of a mobile agent A to that of its mailbox such that for every hak∈ Sa(A)

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

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

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

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 Pathm(A) for each migration. • The migration overhead will increase continuously without an upper bound as Pathm(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 wheneverit sends a message to an outdated address of MA.

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)