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
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
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
IP multicast between mobile agents
Context
12
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 hak is 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 hmk is on Pathm(A).
• Sm (A) ? Sa(A) and hm0ha0
• 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 MA in 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 MAs current location

1. send message

Receiver
Receiver
MB
MB
(2) forward the message To MAs 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
  whenever it 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 Hosts message forwarding and
  the Mailboxs migration
• Synchronizing the Mailboxs message forwarding
  and the Agents 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)