Load Balancing using Mobile Agent Approach Prepared by: Wong Tsz Yeung,Ah Mole Supervisor : Prof. Michael Lyu 18 December 2000

Introduction (1)  Autonomous Agents  2 kinds of research going on :  Multi-Agent System; and  Mobile Agent  How do they different??  What are the advantages and disadvantages of using them??

Introduction (2)  Parallel Computing  Load Balancing  In the past - Super Computer with multi- processor  Nowadays - Cluster of Single of multi-processor machines  Can we build a system that combine the advantages of agent and load balancing??

Multi-Agent System (MAS) (1)  The goal of MAS :  Creating a system that interconnects separately developed agents, thus enabling the ensemble to function beyond the capabilities of any singular agent in the system.  Implication: Specialization on agents.

Multi-Agent System (MAS) (2)  Every Agent is specialized to perform particular task.  To perform a task, an agent that is on behalf of the user need to communicate with one or more agents in order to complete a task.

Multi-Agent System (MAS) (3)  All the agents in a MAS can be provided by one by more venders given that:  Agents are using the same language in communication.  Agents are having the same kind of knowledge.

Multi-Agent System (MAS) (4)  For Example:  A business from US wants to arrange a trip from New York to Hong Kong.  He has to plan:  Which airline will he take??  Which hotel will he stay??

Multi-Agent System (MAS) (5)  Fortunately, the business man has a personal agent.  i.e. his secretary  Then, the secretary phones the airline companies and hotels for information.

Multi-Agent System (MAS) (6)  She can make a final decision based on the criteria given by her boss.  E.g.  Choose the cheapest airline.  Choose the most comfortable hotel.  The above case shows how human agents work.

Multi-Agent System (MAS) (7)  We can treat the above case as: Agent user Airline Agent 1 Airline Agent 2 Hotel Agent 1 Hotel Agent 2

Multi-Agent System (MAS) (8)  Advantages  Technically speaking  It is autonomous in the sense that the agent can find a service provider, query for suitable information and determine the final result.  Every service provider has its own implementation. However, it is transparent to the user agent.

Multi-Agent System (MAS) (9)  Economically speaking  Every agent is specialized, so it can sell the service. User can buy the service which meets he/she criteria.

Challenges in MAS (1)  Information Discovery Problem  Human Agent : Go to Yahoo! to search for the related information.  How can software agent locate other agents??

Challenges in MAS (2) Service-seeking agent Discovery server Lookup server service provider Searching for service provider. Return a list of name of service provider. Lookup the address of a service provider. Successfully locate a service provider.

Challenges in MAS (3)  The Discover server provides yellow page service.  The Lookup server provides white page service.  Jini also has such discovery-and-lookup mechanism.

Challenges in MAS (4)  Communication Problem  It is the communication language problem.  E.g. On the Internet, we have HTML which is widely used.  An agent-to-agent language is more preferable.  KQML - Knowledge Query Markup Language.  ACL - Agent Communication Language from FIPA.

Challenges in MAS (5)  Ontology Problem  It is problem dealing with the context of the communication language.  E.g. Bus has a meaning in the transportation field while it is different in computer field.  The agents involved in a MAS must agree on and share a common definition of concepts.

Challenges in MAS (6)  This problem hinders the development of agent interoperability.  Systems tend to use their own knowledge database.  we cannot plug another agent into the current existing MAS, unless we are using the same knowledge base.

Mobile Agent (MA) (1)  The goal of Mobile Agent  You delegate tasks to an agent. The agent will do the tasks for you.  Instead of passing message among agents, mobile agent can migrate across the network (hence mobile) representing users in various tasks (hence agents).

Mobile Agent (MA) (2)  Potential application domains of MA  Data-intensive application.  Disconnected computing.  However, the sad fact is  there is no application that would not exist without mobile agents.  Every mobile agent application will have its client-server counterpart such as RPC or sockets.

Mobile Agent (MA) (3)  The difference between MA and MAS  They have similar properties.  Mobile agent can migrate itself to other hosts.

Load Balancing (1)  Imagine that you are inside a factory :  Our Goal : to minimize the total length of time needed to process a fixed set of tasks. Machine B Machine C Machine A ? ? ?

Load Balancing (2)  Our approach is a greedy approach.  Whenever a new job comes in the system, we search for the machine that has the minimum load.  We assign the new job to the minimum- load machine.

Description of the System (1)  Suppose we are given:  n identical processing units, namely Pi where 1 <= i <= n  A set of tasks: T = {T1, T2, …, Tm}  A partial-order < on T and a function where is mapping that maps T to real number >= 0

Description of the System (2)  Once a processor Pi begins a task Tj, It works without interruption on Tj until completion  The time that is taken : (Tj).  If Ti < Tj, Tj cannot be started until Ti is completed.

Description of the System (3)  Pi executes the task Tj in the following way:  We are given a linear ordering  L is called a task list.  In any time t, a Pi completes a task, it immediately scans the list L. L : (Tk1, …, Tkm)

Description of the System (4)  Pi scans from the beginning of L until it comes to the first task Tj which has not yet begun to be executed.  If Ti < Tj and Ti has been finished, Pi begins to executes Tj.  Otherwise, Pi proceeds to the next task in L which has not begun executing.

Description of the System (5)  If Pi proceeds through the entire list L without finding a task to execute, then Pi becomes idle.  Idle means Pi is executing an empty task.  Pi remains idle until some other Pj completes a task.

Description of the System (6)  At that time, Pi immediately scans the list L as before for possible tasks to execute.  If Pi and Pj, i < j, simultaneously attempt to begin the same task Tk, the processor with the smaller index will execute Tk, i.e. Pi.

Description of the System (7)  The processors all start scanning L at time t = 0 and proceed in the above- mentioned fashion until some time w.  Our aim is to minimize w.

Description of the System (8)  E.g. 1.  n = 3  L : (T3, T1, T2, T4, T6, T5, T7, T8)  Partial relation : T1/4T2/3 T4/5 T6/2T7/2 T3/1T5/3 T8/3

Description of the System (9)  E.g 1 (continued) P1 P2 P3 T1/4T2/3 T4/5 T6/2T7/2 T3/1T5/3 T8/ L : (T3, T1, T2, T4, T6, T5, T7, T8) 2 T1 T4 T6T7 3 T2 T3 1 T8 3 T5 3 E1 2 E2 2

Description of the System (13)  E.g. 3

Description of the System (14)  From the above observations, we can conclude that w is a function of :  Task list L  Partial order <  Time function  Number of processors n

Description of the System (14)  It seems that we can improve w by:  Change the task list L  Decrease the function  Relax the partial-order <  Change the number of processors from n to n'

Description of the System (15)  However, there are counter-examples show that is not always the case!!  The bound is:

Description of the System (16)  Back to our greedy approach  We know that no matter how bad our design is, there is still a bound that governs the maximum time needed.  It can be proved that the bound for such a system is:

Load Balancing using Mobile Agent Approach (1)  Currently, load balancing decision is centralized.  There is a switch which gathers load information of all servers.  Then, it decides which machine should be chosen to assign an incoming task.  The switch may collect loading status from all machines periodically, say every 1 second.

Load Balancing using Mobile Agent Approach (2)  Our approach for load-balancing decision is a decentralized one.  The computations of load balancing decision making are not performed on the switch, but on the back-end servers.

Load Balancing using Mobile Agent Approach (3)  When a customer arrives, it will encapsulate the customer's request into an mobile agent  The agent will go to find a server that has the minimum load autonomously.

Load Balancing using Mobile Agent Approach (4)  Multiple-Hop Mobile Agent Approach switch server

Load Balancing using Mobile Agent Approach (5)  Advantage  We distribute the load of the switch to the server, this can increase the efficiency of the switch in creating agents.  We can have a platform-independent load balancing scheme since the dispatched agent can run on the different machines given that a unique agent execution environment is provided.

Load Balancing using Mobile Agent Approach (5)  Disadvantage  our scheme will be a failure if the number of servers is too large.  As we have to travel all server once, the load information will be out-of-date or incorrect at the time when decision is made.  If the number of servers is small and the agents are migrating fast enough, this will be a very efficient scheme.

Load Balancing using Mobile Agent Approach (6)  Multi-Multi-Hop Mobile Agent Approach  Since the efficiency of the multi-hop approach is restricted by the number of servers, we are now sending multiple agents in this new scheme.  After all the agents finished calculating the sub-minimal, they will gather together to calculate global minimum load.

Load Balancing using Mobile Agent Approach (7)  Advantage  By using mobile agent, we can calculate the load status with respect to the nature of the service.  For example, if the task is a memory intensive process, we have no reason to treat the CPU load as the load information.  Therefore, we can plug a suitable instruction to the mobile agent in order to calculate the load status.

Load Balancing using Mobile Agent Approach (8)  Disadvantage  The mobile agent approach introduces undesirable load to servers as the agents calculate the load information before the execution by incoming tasks.  Mobile agent is typically written by script language or Java. They are much slower than currently adopted approaches.

Conclusion (1)  Two kinds of agents are examined: Multi-agent system and Mobile agent.  Their advantages as well as disadvantages are discussed.  Load Balancing is an old research topic, however, many domains are adopting this issues such as clusters of computers.

Conclusion (2)  The possibilities of combining mobile agent and load balancing are illustrated.  This shows that with the autonomous characteristics of agents, we can improve the current load balancing decision schemes.

Future Works  Continue to investigate more about agent.  Continue to think of the possibilities of combining mobile agent and load balancing techniques.

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