distributed process implementaion n.
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  2. OBJECTIVE • Logical Model Of Local And Remote Processes • Three application scenarios • Remote Service • Remote Execution • Process Migration • Mobile agent • Process migration vs. mobile agents

  3. Logical Model Of Local And Remote Processes

  4. THREE APPLICATION SCENARIOS • Depending on how request messages are interpreted, • there are three significant application scenarios : • Remote Service • Remote Execution • Process Migration

  5. REMOTE SERVICE • Its primary application : resource sharing in distributed systems. • request message for remote service can be generated at three different software levels. • As remote procedure calls at the language level • As remote commands at the operating system level • As interpretive messages at the application level

  6. Remote Procedure Calls At The Language Level • At language level for remote service requests Most suitable model : RPC It is service oriented and provides both access and location transparency At the operating system level There are some frequently used commands that need to invoke remote objects. These commands can be built in as part of the command shell and recognized by the local operating system

  7. Remote Commands At The Operating System Level Remote commands are limited only to shell commands. The concept can be generalized to process messages. Want to send message Based on the content of message user Remote host invoke Some user-defined operations at remote host Stub process at Server site has capability of -- Interpreting messages sent from client stub -- invoking respective operations Rules  application communication protocol

  8. Interpretive Messages At The Application Level Remote procedure calls remote commands interpretive messages Initiated by Remote operations Constrained to Services that are supported at the remote host Primary implementation issues I/O redirection security copies Client stub server stub Client process’ standard input to the remote command Standard output and error of the remote command to client process Access to remote resources required authorization copies

  9. REMOTE EXECUTION • Remote operation initiated by client is created by the client • message sent from client to server is client program to be executed at the server Means generating process at remote host Selected host System with specific resources for resource sharing System with purpose of load sharing Remote Execution Remote Service Implementation issue Load sharing algorithm location independence system heterogeneity protection and security

  10. Load sharing algorithm Process server Maintaining load information negotiating remote host invoking remote operation creating stub processes for linking client& server Responsible for Remote execution Implicitly – local process server Initiated explicitly – process Parent/child or disjoint Relationship of process

  11. Load sharing algorithm Practical implementation Each process server maintain list of registered hosts First step is to select remote host Client process server Resource requirement to process server at remote site indicate If authenticated and its resource request can be met Server grants permission for remote execution

  12. LOCATION INDEPENDANCE Process created by remote execution Coordination to accomplish common task require So, it is necessary to support logical view for the processes Each remote process is represented by an agent process at the originating host

  13. SYSTEM HETEROGENEITY If remote execution is invoked on heterogeneous host It is necessary to recompile the program Overhead may be too high Solution Use canonical machine-independent intermediate language for program execution.

  14. PROTECTION AND SECURITY Remote execution powerful Foreign code image can be Trojan horse Solution • Accept only remote execution in source or intermediate codes • Language used to describe a remote execution could be restricted to exclude potential problems • Run-time checking of parameters and stack overflow is also necessary to protect the integrity of the remote hosts

  15. Time Source Site Destination Site Process P1 : : : : Execution suspended Freezing time Transfer of control Execution Resumed : : : : Process P1 PROCESS MIGRATION

  16. LINK REDIRECTION Pretransferring Total Freezing Source node Source node Destination node Destination node Migration decision Migration decision Suspended Transfer of address space Transfer of address space Freezing time Suspended Freezing time resumed resumed Merits: easy implementation Demerits: long delay time Merits: freezing time reduce Demerits: total time extended

  17. MESSAGE FORWARDING Three types of messages: 1. received when the process execution is stopped on the source node and has not restarted on the destination node 2. received on the source node after the execution started on destination node 3. sent to the migrant process after it started execution on destination node

  18. Origin Receiver Sender Resend Migrate Dest 1 Resend again Migrate again Dest 2 MESSAGE FORWARDING Resending messages Ask origin site Origin Receiver Sender Send Send Migrate Forward Dest 1 Migrate again Dest 2 messages of type 1 and 2 are either dropped or negatively ack-ed, the sender is notified and it needs to locate the migrant process origin node keeps the info on the current location of the process created there, all messages are sent to origin which forwards them to migrant process

  19. Link Link MESSAGE FORWARDING Link traversal Origin Receiver Sender messages of type 1 are queued and sent to destination node as part of migration procedure Send Forward Send Migrate link is left on source node to redirect messages of type 2 and 3, link contains the system-wide unique id of a process and its last known location Dest 1 Forward Migrate again Dest 2

  20. MESSAGE FORWARDING Link Update Origin during the transfer the source node sends the notification (link update) of the transfer to all the nodes to which the process communicates: Receiver Sender Send New location Migrate messages of type 1 and 2 are forwarded by the source node messages of type 3 are sent directly to the destination node Send Dest 1 New location Send Migrate again Current location Dest 2

  21. MOBILE AGENTS • it is composition of computer software and data which is able to move from one computer to another autonomously and continue its execution on the destination computer. • It refers to a process that can transport its state from one environment to another, with its data intact • Mobile agents can decide when and where to move next • When a mobile agent decides to move, it saves its own state and transports this saved state to next host and resume execution from the saved state. • Common applications include: • Resource availability, discovery, monitoring • Information retrieval • Network management • Dynamic software deployment

  22. Process migration vs. mobile agents

  23. REFERENCES Distributed operating system and algorithms Randy chow, Theodore johnson A Framework for Process Migration in Software DSM Environments ieeexplore.ieee.org/iel5/6662/17807/00823407.pdf …. ( 2000 ) Presentation on Parallel & Distributed Computing courses.washington.edu/css434/slides/Migration.ppt Mobile agent - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Mobile_agent