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Distributed sytemt - Coggle Diagram

- - - - value
        
        certain value
        
        rate
      - pattern
        
        Text, audio, video
        
        Mobility
        
        Random walk model
    - - Text - small, one after other
      - Audio - small, burst
      - Video - Huge, virus
- - - - Client / source
      - Servers/sink
      - Have different communication protocol
    - - Communication
        
        Speed of commiunication
      - Cost
        
        delay
        
        memory
        
        power consumption
      - Security
- - - - Due to absence of shared memory, communication based on low level messages (eg. signals)
      - When communication, first builds message in own address space.
      - Send message need system call for operating system, two process need to agree on sending.
      - Agreements varying from the low-level details of bit transmission to high-level details
  - - - Allow program to call procedures located on other machines
      - When A call B. the calling process on A is suspended, execution of the called procedure take place on B
      - No message passing at all is visible to programmer
      - Things need to consider
        
        Memory spaces: data structure
        
        Computing resources
      - Goal: Appear to the programmer that normal call is taking place.
      - Implementing RPC
        
        No architectural support for remote procedure calls
        
        Simulation make RPC a language-level construct
      - Problems:
        
        Calling and called procedures run on different machines, cause complications
        
        Parameters and results passed can be complicated
        
        Machines can crash and each of the possible failures causes different problems.
      - Asynchronous RPC
        
        Client immediately continues after issuing the RPC request, because strict request-reply behaviour is unnecessary when there no result to return.
        
        Userful when reply will be return but client is not prepared to wait for it and do nothing
        
        One-way RPCs: client continues executing immediately after sending the request to the server and doesn't wait for an acknowledgement from server Eg. DCE RPC
      - Disadvantage
        
        Supports a limited set of simple data types
        
        Requires programmer to learn a special interface definition language (IDL) to describe the functions
    - - Allow Java objects running on the same or separate computers to communicate with one another via remote method calls.
      - Doesn't require programmer to learn an IDL because all the networking code is generated directly from existing classes
    - - Offer intermediate-term storage capacity for messages, without requiring either the sender or receiver to be active during message transmission.
      - To support message transfers are allowed to take minutes instead of seconds or milliseconds
      - Message-Queuing Model