Distributed Systems: Communications Cont' Processes

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Distributed SystemsCommunications
(Cont.)Processes

• CS 654Lecture 7October 4, 2006

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Message-Oriented Communication
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Message-Oriented Communication

• RPC/RMI are also known as request/response.
• If we assume that there are no responses, we move
  into message-oriented communication.
• MOC is typically more decoupled than RPC/RMI.

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Persistence and Synchronicity in Communication (1)

• General organization of a communication system in
  which hosts are connected through a network

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Persistence and Synchronicity in Communication (2)

• Persistent communication of letters back in the
  days of the Pony Express.
• Also known as store-and-forward.

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Persistence and Synchronicity

• With transient communication, discard the message
  if next hop is down. Persistent communication
  will store.
• How long should it store the message?
• There is also a spectrum between transient and
  persistent.
• Do we wait for the receiver to actually receive
  the message?
• Messages can be synchronous

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Persistence and Synchronicity in Communication (3)
What kinds are these?

• Persistent asynchronous communication
• Persistent synchronous communication

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Persistence and Synchronicity in Communication (4)
2-22.2

• Transient asynchronous communication
• Receipt-based transient synchronous communication

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Persistence and Synchronicity in Communication (5)

• Delivery-based transient synchronous
  communication at message delivery
• Response-based transient synchronous communication

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Examples

• UDP
• IBM MQ series
• Jabber/XMPP
• WS-Notification
• JMS
• JINI

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Berkeley Sockets

• Most popular API for TCP/IP.
• Can be used for more, though not not as common.
• A socket is an endpoint.

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Berkeley Sockets (1)

• Socket primitives for TCP/IP.

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Berkeley Sockets (2)

• Connection-oriented communication pattern using
  sockets.

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Message Passing Interface (MPI)

• Sockets are too low level for scientific
  computing.
• No data types.
• No broadcast.
• No collective operations.
• No message abstraction.
• MPI was written to address that.
• MPI job starts as a group of processes.
• mpirun prog_name host_list
• Each process has an integer rank, which serves
  as the address of that process. Nothing like an
  IP address.
• MPI has specialized implementations over
  specialized hardware.
• Infiniband
• Myrinet
• Quadrics
• FibreChannel

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The Message-Passing Interface (MPI)

• Some of the most intuitive message-passing
  primitives of MPI.

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Message-Queuing

• MPI and sockets are both transient models.
• Often it is useful to have persistence, to handle
  servers being down, network interruptions, etc.

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Message-Queuing Model (1)
2-26

• Four combinations for loosely-coupled
  communications using queues.

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Message-Queuing Model (2)

• Basic interface to a queue in a message-queuing
  system.

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General Architecture of a Message-Queuing System
(1)

• The relationship between queue-level
  addressing and network-level addressing.

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General Architecture of a Message-Queuing System
(2)

• The general organization of a message-queuing
  system with routers.

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Message Brokers
2-30

• The general organization of a message broker in a
  message-queuing
• system.

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Example IBM MQSeries

• Queues managed by queue managers.
• Managers connected by channels.
• Queues managed by message channel agent.

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Channels

• Some attributes associated with message channel
  agents.

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Addressing

• Addresses are a combination of queue manager
  name, and destination queue.
• Routing can be done using routing tables.
• Local aliases can provide a degree of
  indirection, to avoid too much dependency on a
  transport-level name.

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Message Transfer (1)

• Sending from QMA to LA1.

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Message Transfer (2)

• Primitives available in an IBM MQSeries MQI

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Publish-Subscribe

• In MOM, how do the sender and receiver hook up?