Communication Part II Message-Oriented Communication Chapter 4.
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Transcript of Communication Part II Message-Oriented Communication Chapter 4.
Communication
Part II
Message-Oriented Communication
Chapter 4
Most of the lecture notes are based on slides by Prof. Jalal Y. Kawash at Univ. of Calgary
I have modified them and added new slides
Giving credit where credit is due:
CSCE455/855 Distributed Operating Systems
RPC and Message Passing
• RPC enhances access transparency by hiding communication
• RPC is inherently synchronous and is not always appropriate
• What if the receiving side is not executing when the request is sent?
• Sometimes, we need to resort to message-passing
Persistence and Synchronicity in Communication (1)
General organization of a communication system in which hosts are connected through a network
2-20
Persistence and Synchronicity in Communication (2)
Persistent communication of letters back in the days of the Pony Express.
Persistence in Communication
• Persistence: A (sent) message is stored by the communication system until it is delivered.
• Transient: A (sent) message is stored by the communication system as long as both the sender and receiver applications are executing
Synchrony in Communication
• Asynchronous: The sender does not block until the message is delivered, blocks until stored in a buffer at the sending host, or the first communication server
• Synchronous: The sender blocks until the message is stored in a buffer at the receiving host, or delivered to the receiver
Persistent Asynchronous Communication
2-22.1
A message is stored: • until delivered
• at A’s host
• at the first comm server
• e.g.: email
Persistent Synchronous Communication
2-22.1
A message is stored: • until delivered
• at B’s host
• at B’s comm server
Transient Asynchronous Communication
2-22.2
A message is stored: • at A’s host
• at the first comm server
• If B is not running, messageis dropped
• e.g.: asynch. RPC, UDP
Transient Synchronous Communication (1)
2-22.2
Weakest: Receipt-based
Transient Synchronous Communication (2)
Moderate: Delivery-based Strongest: Response-based
Appendix
General Architecture of a Message-Queuing System (1)
SourceQueue
DestinationQueue
• Nearby the sender
• Messages can be put to this queue only
• Nearby the receiver
• Message contains information about this queue
• How the message travels between A and B is the responsibility of the queuing system
A B
General Architecture of a Message-Queuing System (2)
• The collection of queues is distributed across multiple machines
• The system must maintain a (possibly distributed) database of queues (queuing tables)
Queue Name Network Address
Queuing table entry
General Architecture of a Message-Queuing System (3)
The relationship between queue-level addressing and network-level addressing.
General Architecture of a Message-Queuing System (4)
• Queues are managed by queue managers
• A queue manager interacts directly with the sending/receiving application
• Some (special) queue managers act like routers or relays
General Architecture of a Message-Queuing System (5)
• Routing is static• Medium-level scalability (manually configure the routing tables)
2-29
Integrating Differing Message-Based Systems
System A System B
A-specific message format
B-specific message format
MessageBroker
Message Brokers
The general organization of a message broker in a message-queuing system.
2-30