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Chapter 4
Communication
Part II
Message-Oriented Communication
CSCE455/855 Distributed Operating Systems
Giving credit where credit is due:

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
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)
2-20
General organization of a communication system in which hosts are connected
through a network
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
A message is stored:
• until delivered
2-22.1 • at A’s host
• at the first comm server
• e.g.: email
Persistent Synchronous Communication
A message is stored:
• until delivered
• at B’s host
• at B’s comm server
2-22.1
Transient Asynchronous Communication
A message is stored:
• at A’s host
2-22.2
• at the first comm server
• If B is not running, message
is 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)
A
B
Source
Queue
Destination
Queue
•
Nearby the sender
•
Nearby the receiver
•
Messages can be put to
this queue only
•
Message contains
information about this
queue
•
How the message travels
between A and B is the
responsibility of the queuing
system
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)
Queuing table entry
Queue Name
Network Address
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)
2-29
• Routing is static
• Medium-level scalability (manually configure the routing tables)
Integrating Differing Message-Based Systems
A-specific message format
System A
Message
Broker
System B
B-specific message format
Message Brokers
2-30
The general organization of a message broker in a message-queuing system.