1. 1 Prof. Leonardo Mostarda University of Camerino Distributed Systems – Remote Procedure Calls Prof. Leonardo Mostarda-- Camerino,

2. Last lecture zOSI model zMiddleware definition zTypes of Communication zRemote Procedure Calls

3. Outline zBerkeley Sockets zMessage-Passing Interface zMessage-queuing systems zMessage brokers  IBM ’ s WebSphere Message-Queuing System

4. Learning outcomes  Understand Berkeley Sockets  Understand Message-Passing Interface  Understand Message-queuing systems zUnderstand the use of brokers

5. Message oriented comm zRPC and RMI provide communication transparency but sever and client need to run at the same time zRPC blocks until the request is performed which may be not adequate zAlternative communication services are needed zWe study message oriented systems ySocket yMessage-queuing systems Prof. Leonardo Mostarda-- Camerino, 5

6. message-oriented model zMany distributed systems and applications are built directly on top of the simple message-oriented model offered by the transport layer. ytransport-level sockets. zInterfaces at the transport layer need to be standardised zStandard interfaces make it easier to port an application to a different machine yBerkeley UNIX sockets yXTI interface

7. Berkeley Sockets za socket is a communication end point where an application can send/receive data zA socket abstracts the actual communication end point that is used by the local OS for a specific transport protocol. zThe table below describes the TCP/IP socket first 4 primitevs executed by the server client

8. The Message-Passing Interface (1) zConnection-oriented communication pattern using sockets.

9. The Message-Passing Interface (2) zSockets are not suitable the high-speed interconnection networks used in server clusters zMPI is designed for parallel applications and as such is tailored to transient communication. zA (group/D, process/D) pair uniquely identifies the source or destination of a message

10. Message-Oriented Persistent Communication zMessage-queuing systems provide extensive support for persistent asynchronous communication zThe middleware provides storage capacity for messages, without requiring sender/receiver to be active during message transmission. zAn important difference with Berkeley sockets and MPI is that message-queuing systems are typically targeted to support message transfers that are allowed to take minutes instead of seconds or milliseconds.

11. Message-Queuing Model (1) zFour combinations for loosely-coupled communications (in time) using queues.

12. Message-Queuing Model (2) zBasic primitives

13. General Architecture of a Message-Queuing System (1) zIt is important to realise that the collection of queues is distributed across multiple machines. zThe queuing system provides a mapping of queues to network locations. (email example) zFigure below shows the relationship between queue-level addressing and network-level addressing.

14. General Architecture of a Message-Queuing System (2) zThe general organization of a message-queuing system with routers. zThere is no general naming service available zWhen A sends a msg to B the msg is sent to the first router R1. zIn this way, only the routers need to be updated when queues are added or removed.

15. Message Brokers zAn important application area of message-queuing systems is integrating existing and new applications; zThere is the problem of different format of data; zSpecial nodes, known as message brokers handle the conversion; zA message broker converts incoming messages so that they can be understood by the destination application; zA message broker is not considered to be an integral part of the queuing system (It is just an application); zFor instance a broker can handle the conversion between two different database applications zIn publish/subscribe systems brokers deliver messages to subscribers.

16. Message Brokers zThe general organization of a message broker in a message-queuing system.

17. IBM ’ s WebSphere Message-Queuing System  General organization of IBM ’ s message-queuing system.

18. Summary zBerkeley Sockets zMessage-Passing Interface zMessage-queuing systems zMessage brokers  IBM ’ s WebSphere Message-Queuing System