Message Queuing Middle Ware

Message Queuing Middleware What is Message Queuing Middleware? Message Oriented Middleware (MOM) is one of three categories of connectivity middleware that provide programto-program communications by message passing. MOM, because it generally supports multiple protocols comprises an infrastructure that will support reliable and scalable highperformance distributed application networks. Most Message Oriented Middleware is implemented with queued message store-and-forward capability, that is Message Queuing Middleware (MQM). The other categories of connectivity middleware are Remote Procedure Calls (RPC) and conversational programming such as Common Programming Interface for Communications (CPI-C). In general, MOM provides a high performance foundation for application interoperability in diverse and complex environments. For a table summarizing communications models used by middleware products, click here. Quick comparison of MQM, RPC, and CPI-C Attribute MQM RPC CPI-C Communications Queued Call/Return Conversational Style Application NonBlocking Non-blocking Interface blocking Need not Must be Must be Partner be available available available Send/Receive Message Flow All Send/Receive Send/Receive/... Last updated

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What is the Middleware? •

Middleware is connectivity software that consists of a set of enabling services that allow multiple processes running on one or more machines to interact across a network.

History •

Middleware first appeared in the late 1980s to represent network connection management software. Until the mid 1990s, it was general recognized, when network

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technology had accomplished sufficient access to it. Remote Procedure Call (RPC) was the first communicationbased middleware, which was first developed by circa 1982 by Birrell and Nelson.

What are the benefits of middleware? •

Simplicity: Putting middleware in the middle can mean each application needs only one interface—to the middleware— instead of a separate interface to each application it needs to talk to.

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Persistence: Middleware can capture data and hold on to it until it has been recorded appropriately by all the applications or databases that need the information. Services: If your data needs to be checked for integrity, printed out, reconciled with data from other applications, merged, split or reformatted, various kinds of middleware can handle those tasks efficiently.

Middleware can take on the following different forms: •

Remote Procedure Call (RPC) system, which enable the logic of an application to be distributed across the

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network. Program logic on remote systems can be executed as simply as calling a local routine. Message-Oriented Middleware (MOM), which is a specific class of middleware that supports the exchange of general-purpose messages in a distributed application environment.

Continue: •

Transaction processing (TP) monitors, which provide tools and an environment for

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developing and deploying distributed applications. Object Request Brokers (ORBs), which enable the objects that comprise an application to be distributed and shared across varied networks.

Remote Procedure Call (RPC) Origin

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Sun Microsystems developed the first widely used RPC protocol as part of their Open Network Computing (ONC) it was develop in the early 1980s. The specification has been handed off to the Internet Engineering Task Force (IETF) as a step toward making ONC RPC an Internet standard.

What is RPC? •

Remote Procedure Call (RPC) is a client/serverRemote Procedure Call (RPC) is a protocol that one program can

use to request a service from a program located in another computer in a network without having to understand network details.

How does it work? The requesting program is a client and the service-providing program is the server. Like a regular or local procedure call, an RPC is a synchronous(from Greek syn-, meaning "with," and chronos, meaning "time") operation requiring the requesting program to be suspended until

the results of the remote procedure are returned.

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However, the use of lightweight processes that share the same address space allows multiple RPCs to be performed concurrently.

Client Server Requesting Program service-providing program router

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When program statements that use RPC are compiled into an executable program, a stub is included in the compiled code that acts as the representative of the remote procedure code.

What is a stub? •

A stub is a small program routine that substitutes for a longer program For example, a program that

uses Remote Procedure Calls (RPC) is compiled with stubs that substitute for the program that provides a requested procedure. •

When the program is run and the procedure call is issued, the stub receives the request and forwards it to a client runtime program in the local computer. The client runtime program has the knowledge of how to address the remote computer and server application and sends the

message across the network that requests the remote procedure.

How it is performed? •

The network needs to be made invisible, so that everything looks just like ordinary procedure calls. All networking should be done by the RPC implementation, such as connecting to the remote machine. On the remote machine this

simple function gets executed:

int remote_time(char *time_buf) { struct tm *time; time_t t; time(&t); time = localtime(&t); strcpy(time_buf, asctime(time)); return 0; } Tools are available for a programmer to use in developing RPC applications over a wide

variety of platforms, including Windows (3.1, NT, 95), Macintosh, 26 variants of UNIX, OS/2, NetWare, and VMS

http://pandonia.canberra.edu. au/OS/l14_1.html Source: Source: http://www.sei.cmu.edu/str/descrip tions/rpc.html

Summary •

RPC is a protocol which allows a program running on one host to cause code to be executed on another host without the programmer needing to explicitly the code . RPC is an easy and popular paradigm for implementing the client-server model. An RPC is initiated by the caller (client) sending request message to a remote system (the server) to execute a certain procedure using arguments supplied. A result message is returned to the caller.

What is MOM? •

Mediator for messages (Broker)

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Asynchronous communcation architecture

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CORBA 3.0 Messaging (MOM) ORB takes functions from MOM (MOB) no standard

Why do you need a Message-oriented Broker (MOB) ? •

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Accessing to remote data and processes through an internet or intranet Building applications involving multiple servers and clients Simultaneous acces to heterogeneous information (RDBMS, ODBMS, Legacy DB) Decoupling of Client and Server

Types of MOM Message Passing (PtP) • • •

direct communication connection oriented synchronous transfer

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asynchronous transfer (callback)

Message Queuing (MQ) •

indirect communication over message queuing • connectionless • asynchronous transfer (polling,callback)

Publish & Subscribe (Pub/Sub) •

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indirect communication over messageoriented Broker connectionless asynchronous transfer (polling,callback)

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MOM products

Disadvantage MOM incompatible with

other Mom implementation Dependent on the MOM vendor for maintenance and future enhancement

Transaction Processing Monitor Transaction Processing Monitor

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Origin of TP Monitors Purpose of TP Monitors What are TP Monitors? What do TP Monitors do? Example of a TP Monitors Features of TP Monitors References

Origin of TP Monitors •

TP monitor technology emerged 25 years ago when Atlantic Power and Light created an online support environment to share concurrently

applications services and information resources with the batch and time sharing operating systems environment.