rpc and middle ware

RPC and Middleware

By: Mostafa Hassan KhameesOmar Shaaban Ibrahim

Douglas e. comer, computer networks and internets, chapter 38 , RPC and Middleware

outline

Introduction RPC RPC paradigm Communication stubs External data representation Middleware and Object-Oriented

Middleware Common middleware and object-oriented

middleware technologies. Questions.


RPC

RPC is an acronym to Remote Procedure Call. RPC is one of the earliest facilities that help

programmer to write Client-Server software.


The Idea of RPC

Instead of the programmer deal with communication primitives such as socket interface* it hide communication from programmer by using conventional programming language facility.

Programming mechanism is Procedure Call.

*Socket interface such as TCP and UDP interface.


RPC Mechanism

RPC mechanism allow programmer to place procedures in two or more machines and automatically generates code that will allow procedure call to pass from one computer to another.

The structure of conventional program.

Consider the structure of a conventional program.

This graphical representation known as procedure call graph

MainProgram

ProcC

ProcB

Proc A

ProcD

ProcE

ProcF

MainProgram

ProcC

ProcB

MainProgram

ProcC

Proc A

ProcB

MainProgram

ProcC

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

ProcF

ProcE

ProcD

Proc A

ProcB

MainProgram

ProcC

When defining a procedures each procedure is parameterized (take a formal parameters)

Example (C language) int sum(int a , int b)

{ return a+b;}This procedure (sum) take two integer parameters an return

the summation of these inputs


Because parameterized procedure have worked well as a programming abstraction, researcher examined ways to use a procedure abstraction to build client and server.

The premise of the research is: If programmer follow the same procedure call paradigm used to build a conventional programs when building client and server software, the programmer will find the task easier and will make fewer mistakes.


To follow the premise: Researchers have investigate ways to

make client server programming as much like conventional programming as possible.

Most researches have focused on extending existing language.


The idea is to devise a tool that accept a high level program specification, create a code to handle the network communication details and automatically build a client and server programs.


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RPC paradigm

When using RPC: Programmer doesn’t focus on the computer

network or communication protocols. Programmer will be interested in the problem

being solved. The programmer will imagine how the problem

will be solved by a conventional program running on a single computer.

The programmer design and build the program, using the procedure call as basic architectural feature.


After the program has been finished, programmer consider how to divide the program into two pieces.

Programmer must divide the call graph into two parts:

Part contain main program and some procedures it calls, becomes the client.

The remaining procedure become the server.


The programmer must consider the global data that each procedure references.

It must be located on the same computer as the procedure.


ProcF

ProcE

ProcD

Proc A Proc

B

MainProgram

ProcC

Client

Server

Other division of the call graph are possible.

We can not tell from the figure why the programmer made this particular choice.

Example: Procedure A and D may be in the client

because they handle interaction with user or reference global variable.


Instead of procedure call occur on one machine RPC extends call mechanism to allow a procedure in the client to call a remote procedure across the network in the server.


How to call procedure located on the server?

When a procedure call in the client side occurs:

A thread of control appears to pass across the network from the client to server.

When procedure returns: A thread of control appears to pass

back from the server to the client.


RPC tool

Programmer creates a specification that describe the set of procedure that will be remote.

Example:Programmer must specify types it’s

parameters.RPC tool creates software that handle

necessary communications.


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Communication Stubs

It’s uses client server interactions. Uses conventional protocols to send a

request message from client to server. The request identifies the procedure to

invoke. Extra software must be added to each

part of the program to impalement the interaction.


Extra software in the client side

Handles the details of a sending message across the network and waiting for response.


Extra software in the server side

Handles the details of receiving message, specified the calling procedure, and sending a response back to the client.

Each piece of added software is called communication stub or proxy.

The two stubs handle all communication details.

In addition the stubs are constructed to fit local procedure.


How does stubs work?

If a call is made to a procedure in the server side:

Client stub intercept the procedure call. Gathers the values for the arguments

(argument marshalling). Send the message across the network

to the communication stub in the server.


The server stub invoke the specified procedure and send the result back to the client stub.

The client stub receives a responses, it return the result to it’s caller.


Main program

Proc B


RPC vs Conventional program structure

Main program

Client stub for B

Server stub for B

Proc B

Client side Server side


Because the communication stubs interested between two procedures to implement remote procedure call can use exactly the same name and interface as the original procedure call, neither the calling procedure nor the called procedure needed to be changed.


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External data representation

Computers do not all use the same internal data representations:

thus when the client or server send data between heterogeneous computers, they must agree on how to represent these data.

How ?1. Negotiate a representation2. Use a fixed representation and for each the client and server convert

from the local representation to the fixed one. Douglas e. comer, computer networks and internets, chapter 38 , RPC and Middleware

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Middleware and Object-Oriented Middleware

Middleware: a tool can help a programmer build a program that uses RPC, it is called middleware because it provide software that fits “between” a conventional program and a network software.

How to do so?1. The programmer specifies the set of procedures that will be remote.2. Specifies the procedures interface details(i.e. number and type of

arguments) using the tool’s Interface Definition Language (IDL).3. The tool(middleware) reads the IDL specifications and generates the

necessary client and server stubs.4. The programmer then compiles and links two separate programs:

The server program [server stubs + remote procedures] The client program [client stubs + main program + local procedures]


In the 1990s programming language research shifted focus from procedure paradigm to object-oriented paradigm, as a result most new programming language are object-oriented languages [OOP].

The basic structure facility in OOP is (object) which consist of data items plus a set of operation for those items called (methods).

As a result the designers are creating new middleware systems known as distributed object system that mainly depend on OOP.


Middleware and Object-Oriented Middleware

outline





Common middleware and object-oriented middleware technologies

Middleware

1. ONC RPC2. DCE /RPC3. MSRPC

Object-Oriented Middleware

1. CORBA2. MSRPC2 (ORPC)3. COM / DCOM4. Java RMI5. Jini6. SOAP7. UDDI8. XML


Middleware technologies

1- ONC RPC Open Network Computing RPC One of the first RPC mechanisms

developed by Sun Microsystems. Besides Interface Definition Language (IDL) and massage

format, it also defines a representation standards known as eXternal Data Representation (XDR).

It uses TCP/IP protocols, and allows a programmer to choose UDP or TCP transport.

2- DEC /RPC Distributed Computing Environment developed by the Open

Software Foundation, which is composed of multiple components and tools that are designed to work together.

Permits a client to access more than one server. It uses TCP/IP protocols, and allows a programmer to choose

UDP or TCP transport.Douglas e. comer, computer networks and internets, chapter 38 , RPC and Middleware

Middleware technologies cont.

3- MSRPC Microsoft RPC developed by Microsoft Corp., it was derived

from DEC/RPC and hence it shares the same central concepts, the different is that MSRPC defines its own Interface Definition Language (IDL) and its own protocols .


Object-Oriented Middleware technologies

1- CORBA Common Object Request Broker Architecture, the best

known object-oriented middleware tech., Developed by Object Management Group (OMG) .

The main advantage of CORBA its dynamic in terms of creating stubs at runtime, in contrary conventional RPC tech., creates stubs during program construction(i.e. at compile time).


2- MSRPC2 (ORPC) Object RPC, the second generation of MSRPC, extend the

ordinary MSRPC to support object-oriented concept.

3- COM/DCOM1. Component Object Model developed by Microsoft corp.,

the main advantage of implementing objects that can be used in environments different from the one in which they were created, this is done by forcing component implementers to provide well-defined interfaces that are separate from the implementation.

2. Distributed COM, extend COM to include DCE/RPC features.

Object-Oriented Middleware technologies cont.


4- Java RMI Java Remote Procedure Invocation, developed by Sun

Microsystems.

5- Jini Developed also by Sun Microsystems, Jini is designed to permit a

client on one computer to use a service on another computer, more important, Jini allows a program to move from one computer to another.



6- XML Extensible Markup Language, set of rules for encoding documents

specified by World Wide Web Consortium (W3C), and that is used by RPC mechanisms.

7- SOAP Simple Object Access Protocol, lightweight protocol that relies

on Extensible Markup Language (XML) for its message format. proposed to the WWW by a set of designers from Microsoft and

IBM.




8- UDDI Universal Discovery Description and Integration, is a

registry mechanism for web services that allows clients to locate servers in the internet.

Server registers information about the service it offers, and clients search the registry to locate a service on it.

it is not RPC mechanism but it can be used with it.


outline





Questions

Q1: What is the main advantage of CORBA ?

1. creating stubs at runtime likewise other technologies that create stubs at compile time.

Q2: define communication stubs?1.Extra software added to the client and the server sides to

handle message sending and receiving between the two parties.


Thank You


rpc and middle ware

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