well suresh !
DCOM (Distributed Component Object Model) is a set of Microsoft concepts and program interfaces in which client program object s can request services from server program objects on other computers in a network. DCOM is based on the Component Object Model (COM), which provides a set of interfaces allowing clients and servers to communicate within the same computer (that is running Windows 95 or a later version).

For example, you can create a page for a Web site that contains a script or program that can be processed (before being sent to a requesting user) not on the Web site server but on another, more specialized server in the network. Using DCOM interfaces, the Web server site program (now acting as a client object ) can forward a Remote Procedure Call ( RPC ) to the specialized server object, which provides the necessary processing and returns the result to the Web server site. It passes the result on to the Web page viewer.

DCOM can also work on a network within an enterprise or on other networks besides the public Internet. It uses TCP/IP and Hypertext Transfer Protocol . DCOM comes as part of the Windows operating systems. DCOM is or soon will be available on all major UNIX platforms and on IBM's large server products. DCOM replaces OLE Remote Automation.

DCOM is generally equivalent to the Common Object Request Broker Architecture ( CORBA ) in terms of providing a set of distributed services. DCOM is Microsoft's approach to a network-wide environment for program and data objects. CORBA is sponsored by the rest of the information technology industry under the auspices of the Object Management Group ( OMG ).

Answered by Venkata , an ibibo Specialist, at 5:41 PM on November 10, 2008

hi suresh !Short for Distributed Component Object Model, an extension of the Component Object Model (COM) that allows COM components to communicate across network boundaries. Traditional COM components can only perform interprocess communication across process boundaries on the same machine. DCOM uses the RPC mechanism to transparently send and receive information between COM components (i.e., clients and servers) on the same network. DCOM was first made available in 1995 with the initial release of Windows NT 4.
DCOM serves the same purpose as IBM's DSOM protocol, which is the most popular implementation of CORBA. Unlike CORBA, which runs on many operating systems, DCOM is currently implemented only for Windows.

Answered by LAKSHMI V , an ibibo Master, at 4:09 PM on November 10, 2008

Distributed Component Object Model (DCOM) is a proprietary Microsoft technology for communication among software components distributed across networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the communication substrate under Microsoft's COM+ application server infrastructure. It has been deprecated in favor of Microsoft .NET.

The addition of the "D" to COM was due to extensive use of DCE/RPC – more specifically Microsoft's enhanced version, known as MSRPC.

In terms of the extensions it added to COM, DCOM had to solve the problems of

Marshalling – serializing and deserializing the arguments and return values of method calls "over the wire".
Distributed garbage collection – ensuring that references held by clients of interfaces are released when, for example, the client process crashed, or the network connection was lost.
One of the key factors in solving these problems is the use of DCE/RPC as the underlying RPC mechanism behind DCOM. DCE/RPC has strictly defined rules regarding marshalling and who is responsible for freeing memory.

DCOM was a major competitor to CORBA. Proponents of both of these technologies saw them as one day becoming the model for code and service-reuse over the Internet. However, the difficulties involved in getting either of these technologies to work over Internet firewalls, and on unknown and insecure machines, meant that normal HTTP requests in combination with web browsers won out over both of them. Microsoft, at one point, attempted and failed to head this off by adding an extra http transport to DCE/RPC called ncacn_http (Network Computing Architecture, Connection-based, over HTTP). This was later resurrected to support an Exchange 2003 connection over HTTP.

Answered by Koushik , an ibibo Specialist, at 3:45 PM on November 10, 2008

Well, A simple DCOm example is :
An object is registered in a Voyager namespace. A Visual Basic client is able to look up the object and invoke methods on it.

1. Start the examples.calculator.CalcServer class in one window. This will start a Voyager server at port 8000 and bind a Calculator object into its namespace as MyCalculator. In a second window, run the VBCalcClient program.

2. From examples\calculator, compile the calculator files.

javac ICalculator.java Calculator.java CalcServer.java

3. Run CalcServer in one window as follows.

Window 1

java examples.calculator.CalcServer

4. To build the VBCalcClient application, open the Visual Basic project examples\dcom\VBCalcClient.vbp file in Visual Basic 6.0. Go to the Project menu and select References. In the dialog box that pops up, click on the Browse button. A file selection dialog box will appear. Traverse to the Voyager installation directory and select bin\VoyagerBridge.dll. Close all dialog boxes. Go to the File menu and select Make VBCalcClient.exe.

5. To run the client application, the Microsoft Java Virtual Machine (MSVM) must be present on the client machine. Also, the system CLASSPATH on the client machine must include the Voyager installation directory and the Voyager .jar file.

6. Now run the client application in another window as follows, specifying the name of machine running the CalcServer.

Window 2

VBCalcClient calcServerMachineName

A message box will pop up with the message:

3 + 4 = 7

The same message will also appear in the first window.

Window 1

>java examples.calculator.CalcServer

3 + 4 = 7

The source code for VBCalcClient follows.

Module VBCalcClient.bas

Public Sub Main()

Dim namespace As VoyagerLib.INamespace

Dim adder As Object
Dim x As Long


Dim y As Long

Dim sum As Long


' Create namespace bridge

Set namespace = CreateObject("VoyagerLib.Bridge")


' Lookup calculator object in the server namespace

Set adder = namespace.Lookup("//" & Command & ":8000/MyCalculator")


x = 3

y = 4


' Method invocation

sum = adder.Add(x, y)

MsgBox ("3 + 4 = " & sum)

End Sub

For more details , Please visit the source site :

http://www.ifi.uzh.ch/ddis/sta ff/vorburg/doc/Orb/Voyager-23,14.ht m

Answered by Alok Gupta , an ibibo Guru, at 3:28 PM on November 10, 2008