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{{Short description|Software for communication between software components}}
{{Redirect|Dcom|the doctoral degree|Doctor of Commerce|other uses|DCOM (disambiguation)}}
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{{Redirect|Dcom|the doctoral degree|Doctor of Commerce|other uses|DCOM (disambiguation)}}'''Distributed Component Object Model''' ('''DCOM''') is a [[proprietary software|proprietary]] [[Microsoft]] technology for communication between [[software componentry|software components]] on networked [[computer]]s. DCOM, which originally was called "Network [[Object Linking and Embedding|OLE]]", extends Microsoft's [[Component Object Model|COM]], and provides the communication substrate under Microsoft's [[Component Object Model#COM+|COM+]] application server infrastructure.
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{{Citation style|date=October 2011|details=Violates Wikipedia:External links: "Wikipedia articles may include links to web pages outside Wikipedia (external links), but they should not normally be used in the body of an article."}}
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The extension COM into Distributed COM was due to extensive use of [[DCE/RPC]] (Distributed Computing Environment/Remote Procedure Calls) – more specifically Microsoft's enhanced version, known as [[MSRPC]]. <ref>{{Cite web |title=What is Distributed Component Object Model (DCOM)? |url=https://www.techtarget.com/whatis/definition/DCOM-Distributed-Component-Object-Model |access-date=2022-08-03 |website=WhatIs.com |language=en}}</ref>
⚫
'''Distributed Component Object Model''' ('''DCOM''') is a [[proprietary software|proprietary]] [[Microsoft]] technology for communication between [[software componentry|software components]] on networked [[computer]]s. DCOM, which originally was called "Network [[Object Linking and Embedding|OLE]]", extends [[Microsoft]]'s [[Component Object Model|COM]], and provides the communication substrate under [[Microsoft]]'s [[Component Object Model#COM+|COM+]] application server infrastructure.


⚫
In terms of the extensions it added to COM, DCOM had to solve the problems of:
⚫
The addition of the "D" to COM was due to extensive use of [[DCE/RPC]] (Distributed Computing Environment/Remote Procedure Calls) – 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 (computer science)|Marshalling]] – serializing and deserializing the arguments and return values of method calls "over the wire".
*[[Marshalling (computer science)|Marshalling]] – serializing and deserializing the arguments and return values of method calls "over the wire".
*Distributed [[Garbage collection (computer science)|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.
*Distributed [[Garbage collection (computer science)|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.
*It had to combine Hundreds/Tens of Thousands of objects held in the client's browser with a single transmission in order to minimize bandwidth utilization.
*Combining significant numbers of objects in the client's browser into a single transmission in order to minimize bandwidth utilization.


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.
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.<ref>{{Cite web |title=DCE 1.1: Remote Procedure Call - Introduction to the RPC API |url=https://pubs.opengroup.org/onlinepubs/9629399/chap2.htm |access-date=2022-08-03 |website=pubs.opengroup.org}}</ref>


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 [[Firewall (networking)|firewalls]], and on unknown and insecure machines, meant that normal [[HTTP]] requests in combination with [[web browser]]s 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-oriented protocol). This was later resurrected to support a [[Microsoft Exchange Server|Microsoft Exchange]] 2003 connection over HTTP.
DCOM was a major competitor to [[CORBA]].<ref>{{Cite journal |last1=Nowak |first1=Filip |last2=Qasim |first2=Mohsin |title=A Comparison of Distributed Object Technologies CORBA vs DCOM |url=https://middlewares.files.wordpress.com/2008/04/dcom_corba.pdf |archive-url=https://web.archive.org/web/20170829054415/https://middlewares.files.wordpress.com/2008/04/dcom_corba.pdf |archive-date=2017-08-29 |url-status=live |journal=}}</ref> 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 [[Firewall (networking)|firewalls]], and on unknown and insecure machines, meant that normal [[HTTP]] requests in combination with [[web browser]]s won out over both of them.<ref>{{Cite web |title=Object Technology Jeff Sutherland: Web Services: Better than CORBA or DCOM? |url=http://jeffsutherland.com/2003/10/web-services-better-than-corba-or-dcom.html |access-date=2022-08-03 |language=en}}</ref> Microsoft, at one point, attempted to remediate these shortcomings by adding an extra HTTP transport to DCE/RPC called ''ncacn_http'' (Network Computing Architecture connection-oriented protocol).<ref>{{Cite web |last=stevewhims |title=Remote Procedure Calls Using RPC over HTTP - Win32 apps |url=https://docs.microsoft.com/en-us/windows/win32/rpc/remote-procedure-calls-using-rpc-over-http |access-date=2022-08-03 |website=docs.microsoft.com |date=23 August 2019 |language=en-us}}</ref>


DCOM was publicly launched as a beta for Windows 95 September 18, 1996.<ref>[https://news.microsoft.com/1996/09/18/microsoft-releases-beta-version-of-dcom-for-windows-95/#Microsoft Press Release Announcing DCOM Beta]</ref>
DCOM was publicly launched as a beta for Windows 95 September 18, 1996.<ref>[https://news.microsoft.com/1996/09/18/microsoft-releases-beta-version-of-dcom-for-windows-95/#Microsoft Press Release Announcing DCOM Beta]</ref>


DCOM is supported natively in all versions of Windows starting from Windows 95, and all versions of Windows Server since Windows NT 4.0<ref>{{Cite web |date=June 25, 2021 |title=Distributed Component Object Model (DCOM) Remote Protocol |url=https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-DCOM/%5bMS-DCOM%5d.pdf |archive-url=https://web.archive.org/web/20210509140147/https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-DCOM/%5BMS-DCOM%5D.pdf |archive-date=2021-05-09 |url-status=live |access-date=August 3, 2022 |website=Microsoft - Distributed Component Object Model (DCOM) Remote Protocol}}</ref>
DCOM is supported natively in Windows NT 4.0, Windows 2000, Windows XP, and Windows Server 2003, as well as Windows 7, Windows 8, Windows 10, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2 and Windows Server 2016.


== Hardening ==
== Security improvements ==
As part of the initiative that began at Microsoft as part of Secure Development Lifecycle to re-architect insecure code, DCOM saw some significant security-focused changes in Windows XP Service Pack 2.<ref>[https://technet.microsoft.com/en-us/library/bb457156.aspx#EIAA DCOM Security Enhancements]</ref>
As part of the initiative that began at Microsoft as part of Secure Development Lifecycle to re-architect insecure code, DCOM saw some significant security-focused changes in Windows XP Service Pack 2.<ref>[https://technet.microsoft.com/en-us/library/bb457156.aspx#EIAA DCOM Security Enhancements]</ref>

In response to a security vulnerability reported by Tencent Security Xuanwu Lab in June 2021,<ref>{{Cite web |title=Security Update Guide - Microsoft Security Response Center |url=https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26414 |access-date=2022-08-03 |website=msrc.microsoft.com}}</ref> Microsoft released security updates for several versions of Windows and Windows Server, hardening access to DCOM.<ref>{{Cite web |title=KB5004442—Manage changes for Windows DCOM Server Security Feature Bypass (CVE-2021-26414) |url=https://support.microsoft.com/en-us/topic/kb5004442-manage-changes-for-windows-dcom-server-security-feature-bypass-cve-2021-26414-f1400b52-c141-43d2-941e-37ed901c769c |access-date=2022-08-03 |website=support.microsoft.com}}</ref>


== Alternative versions and implementations ==
== Alternative versions and implementations ==
'''COMsource''': Its source code is available, along with full and complete documentation, sufficient to use and also implement an interoperable version of DCOM. According to that documentation, COMsource comes directly from the [[Windows NT]] 4.0 source code, and even includes the source code for a [[Windows Registry|Windows NT Registry Service]].
'''COMsource''' is a Unix based implementation of DCOM, allowing interoperability between different platforms. Its source code is available, along with full and complete documentation, sufficient to use and also implement an interoperable version of DCOM. COMsource comes directly from the [[Windows NT]] 4.0 source code, and includes the source code for a [[Windows Registry|Windows NT Registry Service]]. <ref>{{Cite web |title=DataSheet COMsource for Solaris, Tru64 UNIX and other Platforms |url=http://www.opengroup.org/comsource/datasheet.htm |website=DataSheet COMsource for Solaris, Tru64 UNIX and other Platforms}}</ref>

⚫
In 1995, Digital and [[Microsoft]] announced the Affinity for OpenVMS Program, which was intended to allow OpenVMS to serve as the [[persistence layer]] for [[Windows NT]] [[Client–server model|client-server applications]].<ref name="vms-20-years">{{cite web|url=https://h50146.www5.hpe.com/products/software/oe/openvms/history/vaxvms20/pdf/vmsbook.pdf|date=October 1997|title=OpenVMS at 20 Nothing stops it|publisher=Digital|access-date=2021-02-12}}</ref> As part of this initiative, an implementation of the [[Distributed Component Object Model]] (DCOM) was added to OpenVMS Alpha.<ref name="com-compaq">{{cite book|title=COM Beyond Microsoft: Designing and Implementing COM Servers on Compaq Platforms|url=https://books.google.ie/books/about/COM_Beyond_Microsoft.html?id=i47yKPSDd1gC|isbn=1555582265|author=Gene Cronin, Terence P. Sherlock|date=2000}}</ref> In order to support DCOM, VMS was provided with implementations of the [[Windows Registry]], [[NTLM]] authentication, and a subset of [[Win32]] APIs needed to support COM.<ref>{{cite web|url=http://h30266.www3.hpe.com/odl/vax/opsys/vmsos73/vmsos73/6539/6539pro.html|title=OpenVMS Connectivity Developer Guide
|date=July 2000|access-date=2021-01-01|website=hpe.com}}</ref> DCOM was first added to OpenVMS V7.2-1 for the Alpha.<ref>{{cite web|url=http://odl.sysworks.biz/disk$vaxdocmar002/opsys/vmsos721/6614/6614pro_contents.html|title=OpenVMS Alpha V7.2-1 Release Notes|website=odl.sysworks.biz|access-date=2021-01-01|date=January 1999}}</ref> A similar implementation of DCOM was added to [[Digital Unix]] as part of the AllConnect program.<ref name="com-compaq" />

The [[Wine (software)|Wine]] Team is also implementing DCOM for binary interoperability purposes; they are not currently interested in the networking side of DCOM, which is provided by [[Microsoft RPC|MSRPC]]. They are restricted to implementing [[Network Data Representation|NDR]] (Network Data Representation) through Microsoft's API{{Citation needed|date=June 2007}}, but are committed to making it as compatible as possible with MSRPC.


⚫
In 1995, Digital and [[Microsoft]] announced Affinity for OpenVMS (also known as NT Affinity) which was intended to allow OpenVMS to serve as the [[persistence layer]] for Windows NT [[Client–server model|client-server applications]].<ref name="vms-20-years">{{cite web|url=https://h50146.www5.hpe.com/products/software/oe/openvms/history/vaxvms20/pdf/vmsbook.pdf |archive-url=https://web.archive.org/web/20210419084702/https://h50146.www5.hpe.com/products/software/oe/openvms/history/vaxvms20/pdf/vmsbook.pdf |archive-date=2021-04-19 |url-status=live|date=October 1997|title=OpenVMS at 20 Nothing stops it|publisher=Digital|access-date=2021-02-12}}</ref> As part of this initiative, an implementation of the Distributed Component Object Model (DCOM) was added to OpenVMS Alpha.<ref name="com-compaq">{{cite book|title=COM Beyond Microsoft: Designing and Implementing COM Servers on Compaq Platforms|url=https://books.google.com/books?id=i47yKPSDd1gC|isbn=1555582265|author=Gene Cronin, Terence P. Sherlock|date=2000| publisher=Digital Press }}</ref> In order to support DCOM, VMS was provided with implementations of the Windows Registry, [[NTLM]] authentication, and a subset of [[Win32]] APIs needed to support COM.<ref>{{cite web|url=http://h30266.www3.hpe.com/odl/vax/opsys/vmsos73/vmsos73/6539/6539pro.html|title=OpenVMS Connectivity Developer Guide|date=July 2000|access-date=2021-01-01|website=hpe.com|archive-date=2020-12-04|archive-url=https://web.archive.org/web/20201204205526/http://h30266.www3.hpe.com/odl/vax/opsys/vmsos73/vmsos73/6539/6539pro.html|url-status=dead}}</ref> DCOM was first added to OpenVMS V7.2-1 for the Alpha.<ref>{{cite web|url=http://odl.sysworks.biz/disk$vaxdocmar002/opsys/vmsos721/6614/6614pro_contents.html|title=OpenVMS Alpha V7.2-1 Release Notes|website=odl.sysworks.biz|access-date=2021-01-01|date=January 1999}}</ref> A similar implementation of DCOM was added to [[Digital Unix]] as part of the AllConnect program.<ref name="com-compaq" />
⚫
'''TangramCOM''' is a separate project from [[Wine (software)|Wine]], focusing on implementing DCOM on Linux-based smartphones.


⚫
'''TangramCOM''' was a separate project from Wine, focusing on implementing DCOM on Linux-based smartphones.<ref>{{Cite web |title=Home - TangramCOM |url=http://www.andjoin.com/Home |access-date=2022-08-03 |website=www.andjoin.com}}</ref>
The [[Samba (software)|Samba]] Team is also implementing DCOM for over-the-wire interoperability purposes: unlike the Wine Team, they are not currently interested in binary-interoperability, as the Samba MSRPC implementation is far from binary-interoperable with Microsoft's MSRPC.


== See also ==
== See also ==
* [[ActiveX]]
* [[ActiveX]]
* [[Component Object Model]]
* [[Dynamic Data Exchange]] (DDE)
* [[Dynamic Data Exchange]] (DDE)
* [[.NET Remoting]]
* [[.NET Remoting]]
Line 49: Line 40:
== External links ==
== External links ==
* [https://tools.ietf.org/html/draft-brown-dcom-v1-spec-03 Distributed Component Object Model Protocol -- DCOM/1.0]
* [https://tools.ietf.org/html/draft-brown-dcom-v1-spec-03 Distributed Component Object Model Protocol -- DCOM/1.0]
* [http://opengroup.org/comsource The Open Groups COMsource]
* [http://opengroup.org/comsource The Open Groups COMsource] {{Webarchive|url=https://web.archive.org/web/20200113034910/http://opengroup.org/comsource |date=2020-01-13 }}
* [http://www.opengroup.org/comsource/ COMsource]
* [https://web.archive.org/web/20091213022641/http://tcom.andjoin.com/ TangramCOM]
* [https://web.archive.org/web/20091213022641/http://tcom.andjoin.com/ TangramCOM]
* [http://www.softwareag.com/Corporate/products/lm/leg_integration/downloads/default.asp EntireX DCOM]


{{Microsoft APIs}}
{{Microsoft APIs}}

Latest revision as of 17:04, 20 November 2024

"Dcom" redirects here. For the doctoral degree, see Doctor of Commerce. For other uses, see DCOM (disambiguation).

Distributed Component Object Model (DCOM) is a proprietary Microsoft technology for communication between software components on 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.

The extension COM into Distributed COM was due to extensive use of DCE/RPC (Distributed Computing Environment/Remote Procedure Calls) – more specifically Microsoft's enhanced version, known as MSRPC. [1]

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.
  • Combining significant numbers of objects in the client's browser into a single transmission in order to minimize bandwidth utilization.

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.[2]

DCOM was a major competitor to CORBA.[3] 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.[4] Microsoft, at one point, attempted to remediate these shortcomings by adding an extra HTTP transport to DCE/RPC called ncacn_http (Network Computing Architecture connection-oriented protocol).[5]

DCOM was publicly launched as a beta for Windows 95 September 18, 1996.[6]

DCOM is supported natively in all versions of Windows starting from Windows 95, and all versions of Windows Server since Windows NT 4.0[7]

Security improvements

[edit]

As part of the initiative that began at Microsoft as part of Secure Development Lifecycle to re-architect insecure code, DCOM saw some significant security-focused changes in Windows XP Service Pack 2.[8]

In response to a security vulnerability reported by Tencent Security Xuanwu Lab in June 2021,[9] Microsoft released security updates for several versions of Windows and Windows Server, hardening access to DCOM.[10]

Alternative versions and implementations

[edit]

COMsource is a Unix based implementation of DCOM, allowing interoperability between different platforms. Its source code is available, along with full and complete documentation, sufficient to use and also implement an interoperable version of DCOM. COMsource comes directly from the Windows NT 4.0 source code, and includes the source code for a Windows NT Registry Service. [11]

In 1995, Digital and Microsoft announced Affinity for OpenVMS (also known as NT Affinity) which was intended to allow OpenVMS to serve as the persistence layer for Windows NT client-server applications.[12] As part of this initiative, an implementation of the Distributed Component Object Model (DCOM) was added to OpenVMS Alpha.[13] In order to support DCOM, VMS was provided with implementations of the Windows Registry, NTLM authentication, and a subset of Win32 APIs needed to support COM.[14] DCOM was first added to OpenVMS V7.2-1 for the Alpha.[15] A similar implementation of DCOM was added to Digital Unix as part of the AllConnect program.[13]

TangramCOM was a separate project from Wine, focusing on implementing DCOM on Linux-based smartphones.[16]

See also

[edit]

References

[edit]
  1. ^ "What is Distributed Component Object Model (DCOM)?". WhatIs.com. Retrieved 2022-08-03.
  2. ^ "DCE 1.1: Remote Procedure Call - Introduction to the RPC API". pubs.opengroup.org. Retrieved 2022-08-03.
  3. ^ Nowak, Filip; Qasim, Mohsin. "A Comparison of Distributed Object Technologies CORBA vs DCOM" (PDF). Archived (PDF) from the original on 2017-08-29. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ "Object Technology Jeff Sutherland: Web Services: Better than CORBA or DCOM?". Retrieved 2022-08-03.
  5. ^ stevewhims (23 August 2019). "Remote Procedure Calls Using RPC over HTTP - Win32 apps". docs.microsoft.com. Retrieved 2022-08-03.
  6. ^ Press Release Announcing DCOM Beta
  7. ^ "Distributed Component Object Model (DCOM) Remote Protocol" (PDF). Microsoft - Distributed Component Object Model (DCOM) Remote Protocol. June 25, 2021. Archived (PDF) from the original on 2021-05-09. Retrieved August 3, 2022.
  8. ^ DCOM Security Enhancements
  9. ^ "Security Update Guide - Microsoft Security Response Center". msrc.microsoft.com. Retrieved 2022-08-03.
  10. ^ "KB5004442—Manage changes for Windows DCOM Server Security Feature Bypass (CVE-2021-26414)". support.microsoft.com. Retrieved 2022-08-03.
  11. ^ "DataSheet COMsource for Solaris, Tru64 UNIX and other Platforms". DataSheet COMsource for Solaris, Tru64 UNIX and other Platforms.
  12. ^ "OpenVMS at 20 Nothing stops it" (PDF). Digital. October 1997. Archived (PDF) from the original on 2021-04-19. Retrieved 2021-02-12.
  13. ^ a b Gene Cronin, Terence P. Sherlock (2000). COM Beyond Microsoft: Designing and Implementing COM Servers on Compaq Platforms. Digital Press. ISBN 1555582265.
  14. ^ "OpenVMS Connectivity Developer Guide". hpe.com. July 2000. Archived from the original on 2020-12-04. Retrieved 2021-01-01.
  15. ^ "OpenVMS Alpha V7.2-1 Release Notes". odl.sysworks.biz. January 1999. Retrieved 2021-01-01.
  16. ^ "Home - TangramCOM". www.andjoin.com. Retrieved 2022-08-03.
[edit]
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