Distributed Computing Environment
Encyclopedia
The Distributed Computing Environment (DCE) is a software system developed in the early 1990s by a consortium that included Apollo Computer
(later part of Hewlett-Packard
), IBM
, Digital Equipment Corporation
, and others. The DCE supplies a framework and toolkit for developing client/server applications. The framework includes a remote procedure call
(RPC) mechanism known as DCE/RPC
, a naming (directory) service, a time service, an authentication
service and a distributed file system
(DFS) known as DCE/DFS
.
DCE was a big step in direction to standardisation of architectures, which were manufacturer dependent before. Transforming the concept in software for different platforms has been given up after a short period. Similar to the OSI model
DCE was not granted success, the underlying concepts however prevailed.
(OSF) came about to a large degree as part of the Unix wars
of the 1980s. After Sun Microsystems
and AT&T
worked together to produce UNIX System V Release 4
(SVR4) and refused to commit to fair and open licensing of Unix source code, many of the other Unix vendors felt their own market opportunities were unduly disadvantaged. The Distributed Computing Environment is a component of the OSF offerings, along with Motif and Distributed Management Environment (DME).
As part of the formation of OSF, various members contributed many of their ongoing research projects as well as their commercial products. For example, HP/Apollo contributed its Network Computing Environment (NCS) and CMA Threads products. Siemens Nixdorf contributed its X.500 server and ASN/1 compiler tools. At the time, network computing was quite popular, and many of the companies involved were working on similar RPC
-based systems. By integrating security, RPC and other distributed services on a single "official" distributed computing environment, OSF could offer a major advantage over SVR4, allowing any DCE-supporting system (namely OSF/1) to interoperate in a larger network.
The DCE system was, to a large degree, based on independent developments made by each of the partners. DCE/RPC
was derived from the Network Computing System
(NCS) created at Apollo Computer
. The naming service was derived from work done at Digital. DCE/DFS was based on the Andrew File System
(AFS) originally developed at Carnegie Mellon University
. The authentication system was based on Kerberos, and the authorization system based on Access Control List
s (ACLs). By combining these features, DCE offers a fairly complete C
-based system for network computing. Any machine on the network can authenticate its users, gain access to resources, and then call them remotely using a single integrated API
.
The rise of the Internet
, Java
and web services stole much of DCE's mindshare through the mid-to-late 1990s, and competing systems such as CORBA
muddied the waters as well.
One of the major uses of DCE today is Microsoft
's DCOM
and ODBC systems, which use DCE/RPC (in MSRPC
) as their network transport layer.
OSF and its projects eventually became part of The Open Group
, which released DCE 1.2.2 under a free software license (the LGPL
) on 12 January 2005. DCE 1.1 was available much earlier under the OSF BSD license, and resulted in FreeDCE
being available since 2000. FreeDCE contains an implementation of DCOM.
Major components of DCE within every cell are:
Modern DCE implementations such as IBM's are fully capable of interoperating with Kerberos as the security server, LDAP for the CDS and the Network Time Protocol
implementations for the time server.
While it is possible to implement a distributed file system using the DCE underpinnings by adding filenames to the CDS and defining the appropriate ACLs on them, this is not user-friendly. DCE/DFS is a DCE based application which provides a distributed filesystem on DCE. DCE/DFS can support replicas of a fileset (the DCE/DFS equivalent of a filesystem) on multiple DFS servers - there is one read-write copy and zero or more read only copies. Replication is supported between the read-write and the read-only copies. In addition, DCE/DFS also supports what are called "backup" filesets, which if defined for a fileset are capable of storing a version of the fileset as it was prior to the last replication.
DCE/DFS is believed to be the world's only distributed filesystem that correctly implements the full POSIX filesystem semantics, including byte range locking. DCE/DFS was sufficiently reliable and stable to be utilised by IBM
to run the back-end filesystem for the 1996 Olympics web site, seamlessly and automatically distributed and edited worldwide in different timezones.
Apollo Computer
Apollo Computer, Inc., founded 1980 in Chelmsford, Massachusetts by William Poduska and others, developed and produced Apollo/Domain workstations in the 1980s. Along with Symbolics and Sun Microsystems, Apollo was one of the first vendors of graphical workstations in the 1980s...
(later part of Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
), IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
, and others. The DCE supplies a framework and toolkit for developing client/server applications. The framework includes a remote procedure call
Remote procedure call
In computer science, a remote procedure call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space without the programmer explicitly coding the details for this remote interaction...
(RPC) mechanism known as DCE/RPC
DCE/RPC
DCE/RPC, short for "Distributed Computing Environment / Remote Procedure Calls", is the remote procedure call system developed for the Distributed Computing Environment...
, a naming (directory) service, a time service, an authentication
Authentication
Authentication is the act of confirming the truth of an attribute of a datum or entity...
service and a distributed file system
Distributed file system
Network file system may refer to:* A distributed file system, which is accessed over a computer network* Network File System , a specific brand of distributed file system...
(DFS) known as DCE/DFS
DCE Distributed File System
The DCE Distributed File System is the remote file access protocol used with the Distributed Computing Environment. It was based on the AFS Version 3.0 protocol that was developed commercially by Transarc Corporation...
.
DCE was a big step in direction to standardisation of architectures, which were manufacturer dependent before. Transforming the concept in software for different platforms has been given up after a short period. Similar to the OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
DCE was not granted success, the underlying concepts however prevailed.
History
Open Software FoundationOpen Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
(OSF) came about to a large degree as part of the Unix wars
Unix wars
The Unix wars were the struggles between vendors of the Unix computer operating system in the late 1980s and early 1990s to set the standard for Unix thenceforth.- Origins :...
of the 1980s. After Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
and AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
worked together to produce UNIX System V Release 4
UNIX System V
Unix System V, commonly abbreviated SysV , is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4...
(SVR4) and refused to commit to fair and open licensing of Unix source code, many of the other Unix vendors felt their own market opportunities were unduly disadvantaged. The Distributed Computing Environment is a component of the OSF offerings, along with Motif and Distributed Management Environment (DME).
As part of the formation of OSF, various members contributed many of their ongoing research projects as well as their commercial products. For example, HP/Apollo contributed its Network Computing Environment (NCS) and CMA Threads products. Siemens Nixdorf contributed its X.500 server and ASN/1 compiler tools. At the time, network computing was quite popular, and many of the companies involved were working on similar RPC
Remote procedure call
In computer science, a remote procedure call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space without the programmer explicitly coding the details for this remote interaction...
-based systems. By integrating security, RPC and other distributed services on a single "official" distributed computing environment, OSF could offer a major advantage over SVR4, allowing any DCE-supporting system (namely OSF/1) to interoperate in a larger network.
The DCE system was, to a large degree, based on independent developments made by each of the partners. DCE/RPC
DCE/RPC
DCE/RPC, short for "Distributed Computing Environment / Remote Procedure Calls", is the remote procedure call system developed for the Distributed Computing Environment...
was derived from the Network Computing System
Network Computing System
The Network Computing System was an implementation of the Network Computing Architecture . It was created at Apollo Computer in the 1980s...
(NCS) created at Apollo Computer
Apollo Computer
Apollo Computer, Inc., founded 1980 in Chelmsford, Massachusetts by William Poduska and others, developed and produced Apollo/Domain workstations in the 1980s. Along with Symbolics and Sun Microsystems, Apollo was one of the first vendors of graphical workstations in the 1980s...
. The naming service was derived from work done at Digital. DCE/DFS was based on the Andrew File System
Andrew file system
The Andrew File System is a distributed networked file system which uses a set of trusted servers to present a homogeneous, location-transparent file name space to all the client workstations. It was developed by Carnegie Mellon University as part of the Andrew Project. It is named after Andrew...
(AFS) originally developed at Carnegie Mellon University
Carnegie Mellon University
Carnegie Mellon University is a private research university in Pittsburgh, Pennsylvania, United States....
. The authentication system was based on Kerberos, and the authorization system based on Access Control List
Access control list
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
s (ACLs). By combining these features, DCE offers a fairly complete C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
-based system for network computing. Any machine on the network can authenticate its users, gain access to resources, and then call them remotely using a single integrated API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
.
The rise of the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and web services stole much of DCE's mindshare through the mid-to-late 1990s, and competing systems such as CORBA
Çorba
Chorba , ciorbă , shurpa , shorpo , or sorpa is one of various kinds of soup or stew found in national cuisines across Middle East...
muddied the waters as well.
One of the major uses of DCE today is Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's DCOM
Distributed component object model
Distributed Component Object Model 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+...
and ODBC systems, which use DCE/RPC (in MSRPC
MSRPC
Microsoft RPC is a modified version of DCE/RPC. Additions include support for Unicode strings, implicit handles, inheritance of interfaces , and complex calculations in the variable-length string and structure paradigms already present in DCE/RPC.- Example :The DCE 1.0 reference implementation...
) as their network transport layer.
OSF and its projects eventually became part of The Open Group
The Open Group
The Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
, which released DCE 1.2.2 under a free software license (the LGPL
GNU Lesser General Public License
The GNU Lesser General Public License or LGPL is a free software license published by the Free Software Foundation . It was designed as a compromise between the strong-copyleft GNU General Public License or GPL and permissive licenses such as the BSD licenses and the MIT License...
) on 12 January 2005. DCE 1.1 was available much earlier under the OSF BSD license, and resulted in FreeDCE
FreeDCE
FreeDCE is The Open Group's reference implementation of DCE/RPC 1.1 updated to be interoperable with free software development practices. FreeDCE is Distributed Computing Environment/Remote Procedure Calls 1.1 reworked, and it includes an up-to-date implementation of DCEThreads that actually works...
being available since 2000. FreeDCE contains an implementation of DCOM.
Architecture
The largest unit of management in DCE is a cell. The highest privileges within a cell are assigned to a role called cell administrator, normally assigned to the "user" cell_admin. Note that this need not be a real OS-level user. The cell_admin has all privileges over all DCE resources within the cell. Privileges can be awarded to or removed from the following categories : user_obj, group_obj, other_obj, any_other for any given DCE resource. The first three correspond to the owner, group member, and any other DCE principal respectively. The last group contains any non-DCE principal. Multiple cells can be configured to communicate and share resources with each other. All principals from external cells are treated as "foreign" users and privileges can be awarded or removed accordingly. In addition to this, specific users or groups can be assigned privileges on any DCE resource, something which is not possible with the traditional UNIX filesystem, which lacks ACLs.Major components of DCE within every cell are:
- The Security Server that is responsible for authentication
- The Cell Directory Server (CDS) that is the respository of resources and ACLs and
- The Distributed Time Server that provides an accurate clock for proper functioning of the entire cell
Modern DCE implementations such as IBM's are fully capable of interoperating with Kerberos as the security server, LDAP for the CDS and the Network Time Protocol
Network Time Protocol
The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L...
implementations for the time server.
While it is possible to implement a distributed file system using the DCE underpinnings by adding filenames to the CDS and defining the appropriate ACLs on them, this is not user-friendly. DCE/DFS is a DCE based application which provides a distributed filesystem on DCE. DCE/DFS can support replicas of a fileset (the DCE/DFS equivalent of a filesystem) on multiple DFS servers - there is one read-write copy and zero or more read only copies. Replication is supported between the read-write and the read-only copies. In addition, DCE/DFS also supports what are called "backup" filesets, which if defined for a fileset are capable of storing a version of the fileset as it was prior to the last replication.
DCE/DFS is believed to be the world's only distributed filesystem that correctly implements the full POSIX filesystem semantics, including byte range locking. DCE/DFS was sufficiently reliable and stable to be utilised by IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
to run the back-end filesystem for the 1996 Olympics web site, seamlessly and automatically distributed and edited worldwide in different timezones.
External links
- The Open Group's DCE Portal - with link to its DCE implementation
- FreeDCE and DCOM for Linux (SourceForge)
- DCE Replacement Strategies