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Distributed Computing Environment
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The Distributed Computing Environment (DCE) is a software system developed in the early 1990s from the work of the Open Software Foundation (OSF), a consortium founded in 1988 that included Apollo Computer (part of Hewlett-Packard from 1989), IBM, Digital Equipment Corporation, and others.[1][2] The DCE supplies a framework and a toolkit for developing client/server applications.[3] The framework includes:
- a remote procedure call (RPC) mechanism[4] known as DCE/RPC
- a naming (directory) service[4]
- a time service[4]
- an authentication service[4]
- a distributed file system (DFS)[4] known as DCE/DFS
The DCE did not achieve commercial success.
As of 1995, all major computer hardware vendors had an implementation of DCE, seen as an advantage compared to alternatives like CORBA which all had more limited support.[4]: 13
History
[edit]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 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 "request for technology" was issued by the OSF in 1989. The first OSF DCE vendor product came out in 1992.[4]: 3
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. By combining these features, DCE offers a fairly complete system for network computing. Any machine on the network can authenticate its users, gain access to resources, and 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 appeared 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.[citation needed]
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.[5][6]
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.[7]
One of the major systems built on top of DCE was Encina, developed by Transarc (later acquired by IBM). IBM used Encina as a foundation to port its primary mainframe transaction processing system (CICS) to non-mainframe platforms, as IBM TXSeries. (However, later versions of TXSeries have removed the Encina component.)
Architecture
[edit]DCE is intended to support high availability systems: when a server does not respond (because of server failure or communications failure), clients can be constructed to automatically use a replica of that server instead.[4]: 11 : 21
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. 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 ACL's.
Major components of DCE within every cell are:
- The Security Server that is responsible for authentication
- The Cell Directory Server (CDS) that is the repository 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 implementations for the time server.
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.[7]
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 time zones.[7]
References
[edit]- ^ Weijia Jia; Wanlei Zhou (15 December 2004). Distributed Network Systems: From Concepts to Implementations. Springer Science & Business Media. p. 135. ISBN 978-0-387-23839-5.
- ^ PRADEEP K. SINHA (1 January 1998). DISTRIBUTED OPERATING SYSTEMS: CONCEPTS AND DESIGN. PHI Learning Pvt. Ltd. p. 35. ISBN 978-81-203-1380-4.
- ^ Hans-Arno Jacobsen (30 November 2003). Distributed Infrastructure Support for Electronic Commerce Applications. Springer Science & Business Media. p. 14. ISBN 978-1-4020-7648-0.
- ^ a b c d e f g h J. Mansfield and J. Clothier. "Distributed Computing Environment: An Architecture for Supporting Change?". 1995.
- ^ "DCE Open Source Licensing". 2005.
- ^ "DCE to be released under the LGPL". 2005.
- ^ a b c "The Open Group releases DCE 1.2.2 as LGPL'd Free Software".
External links
[edit]Distributed Computing Environment
View on Grokipediafrom Grokipedia
The Distributed Computing Environment (DCE) is an industry-standard, vendor-neutral middleware infrastructure developed by the Open Software Foundation (OSF) in the early 1990s to enable the creation, deployment, and management of distributed applications across heterogeneous hardware and software platforms.[1] It provides a comprehensive set of integrated services, including remote procedure call (RPC) for inter-process communication, distributed file services (DFS) for shared data access, security mechanisms based on Kerberos for authentication and authorization, directory services for resource location, and time synchronization to ensure consistency in networked environments.[2][3]
Originally released as an open specification in 1990, DCE evolved through three major versions, with DCE 1.2.2 made freely available under the LGPL license in 2000 by The Open Group, the successor to OSF, facilitating widespread adoption without vendor lock-in.[1] Key features emphasize scalability, fault tolerance, and interoperability, supporting single sign-on, legacy system integration, and distributed object technologies compatible with standards like CORBA, making it suitable for enterprise-level applications in sectors such as telecommunications, government, and finance.[2] For instance, it has been deployed in large-scale environments, including over 8,500 users at MCI and 5,000 client licenses at NASA's Jet Propulsion Laboratory (JPL), where it underpins secure, cross-platform resource sharing.[2][3] Although largely superseded by modern frameworks like CORBA and web services in contemporary distributed systems, DCE remains influential in legacy infrastructures and as a foundational model for middleware design.[1]
Overview
Definition and Scope
The Distributed Computing Environment (DCE) is a set of integrated software services developed by the Open Software Foundation (OSF) in the late 1980s to enable transparent distributed computing across networked systems.[4] As a middleware framework, DCE provides a layered architecture that facilitates the development and deployment of distributed applications by abstracting the underlying complexities of network communication and resource management.[3][1] The scope of DCE encompasses interoperability in multi-vendor environments, supporting heterogeneous hardware and software platforms including UNIX, VMS, and other major operating systems.[4] It allows processes on different systems to communicate seamlessly without vendor-specific dependencies, promoting a unified computing model across diverse infrastructures.[1] This broad applicability extends to critical business and scientific applications requiring scalable, secure distributed operations.[3] At its core, DCE aims to deliver a common environment for distributed applications that operates independently of changes to underlying operating systems, thereby reducing development barriers and enhancing portability.[4] By serving as a "distributed computing environment," it hides network intricacies—such as location transparency and protocol differences—from developers, enabling focus on application logic rather than infrastructure details.[1] High-level components, including remote procedure calls and security services, contribute to this abstraction without altering host systems.[3]Key Objectives and Benefits
The Distributed Computing Environment (DCE) was designed to achieve location transparency, allowing applications to access remote resources as if they were local, thereby insulating developers from underlying network complexities. This objective facilitates seamless interaction between clients and servers across diverse environments, supporting a unified global namespace for resources like files without requiring knowledge of physical locations. Additionally, DCE emphasizes fault tolerance through mechanisms such as data replication and automatic server failover, enabling systems to maintain availability even if individual components fail. Scalability is another core goal, accommodating growth from small networks to enterprise-scale systems with thousands of clients, while security is addressed via integrated authentication and encryption protocols to protect distributed interactions. Key benefits of DCE include reduced developer effort in network programming, as its remote procedure call (RPC) mechanism automates communication stubs and handles low-level details, allowing programmers to focus on application logic rather than platform-specific code. It supports heterogeneous hardware and software environments, operating across multiple vendors and operating systems like AIX and Solaris, which promotes interoperability without custom adaptations. Standardization of distributed services, through open specifications and conformance testing, ensures consistent behavior across implementations, fostering widespread adoption by organizations such as the Jet Propulsion Laboratory. DCE enables robust client-server models by providing a comprehensive suite for resource sharing across networks, including distributed file systems that support high client-to-server ratios and caching for efficient data access. Unlike earlier systems such as NFS, which was limited to basic file sharing without strong security or replication, or Sun RPC, which offered only rudimentary remote calls, DCE delivers an integrated framework that overcomes these constraints with enhanced fault tolerance, security, and scalability for complex, vendor-neutral applications.Historical Development
Origins and Creation
The Open Software Foundation (OSF) was established in May 1988 as a non-profit consortium aimed at developing open software standards, with initial funding exceeding $90 million from its founding members.[5] Key participants included Apollo Computer, Digital Equipment Corporation (DEC), Hewlett-Packard (HP), IBM, as well as European firms such as Bull, Nixdorf Computing, and Siemens, totaling seven primary sponsors at inception.[6] This formation represented a collaborative effort among major computing vendors to advance vendor-neutral technologies, particularly in response to the fragmented Unix marketplace dominated by proprietary extensions.[7] The primary motivations for OSF's creation arose from the intensifying "UNIX wars," a period of intense competition in the late 1980s where vendors like AT&T (with its UNIX System V) and Sun Microsystems (promoting its own extensions via Open Software Foundation alternatives) sought to control Unix standards, leading to interoperability challenges across heterogeneous systems.[8] OSF sought to counter AT&T's influence by fostering a unified, open approach to distributed computing, emphasizing transparency, scalability, and cross-vendor compatibility to enable seamless resource sharing in networked environments.[9] This initiative was driven by the need for a standardized middleware layer that could support emerging distributed applications without tying developers to specific hardware or operating system vendors.[8] A pivotal milestone occurred in 1989 when OSF issued a Request for Technology (RFT) to solicit contributions for its flagship project, the Distributed Computing Environment (DCE), inviting submissions from members and external parties to build core distributed system components.[9] Following evaluations of proposals, OSF selected key technologies in 1990, including Apollo's Network Computing System (NCS) for the remote procedure call (RPC) mechanism, which was adapted and contributed by HP after its acquisition of Apollo, alongside inputs from DEC for other elements like directory services.[10] These choices prioritized proven, interoperable solutions to form the foundation of DCE's architecture. Early integration efforts began with prototypes combining the selected technologies, culminating in the announcement of DCE 1.0 in 1991 as a cohesive, integrated environment for distributed computing, with a developer kit released in January 1991 and initial "snapshot" releases distributed to developers for testing and refinement.[11] This marked the transition from conceptual planning to a functional prototype, incorporating contributions such as RPC, naming services, and security frameworks to address real-world distributed system needs.[9]Evolution and Standardization
The Distributed Computing Environment (DCE) progressed from its initial release as version 1.0 in 1991, which established core services including remote procedure calls and directory services, to subsequent updates that addressed performance and interoperability needs.[12] This foundational version was developed by the Open Software Foundation (OSF) through collaborative efforts among vendors such as Digital Equipment Corporation and Hewlett-Packard, focusing on a unified middleware layer for heterogeneous systems.[13] In 1994, OSF released DCE 1.1, incorporating significant enhancements such as improved administration tools, security mechanisms, internationalization support, and refinements to the Distributed File System (DFS) for better scalability and fault tolerance in file sharing across distributed cells.[12][14] These updates also included bug fixes and performance optimizations derived from early deployments, enabling broader platform support including Unix variants, VMS, and initial integrations with emerging systems like Windows NT.[14] Vendor contributions, particularly from IBM and Digital, played a key role in these evolutions by providing tested components and extensions, such as DFS gateways and RPC enhancements tailored for Windows NT environments by mid-1994.[15][16] Subsequent releases included DCE 1.2 in 1997 and further updates, with DCE 1.2.2 made freely available under the GNU Lesser General Public License (LGPL) in 2000 by The Open Group, promoting wider adoption and standardization.[1] DCE's architecture influenced international standardization efforts, particularly through its conformance to ISO 9594 (X.500) for directory services, which provided a foundation for global naming and interoperability in OSI environments, and partial alignment with ISO/IEC 10021-2 (X.402) for directory access protocols.[17] The RPC mechanism in DCE contributed to discussions within ISO and ITU-T working groups on remote operations, promoting standardized bindings for distributed invocations, while components like DCE Threads achieved partial integration with POSIX standards, specifically Draft 10 of IEEE 1003.4a for threading interfaces.[17][4] A pivotal event in DCE's trajectory occurred in 1996 when OSF merged with X/Open to form The Open Group, consolidating open systems initiatives and facilitating the eventual open-sourcing of DCE technologies.[17] This merger streamlined vendor collaborations but coincided with DCE's decline in the mid-1990s, as competing paradigms like CORBA's object-oriented middleware and Java's platform-independent distributed computing gained prominence for their simplicity and web integration, overshadowing DCE's procedural model in enterprise adoption.[14][18]Core Architecture
Overall Design Principles
The Distributed Computing Environment (DCE) was designed to create a unified middleware layer that abstracts the complexities of distributed systems, enabling applications to function as if operating in a single, homogeneous environment. A core principle is transparency, which encompasses location, access, failure, and migration aspects to make distributed resources appear local to users and developers. Location transparency is achieved through the Cell Directory Service (CDS), which allows resources to be accessed via logical pathnames (e.g.,/.../my_cell/subsys/my_company/greet_server) without knowledge of their physical hosts. Access transparency is provided by mechanisms like Remote Procedure Calls (RPC) and the Distributed File System (DFS), where client stubs handle network communication and data formatting seamlessly. Failure transparency relies on replication, such as duplicated CDS directories, to maintain availability and mask outages. Migration transparency supports the relocation of servers or filesets without disrupting access, facilitated by directory updates and file location services.[4]
DCE adopts a layered architectural approach to promote modularity and separation of concerns, dividing functionality into presentation, application, and system support layers. The presentation layer manages user interfaces and protocol interactions, including RPC interfaces and APIs like XDS/XOM for directory access, ensuring consistent data representation across heterogeneous systems. The application layer handles distributed operations through services such as DFS for file sharing and RPC for inter-process communication, allowing developers to build scalable client-server applications. The system support layer provides foundational infrastructure, incorporating threads for concurrency, CDS and Global Directory Agent (GDA) for naming, Distributed Time Service (DTS) for synchronization, and operating system integrations to support reliable execution. This stratification enables independent development and maintenance of each layer while facilitating high-level interactions among components.[4]
Extensibility, interoperability, and security form foundational tenets of DCE's design, ensuring adaptability and robustness in diverse environments. Extensibility is inherent in the modular structure, permitting the addition of new RPC protocols (e.g., ISO standards) or services like DFS without overhauling the core system. Interoperability is emphasized through conformance to open standards such as X.500 for directories and DNS for naming, alongside support for heterogeneous platforms via standardized threads and RPC, allowing seamless integration across vendor systems. Security is embedded as a cross-cutting concern, utilizing Kerberos-based authentication, Access Control Lists (ACLs), and encryption to protect communications and resources during authenticated RPC invocations.[4]
Orthogonality guides DCE's architecture by promoting independent yet integrable services, minimizing interdependencies to avoid bottlenecks and enhance flexibility. Services like naming (CDS), time synchronization (DTS), security, and RPC operate as self-contained modules that can be configured or extended individually, while their mutual integrations—such as RPC leveraging security for authenticated calls—enable cohesive distributed functionality without overlap or redundancy. This principle supports decentralized management, where components like DFS and directory services function autonomously within a cell or across federated environments.[4]
Fundamental Layers and Interactions
The Distributed Computing Environment (DCE) is structured as a layered architecture that promotes modularity and transparency in distributed systems. The transport layer forms the foundation, providing end-to-end network connectivity through operating system interfaces such as sockets or X/Open Transport Interface (XTI), and supporting protocols like TCP for reliable, connection-oriented communication or UDP for lightweight, connectionless exchanges, thereby achieving transport independence.[19] This layer hides underlying network complexities, including local area networks (LANs) and wide area networks (WANs), to enable seamless data transmission across heterogeneous environments.[20] Above the transport layer, the Remote Procedure Call (RPC) layer facilitates client-server interactions by implementing synchronous procedure calls over the network, utilizing the DCE RPC protocol for interoperability.[19] The RPC layer relies on the transport services below it while offering standardized interfaces to higher layers, including runtime support for argument marshaling via Network Data Representation (NDR) and stub generation from Interface Definition Language (IDL) specifications.[20] The management layer, in turn, encompasses services for system configuration and resource discovery, such as the Cell Directory Service (CDS) for naming and the Distributed Time Service (DTS) for synchronization, providing administrative tools that integrate across the distributed domain.[19] At the top, the application layer hosts user-developed code that consumes these services, enabling transparent access to remote resources without explicit awareness of the underlying distribution.[20] Interactions among these layers are orchestrated through key mechanisms that ensure reliable and secure communication. RPC invocations begin at the application layer, where a client stub creates a binding handle—encapsulating protocol sequences, server addresses, and endpoints—and resolves names to network locations via the management layer's directory services, such as CDS, which maps symbolic names to endpoint identifiers.[19] This data flow proceeds downward: the RPC layer marshals parameters using Universally Unique Identifiers (UUIDs) for interface and object identification, transmits via the transport layer, and on the server side, unmarshals and executes the procedure before returning results along the reverse path.[20] Access Control Lists (ACLs) integrate at multiple layers, particularly in the management and RPC levels, to enforce permissions during binding and invocation, preventing unauthorized interactions.[19] To address distribution challenges at the architectural level, DCE incorporates mechanisms like endpoint mapping for dynamic load balancing, where the Endpoint Mapper Service in the management layer directs RPC calls to available server instances, and replication protocols in directory and file services to maintain data consistency and availability across cells.[19] These features, supported by threading in the RPC and application layers for concurrency, allow the system to scale horizontally while abstracting fault tolerance and resource allocation from application developers.[20]Major Components
Remote Procedure Call Mechanism
The Remote Procedure Call (RPC) mechanism in the Distributed Computing Environment (DCE) serves as the foundational communication primitive, enabling transparent invocation of procedures across distributed nodes as if they were local calls. DCE/RPC is derived from Apollo Computer's Network Computing System (NCS), which provided an early model for remote invocations using interface definitions and stub-based transparency.[21] In DCE 1.0, this was extended to support advanced semantics such as at-most-once execution guarantees, idempotent operations to handle retries safely, and broadcast RPC for one-to-many invocations.[21] These enhancements addressed limitations in NCS by incorporating standardized data representation and security primitives, making DCE/RPC suitable for enterprise-scale distributed applications.[22] Central to DCE/RPC is the Interface Definition Language (IDL), a declarative syntax for specifying remote interfaces, including procedure signatures, parameter directions (in, out, or in/out), and data types compatible with C. Developers define an interface header with a unique UUID for versioning, followed by procedure declarations annotated with attributes like [idempotent] for retry semantics or [context_handle] for stateful sessions. The IDL compiler processes these definitions to generate client and server stubs—skeletal code that handles parameter marshalling, network transmission, and unmarshalling—ensuring location transparency without requiring programmers to manage low-level details.[23] This stub generation process automates the conversion of local procedure calls into RPC protocol data units (PDUs), with client stubs initiating binds and invocations while server stubs dispatch to actual implementations.[22] At the protocol level, DCE/RPC employs Network Data Representation (NDR) for marshalling parameters into a canonical octet stream, independent of host endianness or data formats, to facilitate interoperability across heterogeneous systems. NDR defines representations for primitive types (e.g., 32-bit integers in little-endian by default, with negotiation for big-endian) and constructed types like arrays, structures, and unions, using alignment rules (e.g., 4-octet boundaries for integers) and conformance descriptions to describe variable-length data such as strings.[24] Interface versioning and identification rely on UUIDs—128-bit globally unique identifiers—for procedures, objects, and bindings, preventing conflicts in dynamic environments. Authentication integrates with the Generic Security Service API (GSS-API), allowing clients to specify protection levels (e.g., none, connect, or call) and services like Kerberos, with the runtime handling token exchange and integrity checks transparently.[22] Key features enhance DCE/RPC's flexibility for complex interactions. Asynchronous calls are supported through multithreading, where clients can issue non-blocking invocations and poll for completion, while servers process requests concurrently by default. Context handles maintain state across calls, represented as opaque handles in IDL for operations like file access that require session continuity. Dynamic binding uses endpoint mappers—registry services on well-known ports—to map UUIDs and protocol sequences (e.g., ncacn_ip_tcp for TCP/IP) to server endpoints, enabling location-independent resolution. For name resolution, DCE/RPC integrates briefly with directory services like the Cell Directory Service (CDS) during runtime binding.[21] A typical workflow begins with an application developer writing an IDL file defining the interface, compiling it with the IDL compiler to produce header files and stub source code in languages like C. The client links against the client stub and runtime library, obtains a binding handle (e.g., via rpc_binding_from_string_binding), and invokes procedures, which the stub marshals using NDR and transmits via the chosen protocol. On the server side, the server stub unmarshals incoming PDUs, dispatches to the procedure implementation, and returns results or faults. Error handling employs standardized status codes (e.g., rpc_s_call_failed for communication errors), returned synchronously or via asynchronous checks, with facilities for cancellation and retry based on idempotency.[22] This process ensures robust, fault-tolerant communication in distributed settings.[21]Directory and Naming Services
The Directory and Naming Services in the Distributed Computing Environment (DCE) provide a unified mechanism for locating and managing distributed resources across networked systems, enabling location-independent naming within and between administrative domains known as cells. These services consist of the Cell Directory Service (CDS) for intra-cell operations and the Global Directory Service (GDS) for inter-cell resolution, forming a hierarchical namespace that supports scalability and fault tolerance through replication and caching.[4][25] The Cell Directory Service (CDS) serves as the primary repository for naming and attributes of resources within a single DCE cell, an administrative domain typically encompassing a group of machines under common management. CDS organizes resources in a hierarchical, tree-like namespace modeled after file systems, where names are constructed as paths starting from the cell root. For example, cell-relative names begin with "/.:/" followed by the path to the resource, such as "/.:/subsys/dfs" for the Distributed File Service subsystem or "/.:/subsys/Hypermax/printQ/server1" for a specific print queue server.[4][26][27] This structure supports directories for grouping entries, object entries for individual resources with attributes (e.g., server addresses or user details), and soft links for aliases, ensuring a flat or nested organization as needed. CDS operates through distributed clearinghouses—physical databases on servers that store replicas of the directory data—allowing multiple read-only replicas alongside a master replica per cell to enhance availability and balance load.[4][25][28] CDS employs a client-server architecture with clerks on the client side and servers managing the clearinghouses. Clerks handle application requests by interfacing with the Name Service Independent (NSI) or X/Open Directory Services (XDS) APIs, caching resolved names and attributes locally to minimize network traffic; cached data is periodically written to disk for persistence and can be bypassed for fresh queries if required.[4][29][30] Servers process these requests concurrently using DCE threads, propagate updates from the master replica to read-only ones via immediate or scheduled "skulking" (typically every 12-24 hours), and ensure consistency across the cell.[4][25][31] Key operations include binding searches to resolve names to resource locations (e.g., generating binding handles for RPC use), attribute queries to retrieve details like server endpoints, and administrative actions such as creating, modifying, or deleting entries, all optimized for local performance within the cell.[4][28] For inter-cell operations, the Global Directory Service (GDS) extends the namespace across cells using a global root "/.../" prefix, integrating with external X.500 directory services via the Directory Access Protocol (DAP). GDS employs a Global Directory Agent (GDA) in each cell to resolve foreign names by querying X.500 directories or DNS for cell locations, cataloging attributes like CDS-Cell (cell name) and CDS-Replica (clearinghouse details) to enable transparent access.[4][32][28] This federation supports scalable global naming, where a full name like "/.../my_cell/subsys/dfs" routes through the GDA to the target CDS, with clerks caching inter-cell results for efficiency.[4][28]Security and Authentication Framework
The Distributed Computing Environment (DCE) Security Service provides a comprehensive framework for authentication and authorization in distributed systems, ensuring secure identification of principals and controlled access to resources across networked environments.[33] It integrates Kerberos-based mechanisms for mutual authentication with access control lists (ACLs) for fine-grained authorization, forming a trusted computing base that spans administrative domains known as cells.[4] This service supports both intra-cell and inter-cell operations, enabling secure interactions in heterogeneous computing setups without compromising performance through features like credential caching.[34] Authentication in the DCE Security Service relies on the Kerberos protocol, adapted from MIT's design, to verify the identities of users, services, and hosts.[34] Principals—representing users, groups, or services—are stored in a principal database managed by the Registry Service (RS), which uses unique identifiers (UUIDs) and string names for identification, along with long-term secret keys such as DES-encrypted passwords.[33] Key Distribution Centers (KDCs), implemented as part of the Kerberos Key Distribution Service (KDS), issue tickets to clients; these include ticket-granting tickets (TGTs) for initial authentication via the Authentication Service (AS) and service tickets via the Ticket-Granting Service (TGS).[34] Tickets encapsulate the client's identity, a session key, timestamps, and authorization data, encrypted with the target's long-term key to prevent tampering and ensure mutual authentication between client and server.[4] Cross-cell authentication is facilitated by surrogate principals and shared keys, allowing trust establishment between independent security domains.[34] Authorization is handled through ACLs attached to protected objects, such as files, directories, or RPC interfaces, which define permissions based on principal identities.[33] ACLs support three access types: unauthenticated access via the ANY_OTHER entry for anonymous operations; authenticated access requiring a validated identity from a login context; and privileged access using Privilege Attribute Certificates (PACs) or extended PACs (EPACs) for elevated rights, such as administrative actions.[4] Permissions include standard operations like read, write, and control, enforced by ACL managers that evaluate entries against the caller's credentials, including group affiliations and privilege attributes.[33] This model ensures that only authorized principals can perform actions, with ACLs applied uniformly across DCE components like naming services. The Security Service integrates with the Remote Procedure Call (RPC) mechanism via the Generic Security Service API (GSS-API), providing a portable interface for establishing security contexts without tying applications to specific mechanisms.[4] Developers use functions likerpc_binding_set_auth_info to specify authentication (e.g., rpc_c_authn_dce_secret for Kerberos) and authorization (rpc_c_authz_dce for PAC-based checks), creating contexts that protect RPC communications.[35] Protection levels offer graduated security: none for unprotected calls; connect for integrity during binding establishment; call for integrity over headers and bodies per invocation; and data (or privacy) for both integrity and confidentiality of entire messages, using session keys derived from tickets.[35] Delegation is supported through EPACs and delegation tokens, allowing a principal to grant limited rights to intermediaries in a call chain while preserving traceability via the Common Access Determination Algorithm, which verifies privileges across delegation paths.[33]
Key concepts enhancing the framework include protection domains defined by cells, each comprising an RS, KDS, and Privilege Service (PS) triple that acts as a self-contained trust boundary, with inter-domain trust via key sharing.[4] Audit trails are generated by the Audit Service, which logs security-relevant events (e.g., authentications, access denials) into files managed by the auditd daemon, using configurable filters and predicates for analysis to detect intrusions or policy violations.[36] Credential caching optimizes performance by storing TGTs and service tickets locally on clients for their lifetimes—typically several hours—reducing KDC interactions while maintaining security through expiration and secure storage.[34]
Threading and Process Management
The Distributed Computing Environment (DCE) provides a threading model through DCE Threads, a user-level library that implements the POSIX 1003.4a Draft 4 standard for threads, commonly known as pthreads. This API enables the creation and management of multiple threads within a single process, facilitating concurrent execution in distributed applications. DCE Threads supports multi-threaded servers that can handle multiple client requests simultaneously and allows clients to perform concurrent operations, such as parallel remote procedure calls (RPCs), without blocking the entire application.[4] Process management in DCE extends beyond local threading to distributed coordination, primarily through the Distributed Time Service (DTS), which ensures clock synchronization across networked hosts. DTS maintains a global notion of time based on Coordinated Universal Time (UTC), using a client-server architecture where time clerks on client machines query time servers to adjust local clocks periodically. This synchronization supports accurate event ordering, duration measurement, and scheduling in distributed systems, with time expressed alongside inaccuracy intervals to account for potential drifts. DTS employs an ensemble approach for clock agreement, utilizing Marzullo's intersection algorithm to select the optimal time estimate from multiple server responses by finding the maximum overlap of their confidence intervals.[4][37] Resource management in DCE Threads focuses on efficient allocation and control of computational resources in concurrent environments. Threads are created using API calls likepthread_create, which spawn new threads sharing the process's address space, and terminated via pthread_join or pthread_exit for cleanup. Synchronization primitives include mutexes, which provide mutual exclusion to protect shared resources such as variables or data structures from simultaneous access by multiple threads, and condition variables, which allow threads to wait for specific conditions (e.g., via pthread_cond_wait) while paired with a mutex, signaling completion with pthread_cond_signal or pthread_cond_broadcast. Thread cancellation is supported through asynchronous or deferred modes, enabling safe interruption of threads with cleanup handlers to release resources like locks or memory. These mechanisms ensure reliable concurrency in distributed tasks, such as coordinating access to shared distributed resources.[4][38]
Integration of threading with other DCE components enhances distributed process handling. DCE RPC calls are thread-safe, allowing multiple threads to invoke remote procedures concurrently without interference, as the RPC runtime manages thread contexts independently and supports secure, authenticated invocations across hosts.[4]