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107-751: DECnet was built right into the DEC flagship operating system OpenVMS since its inception. Later Digital ported it to Ultrix , OSF/1 (later Tru64 ) as well as Apple Macintosh and IBM PC running variants of DOS , OS/2 and Microsoft Windows under the name PATHWORKS , allowing these systems to connect to DECnet networks of VAX machines as terminal nodes. While the DECnet protocols were designed entirely by Digital Equipment Corporation, DECnet Phase II (and later) were open standards with published specifications, and several implementations were developed outside DEC, including ones for FreeBSD and Linux . DECnet code in

214-671: A Microsoft Windows , macOS or Linux workstation. DEC created a number of optional database products for VMS, some of which were marketed as the VAX Information Architecture family. These products included: In 1994, DEC sold Rdb, DBMS and CDD to Oracle , where they remain under active development. In 1995, DEC sold DSM to InterSystems , who renamed it Open M , and eventually replaced it with their Caché product. Examples of third-party database management systems for OpenVMS include MariaDB , Mimer SQL ( Itanium and x86-64 ), and System 1032 . VMS

321-449: A single system image abstraction. Nodes may be connected to each other via a proprietary hardware connection called Cluster Interconnect or via a standard Ethernet LAN . OpenVMS supports up to 96 nodes in a single cluster. It also allows mixed-architecture clusters. OpenVMS clusters allow applications to function during planned or unplanned outages. Planned outages include hardware and software upgrades. The DECnet protocol suite

428-637: A terminal server such as one of the DECserver family. DEC (and its successor companies) provided a wide variety of programming languages for VMS. Officially supported languages on VMS, either current or historical, include: Among OpenVMS's notable features is the Common Language Environment , a strictly defined standard that specifies calling conventions for functions and routines, including use of stacks , registers , etc., independent of programming language. Because of this, it

535-481: A VirtualBox VM with certain limitations; most significantly, few layered products were available, and code can only be compiled for x86-64 using cross compilers which run on Itanium-based OpenVMS systems. Following the V9.0 release, VSI released a series of updates on a monthly or bimonthly basis which added additional functionality and hypervisor support. These were designated V9.0-A through V9.0-H. In June 2021, VSI released

642-744: A common definition. DEC provided a collection of software development tools in a layered product named DECset (originally named VAXset ). This consisted of the following tools: The OpenVMS Debugger supports all DEC compilers and many third-party languages. It allows breakpoints, watchpoints and interactive runtime program debugging using either a command line or graphical user interface . A pair of lower-level debuggers, named DELTA and XDELTA , can be used to debug privileged code in additional to normal application code. In 2019, VSI released an officially supported Integrated Development Environment for VMS based on Visual Studio Code . This allows VMS applications to be developed and debugged remotely from

749-942: A comprehensive description of networking, the model failed to garner reliance during the design of the Internet , which is reflected in the less prescriptive Internet Protocol Suite , principally sponsored under the auspices of the Internet Engineering Task Force (IETF). In the early- and mid-1970s, networking was largely either government-sponsored ( NPL network in the UK, ARPANET in the US, CYCLADES in France) or vendor-developed with proprietary standards, such as IBM 's Systems Network Architecture and Digital Equipment Corporation 's DECnet . Public data networks were only just beginning to emerge, and these began to use

856-477: A corresponding entity at the same layer in another host. Service definitions, like the OSI model, abstractly describe the functionality provided to a layer N by a layer N−1 , where N is one of the seven layers of protocols operating in the local host. At each level N , two entities at the communicating devices (layer N peers ) exchange protocol data units (PDUs) by means of a layer N protocol . Each PDU contains

963-477: A distinction between 32-bit and 64-bit executables, but instead allows for both 32-bit and 64-bit pointers to be used within the same code. This is known as mixed pointer support. The 64-bit OpenVMS Alpha releases support a maximum virtual address space size of 8TiB (a 43-bit address space), which is the maximum supported by the Alpha 21064 and Alpha 21164 . One of the more noteworthy Alpha-only features of OpenVMS

1070-709: A format specified by the application layer during the encapsulation of outgoing messages while being passed down the protocol stack , and possibly reversed during the deencapsulation of incoming messages when being passed up the protocol stack. For this very reason, outgoing messages during encapsulation are converted into a format specified by the application layer, while the conversion for incoming messages during deencapsulation are reversed. The presentation layer handles protocol conversion, data encryption, data decryption, data compression, data decompression, incompatibility of data representation between operating systems, and graphic commands. The presentation layer transforms data into

1177-541: A higher level of privilege than most user code. This is in order to prevent accidental or malicious manipulation of the CLI's code and data structures by user-mode code. OpenVMS supports clustering (first called VAXcluster and later VMScluster ), where multiple computers run their own instance of the operating system. Clustered computers (nodes) may be fully independent from each other, or they may share devices like disk drives and printers. Communication across nodes provides

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1284-451: A lack of common protocols. For a period in the late 1980s and early 1990s, engineers, organizations and nations became polarized over the issue of which standard , the OSI model or the Internet protocol suite , would result in the best and most robust computer networks. However, while OSI developed its networking standards in the late 1980s, TCP/IP came into widespread use on multi-vendor networks for internetworking . The OSI model

1391-466: A layered architecture, consisting of a privileged Executive , an intermediately privileged Command Language Interpreter, and unprivileged utilities and run-time libraries (RTLs). Unprivileged code typically invokes the functionality of the Executive through system services (equivalent to system calls in other operating systems). OpenVMS' layers and mechanisms are built around certain features of

1498-584: A light pulse. For example, a 1 bit might be represented on a copper wire by the transition from a 0-volt to a 5-volt signal, whereas a 0 bit might be represented by the transition from a 5-volt to a 0-volt signal. As a result, common problems occurring at the physical layer are often related to the incorrect media termination, EMI or noise scrambling, and NICs and hubs that are misconfigured or do not work correctly. The data link layer provides node-to-node data transfer —a link between two directly connected nodes. It detects and possibly corrects errors that may occur in

1605-464: A major advance in the standardisation of network concepts. It promoted the idea of a consistent model of protocol layers, defining interoperability between network devices and software. The concept of a seven-layer model was provided by the work of Charles Bachman at Honeywell Information Systems . Various aspects of OSI design evolved from experiences with the NPL network, ARPANET, CYCLADES, EIN , and

1712-562: A network management architecture, and gateways to other types of networks including IBM's SNA and CCITT Recommendation X.25 . CTERM: Command Terminal MOP: Maintenance Operations Protocol Phase IV and Phase IV+ (1982). Phase IV was released initially to RSX-11 and VMS systems, later TOPS-20 , TOPS-10 , ULTRIX , VAXELN , and RSTS/E gained support. Support for networks of up to 64,449 nodes (63 areas of 1023 nodes) with 16-bit addresses, datalink capabilities expanded beyond DDCMP to include Ethernet local area network support as

1819-477: A network-layer protocol, if the encapsulation of the payload takes place only at the endpoint, GRE becomes closer to a transport protocol that uses IP headers but contains complete Layer 2 frames or Layer 3 packets to deliver to the endpoint. L2TP carries PPP frames inside transport segments. Although not developed under the OSI Reference Model and not strictly conforming to the OSI definition of

1926-486: A new network management model, local or distributed name service, improved performance over Phase IV. Move from a proprietary network to an Open Systems Interconnection (OSI) by integration of ISO standards to provide multi-vendor connectivity and compatibility with DNA Phase IV, the last two features resulted in a hybrid network architecture (DNA and OSI) with separate "towers" sharing an integrated transport layer. Transparent transport level links to TCP/IP were added via

2033-459: A payload, called the service data unit (SDU), along with protocol-related headers or footers. Data processing by two communicating OSI-compatible devices proceeds as follows: The OSI model was defined in ISO/IEC 7498 which consists of the following parts: ISO/IEC 7498-1 is also published as ITU-T Recommendation X.200. The recommendation X.200 describes seven layers, labelled 1 to 7. Layer 1

2140-451: A physical layer can be described in terms of the network topology . Physical layer specifications are included in the specifications for the ubiquitous Bluetooth , Ethernet , and USB standards. An example of a less well-known physical layer specification would be for the CAN standard. The physical layer also specifies how encoding occurs over a physical signal, such as electrical voltage or

2247-628: A project to design a 32-bit extension to its PDP-11 computer line. The hardware component was code named Star ; the operating system was code named Starlet . Roger Gourd was the project lead for VMS. Software engineers Dave Cutler , Dick Hustvedt , and Peter Lipman acted as technical project leaders. The Star and Starlet projects culminated in the VAX-11/780 computer and the VAX/VMS operating system. The Starlet project's code name survives in VMS in

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2354-524: A prototype Alpha EV3 -based Alpha Demonstration Unit in early 1991. The main challenge in porting VMS to a new architecture was that VMS and the VAX were designed together, meaning that VMS was dependent on certain details of the VAX architecture. Furthermore, a significant amount of the VMS kernel, layered products, and customer-developed applications were implemented in VAX MACRO assembly code. Some of

2461-423: A team was set up to design new VAX/VMS systems of comparable performance to RISC -based Unix systems. After a number of failed attempts to design a faster VAX-compatible processor, the group demonstrated the feasibility of porting VMS and its applications to a RISC architecture based on PRISM. This led to the creation of the Alpha architecture. The project to port VMS to Alpha began in 1989, and first booted on

2568-468: Is 1500 bytes, the minimum size of a TCP header is 20 bytes, and the minimum size of an IPv4 header is 20 bytes, so the maximum segment size is 1500−(20+20) bytes, or 1460 bytes. The process of dividing data into segments is called segmentation ; it is an optional function of the transport layer. Some connection-oriented transport protocols, such as TCP and the OSI connection-oriented transport protocol (COTP), perform segmentation and reassembly of segments on

2675-564: Is a data link layer protocol that can operate over several different physical layers, such as synchronous and asynchronous serial lines. The ITU-T G.hn standard, which provides high-speed local area networking over existing wires (power lines, phone lines and coaxial cables), includes a complete data link layer that provides both error correction and flow control by means of a selective-repeat sliding-window protocol . Security, specifically (authenticated) encryption, at this layer can be applied with MACsec . The network layer provides

2782-411: Is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. Also, all OSI TP connection-mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of TP0–4 classes are shown in the following table: An easy way to visualize the transport layer is to compare it with a post office, which deals with

2889-501: Is developed and supported by VMS Software Inc. (VSI). OpenVMS offers high availability through clustering —the ability to distribute the system over multiple physical machines. This allows clustered applications and data to remain continuously available while operating system software and hardware maintenance and upgrades are performed, or if part of the cluster is destroyed. VMS cluster uptimes of 17 years have been reported. In April 1975, Digital Equipment Corporation embarked on

2996-617: Is further subdivided between the Kernel , which consists of the code which runs at the kernel access mode, and the less-privileged code outside of the Kernel which runs at the executive access mode. The components of the Executive which run at executive access mode include the Record Management Services , and certain system services such as image activation. The main distinction between the kernel and executive access modes

3103-587: Is limited to 2 TiB volumes. DEC attempted to replace it with a log-structured file system named Spiralog, first released in 1995. However, Spiralog was discontinued due to a variety of problems, including issues with handling full volumes. Instead, there has been discussion of porting the open-source GFS2 file system to OpenVMS. An OpenVMS Command Language Interpreter (CLI) implements a command-line interface for OpenVMS, responsible for executing individual commands and command procedures (equivalent to shell scripts or batch files ). The standard CLI for OpenVMS

3210-483: Is not usually a fatal problem. The OSI connection-oriented transport protocol defines five classes of connection-mode transport protocols, ranging from class 0 (which is also known as TP0 and provides the fewest features) to class 4 (TP4, designed for less reliable networks, similar to the Internet). Class 0 contains no error recovery and was designed for use on network layers that provide error-free connections. Class 4

3317-584: Is possible to call a routine written in one language (for example, Fortran) from another (for example, COBOL), without needing to know the implementation details of the target language. OpenVMS itself is implemented in a variety of different languages and the common language environment and calling standard supports freely mixing these languages. DEC created a tool named the Structure Definition Language (SDL), which allowed data type definitions to be generated for different languages from

DECnet - Misplaced Pages Continue

3424-486: Is still used as a reference for teaching and documentation; however, the OSI protocols originally conceived for the model did not gain popularity. Some engineers argue the OSI reference model is still relevant to cloud computing . Others say the original OSI model does not fit today's networking protocols and have suggested instead a simplified approach. Communication protocols enable an entity in one host to interact with

3531-447: Is that most of the operating system's core data structures can be read from executive mode, but require kernel mode to be written to. Code running at executive mode can switch to kernel mode at will, meaning that the barrier between the kernel and executive modes is intended as a safeguard against accidental corruption as opposed to a security mechanism. The Kernel comprises the operating system's core data structures (e.g. page tables,

3638-529: Is the DIGITAL Command Language , although other options are available. Unlike Unix shells , which typically run in their own isolated process and behave like any other user-mode program, OpenVMS CLIs are an optional component of a process, which exist alongside any executable image which that process may run. Whereas a Unix shell will typically run executables by creating a separate process using fork-exec , an OpenVMS CLI will typically load

3745-556: Is the function of the payload that makes these belong to the network layer, not the protocol that carries them. The transport layer provides the functional and procedural means of transferring variable-length data sequences from a source host to a destination host from one application to another across a network, while maintaining the quality-of-service functions. Transport protocols may be connection-oriented or connectionless. This may require breaking large protocol data units or long data streams into smaller chunks called "segments", since

3852-423: Is the layer of the OSI model that is closest to the end user, which means both the OSI application layer and the user interact directly with a software application that implements a component of communication between the client and server, such as File Explorer and Microsoft Word . Such application programs fall outside the scope of the OSI model unless they are directly integrated into the application layer through

3959-411: Is the lowest layer in this model. The physical layer is responsible for the transmission and reception of unstructured raw data between a device, such as a network interface controller , Ethernet hub , or network switch , and a physical transmission medium . It converts the digital bits into electrical, radio, or optical signals. Layer specifications define characteristics such as voltage levels,

4066-549: Is tightly integrated into VMS, allowing remote logins, as well as transparent access to files, printers and other resources on VMS systems over a network. VAX/VMS V1.0 featured support for DECnet Phase II, and modern versions of VMS support both the traditional Phase IV DECnet protocol, as well as the OSI-compatible Phase V (also known as DECnet-Plus ). Support for TCP/IP is provided by the optional TCP/IP Services for OpenVMS layered product (originally known as

4173-440: The $ CMEXEC and $ CMKRNL system services, respectively. This allows code outside of system space to have direct access to the Executive's routines and system services. In addition to allowing third-party extensions to the operating system, Privileged Images are used by core operating system utilities to manipulate operating system data structures through undocumented interfaces. The typical user and application interface into

4280-592: The Apple Macintosh to serve as a terminal for VMS systems, or to use VMS systems as a file or print server. PATHWORKS was later renamed to Advanced Server for OpenVMS , and was eventually replaced with a VMS port of Samba at the time of the Itanium port. DEC provided the Local Area Transport (LAT) protocol which allowed remote terminals and printers to be attached to a VMS system through

4387-540: The IETF RFC 1006 (OSI over IP) and RFC 1859 (NSP over IP) standards (see diagram) . It was later renamed DECnet/OSI to emphasize its OSI interconnectability, and subsequently DECnet-Plus as TCP/IP protocols were incorporated. DEC's internal corporate network was a DECnet network called Easynet, which had evolved from DEC's Engineering Net (E-NET). It included over 2,000 nodes as of 1984, 15,000 nodes (in 39 countries) as of 1987, and 54,000 nodes as of 1990. DECnet

DECnet - Misplaced Pages Continue

4494-567: The International Network Working Group ( IFIP WG6.1). In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it and provided facilities for use by the layer above it. The OSI standards documents are available from the ITU-T as the X.200 series of recommendations. Some of

4601-755: The VMS/ULTRIX Connection , then as the ULTRIX Communications Extensions or UCX). TCP/IP Services is based on a port of the BSD network stack to OpenVMS, along with support for common protocols such as SSH , DHCP , FTP and SMTP . DEC sold a software package named PATHWORKS (originally known as the Personal Computer Systems Architecture or PCSA) which allowed personal computers running MS-DOS , Microsoft Windows or OS/2 , or

4708-444: The X.25 standard in the late 1970s. The Experimental Packet Switched System in the UK c.  1973 –1975 identified the need for defining higher level protocols. The UK National Computing Centre publication, Why Distributed Computing , which came from considerable research into future configurations for computer systems, resulted in the UK presenting the case for an international standards committee to cover this area at

4815-573: The file system is the Record Management Services (RMS), although applications can interface directly with the underlying file system through the QIO system services. The file systems supported by VMS are referred to as the Files-11 On-Disk Structures (ODS), the most significant of which are ODS-2 and ODS-5 . VMS is also capable of accessing files on ISO 9660 CD-ROMs and magnetic tape with ANSI tape labels . Files-11

4922-497: The protocols which operate within each layer. Although network protocol analyzer tools tend to categorize all protocols from DIGITAL as "DECnet", strictly speaking, non-routed DIGITAL protocols such as LAT , SCS, AMDS, LAST/LAD are not DECnet protocols and are not part of the DIGITAL Network Architecture. To trace the evolution of DECnet is to trace the development of DNA. The beginnings of DNA were in

5029-400: The teardown , between two or more computers, which is called a "session". Common functions of the session layer include user logon (establishment) and user logoff (termination) functions. Including this matter, authentication methods are also built into most client software, such as FTP Client and NFS Client for Microsoft Networks. Therefore, the session layer establishes, manages and terminates

5136-522: The 1990s and 2000s, there were approximately half a million VMS systems in operation worldwide. It was first announced by Digital Equipment Corporation (DEC) as VAX/VMS ( Virtual Address eXtension/Virtual Memory System ) alongside the VAX-11/780 minicomputer in 1977. OpenVMS has subsequently been ported to run on DEC Alpha systems, the Itanium -based HPE Integrity Servers , and select x86-64 hardware and hypervisors . Since 2014, OpenVMS

5243-492: The 21st century. These include: OpenVMS OpenVMS , often referred to as just VMS , is a multi-user , multiprocessing and virtual memory -based operating system . It is designed to support time-sharing , batch processing , transaction processing and workstation applications. Customers using OpenVMS include banks and financial services, hospitals and healthcare, telecommunications operators, network information services, and industrial manufacturers. During

5350-703: The Alpha architecture in favour of adopting the then-new Itanium architecture. The porting began in late 2001, and the first boot on took place on January 31, 2003. The first boot consisted of booting a minimal system configuration on a HP i2000 workstation, logging in as the SYSTEM user, and running the DIRECTORY command. The Itanium port of OpenVMS supports specific models and configurations of HPE Integrity Servers . The Itanium releases were originally named HP OpenVMS Industry Standard 64 for Integrity Servers , although

5457-510: The I/O database and scheduling data), and the routines which operate on these structures. The Kernel is typically described as having three major subsystems: I/O, Process and Time Management, Memory Management. In addition, other functionality such as logical name management, synchronization and system service dispatch are implemented inside the Kernel. OpenVMS allows user-mode code with suitable privileges to switch to executive or kernel mode using

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5564-689: The ISO meeting in Sydney in March 1977. Beginning in 1977, the ISO initiated a program to develop general standards and methods of networking. A similar process evolved at the International Telegraph and Telephone Consultative Committee (CCITT, from French: Comité Consultatif International Téléphonique et Télégraphique ). Both bodies developed documents that defined similar networking models. The British Department of Trade and Industry acted as

5671-541: The Linux kernel was marked as orphaned on February 18, 2010 and removed August 22, 2022. DECnet refers to a specific set of hardware and software networking products which implement the DIGITAL Network Architecture (DNA). The DIGITAL Network Architecture has a set of documents which define the network architecture in general, state the specifications for each layer of the architecture, and describe

5778-456: The OSI model has well-defined functions, and the methods of each layer communicate and interact with those of the layers immediately above and below as appropriate. The Internet protocol suite as defined in RFC   1122 and RFC   1123 is a model of networking developed contemporarily to the OSI model, and was funded primarily by the U.S. Department of Defense. It was the foundation for

5885-584: The OSI model started in the late 1970s to support the emergence of the diverse computer networking methods that were competing for application in the large national networking efforts in the world (see OSI protocols and Protocol Wars ). In the 1980s, the model became a working product of the Open Systems Interconnection group at the International Organization for Standardization (ISO). While attempting to provide

5992-429: The OSI physical and datalink layers with DECnet and LAT terminal servers used MOP for the server image download and related bootstrap processing. Enhancements made to DECnet Phase IV eventually became known as DECnet Phase IV+, although systems running this protocol remained completely interoperable with DECnet Phase IV systems. Phase V and Phase V+ (1987). Support for very large (architecturally unlimited) networks,

6099-545: The PATHWORKS 32 client, that implemented much of DECnet Phase IV for DOS, and 16 and 32 bit Microsoft Windows platforms (all the way through to Windows Server 2003). Phase IV implemented an 8 layer architecture similar to the OSI (7 layer) model especially at the lower levels. Since the OSI standards were not yet fully developed at the time, many of the Phase IV protocols remained proprietary. The Ethernet implementation

6206-698: The V3.0 release, all compatibility-mode utilities were replaced with native implementations. In VAX/VMS V4.0, RSX AME was removed from the base system, and replaced with an optional layered product named VAX-11 RSX . A number of distributions of VAX/VMS were created: With the V5.0 release in April 1988, DEC began to refer to VAX/VMS as simply VMS in its documentation. In July 1992, DEC renamed VAX/VMS to OpenVMS as an indication of its support of open systems industry standards such as POSIX and Unix compatibility, and to drop

6313-588: The V9.1 Field Test, making it available to VSI's customers and partners. V9.1 shipped as an ISO image which can be installed onto a variety of hypervisors, and onto HPE ProLiant DL380 servers starting with the V9.1-A release. During the 1980s, the MICA operating system for the PRISM architecture was intended to be the eventual successor to VMS. MICA was designed to maintain backwards compatibility with VMS applications while also supporting Ultrix applications on top of

6420-402: The VAX architecture, including: These VAX architecture mechanisms are implemented on Alpha, Itanium and x86-64 by either mapping to corresponding hardware mechanisms on those architectures, or through emulation (via PALcode on Alpha, or in software on Itanium and x86-64). The OpenVMS Executive comprises the privileged code and data structures which reside in the system space. The Executive

6527-813: The VAX connection since a migration to a different architecture was underway. The OpenVMS name was first used with the OpenVMS AXP V1.0 release in November 1992. DEC began using the OpenVMS VAX name with the V6.0 release in June 1993. During the 1980s, DEC planned to replace the VAX platform and the VMS operating system with the PRISM architecture and the MICA operating system. When these projects were cancelled in 1988,

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6634-499: The application layer, known as HTTP, FTP, SMB/CIFS, TFTP, and SMTP. When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit. The most important distinction in the application layer is the distinction between the application-entity and the application. For example, a reservation website might have two application-entities: one using HTTP to communicate with its users, and one for

6741-492: The changes included using the Extensible Firmware Interface (EFI) to boot the operating system, reimplementing the functionality previously provided by Alpha PALcode inside the kernel, using new executable file formats ( Executable and Linkable Format and DWARF ), and adopting IEEE 754 as the default floating point format. As with the VAX to Alpha port, a binary translator for Alpha to Itanium

6848-595: The changes needed to decouple VMS from the VAX architecture included the creation of the MACRO-32 compiler, which treated VAX MACRO as a high-level language , and compiled it to Alpha object code , and the emulation of certain low-level details of the VAX architecture in PALcode , such as interrupt handling and atomic queue instructions. The VMS port to Alpha resulted in the creation of two separate codebases: one for VAX , and another for Alpha. The Alpha code library

6955-558: The connections between the local and remote application. The session layer also provides for full-duplex , half-duplex , or simplex operation, and establishes procedures for checkpointing, suspending, restarting, and terminating a session between two related streams of data, such as an audio and a video stream in a web-conferencing application. Therefore, the session layer is commonly implemented explicitly in application environments that use remote procedure calls . The presentation layer establishes data formatting and data translation into

7062-490: The datalink of choice, expanded adaptive routing capability to include hierarchical routing (areas, level 1 and level 2 routers), VMScluster support (cluster alias) and host services (CTERM). CTERM allowed a user on one computer to log into another computer remotely, performing the same function that Telnet does in the TCP/IP protocol stack. Digital also released a product called the PATHWORKS client, and more commonly known as

7169-430: The development of the Internet . It assumed the presence of generic physical links and focused primarily on the software layers of communication, with a similar but much less rigorous structure than the OSI model. In comparison, several networking models have sought to create an intellectual framework for clarifying networking concepts and activities, but none have been as successful as the OSI reference model in becoming

7276-551: The dispatch and classification of mail and parcels sent. A post office inspects only the outer envelope of mail to determine its delivery. Higher layers may have the equivalent of double envelopes, such as cryptographic presentation services that can be read by the addressee only. Roughly speaking, tunnelling protocols operate at the transport layer, such as carrying non-IP protocols such as IBM 's SNA or Novell 's IPX over an IP network, or end-to-end encryption with IPsec . While Generic Routing Encapsulation (GRE) might seem to be

7383-1265: The early 1970s. DIGITAL published its first DNA specification at about the same time that IBM announced its Systems Network Architecture (SNA). Since that time, development of DNA has evolved through the following phases: Phase I (1974) Support limited to two PDP-11s running the RSX-11 operating system, or a small number of PDP-8s running the RTS-8 operating system, with communication over point-to-point ( DDCMP ) links between nodes. Phase II (1975) Support for networks of up to 32 nodes with multiple, different implementations which could inter-operate with each other. Implementations expanded to include RSTS , TOPS-10 , TOPS-20 and VAX/VMS with communications between processors still limited to point-to-point links only. Introduction of downline loading (MOP), and file transfer using File Access Listener (FAL), remote file access using Data Access Protocol (DAP), task-to-task programming interfaces and network management features. Phase III (1980). Support for networks of up to 255 nodes with 8-bit addresses, over point-to point and multi-drop links. Introduction of adaptive routing capability, record access,

7490-407: The establishment of the company, as well as the development of VSI's own Itanium and Alpha releases of OpenVMS V8.4-x. The x86-64 port is targeted for specific servers from HPE and Dell , as well as certain virtual machine hypervisors . Initial support was targeted for KVM and VirtualBox . Support for VMware was announced in 2020, and Hyper-V is being explored as a future target. In 2021,

7597-430: The executable image into the same process, transfer control to the image, and ensure that control is transferred back to CLI once the image has exited and that the process is returned to its original state. Because the CLI is loaded into the same address space as user code, and the CLI is responsible for invoking image activation and image rundown, the CLI is mapped into the process address space at supervisor access mode,

7704-576: The fact; the reverse of the traditional approach to developing standards. Although not a standard itself, it was a framework in which future standards could be defined. In May 1983, the CCITT and ISO documents were merged to form The Basic Reference Model for Open Systems Interconnection , usually referred to as the Open Systems Interconnection Reference Model , OSI Reference Model , or simply OSI model . It

7811-518: The flow of data in a communication system into seven abstraction layers to describe networked communication from the physical implementation of transmitting bits across a communications medium to the highest-level representation of data of a distributed application . Each intermediate layer serves a class of functionality to the layer above it and is served by the layer below it. Classes of functionality are implemented in software development using established communication protocols . Each layer in

7918-670: The form that the application layer accepts, to be sent across a network. Since the presentation layer converts data and graphics into a display format for the application layer, the presentation layer is sometimes called the syntax layer. For this reason, the presentation layer negotiates the transfer of syntax structure through the Basic Encoding Rules of Abstract Syntax Notation One (ASN.1), with capabilities such as converting an EBCDIC -coded text file to an ASCII -coded file, or serialization of objects and other data structures from and to XML . The application layer

8025-531: The four privilege levels of OpenVMS in software since only two of x86-64's privilege levels are usable by OpenVMS. The first boot was announced on May 14, 2019. This involved booting OpenVMS on VirtualBox, and successfully running the DIRECTORY command. In May 2020, the V9.0 Early Adopter's Kit release was made available to a small number of customers. This consisted of the OpenVMS operating system running in

8132-407: The functional and procedural means of transferring packets from one node to another connected in "different networks". A network is a medium to which many nodes can be connected, on which every node has an address and which permits nodes connected to it to transfer messages to other nodes connected to it by merely providing the content of a message and the address of the destination node and letting

8239-413: The functions of communication, as is the case with applications such as web browsers and email programs . Other examples of software are Microsoft Network Software for File and Printer Sharing and Unix/Linux Network File System Client for access to shared file resources. Application-layer functions typically include file sharing, message handling, and database access, through the most common protocols at

8346-851: The name of several of the system libraries, including STARLET.OLB and STARLET.MLB . VMS was mostly written in VAX MACRO with some components written in BLISS . One of the original goals for VMS was backward compatibility with DEC's existing RSX-11M operating system. Prior to the V3.0 release, VAX/VMS included a compatibility layer named the RSX Application Migration Executive (RSX AME), which allowed user-mode RSX-11M software to be run unmodified on top of VMS. The RSX AME played an important role on early versions of VAX/VMS, which used certain RSX-11M user-mode utilities before native VAX versions had been developed. By

8453-487: The names OpenVMS I64 or OpenVMS for Integrity Servers are more commonly used. The Itanium port was accomplished using source code maintained in common within the OpenVMS Alpha source code library, with the addition of conditional code and additional modules where changes specific to Itanium were required. This required certain architectural dependencies of OpenVMS to be replaced, or emulated in software. Some of

8560-502: The network find the way to deliver the message to the destination node, possibly routing it through intermediate nodes. If the message is too large to be transmitted from one node to another on the data link layer between those nodes, the network may implement message delivery by splitting the message into several fragments at one node, sending the fragments independently, and reassembling the fragments at another node. It may, but does not need to, report delivery errors. Message delivery at

8667-449: The network layer imposes a maximum packet size called the maximum transmission unit (MTU), which depends on the maximum packet size imposed by all data link layers on the network path between the two hosts. The amount of data in a data segment must be small enough to allow for a network-layer header and a transport-layer header. For example, for data being transferred across Ethernet , the MTU

8774-426: The network layer is not necessarily guaranteed to be reliable; a network layer protocol may provide reliable message delivery, but it does not need to do so. A number of layer-management protocols, a function defined in the management annex , ISO 7498/4, belong to the network layer. These include routing protocols, multicast group management, network-layer information and error, and network-layer address assignment. It

8881-437: The notable exception of RT-11 . DECnet stacks are found on Linux, SunOS and other platforms, and Cisco and other network vendors offer products that can cooperate with and operate within DECnet networks. Full DECnet Phase IV specifications are available. At the same time that DECnet Phase IV was released, the company also released a proprietary protocol called LAT for serial terminal access via Terminal servers . LAT shared

8988-491: The operations staff at the various sites, all of which were using a variety of DEC computers. As of March 1983, it included Columbia University , Carnegie Mellon University , and Case Western Reserve University . By May 1986, New York University , Stevens Institute of Technology , Vassar College and Oberlin College had been added. Several other universities joined later. Hobbyist DECnet networks have been in use during

9095-435: The physical layer. It defines the protocol to establish and terminate a connection between two physically connected devices. It also defines the protocol for flow control between them. IEEE 802 divides the data link layer into two sublayers: The MAC and LLC layers of IEEE 802 networks such as 802.3 Ethernet , 802.11 Wi-Fi , and 802.15.4 Zigbee operate at the data link layer. The Point-to-Point Protocol (PPP)

9202-538: The pre-production quality releases of OpenVMS AXP confused some customers, and was not repeated in the subsequent ports of OpenVMS to new platforms. When VMS was ported to Alpha, it was initially left as a 32-bit only operating system. This was done to ensure backwards compatibility with software written for the 32-bit VAX. 64-bit addressing was first added for Alpha in the V7.0 release. In order to allow 64-bit code to interoperate with older 32-bit code, OpenVMS does not create

9309-681: The primary command language interpreter (CLI) of OpenVMS since the first release. Other official CLIs available for VMS include the RSX-11 Monitor Console Routine (MCR) (VAX only), and various Unix shells . DEC provided tools for creating text-based user interface applications – the Form Management System (FMS) and Terminal Data Management System (TDMS), later succeeded by DECforms . A lower level interface named Screen Management Services (SMG$ ), comparable to Unix curses , also exists. Over

9416-482: The protocol specifications were also available as part of the ITU-T X series. The equivalent ISO/IEC standards for the OSI model were available from ISO. Not all are free of charge. OSI was an industry effort, attempting to get industry participants to agree on common network standards to provide multi-vendor interoperability. It was common for large networks to support multiple network protocol suites, with many devices unable to interoperate with other devices because of

9523-436: The receiving side; connectionless transport protocols, such as UDP and the OSI connectionless transport protocol (CLTP), usually do not. The transport layer also controls the reliability of a given link between a source and destination host through flow control, error control, and acknowledgments of sequence and existence. Some protocols are state- and connection-oriented . This means that the transport layer can keep track of

9630-613: The same kernel. MICA was ultimately cancelled along with the rest of the PRISM platform, leading Dave Cutler to leave DEC for Microsoft. At Microsoft, Cutler led the creation of the Windows NT operating system, which was heavily inspired by the architecture of MICA. As a result, VMS is considered an ancestor of Windows NT , together with RSX-11 , VAXELN and MICA, and many similarities exist between VMS and NT. A now-defunct project named FreeVMS attempted to develop an open-source operating system following VMS conventions. FreeVMS

9737-736: The secretariat, and universities in the United Kingdom developed prototypes of the standards. The OSI model was first defined in raw form in Washington, D.C. , in February 1978 by French software engineer Hubert Zimmermann , and the refined but still draft standard was published by the ISO in 1980. The drafters of the reference model had to contend with many competing priorities and interests. The rate of technological change made it necessary to define standards that new systems could converge to rather than standardizing procedures after

9844-585: The segments and retransmit those that fail delivery through the acknowledgment hand-shake system. The transport layer will also provide the acknowledgement of the successful data transmission and sends the next data if no errors occurred. Reliability, however, is not a strict requirement within the transport layer. Protocols like UDP, for example, are used in applications that are willing to accept some packet loss, reordering, errors or duplication. Streaming media , real-time multiplayer games and voice over IP (VoIP) are examples of applications in which loss of packets

9951-589: The standard model for discussing and teaching networking in the field of information technology . The model allows transparent communication through equivalent exchange of protocol data units (PDUs) between two parties, through what is known as peer-to-peer networking (also known as peer-to-peer communication). As a result, the OSI reference model has not only become an important piece among professionals and non-professionals alike, but also in all networking between one or many parties, due in large part to its commonly accepted user-friendly framework. The development of

10058-433: The timing of voltage changes, physical data rates, maximum transmission distances, modulation scheme, channel access method and physical connectors. This includes the layout of pins , voltages , line impedance , cable specifications, signal timing and frequency for wireless devices. Bit rate control is done at the physical layer and may define transmission mode as simplex , half duplex , and full duplex . The components of

10165-651: The transport layer, the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite are commonly categorized as layer 4 protocols within OSI. Transport Layer Security (TLS) does not strictly fit inside the model either. It contains characteristics of the transport and presentation layers. The session layer creates the setup, controls the connections, and ends

10272-604: The use of either "poor man's routing" (PMR) or address translation gateways. In December 1988, VAX/VMS hosts on the DECnet Internet were attacked by the Father Christmas worm . CCNET (Computer Center Network) was a DECnet network that connected the campuses of various universities in the eastern regions of the United States during the 1980s. A key benefit was the sharing of systems software developed by

10379-413: The x86-64 port was demonstrated running on an Intel Atom -based single-board computer . As with the Alpha and Itanium ports, the x86-64 port made some changes to simplify porting and supporting OpenVMS on the new platform including: replacing the proprietary GEM compiler backend used by the VMS compilers with LLVM , changing the boot process so that OpenVMS is booted from a memory disk, and simulating

10486-585: The years, VMS has gone through a number of different GUI toolkits and interfaces: OSI model The Open Systems Interconnection ( OSI ) model is a reference model from the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems interconnection." In the OSI reference model, the communications between systems are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The model partitions

10593-526: Was OpenVMS Galaxy , which allowed the partitioning of a single SMP server to run multiple instances of OpenVMS. Galaxy supported dynamic resource allocation to running partitions, and the ability to share memory between partitions. In 2001, prior to its acquisition by Hewlett-Packard , Compaq announced the port of OpenVMS to the Intel Itanium architecture. The Itanium port was the result of Compaq's decision to discontinue future development of

10700-413: Was based on a snapshot of the VAX/VMS code base circa V5.4-2. 1992 saw the release of the first version of OpenVMS for Alpha AXP systems, designated OpenVMS AXP V1.0 . In 1994, with the release of OpenVMS V6.1, feature (and version number) parity between the VAX and Alpha variants was achieved; this was the so-called Functional Equivalence release. The decision to use the 1.x version numbering stream for

10807-543: Was built on top of the L4 microkernel and supported the x86-64 architecture. Prior work investigating the implementation of VMS using a microkernel-based architecture had previously been undertaken as a prototyping exercise by DEC employees with assistance from Carnegie Mellon University using the Mach 3.0 microkernel ported to VAXstation 3100 hardware, adopting a multiserver architectural model. The OpenVMS operating system has

10914-708: Was made available, allowing user-mode OpenVMS Alpha software to be ported to Itanium in situations where it was not possible to recompile the source code. This translator is known as the Alpha Environment Software Translator (AEST), and it also supported translating VAX executables which had already been translated with VEST. Two pre-production releases, OpenVMS I64 V8.0 and V8.1, were available on June 30, 2003, and on December 18, 2003. These releases were intended for HP organizations and third-party vendors involved with porting software packages to OpenVMS I64. The first production release, V8.2,

11021-630: Was originally designed to be used and managed interactively using DEC's text-based video terminals such as the VT100 , or hardcopy terminals such as the DECwriter series. Since the introduction of the VAXstation line in 1984, VMS has optionally supported graphical user interfaces for use with workstations or X terminals such as the VT1000 series. The DIGITAL Command Language (DCL) has served as

11128-668: Was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT (now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU-T ) as standard X.200. OSI had two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols . The OSI reference model was

11235-424: Was released in February 2005. V8.2 was also released for Alpha; subsequent V8.x releases of OpenVMS have maintained feature parity between the Alpha and Itanium architectures. When VMS Software Inc. (VSI) announced that they had secured the rights to develop the OpenVMS operating system from HP, they also announced their intention to port OpenVMS to the x86-64 architecture. The porting effort ran concurrently with

11342-646: Was unusual in that the software changed the physical address of the Ethernet interface on the network to AA-00-04-00-xx-yy where xx-yy reflected the DECnet network address of the host. This allowed ARP-less LAN operation because the LAN address could be deduced from the DECnet address. This precluded connecting two NICs from the same DECnet node onto the same LAN segment, however. The initial implementations released were for VAX/VMS and RSX-11, later this expanded to virtually every operating system DIGITAL ever shipped with

11449-545: Was used at various scientific research centers which linked their networks to form an international network called the DECnet Internet. This included the U.S. Space Physics Analysis Network (US-SPAN), the European Space Physics Analysis Network (E-SPAN), Energy Sciences Network , and other research and education networks. The network consisted of over 17,000 nodes as of 1989. Routing between networks with different address spaces involved

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