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64-549: SNA was made public as part of IBM's "Advanced Function for Communications" announcement in September, 1974, which included the implementation of the SNA/SDLC ( Synchronous Data Link Control ) protocols on new communications products: They were supported by IBM 3704/3705 communication controllers and their Network Control Program (NCP), and by System/370 and their VTAM and other software such as CICS and IMS. This announcement

128-667: A "Line" connection can be defined using various possible solutions (such as a Token Ring interface on the 3745, a 3172 Lan Channel Station, or a Cisco ESCON -compatible Channel Interface Processor). The proprietary networking architecture for Honeywell Bull mainframes is Distributed Systems Architecture (DSA). The Communications package for DSA is VIP . DSA is also no longer supported for client access. Bull mainframes are fitted with Mainway for translating DSA to TCP/IP and VIP devices are replaced by TNVIP Terminal Emulations ( GLink , Winsurf ). GCOS 8 supports TNVIP SE over TCP/IP. The networking architecture for Univac mainframes

192-740: A "shut-off sequence", forcing them to abort transmission. ) ITU-T The International Telecommunication Union Telecommunication Standardization Sector ( ITU-T ) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Communication Technology , such as X.509 for cybersecurity, Y.3172 and Y.3173 for machine learning, and H.264/MPEG-4 AVC for video compression, between its Member States, Private Sector Members, and Academia Members. The World Telecommunication Standardization Assembly (WTSA),

256-470: A calendar issued by the TSB. SGs are augmented by Focus Groups (FGs), an instrument created by ITU-T, providing a way to quickly react to ICT standardization needs and allowing great flexibility in terms of participation and working methods. The key difference between SGs and FGs is that the latter have greater freedom to organize and finance themselves, and to involve non-members in their work, but they do not have

320-502: A distinction between LU types, as the application must take the functionality of the terminal equipment into account (e.g. screen sizes and layout). Within SNA there are three types of data stream to connect local display terminals and printers; there is SNA Character String (SCS), used for LU1 terminals and for logging on to an SNA network with Unformatted System Services (USS), there is the 3270 data stream mainly used by mainframes such as

384-432: A one-bit delay. A similar opportunity is used to go "off-loop" as part of a clean shutdown. In SDLC loop mode, frames arrive in a group, ending (after the final flag) with an all-ones idle signal. The first seven 1-bits of this (the pattern 01111111) constitute a "go-ahead" sequence (also called EOP, end of poll) giving a secondary permission to transmit. A secondary which wishes to transmit uses its 1-bit delay to convert

448-416: A profusion of software firms around the world were still furiously competing to shape the future of the electronic office , and was completed in 1999 long after Microsoft Office 's then-secret binary file formats had become established as the global de facto standard. The ITU-T now operates under much more streamlined processes. The time between an initial proposal of a draft document by a member company and

512-405: A special "turnaround" frame at the end of its commands to separate them from the responses. Any unique sequence which will not be interpreted by the secondaries will do, but the conventional one is a single all-zero byte. This is a "runt frame" with an address of 0 (reserved, unused) and no control field or frame check sequence. (Secondaries capable of full-duplex operation also interpret this as

576-475: A very stripped-down protocol which suited only a specific type of terminal. As a result, several multi-layer communications protocols were proposed in the 1970s, of which IBM's SNA and ITU-T 's X.25 became dominant later. The most important elements of SNA include: SNA removed link control from the application program and placed it in the NCP. This had the following advantages and disadvantages: SNA at its core

640-473: A wide array of topics in the field of information and communication technologies (ICT) and attract high-ranking experts as speakers, and attendees from engineers to high-level management from all industry sectors. The technical work, the development of Recommendations, of ITU-T is managed by Study Groups (SGs), such as Study Group 13 for network standards, Study Group 16 for multimedia standards, and Study Group 17 for security standards, which are created by

704-534: Is a computer serial communications protocol first introduced by IBM as part of its Systems Network Architecture (SNA). SDLC is used as layer 2, the data link layer , in the SNA protocol stack . It supports multipoint links as well as error correction. It also runs under the assumption that an SNA header is present after the SDLC header. SDLC was mainly used by IBM mainframe and midrange systems; however, implementations exist on many platforms from many vendors. In

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768-582: Is a fast-track approval procedure that was developed to allow standards to be brought to market in the timeframe that industry now demands. The AAP is defined in ITU-T Recommendation A.8. This dramatic overhaul of standards-making by streamlining approval procedures was implemented in 2001 and is estimated to have cut the time involved in this critical aspect of the standardization process by 80 to 90 percent. This means that an average standard that took around four years to approve and publish until

832-616: Is followed by a period and the Recommendation number, which uniquely identifies the Recommendation within the series. Often, a range of related Recommendations are further grouped within the series and given adjacent numbers, such as "H.200-H.499: Infrastructure of audiovisual services" or "H.260-H.279: Coding of moving video". Many numbers are "skipped" to give room for future Recommendations to be adjacent to related Recommendations. Recommendations can be revised or "superseded" and keep their existing Recommendation number. In addition to

896-579: Is its ability to mix half-duplex secondary stations with full-duplex primary stations on four-wire circuits, thus reducing the cost of dedicated facilities. This de facto standard has been adopted by ISO as High-Level Data Link Control (HDLC) in 1979 and by ANSI as Advanced Data Communication Control Procedures (ADCCP). The latter standards added features such as the Asynchronous Balanced Mode , frame sizes that did not need to be multiples of bit-octets, but also removed some of

960-661: Is mostly an extension of SDLC, but some features were deleted or renamed. Features present in HDLC, but not SDLC, are: Also not in SDLC are later HDLC extensions in ISO/IEC 13239 such as: HDLC renamed some SDLC frames. The HDLC names were incorporated into later versions of SDLC: Some features were added in HDLC, and subsequently added back to later versions of SDLC. Two U frames in SDLC which do not exist in HDLC are: Several U frames are almost entirely unused in HDLC, existing primarily for SDLC compatibility: The TEST U frame

1024-460: Is now free of charge online. (About 30 specifications jointly maintained by the ITU-T and ISO/IEC are not available for free to the public. ) ITU-T has moreover tried to facilitate cooperation between the various forums and standard-developing organizations (SDOs). This collaboration is necessary to avoid duplication of work and the consequent risk of conflicting standards in the market place. In

1088-914: Is now named Microsoft Host Integration Server . Digital Equipment Corporation had VMS/SNA for VMS . Third-party SNA software packages for VMS, such as the VAX Link products from Systems Strategies, Inc., were also available. Hewlett-Packard offered SNA Server and SNA Access for its HP 3000 systems. Brixton Systems developed several SNA software packages, sold under the name " Brixton ", such as Brixton BrxPU21, BrxPU5, BrxLU62, and BrxAPPC, for systems such as workstations from Hewlett-Packard , and Sun Microsystems . IBM supported using several non-IBM software implementations of APPC/PU2.1/LU6.2 to communicate with z/OS , including SNAplus2 for systems from HP , Brixton 4.1 SNA for Sun Solaris , and SunLink SNA 9.1 Support for Sun Solaris. Synchronous Data Link Control Synchronous Data Link Control ( SDLC )

1152-432: Is to ensure the efficient and timely production of standards covering all fields of telecommunications and Information Communication Technology (ICTs) on a worldwide basis, as well as defining tariff and accounting principles for international telecommunication services. The international standards that are produced by the ITU-T are referred to as " Recommendations " (with the word capitalized to distinguish its meaning from

1216-851: The Plenipotentiary Conference (the top policy-making conference of ITU) saw a reform of ITU, giving the Union greater flexibility to adapt to an increasingly complex, interactive and competitive environment. The CCITT was renamed the Telecommunication Standardization Sector (ITU-T), as one of three Sectors of the Union alongside the Radiocommunication Sector ( ITU-R ) and the Telecommunication Development Sector ( ITU-D ). Historically,

1280-706: The System/370 and successors, including the zSeries family, and the 5250 data stream mainly used by minicomputers/servers such as the System/34 , System/36 , System/38 , and AS/400 and its successors, including System i and IBM Power Systems running IBM i . SNA defines several kinds of devices, called Logical Unit types: The primary ones in use are LU1, LU2, and LU6.2 (an advanced protocol for application to application conversations). The term 37xx refers to IBM's family of SNA communications controllers. The 3745 supports up to eight high-speed T1 circuits,

1344-642: The World Telecommunication Standardization Assembly (WTSA) which is held every four years. As part of the deliberations, WTSA has instructed ITU to hold the Global Standards Symposium , which unlike WTSA is open to public for participation. The people involved in these SGs are experts in telecommunications from all over the world. There are currently 11 SGs. Study groups meet face to face (or virtually under exceptional circumstances) according to

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1408-478: The 1980s included Zilog , Motorola , and National Semiconductor . As a result, a wide variety of equipment in the 1980s used it and it was very common in the mainframe-centric corporate networks which were the norm in the 1980s. The most common alternatives for SNA with SDLC were probably DECnet with Digital Data Communications Message Protocol (DDCMP), Burroughs Network Architecture (BNA) with Burroughs Data Link Control (BDLC), and ARPANET with IMPs . HDLC

1472-456: The 3725 is a large-scale node and front-end processor for a host, and the 3720 is a remote node that functions as a concentrator and router . VTAM/NCP PU4 nodes attached to IBM Token Ring networks can share the same Local Area Network infrastructure with workstations and servers. NCP encapsulates SNA packets into Token-Ring frames, allowing sessions to flow over a Token-Ring network. The actual encapsulation and decapsulation takes place in

1536-458: The 3745. As mainframe-based entities looked for alternatives to their 37XX-based networks, IBM partnered with Cisco in the mid-1990s and together they developed Data Link Switching , or DLSw. DLSw encapsulates SNA packets into IP datagrams, allowing sessions to flow over an IP network. The actual encapsulation and decapsulation takes place in Cisco routers at each end of a DLSw peer connection. At

1600-751: The French government invited international participants to a conference in Paris in 1865 to facilitate and regulate international telegraph services. A result of the conference was the founding of the forerunner of the modern ITU. At the 1925 Paris conference, the ITU created two consultative committees to deal with the complexities of the international telephone services, known as CCIF ( Comité Consultatif International Téléphonique ) and with long-distance telegraphy CCIT ( Comité Consultatif International des Communications Téléphoniques à grande distance ). In view of

1664-868: The ITU-T Recommendations, which have non-mandatory status unless they are adopted in national laws, ITU-T is also the custodian of a binding international treaty, the International Telecommunication Regulations. The ITRs go back to the earliest days of the ITU when there were two separate treaties, dealing with telegraph and telephone. The ITRs were adopted, as a single treaty, at the World Administrative Telegraphy and Telephone Conference held in Melbourne, 1988 (WATTC-88). The ITRs comprise ten articles which deal, inter alia , with

1728-523: The Recommendations of the CCITT were presented at plenary assemblies for endorsement, held every four years, and the full set of Recommendations were published after each plenary assembly. However, the delays in producing texts, and translating them into other working languages, did not suit the fast pace of change in the telecommunications industry. The rise of the personal computer industry in

1792-476: The SG chairman, in consultation with TSB, sets up a comment resolution process by the concerned experts. The revised text is then posted on the web for an additional review period of three weeks. Similar to the last call phase, in additional review the Recommendation is considered as approved if no comments are received. If comments are received, it is apparent that there are some issues that still need more work, and

1856-761: The TCP/IP session. This protocol is widely used to replace legacy SNA connectivity more than Data-Link Switching (DLSw) and other SNA replacement technologies. A similar TN5250 (Telnet 5250) variant exists for the IBM 5250 . Non-IBM SNA software allowed systems other than IBM's to communicate with IBM's mainframes and AS/400 midrange computers using the SNA protocols. Some Unix system vendors, such as Sun Microsystems with its SunLink SNA product line, including PU2.1 Server, and Hewlett-Packard / Hewlett Packard Enterprise , with their SNAplus2 product, provided SNA software. Microsoft introduced SNA Server for Windows in 1993; it

1920-510: The United States and Canada, SDLC can be found in traffic control cabinets. SDLC was released in 1975, based on work done for IBM in the early 1970s. SDLC operates independently on each communications link in the network and can operate on point-to-point multipoint or loop facilities, on switched or dedicated, two-wire or four-wire circuits, and with full-duplex and half-duplex operation. A unique characteristic of SDLC

1984-579: The amendment of ITRs through a World Conference on International Telecommunications (WCIT). Accordingly, in 1998 there began a process of review of the ITRs; and in 2009 extensive preparations began for such a conference, WCIT-12. In addition to "regional preparatory meetings", the ITU Secretariat developed 13 "Background Briefs on key issues" that were expected to be discussed at the conference. Convened by former ITU secretary-general Hamadoun Touré,

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2048-429: The approval process by providing equal opportunities for both sector members and member states in the approval of technical standards. A panel of SG experts drafts a proposal that is then forwarded at an SG meeting to the appropriate body which decides if it is sufficiently ready to be designated a draft text and thus gives its consent for further review at the next level. After this Consent has been given, TSB announces

2112-595: The authority to approve Recommendations. Focus Groups can be created very quickly, are usually short-lived and can choose their own working methods, leadership, financing, and types of deliverables. Current Focus Groups include the ITU-WHO Focus Group on Artificial Intelligence for Health (FG-AI4H) as well as Machine Learning for 5G (which developed Y.3172 ), Quantum Information Technologies for Networks , and Artificial Intelligence for Assisted and Autonomous Driving . The Alternative Approval Process (AAP)

2176-711: The basic similarity of many of the technical problems faced by the CCIF and CCIT , a decision was taken in 1956 to merge them into a single entity, the International Telegraph and Telephone Consultative Committee ( CCITT , in French : Comité Consultatif International Téléphonique et Télégraphique ). The first Plenary Assembly of the new organization was held in Geneva, Switzerland in December 1956. In 1992,

2240-421: The common parlance sense of the word "recommendation"), as they become mandatory only when adopted as part of a national law. Since the ITU-T is part of the ITU, which is a United Nations specialized agency, its standards carry more formal international weight than those of most other standards development organizations that publish technical specifications of a similar form. At the initiative of Napoleon III ,

2304-406: The connections and protect the session information. Network Addressable Units in a SNA network are any components that can be assigned an address and can send and receive information. They are distinguished further as follows: SNA essentially offers transparent communication: equipment specifics that do not impose any constraints onto LU-LU communication. But eventually it serves a purpose to make

2368-520: The data center. Subsequently, the IETF expanded on this work with multiple other RFCs. TN3270 (Telnet 3270), defined by those RFCs, supports direct client-server connections to the mainframe using a TN3270 server on the mainframe, and a TN3270 emulation package on the computer at the end user site. This protocol allows existing VTAM applications (CICS, TSO) to run with little or no change from traditional SNA by supporting traditional 3270 terminal protocol over

2432-522: The definition of international telecommunication services, cooperation between countries and national administrations, safety of life and priority of telecommunications and charging and accounting principles. The adoption of the ITRs in 1988 is often taken as the start of the wider liberalization process in international telecommunications, though a few countries, including United States and United Kingdom, had made steps to liberalize their markets before 1988. The Constitution and Convention of ITU provides for

2496-601: The draft text and all comments are sent to the next Study Group meeting for further discussion and possible approval. Those Recommendations considered as having policy or regulatory implications are approved through what is known as the Traditional Approval Process (TAP), which allows a longer period for reflection and commenting by member states. TAP Recommendations are also translated into the six working languages of ITU (Arabic, Chinese, English, French, Russian, and Spanish). ITU-T Recommendations are

2560-505: The early 1980s created a new common practice among both consumers and businesses of adopting " bleeding edge " communications technology even if it was not yet standardized. Thus, standards organizations had to put forth standards much faster, or find themselves ratifying de facto standards after the fact. One of the most prominent examples of this was the Open Document Architecture project, which began in 1985 when

2624-399: The final 1 bit in this sequence to a 0 bit, making it a flag character, and then transmits its own frames. After its own final flag, it transmits an all-ones idle signal, which will serve as a go-ahead for the next station on the loop. The group starts with commands from the primary, and each secondary appends its responses. When the primary receives the go-ahead idle sequence, it knows that

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2688-412: The final approval of a full-status ITU-T Recommendation can now be as short as a few months (or less in some cases). This makes the standardization approval process in the ITU-T much more responsive to the needs of rapid technology development than in the ITU's historical past. New and updated Recommendations are published on an almost daily basis, and nearly all of the library of over 3,270 Recommendations

2752-409: The first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s. SNA also competed with ISO 's Open Systems Interconnection , which was an attempt to create a vendor-neutral network architecture that failed due to the problems of " design by committee ". OSI systems are very complex, and the many parties involved required extensive flexibilities that hurt

2816-436: The interoperability of OSI systems, which was the prime objective to start with. The TCP/IP suite for many years was not considered a serious alternative by IBM, due in part to the lack of control over the intellectual property. The 1988 publication of RFC   1041 , authored by Yakov Rekhter , which defines an option to run IBM 3270 sessions over Telnet , explicitly recognizes the customer demand for interoperability in

2880-465: The local, or mainframe site, the router uses Token Ring topology to connect natively to VTAM. At the remote (user) end of the connection, a PU type 2 emulator (such as an SNA gateway server) connects to the peer router via the router's LAN interface. End user terminals are typically PCs with 3270 emulation software that is defined to the SNA gateway. The VTAM/NCP PU type 2 definition becomes a Switched Major Node that can be local to VTAM (without an NCP), and

2944-426: The main non-computer costs and other difficulties in operating large networks using earlier communications protocols. The difficulties included: As a result, running a large number of terminals required a lot more communications lines than the number required today, especially if different types of terminals needed to be supported, or the users wanted to use different types of applications (.e.g. under CICS or TSO) from

3008-518: The mid nineties, and two years until 1997, can now be approved in an average of two months, or as little as five weeks. Besides streamlining the underlying procedures involved in the approval process, an important contributory factor to the use of AAP is electronic document handling. Once the approval process has begun the rest of the process can be completed electronically, in the vast majority of cases, with no further physical meetings. The introduction of AAP also formalizes public/private partnership in

3072-421: The names given to telecommunications and computer protocol specification documents published by ITU-T. ITU-T assigns each Recommendation a name based on the series and Recommendation number. The name starts with the letter of the series the Recommendation belongs to. Each series encompasses a broad category of Recommendations, such as "H-Series Recommendations: Audiovisual and multimedia systems". The series letter

3136-481: The popularity and growth of TCP/IP, SNA is changing from being a true network architecture to being what could be termed an "application and application access architecture." In other words, there are many applications that still need to communicate in SNA, but the required SNA protocols are carried over the network by IP. IBM in the mid-1970s saw itself mainly as a hardware vendor and hence all its innovations in that period aimed to increase hardware sales. SNA's objective

3200-441: The primary pieces of hardware, the 3745 /3746 communications controller, has been withdrawn from the market by IBM. IBM continues to provide hardware maintenance service and microcode features to support users. A robust market of smaller companies continues to provide the 3745/3746, features, parts, and service. VTAM is also supported by IBM, as is the NCP required by the 3745/3746 controllers. In 2008 an IBM publication said: with

3264-507: The procedures and messages (such as the TEST message). Intel used SDLC as a base protocol for BITBUS , still popular in Europe as fieldbus and included support in several controllers (i8044/i8344, i80152). The 8044 controller is still in production by third-party vendors. Other vendors putting hardware support for SDLC (and the slightly different HDLC) into communication controller chips of

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3328-414: The rest of the ring and eventually return to the primary. Except for this copying, a secondary operates in half-duplex mode; it only transmits when the protocol guarantees it will receive no input. When a secondary is powered off, a relay connects its input directly to its output. When powering on, a secondary waits for an opportune moment and then goes "on-loop" inserting itself into the data stream with

3392-490: The same location. In purely financial terms SNA's objectives were to increase customers' spending on terminal-based systems and at the same time to increase IBM's share of that spending, mainly at the expense of the telecommunications companies. SNA also aimed to overcome a limitation of the architecture which IBM's System/370 mainframes inherited from System/360 . Each CPU could connect to at most 16 I/O channels and each channel could handle up to 256 peripherals - i.e. there

3456-459: The secondaries are finished and it may transmit more commands. The beacon (BCN) response is designed to help locate breaks in the loop. A secondary which does not see any incoming traffic for a long time begins sending "beacon" response frames, telling the primary that the link between that secondary and its predecessor is broken. Because the primary also receives a copy of the commands it sent, which are indistinguishable from responses, it appends

3520-614: The sector's governing conference, convenes every four years. ITU-T has a permanent secretariat called the Telecommunication Standardization Bureau (TSB), which is based at the ITU headquarters in Geneva, Switzerland . The current director of the TSB is Seizo Onoe (of Japan), whose 4-year term commenced on 1 January 2023. Seizo Onoe succeeded Chaesub Lee of South Korea, who was director from 1 January 2015 until 31 December 2022. The ITU-T mission

3584-549: The start of the AAP procedure by posting the draft text to the ITU-T website and calling for comments. This gives the opportunity for all members to review the text. This phase, called last call , is a four-week period in which comments can be submitted by member states and sector members. If no comments other than editorial corrections are received, the Recommendation is considered approved since no issues were identified that might need any further work. However, if there are any comments,

3648-637: The work of standardization, ITU-T cooperates with other SDOs, e.g., the International Organization for Standardization (ISO) and the Internet Engineering Task Force (IETF). Most of the work of ITU-T is carried out by its Sector Members and Associates, while the Telecommunication Standardization Bureau (TSB) is the executive arm of ITU-T and coordinator for a number of workshops and seminars to progress existing work areas and explore new ones. The events cover

3712-437: Was a maximum of 4096 peripherals per CPU. At the time when SNA was designed, each communications line counted as a peripheral. Thus the number of terminals with which powerful mainframes could otherwise communicate was limited. Improvements in computer component technology made it feasible to build terminals that included more powerful communications cards which could operate a single standard communications protocol rather than

3776-408: Was designed with the ability to wrap different layers of connections with a blanket of security. To communicate within an SNA environment you would first have to connect to a node and establish and maintain a link connection into the network. You then have to negotiate a proper session and then handle the flows within the session itself. At each level there are different security controls that can govern

3840-514: Was followed by another announcement in July, 1975, which introduced the IBM 3760 data entry station, the IBM 3790 communication system, and the new models of the IBM 3270 display system. SNA was designed in the era when the computer industry had not fully adopted the concept of layered communication. Applications, databases, and communication functions were mingled into the same protocol or product, which made it difficult to maintain and manage. SNA

3904-648: Was mainly designed by the IBM Systems Development Division laboratory in Research Triangle Park , North Carolina , USA, helped by other laboratories that implemented SNA/SDLC. IBM later made the details public in its System Reference Library manuals and IBM Systems Journal . It is still used extensively in banks and other financial transaction networks, as well as in many government agencies. In 1999 there were an estimated 3,500 companies "with 11,000 SNA mainframes." One of

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3968-507: Was not included in early HDLC standards, but was added later. A special mode of SDLC operation which is supported by e.g. the Zilog SCC but was not incorporated into HDLC is SDLC loop mode. In this mode, a primary and a number of secondaries are connected in a unidirectional ring network , with each one's output connected to the next's input. Each secondary is responsible for copying all frames which arrive at its input so that they reach

4032-721: Was the Distributed Computing Architecture (DCA), and the networking architecture for Burroughs mainframes was the Burroughs Network Architecture (BNA); after they merged to form Unisys , both were provided by the merged company. Both were largely obsolete by 2012. International Computers Limited (ICL) provided its Information Processing Architecture (IPA). DECnet is a suite of network protocols created by Digital Equipment Corporation , originally released in 1975 to connect two PDP-11 minicomputers . It evolved into one of

4096-544: Was to reduce the costs of operating large numbers of terminals and thus induce customers to develop or expand interactive terminal-based systems as opposed to batch systems. An expansion of interactive terminal-based systems would increase sales of terminals and more importantly of mainframe computers and peripherals - partly because of the simple increase in the volume of work done by the systems and partly because interactive processing requires more computing power per transaction than batch processing. Hence SNA aimed to reduce

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