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Universal Architecture Seek to Oust SNA As Network Standard.

George Orewll may never have envisioned it, but 1984 marks the tenth anniversary of IBM's Systems Network Architecture. Despite a slow start, SNA is today's most widely used network architecture, with an installed base of over 15,000 SNA hosts. Even so, IB, is hardly resting on its laurels. SNA has undergone an almost continuous evolution since its introduction in 1974, making it more powerful and flexible, while simplifying its use and the conversion effort required of the user. IBM has also responded to user-directed trends, such as distributed processing and office automation by enhancing SNA and supplementing it with architectures designed for document distribution and other office functions.

Rival Xerox has also aided document distribution by publishing its Interpress Printing Architecture, a new set of protocols and formats that for the first time will enable a variety of office machines from different manufacturers to wrk together to produce and distribute complex, high-quality business documents on electronic printers. Since the introduction of its Ethernet local area network, Xerox has adopted a policy of openly publishing its network protocols, presumably bnelieving that the benefits of promoting interconnection with Ethernet outweigh the risk of competitiors duplicating its products. The initial layers of the network protocols have been publicly available since 1981. IPA incorporates these and additional protocols for directory and security services. Xerox has also offered to help organizations in achieving compatible implementations of the protocols and formats, and will amke technical consulting and certiciation services available later this year.

Data General has also followed an open system strategy with the introduction of several multivendor interfaces during the past year, while Hewlett-Packard has announced its intention to support IBM's new document architectures as part of its Advance Net offering. Described as a "second-generation" network, AdvanceNet will provide links between HP and other vendors' computers. It supports local and remote communications at the personal, departments and corporate levels across and within HP product lines, with links to other vendors' equipment, including Digital Equipment and IBM. HP also intends to support future automatic conversion between Wang and HP word processing files.

Wang has also released information on its word processing document format, opening the way for greater exchange of documents between Wang and non-Wang system. It has also introduced a set of networking products, known as Wang Systems Networker, to link various Wang systems and provide gateways to IBM and other vendor environments. Meanwhile, IBM has reciprocated, somewhat, by supporting certain non-IBM and other vendor environments.

Meanwhile, IBM has reciprocated, somewhat, by supporting certain non-IBM devices under SNA, and by allowing its SNA products to communicate via X.25 and X.21 public links. With this action IBM acknowledged the importance of public networks in the computercommunications environment of the 1980s. Likewise, other mainframe vendors are acknowledging the future reality of having to co-exist with IBM and public networks. Digital Equipment Corporation, Honeywell and NCR, for instance, have adapted their network architectures to support X.25 and to interconnect with SNA networks. Progress with Universal Architecture

Perhaps the most significant development, through, is the progress being made by international standards bodies working on a univeral network architecture. The goal of the architecture is to permit communications among terminals and computers of any vendor supporting the standard. Working under the auspices of the International Organization for Standardization (ISO), one committee had established a reference model for what is called "open systems interconnection." The model views information systems as networks of cooperating workstations which incorporate some or all of seven architectural layers, depending on their function in the network.

Broadly speaking, the model's three lower layers represent the communications function, providing a means of moving information from one system to another. The upper three layers are processing-oriented, while the middle layer is responsible for making sure the information is delivered from the sending to the receiving system (see, "Update on the OSI Reference Model.") The ISO has already approved a standard for the reference model, International Standard 7498, and the CCITT has followd suit with its Recommendation X.200.

According to Richard desJardins, vice president of Englewood, Colorado-based computer Technology Associates, the initial standards required to achieve simple systems interconnection for file transfer and message handling will be finalized by the end of 1984. The level of cooperation between ISO and CCITT, as well as within national bodies and multinational organizations such as the European Computer Manufacturers Association has been unprecedented, according to desJardins. As a result, universally agreed standards are becoming available in every layer of the reference model. Also, govprovide the single family of standards which users need, while computer manufacturers and network suppliers are planning to provide evolutionary growth paths to the OSI standards fof their users.

In July, General Motors and the National Bureau of Standards are co-sponsoring a demonstration of OSI working in a multivendor environment as part of the Vegas. IBM is among the vendors involved in the project, which desJardins claims will be the first public dmonstration of a multivendor OSI environment operating across all seven layers. The demonstration will support a variety of applications using three major international standard protocols: ISO Transport Protocol Class 4, ISO File Transfer Protocol Subset and the IEEE-802 CSMA/CD and Token Bus local area network protocols.

As chairman of subcommittee 16 of the ISO technical committee 97, desJardins heads the group responsible for OSI standards. Writing in a special issue of the Proceedings of the IEEE dealing with OSI developments (December 1983), desJardins states that, by year's end, st andards will be available for achieving worldwide digital networking through local area networks, public and private wide area networks and forerunners to the new generation of integrated services digital networks.

In addition, standards will be available for end-to-end universal sesion and transport control as well as several important applications, including file transfer, message handling, videotex and teletext. These standards will form the basic worldwide capabilities for open systems interconnection, which he says will become widely available and ultimately routine in the second half of 1980s. "By the end of the decade, open systems informtion exchange will be commonplace in North America, Europe and Japan," desJardins states. SNA Continues Evolution

Since its introduction in 1974, SNA has undergone an almost continuous evolution to correct some drawbacks, to accommodate the latest hardware and software developments and to adjust to chaning user needs. Before the inforduction of SNA, IBM says it had more than 200 communications products in its line, requiring 35 different teleprocessing access methods and 15 different data link controls. These diverse link controls, access methods and terminal types complicate network planning and make for inefficient network operations. SNA attacked these inefficiencies by establishing a single access method (Vtam) residing in the virtual storage System 370, and a single line discipline, synchronous Data Link Control (SDLC), independent of device and code.

IBM says it original design goal with SNA was to provide an open-ended system that could grow as new technologies and requirements appeared. In this, the firm has had some notable successes. SNA networking capability has gone from a limited tree structure to a fully meshed capability, with the ability to support any combination of these structures. While this calls for significant changes in the key system-control programs, such as Vtam and the Network Control Program, no changes were needed in any terminals or cluster controllers, or in any operating system and subsystems such as CICS.

Also, when SNA was first released, it supported only analog leased lines. Today, SNA also supports circuit and packet-switched services, and analog or digital facilities may be used with either terrestrial or satellite links. further, all combinations fo these services can be supporte simultaneously. Again, this evolution required limited modifications, primarily to the NCP, and no changes were needed in application programs. In fact, the user need not be aware of which services are used.

The key to this orderly evolution is SNA's layered structure, which allows users to exchange information without being involved in such procedures as controlling a communications line or routing data units through the network. Also, the layered structure minimizes the impact of hardware and software changes on other network elements.

Much of SNA's evolution appears to have been directed by user needs. For instance, early complaints about SNA described the software as unwieldy and inefficient in its use of system resources, with special criticism reserved for Vtam. Early in 1976, IBM responded by extending SNA support to users of the Telecommunications Access Method (Tcam). Another early drawback was SNA's considerable requirement for mainframe resources. Again, IBM responded with a series of program products, known as Advanced Communications Function, for supporting multiple-computer networks under SNA to give terminal users access to a wider range of applications. It also introduced low-priced host systems such as the IB, 4300 Series.

In addition, IBM has made a concession to user demand for distributed processing systems by offering software packages that spread their functionality between the host and distributed systems, with SNA providing the unifying bond. What's more, SNA now encompasses a broad range of IB, terminals and office products. IB, has also upgraded SNA network management capabilities with software and microprocessorbased modems.

IBM has also opened its networks considerably by allowing its SNA products to communicate via X.25 and X.21 public links, and by supporting certain independent devices. To accommodate non-SNA terminals, IBM matches the device's protocols in the NCP for communications over the link. Part of NCP, called Network Terminal Option, then places the devicehs end-to-end protocols and its data into an SNA envelope, after which the information is handled in a conventional SNA manner. When the SNA envelope reaches its destination host, the SNA programming "opens" the envelope and passes the device's end-to-end protocols and data to the application program, which understands and interprets them. This means that the non-SNA device enjoys the networking benefits of SNA, but these benefits do not extend fully to the terminal; they terminate instead at the NCP.

To provide X.25 support, IBM uses a software program that operates in selected models of the IBM 3705 communications controller, and hardware for converting SNA's SDLC to and from X.25 communications protocols. (See "SNA Charts Big Blue's Future," communications News, February, 1983, page 44). Three Levels of Network Priority

Among the latest SNA enhancements are the provision of three levels of network priority, alternate path capability, and the ability to establish parallel links between 370X communications controllers. Network management enhancements include System Services Control Point restart or takeover in case of host failure, and the capability of "global" flow control throughout the SNA network.

To accommodate the growth of distributed processing and office automation networks, IBM recently introduced Advanced Program-to-Program Communication (APPC) capability which works with SNA to effectively provide a distributed operating system. IBM has also supplemented SNA with two other architectures for the office environment: Document Content Architecture (DCA) provides the ground rules for describing the internal structure of information for document distribution and similar applications; Document Interchange Architecture (DIA) provides the rules for functions such as distributing, filing and retrieving information. In effect, DIA is the envelope which helps ensure that a message reaches its destination, while DCA takes care of the content of the letter or memo. In this analogy, SNA would be the mailman.

Xerox says its Interpress Printing Architecture allows users to create documents in any layout and containing any combination of line graphics, half tones, scanned images and text in as many font sizes and styles as the user desires. It also provides a way for different manufacturers to use common programs to link their products with each other and with a wide variety of electronic printers.

A key element of the IPA is the Interpress document format, a computer language for describing the appearance of pages in a document. Interpress masters may be created electronically by workstations, word processors, personal computer and mainframe computers. Using the Iterpress document format with other high-level protocols, documents may be printed immediately, stored for later use, sent to remote sites by local area networks or telephone lines, or printed on different printers at different sites.

The other protocols include all Xerox Network Systems Protocols required for printing applications. They are: the Printing Protocol used to transmit Interpress masters to electronic printers; the Clearinghouse Directory Protocol for locating printers, workstations and other network resources; and the Authentication Protocol for information security. Material to be printed may be transmitted via the Ethernet local area network and telephone lines using the Xerox Network Systems communications protocols announced in 1981. documents specifying the Interpress Printing Architecture are available for $250 from Teddy Rosenberg, Xerox Office Systems Division, 3450 Hillview Avenue, Palo Alto, Calfironia 94304. Wang Adds Gateways

Wang Labs' objective in releasing its word processing document format is to encourage the exchange of editable documents between Wang and non-Wang systems. It annoucement of the Wang Word Processing System Communications Specification (WPSCS) and the Wang Information Transfer Architecture (WITA) effectively opens the office automation marketplace to Wang's current word processing document standards, as well as to present and future multi-information (words, data, graphics and voice) document standards.

WPS-CS provides users with the document data stream information required for non-Wang systems to transfer editable documents to and from existing Wang OIs, Alliance, VS/IIS, 2200, Professional computer and wangwriter systems. WITA provides specifications of the structure of documents containing image, graphics, voice and data as well as text. Information on both is available for a one-time license fee of $500 each.

Wang Systems Networking (WSN) is a set of communications products linkig Wang systems and providing gateways to other vendor environments. By following the layered architecture of the OSI reference model, WSN products allow Wang systems to exchange information over local and wide area, host-controlled and public data networks.

WSN products are grouped under four major categories: transport, services, applications and management. Network transports are adaptable system-to-system connections that operate independently of WSM services and applications. Network services manage the exchange of information in a WSN information processing environment, while network applications are Wang system applications extended to run over the network to provide end-user functionality. Network management is accomplished through utilities that maintain, manage and control lines, devices, systems and applications tasks.

Transports are divided into two components: media and protocols. Examples of transport media include coax, fiber optics, twisted pair, terrestrial microwave and satellite. Transport protocols are divided into three groups: Wang-developed, industry standard (X.25) and de facto standard (IBM 3270, SNA and bisync).

Besides extending Wang system applications to run over networks, WSN provides for application gatweays that allow Wang applications to share information with non-Wang applications. Wang says its first announcement in this area is the firm's intention to supply a gatweay to IBM's DIA, where applicable. Digital Supports SNA and X.25

Digital Equipment's Digital Network Architecture is a system of layered protocols that establish links and govern data transmission between computer systems. DECnet products embody the DNA architecture and facilitate construction of distributed processing networks with Digital computers. Digital began to lay the foundation for heterogenous networks with the introduction of its DECnet Phase III products. for IBM users, Digital introduced an emulator for operation in an SNA evnironment; for interconnection with other systems, Digital announced its commitment to support the X.25 standard.

Digital's SNA protocol emulator software allows PDP-11 computers running under the RSX-11M real-time operating system to emulate an IBM 3790 cluster controller. This permits interactive communications with an IBM host supporting an SNA network. With the emulator, the PDP-11 system can function either on a point-to-point line to the IBM host, or on a multipoint line with other SNA devices.

Previously, Digital computers could only communicate with IBM systems through the bisyne protocol.

Also, prior to Phase III, DECnet products only supported point-to-point communications between pairs of nodes that were directly and physical connected. With the multipoint capability of Phase III software, a host or master system can communicate with up to six remote or slave systems over a single line. The host controls communications, polling each slave system in turn. slaves can communicate with each other through the host, and multipoint configurations can exist as subgroups within larger networks. This enables both master and slave systems to participate in message routing, file transfer and resource access with other systems.

Even greater flexibility is afforded by the adaptive path routing capability of Phase III. This allows a DECnet network node to send messages to another node through as many as five intermediate nodes. When more than one path exists between the source and destination nodes, the network automatically selects the "least-cost" path, based on line values assigned by the network manager. The values for each line are primarily determined by its bankwidth, or data rate capability: the higher the data rate, the lower the "cost" assigned to the line.

The line values are included in routing tables which are generated automatically when the software comes on-line. Each node maintains a routing table for the entire network. By using these tables, a node is able to select the optimum path for each on-going message.

To provide the "adaptive" capability, the routing tables are updated whenever changes in line or system status occur. For instance, if service is interrupted on a particular circuit, its line value goes to infinity, which automatically causes messages to be rerouted past the next-least-cost path. This process is completely transparent to the user. However, the network manager can adjust the line values at any time, either to control data flow or to perform line or system testing without disrupting the rest of the network. Data General Adds IEEE 802.3 Products

Data General's new IEEE 802.3 and X.25 offerings mean that the firm's products can now communicate over industrystandard local area networks as well as SNA and X.25 networks. "With these two new capabilities, we believe Data General has the most complete and powerful communications and networking products in the industry . . . mini-to-mainframe, mini-to-mini and mini-to-mmicro," claims David Lyons, vice president and general manager for the Information Systems Division. Data General's first products conforming to the IEEE 802.3 standard are two communications boards, one for the Eclipse MV/Family systems, and the other for Eclipse S/20, C/30 and Desktop Generation Systems. Both are manufactured by Interlan of Westford, Massachusetts.

The DG/XDLC X.25 communications interface allows any Data General system, from the Desktop Generation family to the Eclipse MV/Family to access an IB, mainframe using SNA over an X.25 public data network. DG/XDLC supplements the firm's DG/SNA offering, which lets any Data General information system participate as an integral part of an IBM SNA network; and the Xodiac network management software, which enables users of multiple systems to exchange data and share resources via public or private networks as well as through direct-wire and local area network connections. Further, since DG/SNA runs concurrenly with Xodiac software, users can operate with both SNA and X.25 networks. Honeywell embraces LANs

Honeywell's Distributed Systems Architecture (DSA) conforms to the seven-layer OSI reference model and, as such, supports the X.25 and X.21 packet and circuit-switched network protocols. Last year the firm became the first non-IBM vendor to offer an SNA file transmission facility. Its SNA Release 1.1 allows the transmission of data bases, word processing documents and print files from an IBM host to Honeywell DPS 6 satellites. The enhancements also included simplification of Honeywell's existing SNA Interactive and SNA Remote Job Entry facilities. At the same time, the firm announced OAS Release 2.1, which integrates word and data processing capabilities and further enhances communications between Honeywell and IBM machines. The new OAS document transfer capabilities allow documents to be sent between OAS systems and non-OAS systems using Honeywell's DSA and IBM's SNA and bisync protocols.

Meanwhile Honeywell has also enhanced DSA with products for distributed processing networks. Specifically, Release 3.0 of DPS6-DSA permits the networking of DPS 6 and Level 6 minicomputer systems without the need for a mainframe. In a DSA network, the DPS 6 can function as both switch and endpoint. The network can also consist of DPS 6 systems and DPS 8 large-scale systems with Datanet 8 network processors.

DPS6-DSA helps Honeywell users who have standardized on RNP/6 to migrate easily to DSA should they need to support public network interfaces and other international standards. In addition, DPS6-DSA can co-exist with SNA and bisync for communications with IBM systems. Recent enhancements to RNP/6, known as Release 3.1, support improved file transfer, terminal concentration and batch processing facilities in a distributed environment. Release 3.1 also adds the Application Transport Interface, which allows application-to-application communications.

In April, Honeywell further extended DSA by introducing hardware and software components for local area networks compatible with DSA for the firm's DPS 88 and DPS 8 large-scale computers, DPS 6 small systems and microSystems 6/10 and 6/20. Honeywell's local area network products are compatible with the Ethernet version 1.0 and the IEEE 802.3 electrical specifications, and support the Xerox Network System high-level protocols for network compatibility.
COPYRIGHT 1984 Nelson Publishing
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Author:Edwards, M.
Publication:Communications News
Date:Jun 1, 1984
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