ISDN: Interface Standards Usher in Ultimate Network

Imagine a universal public network for voice, data, image and video traffic, with a universal plug for telephones, facsimile machines, computers and other digital terminals. That's the exciting concept behind the Integrated Services Digital Network (ISDN), whose intent is to provide users with a world-standard hookup for accessing a variety of communications services with the ease of placing a telephone call.

This November, the International Consultative Committee on Telegraphy and Telephony (CCITT) will begin considering proposed standards for the ISDN, including the user/network interface which is so vitally important to users, equipment suppliers and carriers alike. For users, a common interface will prevent changes in the network from obsoleting terminal equipment. It will also assure portability and a broad selection of terminal capabilities. Manufacturers need the well-defined interface to develop families of terminals and switching products; and for carriers, the interface brings freedom to upgrade their network with the latest technology without impacting their customers.

Despite the enormous market potential, terminal manufacturers are apparently unaware of ISDN developments. In a recent study on ISDN, Venture Development Corporation found that 91 per cent of data terminal manufacturers "don't have a clue about what ISDN's are." The Wellesley, Massachusetts-based research firm also learned that, of the nine per cent of data terminal manufacturers who have heard of ISDNs, none has begun an ISDN product-planning strategy. VDC believes this situation may prompt foreign manufacturers to flood the United States market with ISDN-compatible terminals, since there is considerably greater awareness of ISDN abroad.

Aware of the rapid progress being made towards ISDN standards, and concerned lest the United States position be inadequately represented, the Federal Communications Commission adopted a Notice of Inquiry on ISDNs last August, giving users and vendors a chance to express their views before any standards are set. The comments are expected to aid the FCC in setting ISDN regulatory goals as well as involving a larger number of diverse firms and user organizations in the United States CCITT input process.

Among the user organizations responding, the primary concern was for the preservation of flat-rate leased private lines as an alternative to ISDNs. "Virtual private line circuits over ISDNs are not effective technical, operational and economic substitutes for existing private line services," commented the International Communications Association. Likewise, the Association of Data Communications Users (ADCU) stated that "users must have fredom of choice as to whether to use ISDNs or not." ADCU also advocates interconnection amongst ISDN and non-ISDN networks, including industry-shared networks, private networks, local area networks and others. In addition, the association wants ISDNs to support specialized data and voice applications requiring mimimum network delay, and to provide identification, authentication and encryption within the network for all messages handled. ISDN Architecture

In reality, the United States has had a strong voice in the CCITT deliberations over ISDNs since responsibility for ISDN was assigned to Study Group XVIII at the Seventh Plenary Assembly, held in Geneval in November, 1980. According to Marc Rudov, manager of VDC's Communications Division, of the 211 members from 24 nations attending the Study Group's first meeting, 32 were from the United States, including 14 from AT&T alone.

Among the principles established by the CCITT governing ISDNs:

* The ISDN will be based on, and evolve from, the telephone network by progressively incorporating additional functions and network features, with the idea of supporting voice and non-voice services in the same network.

* NEw services introduced into the ISDN should be compatible with 64-kbps switched digital connections. However, at later states, the evolving ISDN may also include switched connections. However, at later stages, the evolving ISDN may also include switched conections at bit rates higher and lower than 64-kbps. Both circuit- and packet-switched connections should be accommodated.

* The transition to a comprehensive ISDN may extend over one or two decades and must allow for usge of present equipment such as space division switching. During the transition, provision must be made for interworking of ISDNs and other networks.

* The ISDN will have sufficient intelligence to provide service features, maintenance and network management functions. For some new services, the network intelligence may be supplemented with compatible intelligence in the customer terminals.

* A layered functional set of protocols should be developed for ISDN access based on the Open System Interconnection referencd model and incorporating CCITT Signaling System Number 7.

CCITT Draft REcommendations on ISDN are covered under the newly established I Series. Draft Recommendation I.110 covers ISDN terminology, description, service capabilities and functions, including the user/network and internetwork interfaces, which VDC's Rudov considers the two most important aspects of ISDNs. "Since many private and public circuit- and packet-switched networks will collectively comprise ISDNs, they must interface easily and with uncompromising stability," Rudov notes. "More importantly, the user will demand an economical and uncumbersom gateway to the network. After all, it is the user who will determine the ultimate success of ISDNs."

Part IV of I.110 describes and defines the ISDN user/network interfaces and contains an architectural reference model on the way ISDN interface functional groupings and locations, or reference points, will interconnect (see figure). As defined by the CCITT, NT1 (Network Termination 1) contains the functions associated with the physical and electrical termination of the ISDN. The NT1 interface may support a single terminal or multiple terminals via a passive-bus configuration. NT2 contains switching and protocol handling intelligence, such as that provided by PBXs and local area networks, respectively. T is the conceptual interface between NT1 and NT2, whereby NT1 functions are specifically "network" oriented, while NT2 functions are pertinent to each user. In the United States, T is expected to be the demarcation between regulated and unregulated domains. T may not exist in some foreign countries where the PTT chooses to combine NT1 and NT2 into NT12 and control both functions.

TE1 is an ISDN terminal that supports the ISDN interface. It could be a digital telephone set, for example, or an integrated voice/data terminal. S is the interface between a TE1 or multiple TE1s, and an NT2. This all-digital interface will have two or four wires and contain two transparent user channels plus a signaling channel. TE2 is a terminal with an interface pre-dating ISDN standards, such as one with an RS-232 C interface. To allow connection with an ISDN, a TE2 must first attach to a terminal adapter (TA), which converts existing interfaces, known by the CCITT as R interfaces, into an ISDN interface. The TA function could be contained within an NT2 device.

The basic building block of ISDN is the 64-kbps PCM channel, known as the B channel. Signaling for the B channel is sent out-of-band in the associated 16-kbps channel, the D channel. Using packet techniques, the CCITT proposes to carry telemetry and low-speed interactive data over the D channel, in addition to the B channel signaling. Applications such as remote utility meter reading, remote alarm monitoring and remote energy management are envisioned for the telemetry capability. The low-speed interactive data may be from Ascii terminals, X.25 and videotex terminals. Both types of data will play a subordinated role to signaling, which is the main purpose of the D channel.

For the ISDN access channel structure, CCITT envisions basic access at 144 kbps, which will be time-division multiplexed into two 64-kbps B channels, plus the 16-kbps D channel (see figure). Other possible loop rates are 80 kbps (B + D) and 16 kbps. In the transition phase, where analog and digital technology coexists, switching of analog circuits (A) will be signaled by the C channel, a subset of the D channel. Finally, for "primary rate access," intended for interconnecting ISDN and PBXs or broadband digital networks, two aggregate bit rates are specified: 1.544 and 2.048 Mbps for North America and Europe, respectively. Europe Gets Jump on ISDN

In European countries, where analog technology lags considerably behind that of North America, ISDN is viewed as a boon for leapfrogging into state-of-the-art digital communications and attaining parity in technology and quality of service with the United States and Canada. Because there is a greater need in Europe than in the United States to create ISDNs, the general awareness level there is higher and the push for standards stronger, according to the VDC study.

This year the French PTT plans to introduce a digital switched satellite service as part of its ISDN evolution. Called Telecom 1, it will provide telephony and data services to large business customers via strategically located earth stations.

The West German PTT plans to migrate toward an ISDN by 1987. Beginning in 1985, ten German cities will participate in ISDN field trials in which each of the 4,000 planned subscribers will have access to either a Basic Access channel, at the 144 kbps rate, or Primary Access channel at 2.048 Mbs for end-to-end communications. Local exchanges will be modified to incorporate the D channel for out-of-band channel signaling, which will be performed according to CCITT Signaling System No. 7. Also, Theodore Irmer, chairman of CCITT Study Group XVIII, works for the West German PTT, so the nation is most likely to be a model country for ISDN implementation.

The Italian PTT, through its major telephone company, SIP, plans to offer ISDN field trials in early 1984. The participants in these trials will have access to B + D, 80-kbps full-duplex channels, provided via two-wire loops. The services supported in the trials will include digital telephony, interactive data, slow-scan video, digital facsimile, videotex, teletext and circuit-switched access to an X.25 packet-switched network. SIP will distribute standard ISDN equipment in 1986. SIP also projects that all of Italy will be interconnected by an ISDN in 1990, when 90 per cent of local loops will be digital, and broadband services at rates to 2.048 Mbps will be available.

The Swedish PTT has established an ISDN evolution policy, based on the gradual digitization of its telephone network. Attention will be directed initially toward the business community due to the potential market demand there. Sweden began to install digital transmission links inn 1970 and expect 10 per cent of its long-distance network to be digital by 1985. Digital switches were introduced in 1977 and by 1990 will handle 50 per cent of the local loop traffic. Although still undetermined, local access may be made available through either a 2B + D or a B + D channel. Services to be provided will include telephony, teletext, circuit and packet switched data, data base access and facsimile.

British Telecom has established a lead on the rest of the world by beginning to market its ISDN, called Integrated Digital Access (IDA), in 1983. The British have rightfully determined that the user of integrated communications is not concerned with the internal workings of the network, but only interested in access and ease of use; BT has designed its IDA marketing strategy accordingly. It is available initially at 80 kbps and 2.048 Mbps. By the late 1980s, BT expects to offer a 144-kbps rate also. (More details of European ISDN plans will appear in the July "DataComm Update.") ISDN Evolution in United States

In the United States, ISDNs could evolve from the wideband offerings of satellite carriers or the public data networks of value-added network carriers. "I do not believe the ISDN concept necessarily means there will only be one network for each country or a single, totally integrated worldwide network," says AT&T Chairman Charles Brown. "Instead, I think we will see a variety of approaches. In some countries, such as the United States, there will probably be several ISDNs. In some areas of the world, regional ISDN systems may emerge, encompassing several nations.

"Whatever the case, if we can agree on certain basic standards that will permit the interconnection of these various systems, we should be able to achieve the equivalent of a single, global Integrated Services Digital Network."

Some observers believe AT&T is already assembling the building blocks for an ISDN. Its Dataphone Digital Service provides private digital links at speeds to 56 kbps to more than 100 USA cities and interconnects with Canada's Dataroute digital system. AT&T is also planning a 56-kbps switched digital service, called Circuit Switched Digital Capability. As for wideband service, AT&T offers the impressive array of High Capacity Terrestrial Digital Service, High Capacity Satellite Digital Service and High Speed Switched Digital Service. Unit final ISDN standards are set, AT&T will presumably provide digital transmission services close to ISDN concepts.

Another view of the evolution towards ISDNs comes from Dr. Michael Mancusi, vice president, engineering and development for the RCA Cylix Communications Network. "ISDN is a logical extension of the services provided by value-added networks, such as RCA Cylix's," Dr. Mancusi notes. "At this time, RCA Cylix does not have plans to provide ISDN service, though it is safe to say that we will be considering implementing it when it becomes a viable technology."

For the moment, that appears to be a common attitude among value-added network suppliers.

What follows is a rundown of the latest developments with value-added network services. ISDN standards are set, AT&T will presumably provide digital transmission services close to ISDN concepts.

Another view of the evolution towards ISDNs comes from Dr. Michael Mancusi, vice president, engineering and development for the RCA Cylix Communications Network. "ISDN is a logical extension of the services provided by value-added networks, such as RCA Cylix's," Dr. Mancusi notes. "At this time, RCA Cylix does not have plans to provide ISDN service, though it is safe to say that we will be considering implementing it when it becomes a viable technology."

For the moment, that appears to be a common attitude among value-added network suppliers.

What follows is a rundown of the latest developments with value-added network services. AT&T Information Systems

AT&T's net 1000 is a combination of the traditional value-added packet-switched network and an on-line applications-oriented processing service. It is designed to provide compatibility between many different terminals and computers, and to integrate diverse networks, providing access to multiple business applications and data bases from a single terminal. Besides transporting data, it also provides communications processing and storage capabilities, as well as management of data networks.

Net 1000 users connect their terminals and hosts to service points located in major United States cities. At the start of 1984, service was availabe in 17 cities, with plans to expand to 200 cities by year's end. These service points house the computers needed to handle the processing, interfacing and conversion chores, and provide storage for applications software and data.

Users are encouraged to plan and develop network applications and leave their programs in the network for execution on demard. For application software, users employ a subset of the Ansi Cobol programming language. There's also a forms-definition facility which lets users define terminal form and screen displays and establish edit-validation criteria. Authorized use of Net 1000 files and programs is protected by system software.

Net 1000 provides compatibility between different terminals and hosts by performing the necessary code conversion, protocol translation and speed matching. Net 1000 supports three classes of general-purpose terminals: asynchronous contention, synchronous contention and synchronous polled. A user's host computer communicates with Net 1000 as though it were communicating directly with a terminal or cluster controller. Currently, Net 1000 provides Ascii asynchronous emulation and synchronous contention (IBM) 3780) and synchronous polled (IBM) 3270) emulation for host computers. From a station, users can access programs residing within the network or other stations.

Net 1000 provides two basic types of information movement: Call and Message. Two-way, session-oriented Call service is intended for interactive inquiry-response applications; Message service provides one-way transmission of blocks of information using Net 1000's store-and-forward capability. Messages can be edited and stored in the network for one-to-one or one-to-many communications, and delivery can be scheduled or on demand.

Net 1000 offers a set of standard application programs that a user can employ either as stand-alone programs, or in conjunction with other programs. For instance, an IBM 3270 format translation program allows users to interface inexpensive asynchronous terminals with host computers that normally work with IBM 3270-type terminals. It also allows users to dynamically switch between such terminals on the same host or on different hosts, regardless of location, by using a menu-driven authorization interface which is under control of an administrator in the user's organization. Also, a host-network file distribution program allows users to download information from a host data base to a Net 1000 Service Point. Similarly, a file transfer program allows users to move files from host computers or 3780-type workstations to Net 1000 storage areas.

In January, AT&T-IS signaled its intention to encourage third-party software suppliers to develop custom packages for Net 1000. The ocasion was the announcement of an agreement between AGS Computers of Mountainside, New Jersey and Dow Jones Information Services whereby AGS will provide a customized software program for users to electronically sign up for the Dow Jones news/retrieval service via Net 1000. "AGS has worked closely with us during the past year to learn the capabilities of Net 1000, to train its people and to pursue third-parts opportunities like the Dow Jones program," save Allen Rebert, Net 1000 director of product support. "It's the first example of our strategy...to use third-party vendors to write Net 1000 application programs for companies." IBM Information Network

The IBM Information Network began operations in 1982 with the announcement of a coast-to-coast network linking user to IBM data processing facilities in Tampa Florida. Today, the computing center makes advanced IBM operating systems and more than 200 program products available to users through outlets in more than 256 cities, allowing them to supplement their in-house systems or to run special applications such as problem-solving, planning and text processing.

Two categories of services are available: Remote Computing Services and Network Management. With the former, users linked to the network can employ IBM's extensive computer and software facilities to run a variety of applications from processors and terminals in their offices. With the latter, users can link their distributed computer and terminal equipment through a national communications network installed, tested and managed by IBM. Services include planning and installation assistance, network management and problem determination and resolution. IBM systems engineers work closely with users to identify and analyze their organizational information requirements, and to design effective data communications network solutions. IBM staff will even work with the vendors supplying lines and communications devices linking user equipment to the IBM Information Network to ensure that they are properly installed and tested.

Once users have connected their terminals and hosts to the IBM Information Network, on-line menus guide the selection of the specific applications; the networks then links the user's terminals to the appropriate processor. With these capabilities, for instance, a user in Dallas could check inventory status maintained on a computer in New York or do financial forecasting or sales analysis using applications running on a computer in San Francisco. In addition, the user could access IBM remote computing resources in Tampa.

The nationwide network employs high-speed digital links to connect the Tampa computer center to IBM 3705 communications controllers in 16 network access cities. Access, control and management of the network are centralized in a Communications Management Configuration.

User terminals and RJE stations may connect to the network via leased or switched telephone lines at speeds of 2.4, 4.8 and 9.6 kbps. In addition to SNA terminals, the network supports bisync 3270 and selected asynchronous terminals. Both point-to-point and multipoint lines are accommodated. Host attachments are supported at 4.8 and 9.6 kbps on point-to-point lines only.

IBM sees its Information Network with its "Pay-For-What-You-Use" feature, as helpful in a variety of ways. For resource-limited organizations it provides a means for implementing applications quickly as they become justified. Applications can be developed in parallel, tested, put into production and eventually moved in-house when the necessary resources become available. Likewise, the Information Network could help users with pilot projects, again allowing the application to be moved in-house when volume justifies. Alternatively, the facility could help users in balancing their workloads, accommodating peak-load processing and volume fluctuations, and isolating testing from production.

For the first industry-specific offering on its Information Network, IBM has targeted the insurance field. Its Insurance Communication Service is designed to speed and simplify communications between insurance home offices and thousands of independent agencies around country. It permits communications between architecturally dissimilar computers and terminals operated by agencies and insurance companies throughout the United States. That's because, while the IBM Information Network is based on SNA, it uses techniques that enable devices with other protocols to communicate through the network.

Users of the IBM Insurance Communication Service have two basic methods of communications: store-and-forward and interactive processing. The former service permits messages and insurance transactions to be sent immediately to specific users through the Information Network, or retained for transmission when requested. Other capabilities, such as directing a single message to multiple locations and querying network status are also available.

With the interactive processing service, the network's computers validate authorization and security codes and then link the user's equipment to the company's computer. The necessary checking of communications line status and other tasks associated with operating complex data processing networks are handled by the IBM Information Network. GTE Telenet

GTE Telenet's public packet-switching service employs a high-speed backbone network comprising multiple 56-kbps links which interconnect intelligent nodes such that each node connects with at least three others. Each node in turn forms the hub of a local distribution network, linking intelligent concentrators in outlying cities via one or more access lines at speeds to 9.6 kbps.

This network now provides local dial access in more than 290 cities nationwide. Through interconnecting facilities, it also provides service in over 50 countries. Initially, service was limited primarily to communications between computers and asynchronous terminals operating at speeds from 75 to 1200 bps. GTE Telenet has since added network interface facilities for major classes of terminals operating at speeds between 2.4 and 56 kbps. These include IBM 3270-type video display terminals as well as IBM 2780 RJE and Hasp workstations. Also, more than 100 X.25 interface products have been certified by GTE Telenet for use on the network.

With the carrier's multiple host access facility, IBM 3270 users are no longer restricted to accessing a single application on a single host via costly leased-line or direct dial connections to the host. Instead, users have the option of accessing, on demand, any application on any of several host computer systems, which may be in different cities or even different countries.

To provide the switched 3270 access capability, the firm uses its TP 3010 communications processor to interface a user's 3270 terminal clusters and host computer sites to the nearest Telenet nodes. Alternatively, Telenet's Data Network Modified Emulator Program can be used to connect IBM 370-compatible systems without the need for a TP 3010. This X.25 software package operates in a 370X communications processor. Other functions in the 3270 package include elimination of polls and selects through the network, enhanced error-control procedure and enhanced network management capabilities. Besides 3270 support, the TP 3010 can be used to interface bisync 2780/3780 and asynchronous terminals and hosts to the Telenet network.

Last August, GTE Telenet introduced a new service called 3270 Dedicated Access Facility which permits direct leased-line connections between 3270 cluster controllers or computer systems and its public network, eliminating the need for a hardware interface. The network performs all protocol conversion, packetizing/depacketizing and routing functions needed to handle communications between each 3270 terminal attached to the cluster controller and the host computer the terminal user wishes to access. No hardware or software modifications to user equipment are required.

The carrier also offers a service enabling IBM 3270 terminal users to access asynchronous host computers connected to the Telenet network. Called GTE Telenet Interface Program (GTIP), the service combines an IBM-based application program with a Telenet network interface to enable local and remote 3270 terminals to establish switched connections through their host computers to any other asynchronous host application on the Telenet network. GTIP accomplishes 3270-to-asynchronous protocol conversion and establishes connections to the Telenet network without incurring dial-up network access charges. It provides 3270 terminal users with a low-cost way to access public electronic mail services and the hundreds of data base services offered via the Telenet network.

Last November, GTE Telenet became the first VAN carrier to offer the Micro-Com Networking Protocol (MNP) for end-to-end error-free data transmission with personal computers and terminals. Initially, the protocol is available to Telenet users in Washington, New York, Boston, San Francisco, Los Angeles and Chicago.

In addition to its public network service, GTE Telenet supplies private data network systems based on the same technology, hardware and software used in its public network. It has also supplied data networks and X.25 gateways to the communications authorities in 20 countries, as well as dedicated packet networks to a number of large United States corporations. LAst December, the firm won a $5 million contract from Citibank NA to design and install an international packet-switching network. Known as CitiWin, for Citibank Worldwide Intelligent Network, the facility supports the bank's major international centers, including Brussels, London, Bahrain, Singapore and Hong Kong, and also interconnects with a number of Citibank regional networks, providing transit services for more than 100 other Citibank locations. Tymenet

Tymnet provides both data communications and store-and-forward message-switching services over its packet network. The addition of 150 new local access locations and the introduction of new services and products have marked Tymnet's growth in the past year. Local access is now available from more than 500 United States locations and over 50 countries. By year's end, Tymnet expects to extend network availability to all United States cities with a population of 85,000 or more. The network has more than 1,200 installed nodes, growing at a rate of four a week. It supports users of over 1,500 hosts and tens of thousands of terminals. Some eight million sessions a month are carried on the network, which can accommodate in excess of 5,000 users simultaneously.

Tymnet's service are based around two products developed specifically for the network: The Tymnet engine, a series of computers optimized for network node applications; and a software system called ISIS, for Internally Switched Interface System. ISIS enables Tymnet to interconnect previously incompatible and dissimilar devices, and to interconnect different networks such as Telenet and Datapac.

Last year, Tymnet introduced the Micro-Engine, a desk-top processor which supports asynchronous transmission speeds from either 50-1200 or 300-4800 bps. Synchronous rates can be supported at speeds to 19 kbps. The Micro-1, with 256K bytes of memory, can handle up to 16 asynchronous terminal ports and four synchronous lines; the Micro-2, with 512K bytes of memory, supports up to 16 asynchronous and eight synchronous ports simultaneously. Tymnet is now working on the Super-engine as the high-end member of the family. Reportedly, the device will be able to handle wideband data communications, integrated packet and circuit switching, and office-to-office digitial transmission for such application as fasimile and video conferencing. It includes a high-performance CPU with a total communications throughput of up to 30 Mbps, a memory architecture supporting up to 32M bytes of memory, communications I/O at speeds to 6.2 Mbps and interfaces for local area networks.

User terminals access Tymnet via nodes called Tymsats. These nodes support a wide variety of asynchronous Ascii devices, IBM 2741 and other non-Ascii asynchronous terminals, and synchronous devices using the X.25 or IBM SDLC, 3270 bisync or 2780, 3780 or Hasp bisync protocols. Over the past year, Tymnet has certified an additional 20 X.25 products for use on its network, bringing the total to more than 70.

Terminals connect to Tymsats either by dial-up or leased lines, or via local RS-232-C cables. Most Tymsats are public facilities shared by many users, but some are dedicated to individual users who need a permanent connection for several terminals at one location. User host computers connect to nodes called Tymcoms. They can have either asynchronous connections to the host, or synchronous connections using the same protocols supported by Tymsats.

Users outside the local call area can utilize Tymnet's nationwide In-Wats service. Users with concentrated high-volume traffic can utilize an Asynchronous Terminal Concentrator (ATC) with 4 to 16 async ports, or a Dedicated Terminal Interface (DTI) with 8 to 128 async ports. Users with a host interface can configure the ATC or DTI as a Dedicated Customer Facility by connecting it directly to the host interface with a leased line.

Tymnet's versatility is exemplified by its Async-to-3270 service, which provides economical dial-up access to IBM 3270 applications using character- and block-mode asynchronous Ascii terminals and personal computers. Last fall, Tymnet began offering dial-up asynchronous service at 2.4 kbps, allowing users with Digital VT100s and other popular terminals and personal computers to access fullscreen 3270 applications at speeds comparable to leased lines via the Tymnet network. Tyment claims to be the first public data network to offer 2.4-kbps dialup service. It began in Chicago, New York, Washington, and San Francisco, and by year's end will be available in 30 additional locations, including Philadelphia, Dallas, Minneapolis and Atlanta.

In an effort to further enhance the use of personal computers for multi-task business applications on its network. Tymnet has developed a new communications protocol for PC-to-PC and PC-to-host communications. Tymnet says the X.PC protocol is derived from the X.25 standard and is based on the Open Systems Interconnection reference model. With the X.PC protocol, a PC user with a single link into the network can connect to as many as 15 different channels, including connections to host computers, public data bases, terminals or other PCs. Information from these channels is displayed on a PC screen divided into windows. Currently being field-tested, the X.PC protocol is scheduled to be available for use on the network by June. Tymnet also has a program to test and verify vendor software that adds terminal emulation capabilities to personal computers.

In March, the San Jose, California firm introduced an asynchronous outdial service for sending information to unattended terminals or printers from a host, terminal or personal computer. The service is intended to save long-distance charges and to defer transmission until late hours when the originating host, telephone system and network are least heavily used and rates are at their lowest. With the service, the host initiates a call, which then travels across the Tymnet network to a dedicated outdial port on a Tymnet node near the receiving terminal. A 300- or 1200-bps auto-dial modem at the port dials the local telephone number, and the call is answered by an auto-answer modem at the remote terminal site. Tymnet says the service will be available in high-and medium-density population areas.

Last year, parent Tymshare inaugurated two-way messaging service between its OnTyme electronic mail service and FTCC's international telex gateway, with Tymnet providing the connection. This service enables PC users to create and send messages to any telex address any place in the world.

For high-volume users, Tymnet also provides private packet networks which complement and are fully compatible with its public network service. In the past year, Tymnet began supplying a multi-nation dedicated data network to Chase Manhattan Bank to connect the bank's operations in New York City with London, Geneva, Bahrain, Panama City, Singapore, Hong Kong and Jakarta, Tymnet was also awarded a $1.5 million contract to construct a custom data network for the Hongkong Shanghai Banking Corp. of Hong Kong, which will connect some 3,000 branch bank terminals and automated telemachines, located throughout Hong Kong, with the bank's primary and backup computers. In early January, the first Alaska-based public packet data network began service. Supplied by Tymnet, and based on Tymnet II technology, the $2 million advanced network provides statwide access through sites in Anchorage, Fairbanks, Juneau and Prudhoe Bay, with access to the lower 48 states via Seattle, Washington. Autonet

Autonet evolved from the network developed over a 12-year period by Automatic Data Processing, the world's largest independent computer services company, to provide communications between client terminals and ADP computing centers. At present, Autonet supports more than 8,700 access ports linked by 230 intelligent communications processors to more than 175 host computers.

Public service on Autonet began in March 1982 after a nine-month trial. There is direct toll-free access from more than 250 United States locations. Interconnections with other public networks further extend domestic access, while direct connections with international record carriers provide service in more than 50 countries.

Autonet employs its own packet-switching protocol and provides end-to-end error control, intelligent alternatepath routing and automatic-answer dial back-up facilities to minimize the impact of line or node failures. The dial back-up system, which is not generally available on most public networks, enables users to guard against extended circuit outages between hosts and the Autonet service. Two network control centers in the United States and one in London provide round-the-clock monitoring to detect malfunctions and minimize service interruptions. Error control procedures hold the error rate to 1 to 10.sup.12., and the firm claims a network availability that has exceeded 99.7 percent since 1981.

Autonet supports virtually all asynchronous hard-copy and CRT terminals operating at speeds to 240 cps over dial-in lines. Dedicated computers may connect to the network through the X.25 protocol or a simpler asynchronous interface.

Autonet services include electronic mail, an on-line user information directory and a special service called AutoWats, which is designed to accommodate usage levels as low as 50 connect hours per month. With AutoWats, users pay a monthly access fee of $35.35 per Host Access Line. A minimum of two lines are required for each host connected to the service. There is also a minimum charge of 50 connect hours per month for each line. The $6 hourly usage charge increases to $9 in prime time (6 am to 6 pm, Monday through Friday).

For conventional service, monthly charges are based on network access, host interface and data trafffic. The charges are uniform for all Autonet cities and volume discounts are available.

Autonet's Dedicated Terminal Facility (DTF) is a direct-connect access arrangement between a terminal on the user's site and the nearest Autonet Communications Center (ACC). It is designed for large-volume users or for those located beyond a toll-free dialing area for Autonet access. The Asynchronous Terminal Controller (ATC) is an intelligent communications processor that can accommodate multiple terminal connections. Located at the user's site, ATCs connect directly to the nearest ACC via a Terminal Communications Facility (TCF). ATC service is intended for users with a high concentration of terminals in a given location.

Host computers may connect to Autonet via an X.25 or asynchronous interface. RCA Cylix

RCA Cylix Communications Network, offers a satellite-based, value-added network providing medium- to high-speed data communications and complete, end-to-end network management. Headquartered in Memphis, Tenessee, the firm provides on-line, transaction-oriented links to users of IBM 3270 bisync and SDLC protocols as well as the Burroughs Poll/Select communications discipline.

In the RCA Cylix network, traffic from user terminals travels over 4.8- or 9.6-kbps leased lines to the nearest satellite earth station. From there, the traffic is routed via satellite to the firm's central facility in Memphis. The traffic then goes via satellite to the earth station nearest the user's receiving location, finally passing over leased lines to the user. Specially designed RCA Cylix modems are used to provide end-to-end network management.

RCA Cylix links users' locations by permanent, virtual circuit. This means that packetized messages between any two sites always travel over the same transmission path. Unlike a dial-up network, the RCA Cylix network is constructed so that users do not have to go through a long-on procedure each time they want to send or receive data. They have immediate, direct access to information at all times. As a result, the RCA Cylix network is useful for transaction-oriented applications, where users must have continual access to information.

RCA Cylix operates 35 regional earth stations and provides service to the continental United States, Canada and Alaska. The carrier takes full responsibility for managing network performance and reliability, modem-to-modem. In addition to handling all telephone company arrangements, it provides a number of management services, including:

* Designing the network, including least-cost routing from user sites to the RCA Cylix earth station. This takes into account the complexity of inter-and intra-LATA (Local Access Transport Area) and state tariffs;

* Providing and installing modems at user sites for ongoing error-detection and correction;

* Coordinating the installation and testing of all equipment and lines on a user's network;

* Monitoring the entire transmission path for errors and retransmitting damaged data; and

* Providing 800-number customer service for reporting problems to the network's technical staff 24 hours a day, seven days a week.

For maximum reliability, the RCA Cylix network has complete, built-in redundancy. All critical network components are duplicated, so that back-up systems can take over should the primary components fail. Uninet Uninet's packet-switched digital network was developed in the late 1960s for the internal use of the United Telecom Computer Group, an operating group of United Telecommunications, Inc. Uninet began offering network services publicly in 1981 and now serves over 600 commercial customers, with direct access in over 275 cities in the United States. Through international connection arrangements, Uninet also serves users in over 33 countries.

Uninet comprises a series of switching centers, called regional nodes, interconnected by 56-kbps digital trunks. The nodes switch and route data through the network and provide the speed, code and protocol translations needed to permit communications between incompatible terminals and computers. All synchronous terminals interface with Uninet through the nodes, while asynchronous terminals connect via local noce asynchronous (LNA) devices with 8, 16 or 64-channel capacity.

The microprocessor-based regional nodes support up to 32 synchronous channels, ten of which can operate as 56-kbps trunk channels. The LNA 64 consist of a processor and up to two multiplexers, each of which can handle as many as 32 ashynchronous terminals. It also includes a synchronous trunk handler, which provides a 9.6-kbps channel to regional nodes, and a synchronous handler for supporting two 4.8-kbps synchronous channels. The LNA 8/16 is a microprocessor-based statistical multiplexer which supports eight or 16 asynchronous channels. HDLC is used as the network link protocol between the 250 regional nodes and LNAs.

Users can access Uninet via dedicated or public dial ports. For dial-in service, Uninet classes the access ports as either low, medium or high density, depending on the volume of Uninet traffic and equipment in the city. There are also access port for WATS service. Interactive terminals can transmit data asynchronously from 110 to 1200 bps; remote batch terminals transmit synchronously at rates from 2-4.8 kbps.

Dedicate access facilities provide Uninet services via a leased access channel between Uninet and the user's premises with the necessary modems at speeds of 110-1200 bps asynchronous, or 2-56 kbps synchronous. In addition, Uninet offers Enhanced Terminal Access Facilities, which allow direct connection of terminals in a centralized location or dial access through a PBX into Uninet.

Planned enhancement to Uninet include the eventual replacement of telephone lines with satellite links for long-haul communications and digital termination systems (DTS) for regional traffic. United Telecom's Isacomm is one of the carriers approved by the FCC for DTS service.

In March, Uninet announced that it had implemented Micro-Com's MNP protocol in 10 cities in its network. The MNP protocol allows error-free dial-up information exchange among business systems, regardless of hardware. Uninet claims that with the implementation of the protocol in its access network, users of personal computers and terminals will be able to communicate with other personal computers as well as minicomputers and mainframes in an error-free environment over standard voice-grade lines. Uninet plans to have the MNP protocol available in 60 cities by year end.

Uninet supports Control Data's 200 UT and IBM 2780, 3780 and Hasp remote batch terminals. Because it is a protocol-sensing packet network, Uninet can support these different terminals on the same dial-up telephone number. After the protocol has been determined, a virtual connection is made from that dial-in port to the requested host computer port. For transmission through the network, the data is converted into Uninets universal network protocol and code set. At the destination node, the output is reconverted into the protocol desired by the host computer, which may or may not be the originating protocol.

Thanks to its Network Control Center in Kansas City, Missouri, Uninet can claim an available uptime of 99.88 per cent, with scheduled downtime for maintenance included in the remaining 0.12 per cent. The center monitors the network by checking the status of all machines, trunk lines and routes. Each regional and interconnect node has a trunk channel that is used for downline loading of communications software from the Network Control Center, ensuring consistency of operation in each node as well as the use of nodes at unattended sites.

COPYRIGHT 1984 Nelson Publishing
COPYRIGHT 2004 Gale Group