Programmable communications controllers The role of dedicated processors in new communications techniques is examined by Derek Farmer

The rapid expansion of computer communications in several directions has created confusion in the minds of manufacturers over what the user wants. The develop- ment of programmable communications controllers is sketched out to show how these devices have emerged in response to the needs of computer communications users. Their facilities are catalogued and demonstrated in action at some user organisations. Their role as devices which can help smooth the path to new communications products and technologies is described.

The development of computer communications over the last 20 years has been something of a computer salesman's dream. Barely had organizations installed mainframe computers in the early '60s before they were giving user departments remote job-entry terminals linked to their computer centres through modems. As the number of remote job-entry terminals grew the need for front-end processors arose. Display terminals started to proliferate and with them came a new need, this time for communications processors with more intelligence which could relieve the main- frame of some of the mundane communications- handling tasks. At the same time this shift in control brought a further need for new operating systems; operating systems which in turn needed more memory.

However, the path through the communications world has now reached a major crossroads. National communications authorities and some private companies are starting to offer nationwide packet- switching services and talk about completely digital public networks in the not too distant future. Telex networks are bringing a new dimension to the inter- national telex service while viewdata is opening up all sorts of new possibilities.

These developments, plus similar advances in office equipment such as communicating word processors, viewdata, teletex services and facsimile devices have come so rapidly that organizations are understandably hesitating over which direction to take. They wonder whether to continue expanding their traditional hier- archical terminal networks or to rethink their entire computing and communications operations from scratch.

One solution is the programmable communications controller (PCC) which, because it is controlled by software, can be adapted relatively easily to handle links between existing networks and new techniques while at the same time providing many other

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communications-handling facilities. As a simple example, PCCs are being installed by many IBM users to provide the facilities of the company's Systems Network Architecture (SNA) without the need for new terminal equipment and the VTAM access method with its associated extra memory requirements.

PCCs have evolved over the last seven or eight years alongside changes in the patterns of computer use. A closer look at these developments will show how the need for them arose.

D E V E L O P M E N T S IN C O M P U T E R C O M M U N I C A T I O N S

In the early and midsixties disc storage and, in particular, printers were not sufficiently developed to keep up with the central mainframe processors in pro- viding the turnround of information that users wanted. The remote job-entry terminal helped to ease this problem by giving user departments their own card readers to initiate jobs and their own printers to produce reports locally.

Data transmission un i t s - - i n IBM terms the 270X family - - became necessary as the number of remote job-entry terminals grew.

However, the data transmission unit turned out to be only a temporary measure, for data communica- tions was still carried out on a line-by-line basis: a remote job-entry terminal was linked by a line to the data transmission unit and a line from the unit linked the terminal to the mainframe application subchannel required. Another terminal requiring access to another application had its own line to the data transmission unit which was in turn connected to the second application by another line into another mainframe subchannel.

The remote job-entry terminal user did not have the flexibility to switch to another application or data transmission unit unless the mainframe operating system was regenerated to set up the new memory addresses for the new application coding and for the remote card reader, printer and data transmission unit. This was another major limiting factor on early computer communications: everything was controlled by the already overworked mainframe operating system. In fact, the onus was still on the mainframe operating system to poll the data transmission units for work rather than to wait for interrupts from those units.

The most urgent need was to relieve the mainframe of some of these tasks. In IBM terms the next step was the introduction of the 3705 controller which, usingthe Network Control Program (NCP), took on the job of poll ingthe terminals. These facilities allowed datato be

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passed between the mainframe and communicat ions controller in blocks rather than as individual characters thus reducing still further the communications necessary with the mainframe.

Distributed processing

The efficiency of the lines between the communica- tions controllers and the terminals has been increased by the introduction of remote data concentrators and IBM's synchronous datalink control (SDLC) protocol which caters for distr ibuted processing by al lowing data from different (logical units within physical units) devices to travel together in an interleaved and blocked manner.

There are still certain l imitations to some com- munications controllers. With an IBM 3705 not running under SNA, for example, terminals are still l imited to one application in emulation mode of a 270X. In addition, the overall control of the network still rests with the mainframe. The 3705 does not have its own console through which the network manager or operator can bring up the network and test different parts of it.

PCCs Even with the development of the 3705, the NCP and similar devices, there was still considerable need and scope for relieving the mainframe load even further. Display and printer terminals of different speeds and protocols were proliferating and users' communica- tions demands became more sophisticated as the full potential of computers was unleashed through database systems and onl ine enquiry languages using English s tatements--systems which are heavy on mainframe resources.

PCCs have proved to be the answer. They are a logical development of devices like the IBM 3705 and are based on the idea of a dedicated processor manning the boundary between the mainframe and the network. They break down the strong dependence on mainframes. Indeed, the PCCs that have emerged over the last few years from independent suppliers are true computer systems in their own right. As dedicated systems they can provide a much wider choice of facilities than a user organization could reasonably expect if its network was control led by a tradit ional front-end processor and the mainframe, with all its other tasks.

What facilities, then, can users expect from PCCs in addition, of course, to complete compatabi l i ty with their existing equipment and system software?

If the control ler is to have true control of the network it must have its own console. The console can be local or remote, giving the network manager or operator complete control of what might be a very large, scattered network from a single point.

This apparently trivial feature is, in fact, extremely significant, for it epitomises the independence from the mainframe that the PCC can give to the network. The console enables the operator to bring up and test different components of the network - - lines, modems and t e r m i n a l s - and broadcast messages to a single terminal, every terminal on a line or group of lines or every terminal in the network, wi thout involving the mainframe at all. The messages might be about a

mainframe or program fault or the necessity to advise users of impending network changes. It is worth noting that, traditionally, computer manufacturers' front-end processors and communicat ions controllers, including IBM's 3705, have not had their own consoles; all com- munications with the operator have had to be through the mainframe console. Magnetic tape or disc storage in the PCC gives still more power to the operator. It enables the operator to take 'snapshot' dumps of the controller's memory to help sort out communications problems. Statistics can be provided by counting and storing the numers of characters, blocks or read and write commands passing between the terminals and the mainframe.

As a dedicated communications processor claiming full control of the network the PCC can allow any terminal, minicomputer or mainframe to pass messages to any other, providing they are compatible in protocols, again wi thout reference to the central host computer.

FACILITIES PROVIDED BY PCCs

Once the network is connected to the mainframe the PCC ensures smooth communications between users and databases and other application systems in the computer. It relieves the mainframe of the task of poll ing terminals. Individual terminals, even in the same cluster, can access different applications or even mainframes if the controller is l inked to more than one computer. Gone are the restrictions of other front-end processors. Software now sets up the logical links between terminals and applications, removing the need for rigid physical connections from one terminal to just one application. In this case access to any application or database on any mainframe attached to the control ler is available simply by entering the app- lication's reference code through the remote terminal. The controller connects the user to the right sub- channel. If necessary, access to specified applications or files can be restricted by passwords which can be checked by the controller, again relieving the main- frame of mundane tasks. Conversely, two or more applications can communicate one at a t ime with the same remote terminal or minicomputer using the same or different channels.

These facilities significantly increase the efficiency of communications line usage. This efficiency is further increased by the fact that a PCC for asynchronous terminals can detect a terminal's datarate and allow users with terminals of different speeds and protocols to dial into the same asynchronous ports. All the necessary buffering and speed and protocol con- versions are handled by the controller. Users with a variety of terminals can thus use a single group of lines instead of the several groups normally needed to support different types of devices. In addit ion, if channels or lines go out of service the network manager or operator can rearrange the line connections simply by typing in a command at the controller's console.

This enormous f lexibi l i ty of PCCs is further demon- strated by the fact that they can serve several host mainframe computers. At the top of the scale are controllers which can handle eight channel-attached mainframes concurrently and efficiently, giving the potential for organizations with several computers to offer an extremely wide range of applications and

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databases to their terminal users with the ult imate in backup. Important systems can be available on more than one computer so that if one goes down the communicat ions control ler can switch terminals to the other wi thout the remote user's service being significantly affected.

Data concentrators

PCCs can not only control distr ibuted processing networks and switch data traffic between applications and mainframes, they can also communicate with each other. Again, an apparently trivial facility opens up enormous potential in terms of combining the features described so far with the functions of a data concentrator.

The advantages of this for an organization with a network of mainframes can be massive in cost terms alone. Data from a large number of terminals and computers of different types can be concentrated and sent to another part of the country or even to another cont inent with considerable savings in line and modem costs. In addit ion, users anywhere can be switched from any application or mainframe to any other. If a network is arranged as a ring or matrix, the communica- tions controllers can inform the operators through their own consoles if a line goes out of service and find an alternative route for the data. If necessary, any control ler could be loaded from any mainframe in the network, whi le a single network manager could control the entire network using the communications controller's remote consoles. Moreover, with the advent of the packet-switched networks, a user may overlay his existing communicat ions network with the packet-switched network to provide a full backup teleprocessing service in the event of normal network failure.

What emerges from this catalogue of facilities is the complete f lexibi l i ty that PCCs give to organizations with computer and terminal networks. As far as the end users are concerned the mechanics of all these facilities are of no concern. The control ler is responsible for communications between network users, bethey mini- computers, terminals or mainframe programs. The user does not specify the route the data is to take but merely identifies the receiver bya symbolic name. Users ta lkto each other as though they were directly connected, even though their messages may be exchanged over links with different protocols, stored while a route is out of service or concentrated with other data.

PCCs in industry

A look at a handful of organizations which are using PCCs will show some of these devices' facilities in action.

Esso Petroleum has installed an ITT 3805 programm- able communicat ions control ler (Figure 1). The 3805, which is compatible with I BM's 270X and 370X devices, controls a network linked to two large IBM mainframes in London and handles communications with computers at Exxon's headquarters in New York through com- munications controllers installed there. It thus boosts the cost effectiveness of the expensive transatlantic communicat ions l ink by significantly increasing the dataflow. Similar controllers are being installed in computer centres in Europe, al lowing rapid inter-

national exchange of data. Esso expects the arrange- ment to improve real-time and batch processing efficiency substantially.

The control ler in London has six modem interfaces, each with 16 lines. One supports asynchronous devices such as teletypewri ter terminals whi le the others support synchronous communications, handling all types of interactive and batch terminals and providing facilities for new protocols and for SNA.

A similar network has been set up by Phillips Petroleum Company Europe-Africa. The company has also installed a 3805 in London. It is connected to a large IBM mainframe which handles most of the data processing needs of Phillips' operations in Europe and Africa.

Remote users can link to the 3805 for access to the London mainframe or to three IBM computers at Phillips' head office in Bartlesville, USA, for addit ional computing facilities and backup. A further control ler has been installed in Stavanger in Norway. This unit is l inked to four computers in the Stavanger office and acts as a concentrator for communications over two 9 600 bit/s leased lines to the controller in London. The abil i ty of the controllers to switch between applications pn different mainframes at the discretion of remote users was one reason why Phillips chose them.

Another organization which installed a 3805 partly for its abil i ty to communicate with similar equipment overseas is ICI Fibres Division. It has a 3805 control l ing a local network l inked to a powerful IBM mainframe at its headquarters in Harrogate, UK, and a second attached to another IBM machine in Ostringen, FRG. The division saw a link between the two 3805s as a way of giving terminal users access to systems running on either mainframe, with the 3805s directing messages

Figure I. Programmable communications controller

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automatically between the terminals and the computers and concentrating data to get the best use of the international communications line.

Systems developed in the UK are run on the computer in the FRG, thus saving the duplication of development effort. With the link established, programs and amendments can be transmitted from one machine to the other. Previously the programs, and every amendment, had to be transferred by hand with physical media, i.e. magnetic tape. Other applications for the international link include joint planning exercises run by UK and FRG specialists.

Small systems

It is not only organizations with international mainframe networks which need PCCs. A network run by Unichem, a UK-based pharmaceutical wholesaler, demonstrates that smaller companies with single mainframes can use many of the facilities provided.

Unichem has an IBM mainframe at its headquarters in Morden, UK. In 1979 it set up an online system to speed up the processing of orders. Orders are taken by telephone and entered immediately through terminals. The invoice, which also serves as a picking list, is printed straight away and goods can be despatched within an hour.

Unichem's network links terminals of different speeds: 50 printer terminals and 187 display terminals. The need for a PCC to handle these different devices is clear. The flexibil ity of a PCC enables users to choose precisely the facilities they need. This means that ITT Business Systems' controllers can cost anything from £20000 to around £400000 depending on the facilities chosen. The average price of the 50 or so units installed in the UK is around £55 000. The 3805 configuration installed in London by Esso is worth around £190 000 while the two units taken by Phillips cost a total of £150 000.

In addition, the top-end system, the 3809, can effectively replace several small/medium IBM 3705s or the large IBM 3705, again saving considerably in costs.

Digital networks

The ICI installation is a good example of the way PCCs can help organizations to ease their way, relatively cheaply and with the minimum of disruption, into new communications. As such, it points to the important role controllers could play over the next 10 or 20 years as national and international communications services are virtually revolutionized with the introduction of packet-switching and digital public networks such as the planned British Telecom ISDN (integrated subscriber digital network). ICI Fibres Division had been using a computer run byanother ICI division until it decided in 1977 that its workload had grown to such an extent that a computer of its own was justified. As a new installa- tion it did not want the prospect oftoo much disruption when it came to expand its communications facilities. At the same time it foresaw a need for a network supporting a variety of jobs and devices, from online applications and online programming to preparing telex messages.

One way to cater for this variety of work would have been to have duplicate lines, sophisticated modems

and many terminal controllers, but that would have been expensive. I BM's S NA was considered but rejected because as a new installation the Division did not want the disruption of the major change to the access networks that moving to SNA entails.

The PCC was chosen because it was seen as the best way of providing what was wanted relatively cheaply, while the controller's compatibil ity with IBM equip- ment left open the option of migrating gently to SNA in the future.

By not going straight to SNA, but still enjoying the facilities through the PCC, ICI Fibres Division estimated that it saved between £55 000 and £75 000 a year on the extra memory that would have been necessary to support the VTAM systems software needed for SNA.

The path to SNA is further eased by software in the ITT controller which allows terminals using the binary synchronous protocol to switch between BTAM, SNA's VTAM and the SNA version of TCAM, running on any host mainframe attached to the controller. This means that users do not have to cope with the disruption and heavy investment that moving to SNA entails over such a short period. The replacement of binary synchronous terminals by synchronous data link control (SDLC) devices, the amendment of application programs, the investment in new communications lines and the retraining of programmers and operators can all be done at a more gradual, realistically scheduled pace. Users' heavy investment in systems and equipment is protected. In fact one estimate puts the saving from migrating gradually to SNA at around £50 000 a year for a typical user.

All these features of PCCs derive from the fact that they are programmable. Hard-wired techniques have long given way to software control, leading to much greater flexibility, not only for the user but also for the supplier. The user organization can order whatever facilities it needs initially and if it wants others later they can be installed as software modules and the controller can be upgraded quickly on site.

Packet switching networks

As well as enabling the user to add facilities easily in a modular fashion, software control allows the supplier to keep the controllers up to date with new communi- cations techniques and trends. An example is the growing demand for packet-switching services, initially for computer communications. Whether users want to use these services as the main carriers for their own net- works or for getting at commercially available specialist databases they need to be able to interface their own equipment to the international X.25 standard adopted by the national communications authorities for packet- switching networks.

Users can obtain adapters from the authorities or 'black boxes' from terminal manufacturers or indepen- dent suppliers. Or they can add another software module to their PCCs. There is no reason why software could not be added to a controller to provide interfaces to a packet-switching network for asynchronous, binary synchronous and SDLC connections. This is in stark contrast to the adapters provided by some national authorities which interface Teletype and compatible terminals only and even to I BM's'black box' which only supports the company's own SDLC protocol.

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Packet switching brings communications to the major crossroads mentioned above. Until now users have expanded their data communications networks with more of the same: more terminals and distributed minicomputers linked through more intelligent controllers to bigger host mainframes. Packet- switching services sow the first seeds of doubt about whether traditional hierarchical networks are still the way forward for computer communications. When office automation is thrown in, as it eventually must be, the communications world of the last 20 years risks being shaken into complete disarray. For office aiJtomation brings communicating word processors, with all their odd control functions such as centring and indenting to several levels; viewdata, which uses television sets as terminals; facsimile and, of all things, intelligent photocopiers, not to mention voice com- munications. And who knows what lies beyond, in terms of voice recognition and even more integrated personal workstations?

FUTURE DEVELOPMENTS

The development of the automated office has been compared to trying to build a house by starting at the top. New tiles and bricks keep arriving in the form of word processors and other equipment but no firm foundations have been laid in the form of communica- tions carrier or overall organizational strategy. On the communications carrier front there is debate about the respective merits of local area networks and central intelligent switches. As far as strategy is concerned there is much pondering over whether the data pro- cessing manager, the establishment manager or some- one else should become some form of overall com- munidations person, treating communications in its widest possible sense. At the same time, word pro- cessors, microcomputers and other equipment such as facsimile devices, are being bought almost at random by user departments from their own budgets without reference to each other or to the organizations' overall needs or plans, if such plans even exist.

Until some more concrete path forward emerges users will understandably continue with their 'wait and see' philosophy rather than throw away their painful work of the last 20 years and start again from scratch. Progress tends to go at the pace of the slowest factors when so much investment is at stake. In this case, the speed with which the national communications authorities introduce digital networks or considerably enhance the facilities of their packet-switching services could be the deciding factor. It will be sometime, therefore, before the way ahead emerges. The PCC can again provide the solution in this time of uncertainty and indeed form the basis for the future, whatever it has in store. Extra software modules can be added to interface all kinds of devices to each other and to host mainframes, perhaps passing their data and messages through a packet-switching network on the way. Organizations can experiment with exotic devices without disruption to application programmes or system software in their mainframes and without having to invest in extra communications lines or'black box' protocol converters.

Potential market

The potential importance of this role is shown by a recent study of the communications processor market by the research organization Eurodata. The study concluded, 'During the 1980s the market for com- munications processors will grow substantially but the share of the installed base held by integrated office switches will remain small. At the same time advances in technology and design will prepare the ground for substantial shipments of fully integrated systems in the 1990s. The implementation of such integrated systems depends on the matching of technical capability to the precise needs of the user at an economical price and there are many obstacles to its achievement'.

The report added that the availability of public digital networks is 'a major technological consideration'. It went on, 'Although most Western European countries are working towards such networks the service is not expected to become generally available before the end of the decade. In the meantime the benefits of integrated systems will not be fully realized. The first generation of integrated office switches will need to interface to a variety of networks for the various types of information involved'.

The role of the PCC in this time of uncertainty and as a means of providing the interfaces to this variety of networks is well established in the current communica- tions field. Again, the fact that the controllers are programmable is their strength, in that it gives the user and supplier great flexibility. Facilities which are expected to be available in, say, a packet-switching service in the next few years could be simulated in the controller to help users plan ahead. On a more basic, day-to-day level, subsets of important online f i l e s - customer accounts, stock levels and order records, for example - - could be available on local storage with the controller in case the mainframe goes out of action. Message priorities or code conversions for specific application systems could be handled by the controller. The controller could not only capture statistical information but process it to highlight areas where lines or clusters of terminals are not being used efficiently. All these facilities are completely independent of the host mainframe, which is freed to dedicate itself to the job it does best, the processing of the user's application systems and turning round information as quickly as possible.

Not all these features are going to be needed by all users. However, as we have seen from the examples of organizations which are using PCCs, many users need a considerable subset. And installing a £60 000 PCC can bring considerable savings in terms of protecting existing investment in systems and equipment. For the simple communications problems there are modems, time division and statistical multiplexers and 'black box' protocol converters from a large number of suppliers. In the more sophisticated PCC market there is a mere handful of leading suppliers. Codex and Memorex offer small and medium-sized controllers in terms of memory size and the number of lines supported. IBM and NCR Comten cover the market from small to large controllers. In Europe NCR Comten equipment is sold and supported by ITT Business Systems. Finally, Computer Communications Incor- porated specializes in large systems, mainly in the USA.

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Not all these controllers have the facilities described above. For example, not all of them have their own console, fully support SNA or provide full interfaces to packet-switching networks. A close look at the NCR Comten/ITT range will give an idea of the type of networks PCCs can support. The entry level of the range is the 3805-M80A with 256 kbyte of memory and one channel. Users can start with four, 10 or 16 lines and expand up to 128.

The standard ITT 805 has up to 512 kbyte of memory but more flexibility on line costs above 16 lines for mixed asynchronous, bisynchronous and SDLC connections. For systems above 16 lines the network manager must determine the mix of lines currently used and planned, to determine the model to select for his network. The 3805 has a communications interface module which controls the transfer of data between memory and the communications lines. It can support eight modem interface modules, each serving up to 16 lines, thus enabling up to 128 lines to be connected to a 3805.

Any mixture of modem interface modules can be handled by the 3805. There are asynchronous interfaces supporting full-duplex or half-duplex terminal or tele- graph lines with speeds of up to 1 800 bit/s and handling local terminals or external modems with switched auto-answer lines or nonswitched leased or private lines. Synchronous interfaces handle lines with speeds of up to 56 000 bit/s while the SDLC interfaces handle IBM's SDLC protocol as well as synchronous communications over leased, polled or dialled lines, again with speeds of up to 56 000 bit/s.

One option allows line-speed attachments up to 230 400 bit/s. At the top of the range is the 3809 which provides all the modem interfaces of the 3805 but handles bigger networks. Its processor has 1 Mbyte of memory, 16 32-bit general registers and 16 32-bit control registers. It can handle eight multiplexer channel interfaces, compared with two on the 3805,

and can have four communications adapters, each supporting eight modem interface modules. This means 512 lines of different types, if necessary, can be attached to a 3809. An operator's console, a magnetic storage peripheral and all the protocol conversion, line handling and application switching facilities already catalogued are available giving IBM users with the BTAM system software all the benefits of SNA without the need to install VTAM with its extra memory demands.

Facilities such as line tracers, memory examination and modification and line swapping are provided as standard utilities available through the 3800 series consoles. Interfaces to X.25 packet-switching networks are available as software modules. Additionally, all software and most hardware modules are fully com- patible through the ITT range of PCCs from the entry model, the 3805 M80A, the 3805 and the top-end model, the 3809.

CONCLUSIONS

PCCs have established themselves over the last six years as the most flexible way of meeting the very considerable and growing demands of communication users. The communications industry is growing at 25% each year as networks expand and transaction volumes increase. The availability of network services is being forced to its limits and additional facilities and backup can be expensive. At the same time, more new com- municati.ons products are coming on the market as users seek to improve the productivity of office staff. The PCC provides all the advantages of modern net- work architectures without the need for new invest- ment in equipment, software and applications pro- gramming, while spanning the gap between the restric- tions of today's mainframe-based networks and the extreme and sometimes even unforseeable demands of tomorrow's distributed systems.

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