convergence — the pathway to integration

Convergence to integration

m the pathway

As countries world-wide move towards the establishment of integrated services digital networks, Brian Simmons identifies some cost-effective communications techniques that can be used in the interim stages

The convergence of computer and telecommunications technologies into an integrated system solution is now widely accepted as an achievable objective. However, the evolutionary passage towards this goal has been somewhat prolonged and tortuous, and there is still some way to go.

The article reviews that passage, discusses the meanings and implications of the terms 'convergence' and 'integration', and identifies a number of useful cost- effective techniques which can currently be used to achieve some of the benefits of integration now, in advance of the UK System X architecture.

Fully integrated public systems are unlikely to achieve substantial penetration in the UK until System X architecture is widely introduced into the UK network. Until this happens the full benefits of the convergence of telecommunications and computers wil l not be realized.

Computer information is already in digital form, so that little change is envisaged in routing this via System X. Speech is analogue however, and it is here that a number of changes are necessary. The article therefore concen- trates on this aspect, leaving scope for a further contri- bution which could focus on nonvoice information.

In the light of experience, it is not difficult to understand why the hazy vision of those early pioneers has taken several decades to develop. The viability of electronic systems and new transmission techniques has depended heavily on:

• microprocessor technology, • cheap integrated circuits, • digital encoding and transmission, • proven software, • well defined user requirements, • a range of useful facilities, • high reliability and maintenance diagnostics, • system management controls.

Optimists predict that by 1990 the benefits of ISDN and System Xwill bewidely available.Those with memories, and a more realistic approach, prefer to add one more decade to their predictions. But whatever the precise timescale may be, the way towards integration is now established. Office system and computer suppliers, telecommunications equipment manufacturers, and public telephone authorities and users alike are taking active interest in the subject.

Since the early 1950s, when the UK Post Office, now British Telecom (BT), and its 'big five' telecommunications equipment suppliers pooled resources to develop electronic switching systems for the future, it was clear that a prolonged and flexible path would have to be trodden to arrive at the ultimate goal of an integrated and coherent telecommunications network.

The requirements for this network would be a common system of switching and transmission which would be the vehicle for routing all telecommunications services required by every sector of the community. The networkwould be digital and the exchanges electronic, with computer control.

In effect, this is what is about to happen so me 30 years later. The new network will be known as the integrated services digital network (ISDN) and the switching and routing architecture will be System X, which is a very sophisticated stored program control (SPC) electronic switching system.

Despite the lack of detailed information on the precise facilities and tariffs which will be offered, much more is generally known about the architecture and objectives of System X. 1

PA Computers and Telecommunications Ltd., Rochester House, 3 3 Greycoat Street, London SW1P 2QF, UK

C O M P U T E R / T E L E C O M M U N I C A T I O N S RE LATIO N SH I P

There is a growing awareness that many complex business functions and services required for the future can be realistically provided by their integration into an effective operational relationship. Only by so doing can they fully satisfy the complex requirements of a modern industrial society's infrastructure. These services range over:

• management information, • banking transactions, • point-of-sale reporting, • stock control, • enquiry services, • offices of the future.

However, bringing the two together has proved to be difficult because of a number of contrasting factors:

• telephones, and many of the switching system concepts which are still in operation, were invented over 100 years ago; computers have been in exis- tence barely 30 years,

• telephone wave forms are analogue; computerwave forms are digital,

250 0140-3664/80/060250-8502.00 © 1980 I PC Business P r e s s computer communications

• there are over 350 mil l ion interconnectable telephones in the world; but relatively few computers are presently interconnected,

• international te lephone network standards were established well before it was realized that data transmission would be a requirement.

There are therefore fundamental differences which have created various barriers to effective integration of the present technologies. These are aggravated by a number of other factors:

• the Strowger switches of traditional exchanges are electrically noisy and not ideal for data transmission,

• voice lines need to be 'electronically condit ioned' in order to transmit higher data speeds,

• batch data transmission services tend to require long connection times,

• real-time data transmission demands fast connection times, presently unrealistic on the public network.

Voice and data services have therefore tended to remain apart. This too has been reflected in the way in which the two services are frequently organized within companies where, typically, the EDP management will

specify requirements for lines and modems, and control the teleprocessing operation but will have no part in the rest of the telecommunications function, and vice versa. This is, however, beginning to change in more enlight- ened companies where the need for an integrated operation is appreciated.

C O N C E P T S

Before studying the basic requirements for integrated systems to provide a range of services, it is appropriate to consider precisely what is understood by the terms 'convergence' and 'integration'. There are various interpretations and shades of meaning abroad, which it is as well to recognize and understand.

When designers and users first saw the possibility of combining systems to achieve 'economy of scale' factors, integration was seen as the goal. Full integration has tended to be elusive, however, and its extent is often l imited by available techniques and resources. More- over, having defined one way of achieving the integration of certain services, one is often confronted with new factors which either do not fit into the concept or require further consideration.

Therefore, the term 'convergence' has evolved as a

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vol 3 no 6 december 1980 251

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more realistic definit ion of what is actually happening; namely the progressive merging of individual services into more convenient and cost-effective solutions, using common highways and switching.

There are several currently understood meanings of 'integration':

o an SPC private automatic branch exchange (PABX) as shown in Figure 1;

o or a word processing system (Figure 2); o or possibily, a more flexible solution which would

be achieved by a 'black box' distributed microprocessor system (Figure 3);

• the total combination of all business and data communication channels into a common system controlled either by

these would exercise a master control and routing function for communicat ion over common transmission highways.

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252 computer communications

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• The cost-effective routing of services over wideband links in which individual channels are dedicated, or time shared, for routing a range of services which would include: voice, data, telex, facsmile, viewdata, electronic mail and teleconference.

• The combination of several office desk-top communications terminals into an integrated 'work station' for convenience and efficiency, an example of which is shown in Figure 4.

• A local ring or star network which would couple together all communicating equipment within a building or complex (copiers, word processors, VDU terminals, printers, etc.). An estimated 60% of all

communication takes place internally within the office confines. Many solutions are being offered. Ethemet, Ringnet, Hyperchannel, Net/one and the Cambridge ring are but several examples. Twisted pair, coaxial cable and infrared transmission systems have been proposed to provide thewide bandwidth requirements of local networks. The functional environment in which users would be educated to be aware of the services available and their benefits, and trained to operate them cost- effectively, so achieving a more efficient utilization of the facilities than would otherwise be possible. The whole field of data processing and informatics, in

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Figure 5. Public communication services


which an advanced technology architecture - - System X - - would form the common denominator for awide range of user requirements centred around companies' integrated business communications systems. The architecture would be the common basis of service, to which the various user systems, added value networks, and overlayserviceswould be interconnected to meet all the functional requirements of users. The whole would represent a flexible and powerful means of t ransformingthewayin which business and society operates, by comparison with the present methods of telecommunication.

N e w s e r v i c e s

The widening range of public communicat ion services is expected to accelerate over the next decade, as

illustrated in Figure 5. It is probable also that many private network services will be developed to augment these public services, aided by a relaxation in the BT monopoly.

Clearly there is a greater prospect of these services being viable and attractive to users if ways can be found of interconnecting them more cost-effectively through common terminals, transmission highways, and switching systems, than if each remains autonomous.

Not only will these be of benefit to the business community, they should also confer a range of new services in the home, via wired and radio-connected links. One can visualize the total requirements for business, entertainment, education, finance management and energy control invested in an integrated domestic system, as depicted in Figure 6. This would add a new dimension to home life for which many

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Figure 7. Phases in the innovation of information processing and communication

would require re-educating, and which some might regard as being of doubtful benefit!

EVOLUTIONARY PATH

The historical path of progress in the innovation of information processing and communicat ion is shown in Figure 7, as a series of five phases. This began in pre- Christian times, using elementary methods of communication, recording and processing information, and is now at the stage of the on-l ine interfacing of computer and telecommunications systems forming an information network.

The contemporary developments which are making this possible include:

• pulse code modulat ion (PCM) systems, currently being installed by BT which provide frames of 30 X 64 kbit/s channels usable for voice and data services, which will ult imately avoid the need for analogue/ digital waveform converters (modems),

• protocols, such as X.25 for packet switching, to provide compatibi l i ty standards for interfacing terminals and transmission systems,

• new media for transmission, including fibre optics, infra-red wireless local links and satellite microwave communication,

• System X architecture providing 2, 34 and 140 Mbit/s digital transmission highways and common channel signalling to CCITT standards,

• the digital coding of all information, whether voice, data, text or image, at source for direct entry into PCM transmission channels.

INTEGRATION TECHNIQUES

Having discussed some ways in which integration can be achieved, we now focus on several techniqueswhich are currently being used to achieve a degree of integration. These offer cost-benefits that can effectively combat the high cost of long-distance call charges and leased line tariffs, particularly for voice and data communications.

Wideband links

Widebands are commonly engineered as groups of 12 channels in which individual channels are mult iplexed into a frequency spectrum of a nominal 50 kHz per group. Thus:

12 channels = one group 5 groups = one super group (60

channels)

BT tariffs for widebands are typically 70-80% of the rental of 12 individual private circuits, depending on the location of terminals relative to repeater stations. The tariff is made up of two parts:

• local 'tail' circuit costs between customer premises and the BT repeater stations. Circuits are cabled in heavy-duty 'polyquad' balanced transmission lines,

• main 'bearer' circuit costs between BT repeater stations; circuits are routed over the public trunk network links.

Not only is a wideband more cost-effective than an equivalent number of individual lines, but it is also more reliable. BT policy allows a number of different types of service to be routed in adjacent channels (see Figure 8):

• private network voice lines • interswitchboard circuits • data transmission lines • out-of-area exchange lines.

Rental of the wideband link, on a five year minimum contract, can also include the mult iplexing terminal equipment.

The quality of channels for data use is practically equivalent to tariff 'T' (Schedule D) standard. If required, specially condit ioned channels can be rented. Only a maximum of six channels in a group of 1 2 can be used for transmitting data, however, unless the mean power level is reduced. One problem with widebands is that provision time is currently 2-21/2 years.

Time assignment

In the early 1960s0 a technique called time assignment speech interpolation CFASl) was developed for

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Figure 9. Time assignment speech interpolation (TAS/) integration increasing channel capacity on transatlantic cables. It did this by allocating channel 'time' to callers only when they were actually talking. Recently, the technique has become more efficient and cost-effective with the introduction of microelectronic technology. The system is shown in schematic form in Figure 9.

A number of leased lines (N), usually upwards of five, are time-shared between a larger number of voice and data circuits which can number up to 2N-1, i.e. almost double. Access to the leased lines is made on a 'dynamic allocation' basis, i.e. when there is actually live information to be transmitted, via the concentrator/ assigner (CA), and under control of the processor (P).

Incoming speech is digitized and if no spare channel is available, it is held available in a transit store (TS) during a permissible short period of time (of up to 1/4 second), for allocation to the first available channel of the N provided.

Physical input/output circuits thus become 'virtual' circuits on the leased line channels, and any one connection can intermittently be routed via a number of the N channels, one at a time, according to their availability.

If, for any reason, there is insufficient channel capacity available, preventive steps are taken to 'busy out' individual circuit access. In practice, however, the provision of go and return paths (2N), on the leased line channels provides adequate capacity.

At the commencement of each burst of transmitted voice or data on an assigned channel, a prefix signal is sent to the distant end which indentifies the physical output circuit to be allocated, to ensure correct end-to- end routing.

Terminals costs are presently making this technique economic on international lines, but with increasing inland tariffs and the lowering of microelectronic costs, it is probable that theywill soon also find application on long-distance national circuits.

Dynamic allocation

Avariation of the TASI technique can be used to enable the 24 hour capacity of an expensive line or channel (typically a wideband) to dynamically allocated for a number of service requirements, under control of a stored program, thus taking integration a practical stage further. Operational needs, priorities and economies can be effectively achieved by this technique.

All illustration of howthe communications capacity of a link can be dynamically allocated over a number of services is shown in Figure 10. Priority is given to voice connections during the working-day international 'time window', while other less urgent connections, e.g. bulk data and electronic mail, are relegated to off-peak times.

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An interrupt facility can be introduced for overriding any less urgent, store and forward connections, and in their place providing priority real-time data or speech connection capacity.

Voice digitizing

The last technique to be described is voice digitization. This permits the compression of up to four physical channels into the bandwidth of one leased line with only a slight impairment of voice quality.

Several decades ago, a vocoder system was developed in which only the general envelopes of speech waveforms were coded for transmission, and not all the frequency components, thereby considerably restrict- ingthe bandwidth necessaryfor transmission. However, the 'robot-like' voice quality was not of a generally acceptable standard.

More recently, microprocessors and powerful al- gorithms have been used in a technique called adaptive predictive coding (APC), and this has enabled a more faithful voice reproduction to be achieved.

A schematic diagram of the system is shown in Figure 11. Each speech channel is converted in avoice digitizer (VD) into a 2 400 bit/s data stream. Using a 9 600 bit/s, four-port modem, all four channels are 'compressed' on to one voice bandwidth line.

As Figure 11 shows, it is possible to have a mix of voice and data inputs, and a higher quality voice connection can be achieved by using a 4 800 bit/s channel instead of 2 400 bit/s.

The voice channels can either be terminated on telephone sets, or coupled into PABXs for shared service. The cost of a four digitizer system is typically £60 000-70 000, the equivalent of one year's rental of a single leased line between the UK and USA.

A bonus arising from voice digitizers is that the encoded speech is effectively encrypted i~nd therefore offers security against unlawful tapping. This feature is already proving to be a marketing stimulus in the USA and is likely to be progressively so elsewhere, thus offering the double benefit of cost-effective channel integration and security.

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Figure 11. Voice digitizer integration (3 voice + 1 data circuits)


SYSTEM X

The techniques which have been described presently require modems to interface the digital signals at the terminals with analogue transmission lines. This is an extra cost and limits the maximum bit rate of the link to below 10 kHz, unless it is awideband group of 50 kHz or more. System X architecture is based on a hierachy of PCM digital transmission channels which can interface directly to terminals without requiring any analogue/ digital converters.

Once information is in this digital form, exchanges will switch and route connections without the need to convert the signals (Figure 12). Techniques have been developed for retiming pulse trains, and slot changing their position in cyclic stores. This enables pulse trains, using particular input channels to be retimed onto the available output channels on wanted routes. There will also be facilities for coupling high-speed data channels directly into local and trunk exchanges. The control of functions and facilities will be removed from the normal connection path and instead handled via separate channel signalling data links.

System X is a complex integrated solution and it has therefore taken many years to devleop and refine. It now requires a massive capital investment to install at a time when money supply is very restricted, with high interest rates. This is a worrying situation and could delay its introduction. Further heavy increases in BT tariffs to provide the investment required from retained earnings, would not be welcomed by industry or the public.

To realize the full benefits of ISDN and System X, a number of important requirements must be fulfilled:

• the huge BT investment programme must be main- tained,

• a high proportion of the 6 500 UKpublic exchanges will need to be either upgraded, or replaced, by SPC electronic switching systems,

• telephones, ofwhich there are now over 25 million in

the U K alone, will have to be modified to incorporate new microphones, receivers and circuit~/, and ulti- mately incorporate PCM codecs (encoders/de- coders) the entire national trunk network, and later the local network, will require to be digital, protocols and standards will be necessary to ensure complete compatibility, new facilities and signalling systems must be adopt- ed.

All must be fulfilled with the objectives of integration and cost-effectiveness for users.

CONCLUSION

The convergence of computers and telecommunications into an integrated system has been broadly outlined, particularly related to voice services. Several of the techniques which can be used at this interim stage, prior to full integration, have been described. Each offers particular benefits, a major one being line plant economy. The advent of System X and digital transmission will provide the vehicle on which a new range of integrated public and private networks, services and systems will be developed. Unfortunately, this is not expected to achieve a significant impact nationally untill the next decade.

The path to the ultimate goal of full integration is now well defined however, and should facilitate a progressive development and convergence of computers and telecommunications technology towards that goal.

REFERENCES

1 'System X' PO Elec. Eng. J. Vo171 (a series of technical articles starting in January 1979)

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Figure 12. System X - - digital network and switching
