Forecasting International ISDN Requirements

75

Alan L E W I S Teleglobe Canada Inc., Montreal, Quebec, Canada

Abstract. A method for estimating international ISDN capabil- ities and service requirements from the telephone usage pat- terns of "leading edge" business is introduced and illustrated.

Keywords. ISDS, business telecommunications, 64 kb/s, closed user group.

Alan Lewis is the Manager, Traffic planning and Analysis in the Oper- ations department of Teleglobe Canada Inc. He has been active in international meetings of the ITU, In- telsat and other organizations. He is currently the chairman of CCITT Working Party 11/2 which deals with the traffic engineering aspects of net- work operations. He is a member of the International Advisory Committee of the International Teletraffic Con- gress. He holds a B.Sc. degree from

the University of Manitoba and a diploma in public utility management from the University of Michigan. Prior to joining Teleglobe he had worked for a telephone company, another international carrier and a consulting engineering firm.

North-Holland Computer Networks and ISDN Systems 20 (1990) 75-79

1. International I S D N

ISDNs are being introduced around the world at present. Frequently they are providing stan- dardized digital access arrangements established in CCITT Recommendation 1.412 [1] to users in a relatively small area such as the serving area of a digital local telephone exchange. ISDN is con- ceived as an evolutionary development from exist- ing networks [2] so that initial ISDN users will make extensive use of existing services and fea- tures or special connections to communicate with ISDN and other users outside their local area. As ISDNs grow and new and presently unforeseen apphcations develop, new forms of global ISDN networks will develop. However, at the interna- tional level such evolution will probably take a considerable period to develop so that we antic- ipate an extended period where there will be re- quirements for international provision of a few particular ISDN related capabilities and features prior to the provision of full international ISDNs.

The key ISDN capability for international op- eration is circuit switched 64 kb /s . This capability is inherent in the standard ISDN user interfaces and can be exploited by users in a straightforward manner for a wide range of applications. Interna- tional transmission facihties are rapidly digitizing and in so doing are extensively employing Digital Circuit Multiplication Equipment (DCME). As an example, Teleglobe Canada presently uses DCME on less than 10% of its telephone circuits, but plans to increase this proportion to 67% by 1994. This equipment uses a combination of low bit rate encoding (24-40 kb /s ) and speech interpolation to derive up to five telephone circuits from one 64 k b / s digital bearer circuit. DCMEs detect data or facsimile calls using analog modems on telephone connections and adjust the encoding rate to pass the calls without loss of data. However, 64 k b / s digital services must either be routed separately from the DCME equipment or by use of signalling information reserve 64 k b / s bearers on a call by call basis. With either strategy the demand for 64

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76 A. Lewis / Forecasting international 1SDN requirements

k b / s services has a major impact on international transmission facility requirements. The bulk of this paper is concerned with the forecasting of relatively short term requirements for circuit switched 64 k b / s connections.

2. ISDN User Identification

For local ISDN applications, the demand for bearer and teleservices has been calculated from the total population of users to be connected and the assignment of calling rates for average or typical users [3-5]. At least, in the immediate future, the demand for specific ISDN services and features can be expected to be concentrated to limited numbers of business users with more de- manding communication needs than the general population. These businesses can be considered to be the "leading edge" of communications devel- opment. They have already abandoned mature services such as telex and are looking to escape the limitations of newer alternatives such as MHS and group 3 facsimile. They remain major users of the public telephone service only because the ubiquity of the telephone network provides connectivity to many destinations that can not be reached any other way. This is particularly the case for interna- tional service where the uneven state of telecom- munications development in different countries and high tariff levels for dedicated facilities tend to preserve an important role for public telephone even for large, sophisticated telecommunications users.

A reasonable assumption concerning the "lead- ing edge" businesses who will be early users of circuits switched 64 k b / s connections is that they will be mostly found among existing users of 64 k b / s and higher speed leased circuits. These users either have high speed data requirements in their business operations or have already found effi- cient ways to combine lower speed services on to high speed digital streams. In intercontinental telecommunications up to 1989 almost all leased digital capacity at 64 k b / s and higher speeds was provided through the Intelsat Business Service (IBS) using Intelsat satellites. These offerings have proved more popular than originally forecast, leading us to believe that a large portion of the potential present high speed lease users are al- ready customers of the IBS service.

3. Analysis Methodology

Potential circuit switched 64 k b / s users have been identified as being within the community of "leading edge" businesses represented by existing IBS customers. However, not all IBS customers have a need for circuit switched 64 k b / s connec- tions. Some IBS customers might have communi- cation needs concentrated in a few international locations and in some cases could already have satisfied some or all of their needs with IBS or other leased services. The first step in this method is to examine the international public telephone usage of existing IBS customers to identify those with low volumes and those with calling patterns highly concentrated in a few destinations. Such customers are unlikely candidates for switched 64 k b / s services and are not analyzed further.

The telephone usage of the remaining customers is then analyzed to compare calling patterns of this "leading edge" community of users with the general telephone population. This analysis will identify the international destinations to be intro- duced first.

The traffic volumes for each international de- stination are projected by assuming that a certain portion of existing public telephone volumes re- presents applications that would be better handled on a switched 64 k b / s service and applying this portion to a future "leading edge" population and public telephone volumes. This process is some- what speculative, but precise volume forecasts are considered less important than the identification of communities of interest and relative calling patterns. The initial network for circuit switched 64 k b / s will be generously provided in order to stimulate interest in the service.

4. Illustrative Example

Teleglobe's IBS customers as of January 1989 were identified and the incoming international telephone calls to each customer totalled for a 60 day sample taken over six months. It was found that 30% of the customers received less than one call per day. These customers were eliminated from further consideration as early users of switched 64 k b / s services. The call patterns of the remaining customers were examined for con- centration of communication interest and it was

A. Lewis / Forecasting international ISDN requirements 77

found that 21% of the group received more than 65% of their calls from one originating country or more than 80% from two countries. Such customers are considered better candidates for additional leased services than for switched 64 k b / s and are therefore also discarded. This leaves 55% of the original population of IBS customers that are con- sidered to be potential "leading edge" users of switched 64 k b / s services.

Table 1 compares the call patterns of these users with the call patterns for the totality of telephone traffic for Canada. From the table it can be seen that the traffic for the "leading edge" group is only slightly more concentrated in the largest countries of interest than for the general telephone service. This suggests that to satisfy the needs of the "leading edge" group, switched 64 k b / s capability will have to be provided to a fairly broad range of destinations. It can also be seen from Table 1 that the ranking of countries is different for the two groups. In particular, there are countries of high importance to the "leading edge" group that are much less important in the overall telephone service. This suggests an order of introduction of the switched 64 k b / s capability that will be different than the size ranking of telephone routes.

Table 1 gives the relative importance of over- seas countries to the "leading edge" group as a

Table 1

Overseas Potential 64 k b / s users General telephone service

Country Rank % of total Rank % of total

A 1 27.7 1 21.7 B 2 13.8 3 7.0 C 3 7.3 2 7.1 D 4 6.9 4 6.8 E 5 3.9 21 0.8 F 6 3.2 6 4.0 G 7 3.2 11 2.2 H 8 2.4 7 2.7 I 9 2.3 9 2.5 J 10 2.3 18 0.9 K 11 2.2 8 2.6 L 12 2.2 5 4.4 M 13 1.9 16 0.9 N 14 1.5 20 0.8 O 15 1.5 17 0.9 P 16 1.4 24 0.7 Q 17 1.1 14 1.4 R 18 0.9 30 0.4 S 19 0.9 10 2.3 T 20 0.9 31 0.4

whole, but does not indicate if individual users would have their needs met by a network provided in the priority order for the group. Examination of the individual call patterns revealed that for 11% of the group, their individual ~¢ 1 ranked overseas country was not included in the top 5 countries for the group as a whole. For 32%, the 5th ranked country was not included in the top 10 for the group. This result again suggests the need for a broad introduction of the 64 k b / s capability in order to satisfy the needs of most potential users. For 95% of the individual users, their 5th ranked country is included in the top 20 countries overall, and for 90% their 10th ranked country is included in the top 20.

Country A in Table 1 averaged 239 calls per day to the "leading edge" group and Country T averaged 8 calls per day. Between 1989 and 1994, international telephone traffic with major coun- tries is expected to grow at 15% annually and the customer population for IBS and similar services is expected to increase by 90% over the same period. This, taken together with the present ratio of incoming and bothway calls results in 1994 forecasts of 2008 bothway calls with the top ranked country and 67 with the 20th ranked country.

With a small, closely defined group such as this, it is reasonable to assume a v e r y high penetration for switched 64 k b / s services--80% has been chosen. A more difficult estimate is the portion of telephone calls that would use the 64 k b / s capability once it was available. Calls used for only voice don't need 64 kb/s , but data or facsimile calls might benefit from the digital capa- bility. Since this group comprises sophisticated business users, 50% of calls are estimated to use the 64 k b / s services. Combining these two per- centages with the call estimates from the previous paragraph, results in forecast daily call volumes of 803 calls with the most popular destination (Country A) and 27 with the 20th (Country T) destination.

A high concentration of traffic in the busy hour can be expected for this service--15% is assumed. Holding times should be quite short for calls using 64 k b / s connect ions--2 minutes is assumed. This results in a range of busy hour traffic from 0.14 to 4.01 Erlangs for the top 20 countries.

This result indicates that dedicated links to sufficient destinations to satisfy the breadth of interest of key 64 k b / s users would be very lightly

78 A. Lewis / Forecasting international ISDN requirements

loaded and thus probably not economic. As a practical matter, each dedicated international link must have a minimum of two circuits. A better strategy for providing international switched 64 k b / s capability would seem to be dedicated links to only a few destinations with call by call selec- tion of 64 k b / s transmission to a larger group of destinations. The consequences of such a strategy are additional development effort on signalling and interfaces to ensure that the need for 64 k b / s facilities is transmitted accurately through the net- work and that the DCME equipment react prop- erly to such signals. There will also be a need for close monitoring of actual utilization of the 64 k b / s capability to ensure that DCME operation for other traffic is not impaired and to identify when routes should be converted to dedicated 64 k b / s links.

5. Other Services

While 64 k b / s circuit switched capability is the key feature to consider in the extension of ISDN services to the international network, there are also other bearer and tele-services that potentially could have significant impacts [1].

In the early stages of international ISDN users will be predominately sophisticated large busi- nesses. They might well want to exploit multipoint and asymmetric features foreseen in many ISDNs. In the international network it will be necessary to choose between providing this capability as a spe- cial feature in exchange processors to emulate such features without basic changes in the un- derlying network and developing new transmis- sion facility controls to provide true end to end multipoint and asymmetric connections.

Supplementary services such as the Number Identification group will be very difficult to ex- tend internationally where different policy and legal restrictions can be expected to evolve in different countries. An early indication of user demand for such services will make a great dif- ference in the resources to be applied to the asso- ciated problems.

Services requiting consultation with data bases whether for closed user group calling, charging supplementary services or applications not yet de- fined can have great impacts on the traffic loads of common channel signalling networks. This ap-

plies both domestically and internationally, but the international impact can be greater consider- ing the thin signalling networks that are anti- cipated internationally in the 1990s and the possi- bility of regulatory or other legal restrictions on the international extension of such modes of oper- ation.

Closed user groups provide another interesting possibility in the international provision of ISDN services. With a relatively small community of early users such as has been identified in this paper, it is conceivable that the bulk of their ISDN requirements are included in Closed User Groups. If this proves to be the case, it might be possible to delay the introduction of general ISDN features by providing special sub-networks for the Closed User Groups. Alternatively it might be economic to provide general ISDN features to the general population without Closed User Group features and to make such features available to the few interested users by special interface equipment.

User to user information transfer on signalling links has a direct impact on the traffic loading of these links and also raises similar international regulatory and legal problems as Number Identifi- cation services and services involving data base consultation.

In all the cases mentioned in this section, it is impossible to forecast the importance of various services and combinations of services based on existing operations and classical forecasting meth- ods. The identification of a relatively small "lead- ing edge" group of users allows the possibility of in-depth interviews with these users to try to re- duce the vast array of possible ISDN services to a smaller set of those services that will be truly important in the short to medium term. This in turn could lead to a more rational use of resources to provide efficient and useful international ISDN capabilities. Teleglobe Canada intends to pursue such a customer interview approach. Much work remains to be done in defining the structure of the surveys and the selection of key services and capa- bilities.

References

[1] I Series Recommendations, CCITT, ITU, Geneva, 1989. [2] H. Yomada and Y. Suzuki, Network configuration for new

services traffic, in: Proc. ITC-12, Torino (1988).

A. Lewis / Forecasting international ISDN requirements 79

[3] M. Medina and R. Tudela, Traffic characteristics for 1SDN planning studies, Specialist Seminar on 1SDN Traffic Is- sues, Brussels, 1986.

[4] H. Hofstetter and D. Weber, Traffic models for large ISDN-PABXs, in: Proc. ITC-11, Kyoto (1985).

[5] M. Bonatto, G. Giacobbo-Scavo, A. Roveri and L. Verri, Terminal exchange access system for NB-ISDN: Key issues for a traffic references model, in: Proc. ITC-12, Torino (1988).