The Standard Transfer Specification - Past, present and future

The initiative of South African utility Eskom to reap the benefits of standardisation by imposing an open system standard early in the technology life cycle resulted in the publication of the Standard Transfer Specification (STS) in 1993.

Today there is growing global acceptance of the STS as an international industry standard. The STS has had a profound impact on the development of prepayment metering in South Africa, and has laid the foundation for a new South African-based industry with a turnover of more than $20 million a year.

Some history

The introduction of prepayment metering to South Africa in 1989 was driven by social needs and political and economic pressures. Prepaid metering was the natural choice, as the lack of tele-communications and postal infrastructure and the informal nature of many of the areas to be electrified meant that bill delivery was impractical. Prepayment was also seen as the technical solution to ensuring collection of revenue. The lack of communication infrastructure meant that the equipment to vend the tokens had to be stand-alone (off-line) and the initial approach saw many small independent single-computer systems being introduced.

During 1991 it became clear that the standardisation achieved thus far, which was focussed on the meter itself, was insufficient and that the systems would not meet the industry's future needs. This was evidenced by a rapidly growing installed base (about 50,000 meters) of five proprietary systems. This led to lock-ins to the equipment of various manufacturers, and difficulties with the management of points-of-sale and customer databases. Manufacturers also adopted different operating philosophies, making the training of staff difficult. Significantly it was also realised that the systems’ security was in the hands of manufacturers, and security audits showed that the degree of security provided by each manufacturer varied.

The priority was to develop a viable, secure standard interface from the point of sale (POS) terminals to the electricity dispensers (EDs). POS terminals would need to continue to support the installed base of some 300,000 proprietary EDs, as the cost of replacement would have been prohibitive. It was soon realised that a universal point-of-sale capable of servicing the STS and all proprietary systems was not economic and would lead to a further proliferation of proprietary systems. The concept of interface standards based on the OSI model was adopted, and a ‘backward compatibility’ option catered for interfaces to particular proprietary systems.

The main need was to standardise the data format of the instructions to the meter, the encryption algorithm and the encryption key management system (the security ‘heart’ of the credit control mechanism). Eskom, as the main user, established a key management centre (KMC) and support systems, which were made available to all STS users.

The system had to be flexible enough to cater for a restructuring distribution industry while retaining the initial design decisions for uniquely addressed meters. This was achieved by allocating meters to supply groups, whereby groups of meters managed by a single distributor, generally in a specific geographic location, are coded to restrict their use to that particular supply group. It ensures that transactions for meters belonging to a specific distributor are always linked to that distributor’s accounting system through the key management system.

Controlled access to the STS was essential to ensure that only licensed suppliers put certified STS equipment into the market place, so a central body was needed to act as custodian of the STS. Eskom initially assumed this role, by licensing each manufacturer wanting to implement the STS. Later the basic STS protocol was released into the public domain, with control over its application in South Africa still exercised by retaining licensing of the particular encryption/decryption tables. 

The STS Association was formed as a not-for-profit organisation to take over these responsibilities from Eskom, and the intellectual property rights were assigned to the Association. Eskom continued to provide the KMC service for all STS users, as well as an STS certification service to manufacturers of STS equipment. The STS Association would manage and develop the STS, recognising its potential for application in global markets. The formal registration of the STS trademark was finalised in 2001.

The present

An estimated installed base of some 2.5 million STS meters exists in South Africa, in addition to a growing base of some 500,000 STS meters elsewhere in the world. The SA government has committed to another 1.8 million electrification connections over the next four years, most of them to be served by prepayment meters, making it essential that the STS and associated systems continue to be supported and developed. Specifically, the efficient and reliable operation of the KMC is vital and of increasing importance as the STS continues to expand globally.

Despite the efforts of WG 15 of IEC TC13, we still do not have any published international standards for prepayment meters or metering systems. Notwithstanding the time it has taken to get the first in the ‘payment meter’ series of standards to the committee draft stage, the work of WG 15 has at least established the probable framework within which the standards will develop. The delay has given South African industry a window of opportunity to establish the STS as a de facto international industry standard.

The STS Association’s prime goal is to ensure its members (suppliers and users of STS equipment) have STS technology that is supplied and managed effectively and that future enhancements are introduced in a controlled manner. Two STS Association working groups are active, but if serious efforts to develop STS are to be successful, an alternative to the present funding through membership fees will have to be found. A meter and STS vending equipment levy has been proposed, but has not found wide acceptance. Nevertheless, it is probably the only equitable and easily administered funding mechanism available, and members will again be asked to consider it. Without sustained funding, the STS Association will not be able to perform as expected and the future sustainability of the STS is in jeopardy.

The future 

To enhance its credibility internationally, the STS has been offered for publication as a ‘publicly available specification’ (PAS) through IEC TC13. This is a mechanism for standards that already have a level of acceptance in a significant segment of industry to be endorsed by the IEC, as the precursor to eventual acceptance as full international standards. The STS was tabled unopposed as an IEC PAS to IEC TC13 at their plenary meeting in June 2001.

The need is also evident for prepayment systems specifications to cover water metering, and in the longer term gas metering. The STS is designed for this purpose and much work has already been done to develop enhancements to cater for step tariffs – essential if it is to be used in other electricity markets and in the local water metering industry. The next stage will be to circulate formal draft amendments to the membership. However, such developments may not reach implementation, as it is increasingly clear that a more radical upgrade to STS will be needed to ensure its relevance and application in future.

The other active working group is investigating enhanced key management functionality; in particular distributed key management to cater for the application of STS globally.

Other future STS developments could include:

  • National networking enabling inter-utility vending.
  • Support for the acceptance of electronic cash – smart card purses for off-line cash and direct account debits for on-line cash.
  • Two-way communication tokens, providing the functionality to feed information from the meter back to the management information system via the point of sale.

While the 1990s was a period where the basic open system standards for the prepayment metering industry were established in support of the immediate electrification needs, much more will need to be done in the next phase to ensure the STS remains valid. Many utilities have seen the folly of going down the proprietary route, and are looking to the industry to support them with open system standards for the prepayment metering systems of the future. Their widespread application and success, however, will depend not so much on the utilities, but on the willingness of manufacturers to co-operate on the development and rollout of open system standards. In this, the role of the STS Association will be vital.