The Standard Transfer Specification (STS) describes a secure message system for carrying information between a point-of-sale and a meter, and is currently finding wide application in electricity metering and payment systems. STS is not limited to this application (see the section: Future enhancements), but because of the wide interest in this area, this document describes the electricity application. STS is an international industry standard described in IEC62055-41, -51 and -52.
The STS specification does not specify any physical characteristics (such as shape or size) of a prepayment meter. Please note that only the following three specification documents are applicable for STS certification: IEC62055-41, -51 and -52 - any other documents linked from the STS website are for general background information (or as implementation examples) only.
The sketch above illustrates a typical system. The example illustrates a consumer making a payment at the vending station and a token being generated to pass the information concerning this payment on to the meter. To date, disposable magnetic card tokens, as well as number based tokens for keypad entry at the meter, or via online entry using DLMS protocols, are using the STS standard to transfer the information. STS is centered around the information transferred to the meter - this includes the manner in which the vending station encodes the token with the information, and the way in which the meter decodes and interprets the information.
Critical to the successful operation of any payment system are the issues of security and inter-operability of equipment supplied by different manufacturers. STS fully addresses these key issues:
Security issues are of prime importance to the utility supplier and the consumer. The use of the STS standard prevents:
STS provides the facility of generating (e.g. credit transfer) tokens which can only be used by the intended meter, and furthermore in the case of credit tokens, can only be used once in that meter.
In order to achieve the above security, the standard defines the following:
Users have long struggled with various systems performing the same or similar functions but which are not compatible with one another, and with components of these systems which are not inter-operable with those from different manufacturers or suppliers.
STS is an open system specification which defines transfer tokens which may be generated at compliant vending systems manufactured or supplied by any of a number of suppliers, and used in STS compliant meters from any one of a number of suppliers. The functionality at the vending station and the response of meters to certain transfer numbers is also specified in order to achieve inter-operability. This allows utilities to mix and match equipment from suppliers of their choice.
STS ensures inter-operability between system components from different manufacturers, by:
The STS Standard Transfer Specification was initiated by Eskom (the major South African electricity utility) in 1993 through their need to develop compatibility between meters and vending systems from different suppliers. Also paramount was the need to ensure sufficient system security to prevent fraud. The STS venture has been a considerable success, and has enabled different manufacturers vending systems to provide compatible tokens/credit transfer to any STS compliant meter (from a number of manufacturers).
During 1997 the STS Association was formed to take over the STS technology, maintain the necessary infrastructure, promote the technology internationally, and further develop the standard to meet emerging international demands for additional functionality.
It is a non profit association of members, championed by the founder members: Conlog (Pty)Ltd., Energy Measurements (Pty)Ltd., Eskom, and Schlumberger Measurement and Systems (Pty)Ltd.
The main motivating factors for establishing the Association were as follows:
All parties that are interested in the technology and who agree to participate in furthering the aims and objectives of the Association are encouraged to join the Association. Interested parties could include utilities (electricity, water, gas and other), vending equipment or meter manufacturers, standardisation entities, consultants, academics and others involved in this type of market/technology.
The Association has two CLASSES of membership: voting and non-voting.
Voting members are able to influence/participate in the administration and future development of the technology.
Within the voting class (apart from the founder members) there are a number of CATEGORIES of membership (for example: meter manufacturer, vending manufacturer, etc.). Each category of members has the opportunity, once every two years, to elect a director from within its own ranks to represent their interests on the board of directors of the Association for a period of two years.
The Association owns the STS technology and licenses manufacturers to use it.
Security The STS Association carries out the necessary functions to assure the security of STS systems. These include the following:
† IEC - The International Electrotechnical Commission is an international body which generates standards relating to electrical systems - It's Technical committee TC13 is responsible for electricity metering, and working group WG15 for payment systems.
‡ DLMS - 'Device Language Message Specification' is a protocol allowing meters and meter system components from different manufacturers to communicate with one another.