STS is 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 a South African industry specification described in *NRS 009-6, section 6 to 9, and part 7 which are being considered for publication as publicly available standards through IEC TC 13 working group 15 †.
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: NRS009-6-6:2002; NRS009-6-7:2002 and NRS009-6-9:1997 - 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, are using the STS standard to transfer the information. STS is centred 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 interprets the information.
WHY USE STS? 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:
In order to achieve the above security, the standard defines the following:
Inter-operability 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 a vending system from any one 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.
The Association ensures inter-operability between system components from different manufacturers, by:
What is the STS Association? 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:
Membership: 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.
All categories of members are able to influence/participate in the administration and future development of the technology.
Categories of membership The Association has 2 categories of members (apart from the founding members):
Ownership of the technology
The STS Association owns the STS technology and licences manufacturers to use it.
Security The STS Association carries out the necessary functions to assure the security of STS systems. These include the following:
Technical working groups will further enhance STS to meet the emerging needs of users.
FUTURE ENHANCEMENTS Additional Functionality Development of additional functionality is envisaged e.g. the transfer of tariff information and currency credits rather than Kwh transfer; the use of 2 -way communication; etc.
New Applications In addition to the electricity utility application discussed above, STS can easily be expanded to include other utilities such as gas and water.STS transfer numbers, rather than being hand carried, may be transmitted using various communication standards such as DLMS ‡
* NRS - The National Rationalisation of Standards body is responsible for co-ordinating user requirements on a national scale prior to these being tabled as national specifications. † 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.