Prepayment Standard Transfer Specification: An IEC standard


Conference: Metering, Billing, CRM/CIS Latin America 2004
Location: Rio de Janeiro
Presenter: Don Taylor

The Standard Transfer Specification is a secure message protocol between a POS and a Meter, supported by a secure Key Management System and protocol. The STS has been an industry standard since 1994 and is now also published as IEC/PAS 62055-41. It is currently being converted into a full IEC standard and publication is targeted for 1st half of 2006. There are approximately 5 million STS meters installed in about 30 countries and operated by about 300 utility companies. This entire user base is served from one Key Management Center with about 700 Supply Group keys under its management care.

The STS Association is the custodian of the STS and continues to sustain the standard in all its phases from development to application and maintenance. It also assures the integrity and quality of the support infrastructure and facilitates access to services like key management, product certification and the further development of standards. Members currently comprise of 18 manufacturers, 2 utility companies and one AMEU/ESLC representative.

Activities of the STS Association are focusing on facilitation of key management services, product certification services, certification of other key management systems and codes of practice for key management centers. It is actively participating on WG15 of IEC TC13 towards creation of the full IEC standard, developing enhancements to the STS and to the existing key management system.

IEC standards that are relevant to prepayment meters, which are already published or in final stage of publication are IEC 62051 (Glossary of terms), IEC 62052-11: General requirements for metrology, IEC 62053-21: Particular requirements for metrology, IEC 62055-21: Framework for standardization, IEC 62055-31: Particular requirements for payment meters and IEC 62055-41: Standard Transfer Specification.

The IEC 62055-21 Framework looks at the standardization of payment metering systems and covers processes, functions, data elements, system entities and interfaces from a generic perspective. It further advocates a scheme whereby many systems or subsystems may be standardized within the IEC 62055 set of standards, such as the STS, which is thus the first one in the set to be standardized in this fashion. Generic functions and processes with sub-classification of functions for a single part payment meter are also detailed.

The IEC 62055-41 Standard Transfer Specification uses the OSI reference model defining at least an application layer and physical layer protocol with the token carrier as the medium in the physical layer. This makes the standard more versatile and manageable. It also defines the generic structure for a Virtual Meter in terms of Function Objects, which in turn describe the functionality of the payment meter and, which are then specifically defined in Companion Standards under the management of the STS Association.

Enhancements to the STS, currently under development, follow the same IEC reference model and maintain backward compatibility with the present STS version. Main features of the enhancements are: bulk data transfer token; token frame with up to 255 tokens in one frame; feedback data from the meter via the token carrier; 2 way token carrier; 21 digit numeric token; The Companion Standards currently under consideration are: step tariff with auxiliary charges; accounting function with social credit, token credit, credit advance and lifeline credit; metering for water; control valve for water; real-time clock with battery;

Requirements for key management enhancements under consideration are: the key management center should be globally trusted, industry impartial and cater for the deregulated market; services should be automated on 24/7 basis and remotely accessible; variety of secure module formats, remote coding and inter – KMC key exchange protocol.

In conclusion it would be true to say that prepayment is still growing and developing and establishing support infrastructure in the international arena, while maintaining healthy standards.