Getting acquainted with ANSI C12.19 and C12.22

In the last two months, two American National Standards Institute (ANSI) standards have been published that seek to greater consistency for smart meter functionality. In late March, the National Electrical Manufacturers Association (NEMA) published American National Standards Institute ANSI C12.22 (Protocol Specification for Interfacing to Data Communication Networks), marking the first revision to the standard since 1997. A few weeks prior to the publication of C12.22, revisions to ANSI C12.19 (Utility Industry End Device Data Tables) were also published. Both standards represent steps toward enhanced interoperability development for AMI and Smart Grid infrastructure. 

Whereas C12.19 specifies the actual data tables, C12.22 describes the process of transporting C12.19 table data over a variety of networks. The wide variety of information that it covers will be necessary in the implementation of the Smart Grid. As the two standards build upon each other, this article will provide an overview of how both are advancing interoperability among communications modules and meters. 

It should also be noted at the onset of this overview that the use of ANSI standards is completely voluntary; their existence does not in any respect preclude vendors from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standards. 

Background ofANSI meter communications standards
Before discussing the standards, it is likely useful to briefly revisit the context of ANSI communications standards as a whole. The first issue to reconsider is interoperability, which has certainly been one of the “buzz terms” around Smart Grid for a number of years. As utilities go through the process of considering and purchasing AMI / Smart Grid options that make the most sense for their budget, objectives, and service territories, a natural consideration is how well different pieces of the selected infrastructure will coordinate with each other, particularly if those different pieces have been manufactured by various vendors. Interoperability enables utilities to use multiple communication networks or change communications technologies while maintaining their investment in the meter. Using the Internet to send and receive meter data is also topic of discussion at many utilities, and so standards that are being developed often are built around an internet protocol (IP) foundation.

Up until fairly recently, data formats, data structures, and communications protocols for electricity meters were all proprietary. But many utilities have heavily lobbied vendors to develop and offer a compatible communication protocol between ANSI meters so that the utilities would not be limited to single meter-vendor option.  The ANSI protocols are a set of simple but flexible protocols aimed at a wide range of metering products. They were developed by the ANSI C12 Electricity Metering Standards Committee in cooperation with the Utilimetrics and Measurement Canada (the Canadian standards body).  The standards are aimed at a variety of metering products including, meters, recorders, and add-on modules. As a result, the standards all refer to this class of metering related products as end devices instead of meters. Care was taken to be compatible with the needs of Water and Gas industries as well.

ANSI standards were created that describe meter data formats and structures (C12.19, which again specifies the actual data tables that are being transmitted), and provide a simple optical point-to-point communications protocol (C12.18) that allowed them to communicate with ANSI standard meters. C12.18 is the standard that describes a protocol used for two-way communications with an electricity meter, mostly used in North America, and describes every detail of the physical attributes for optical communication ports (dimensions, LED wavelength, etc.). This standard is a very simple transport protocol, (layers 1 though 7) designed to transport data structures as defined in C12.19 via the infra-red optical port currently in use by most North American electricity revenue meters. This standard was needed to build meters with a compatible communication interface. The C12.18 standard was written specifically for meter communications via an ANSI Type 2 Optical Port, and specifies lower-level protocol details.

Soon thereafter users lobbied to receive to send and receive ANSI tables remotely. To address that need, C12.18 was adapted to create C12.21, which extended C12.18 and C12.19 to accommodate modem communications at the meter. C12.21 is considered a meter communications standard and not a modem standard. When C12.21 was created to implement point-to-point communication between meters, the intent was to use it with already existing modems. In other words, C12.21-1999 specified a new version of C12.18 that was modified for telephone modems. Thus, ANSI C12.21 is an extension of C12.18 written for modem instead of optical communications, and is consequently better suited to automatic meter reading. And as noted C12.22 now specifies the protocols for transmitting the C12.19 data tables.

While keeping the various standards straight is often a challenge, the important point is that all of the standards are working together to create enhanced interoperability. 

C12.19
The C12.19 standard provides a common data structure for use in transferring data to and from utility end devices, typically meters. It was previously approved after considerable cooperative effort among utilities, meter manufacturers, automated meter reading service companies, ANSI, NEMA, IEEE, Utilimetrics, and other interested parties.

Put simply, C12.19 defines the table structure for utility application data to be passed between an end device and a computer. Does not define device design criteria nor specify the language or protocol used to transport that data. The purpose of the tables is to define structures for transporting data to and from end devices.

The standard data structure of C12.19 is defined as sets of tables. The tables are grouped together into sections called decades. Each decade pertains to a particular feature-set and related function such as Time-of-Use, Load Profile, etc. Table data is transferred from or to the end device (typically a meter) by reading from or writing to a particular table or portion of a table. This standard covers a broader range of functionality relative to its previous version.

Those familiar with the previous version (ANSI C12.19-1997) will probably observe that the new version of C12.19 contains many new features, including the introduction of new tables, decades and syntax; corrections of errors within the previous version; and the addition of XML-based table data, to name just a few. 

C12.22
The ANSI C12.22 open standard defines how to transmit standardized tables of meter data across wired or wireless networks using various transports such as IP. C12.22 is the standard defining the transport of C12.19 table data over networked connections. The standard presents common structures for encoding data in communication between end devices (meters, home appliances, ANSI C12.22 nodes) and utility enterprise collection and control systems using binary codes and XML content. The tables support gas, water, and electric sensors and related appliances.

This open standard can play a vital role in unifying the information collected from AMI projects and Smart Grid initiatives while allowing utilities to select the communication technologies that make the most sense for their budget, objectives and service territory Further, open standards like C12.22 help utilities evolve their systems over time by enabling new technology to interoperate with existing infrastructure, such as AMI-enabled meters, in-home displays, programmable communicating thermostats, load control switches, and other devices to and from the head-end.

C12.22 is an application layer protocol (e.g. http). Data retrieval consists of six steps:

• Identification Service Request, which is used to obtain information about C12.19 device functionality;
• Logon Service Request, which establishes a session without establishing access permissions and provides for immediate transfer to the session state from the idle state;
• Resolve Service Request, which is used to retrieve the native network address of a C12.22 Node;
• Security Service Request:
• Read/Write Service Request, which is used to cause a transfer of table data to the requesting device; and
• Logoff/Terminate Service Request, which provides for an orderly termination of the session that was established by the Logon Service.

C12.22 is intended for use over already existing communication networks just as C12.21 is intended to for use with already existing modems. Examples of such communication networks covered by C12.22 include TCP/IP over Ethernet, cellular communications such as SMS over GSM, or UDP/IP over PPP over serial port. Just as HTTP provides a common application layer that all web browsers can use, C12.22 provides a common application layer that all meters can use. Elster, Trilliant and Itron Inc. were among the first to publicly vice supported of C12.22. In a joint statement the vendors said, "Interoperability allows utilities to utilize multiple communication networks or change communications technologies without touching the meter. In this way, we believe that open standards in general, and ANSI C12.22 in particular, help protect the investment that utilities, ratepayers and shareholders make in advanced metering." 


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