DNP User Group Approves LAN/WAN Solution and Test Procedures

Since its introduction in 1992, the Distributed Network Protocol (DNP) has proven to be an extremely popular open systems protocol suite for the power utility industry. In February, at the Distributech ’99 show in San Diego, the DNP User’s Group approved two important documents that the group believes will help DNP’s popularity continue in the changing utility environment:

A standard method for carrying DNP over a Local Area Network (LAN) or Wide Area Network (WAN).

The first of several standard test procedures for determining a device’s compliance to the DNP specification and subset definitions.

The LAN/WAN Solution

	Uses the de-facto standard Internet Protocol suite and therefore makes use of widely available and inexpensive third-party products;
	Retains the high reliability of the DNP Data Link Layer checksums;
	Permits "virtual devices" (addressed via the DNP Data Link Layer address) within a physical device (addressed via the IP and Physical Layer addresses);
	Provides the choice of connection-oriented (TCP) or connectionless (UDP) service as appropriate, "on the fly". The two methods complement each other, and both are necessary for a comprehensive solution, as discussed below.
	Permits inexpensive solutions from vendors who already have DNP implementations.

At the DNP User’s Group meeting in San Diego at Distributech ’99 in February, the User’s Group approved the documents for the first official DNP certification test procedures. These procedures have been in demand by DNP users since the User’s Group first started, for the following reasons:

Utilities need a "certification stamp" so they don’t need to be DNP experts. With a certification mechanism in place, the utility need only specify that a device be certified to ensure interoperability.

Vendors need a tool to verify their implementations are correct prior to releasing a product.

Without a certification procedure, there is a high risk of irregular implementations causing interoperability problems and discouraging the use of the protocol.

The new procedures test a device’s compliance to the following documents:

	The DNP V3.00 Basic 4 Document Set
	The DNP V3.00 Subset Definitions, Level 1 or Level 2
	Technical Bulletins issued by the Technical Committee since the release of the Subset Definitions
	Some new interoperability requirements.

The new requirements have been identified through challenges various User’s Group members have had trying to make some existing devices communicate. The test procedures will ensure that in addition to the requirements listed above, a device:

	Employs report-by-exception to ensure efficient use of bandwidth if the device reports many points.
	Correctly operates some previously non-enforced data link layer features.
	Uses application layer confirmations correctly for flow control.
	Accepts both select-before-operate and direct-operate commands on all its outputs.
	Does not flood the link with unsolicited responses, if it supports that feature.
	Correctly implements collision avoidance, if it supports that feature.
	Documents more information on its implementation than previously required.

As can be seen from the list above, these new requirements generally fall into the category of "enforcing common sense" than any change to the protocol. They will be captured in a new release of the Subset Definitions, possibly in late 1999.

The details of the DNP over WAN/LAN proposal and the test procedures are available on the DNP web site, http://www.dnp.org. You must be a member of the User’s Group to access these files. Details on becoming a member are available at the same site.