So you are considering implementing a WITS Field device? This article provides an insight into the factors you may need to consider and the steps you may have to take to do that. By pulling together some of the experiences of current WITS device manufacturers on the PSAC, it also provides a glimpse into the types of issues that others in your position have found important.
To explain a few terms before we dive in to the article, the protocol is called WITS-DNP3 as it is based on DNP3; for the remainder of this article we will just refer to it as the WITS protocol. The PSA is the Protocol Standards Association, set up to manage the protocol and any other protocols developed. The PSAC is the PSA Committee, a group of six users and six vendors of the PSA who are voted onto the PSAC by the members of the PSA every two years.
The majority of the article is presented in an informal and anecdotal style giving you an unordered list of things to consider, together with why they should be considered. The article ends by pulling together a roughly ordered list of the things you will need to do during planning and development. Remember though that each vendor organisation is likely to have a different experience depending upon their exact situation, so please treat this in the advisory sense in which it is written.
As with any project you are going to undertake, having a sound business case will make all the difference in getting the project started and maintaining focus once it is underway. That solid business case, as always, an exercise in comparing your costs against your potential gain. If you can reasonably present gains which outweigh costs, then depending upon other business objectives, you are likely to garner strong support for the project from your stakeholders.
The actual formulation of the business case is an exercise for each organisation alone; however, we present here a few things to consider with respect to costs and potential gain. On the costs side you will need to consider the following items; more discussion of each of the items follows later in the article. All figures are accurate at the time of writing (autumn 2015):
- Membership of the WITS Protocol Standards Association (a £1000 one-time registration fee, then £500 per annum, see the WITS website).
- Membership of DNP3 ($1000 or £650 per annum, see the DNP3 website).
- WITS Test Specification (£3000, available by contacting firstname.lastname@example.org).
- Costs of read in and design.
- Costs of development and testing.
- Possible costs of a test Master Station if you are using this (approx. £10,000, see more detail on the use of test Master Stations on the website here)
- Costs of WITS Certification, including Self Certification and Verification if you are going for this, see more details here.
- Sales and marketing costs.
- Support and remedial costs.
If DNP3 and WITS are new to your organisation, you may be able to mitigate some of the uncertainty in costs by contracting others with pre-existing knowledge in the area to help estimate, plan and/or develop.
Estimating the potential gain is a much trickier procedure as you will need to evaluate the market position and opportunity for deployment of your type of device. Although much of the “magic” associated with this estimation will come from your Sales and Marketing department we offer the following paragraphs for you to consider in doing that.
- Have in mind a unit cost, which should be based on what you already see in the market place, borne against any unique selling points which are going to lift your device above the others in the market. Alternatively, maybe you are going to provide the same or fewer WITS functions but at a much more attractive cost?
- Consider the volumes of your sales that are likely. Where will those sales likely come from? Who are you competing against? Are there industry initiatives or calendar activities (such as the AMP cycle in the UK) which will drive some of those sales?. Do you have something unique about your product which will drive those volumes of sale?
- Carefully consider the the time period over which you might expect that volume of sales to be achieved. Remember that this time period can only start once you have completed development.
- Be aware that a WITS device can also function as a pure DNP3 device. If you plan accordingly then that DNP3 device will be a device capable of much more than just DNP3 Level 2 functions and will open up more market opportunity than a WITS-only device would present.
- Consider whether you can implement the WITS standard on more than one product; this may improve your business case in that you may be able to sell more units in order to recoup your project costs.
Combining all the information above you will be able to develop a model of how long it will take for you to recoup your development costs and reach break-even for the product development.
The Standards and Organisations
To add WITS to your product you will need access to the DNP3 and WITS standards. These are available by joining the relevant organisations. Becoming a member of WITS and DNP3 also gives you various other benefits such as:
- Access to further technical information, including recent technical bulletins.
- The ability to vote for your chosen representatives on the standards committees.
- The ability to get information about your product (once compliant) published on the organisations’ websites.
- The ability to ask technical questions regarding the protocols and have them answered by the organisation or through their forums.
- In the case of WITS, the chance to get news stories about your WITS product published on their `website.
- In both cases the permission to use their logos in some of your marketing.
There is a lot to take in with the DNP3 and WITS standards. This knowledge is required to help you estimate, plan and design your solution. You need to allow a realistic time for read in and then the design and documentation of how you will incorporate the protocols into your product.
Use Device Profiles to Guide Your Thoughts
The WITS device profile is an XML document which defines what a Field Device is capable of within the scope of WITS. Many of the functions provided by WITS are optional. The device profile is the document which defines which of those optional functions a device will perform. As such the device profile is an important document for users, who can gauge how well the functions on the device match their requirements.
Apart from informing the users of the functions provided by your device, filling in the device profile is a good method of working out exactly what will and will not do. It is a good idea to fill in the device profile as early as you can. The device profile contains, for example:
- The version of the WITS protocol you will be compliant with.
- The interfaces implemented by your Field Device.
- The types of points that are supported.
- The types of events that are supported.
- The types of logging that are supported.
Once completed, the WITS device profile will frame your estimations, planning, development and testing. It also acts as a good initial agreement of the capabilities that the device will have on release between the management team and the development team.
To assist you in seeing what other devices are capable of, self-certified and verified devices listed on the WITS website have links to their device profiles. This is a good starting point to let you see what is out there and what those devices can currently do.
The original purpose of the device profile was to provide an automated means by which the WITS Master Stations could determine what a device is capable of and how they should behave with that device. That is why the device profile is written in XML. However, reading XML is never any fun for a human, so, WITS have made available an XSLT file which transforms your XML into a much easier to read HTML version with full English descriptions of what each item is. This is much easier to work with in the project context, although the XML is always the master document.
An example XML document and the XSLT to transform the document into an HTML is available with the application notes once you have become a member of WITS. Also available in the same pack is the XSD file which specifies the exact structure of the XML document and against which any XML document you edit must validate.
What’s Already Available
No one likes building something from scratch if there is already a reliable implementation of it available. This is never more true than in the software industry where huge amounts of money can be saved by building on already available and trusted software. Unfortunately, there is not as yet, a software product available which would implement WITS for you, however, there are options when it comes to DNP3 which is half the battle in building a WITS system. A simple Google search on something like “DNP3 Software Stacks” will show some of what is available.
Within the portfolio of WITS Field Devices and Master Stations already available there are examples of both “roll-your-own” code (starting from scratch, developing everything in house) and also development based on standard commercial stacks. So both methods work, it is really a question of how each method will fit into your development plans.
For an organisation with little experience in DNP3, using a pre-developed software stack can offer many positive points, however it does force your implementation to fit in with the design of that stack. You also have to consider the costs of purchase and support, although these could be balanced against those thorny times when you have to debug a very low level DNP3 problem in your own implementation.
One thing it is worth pointing out is that at the time of writing the open source implementations of DNP3 that we are aware of do not necessarily support all of the DNP3 functions above DNP3 level 2 which are required for a full implementation of WITS. So although the low cost of open source may appeal, be careful to evaluate the functionality of the open source offering to ensure that it is capable of doing all you require.
Testing, Self-Certification and Verification
When you develop a WITS product as a member of WITS, the WITS PSAC have developed two methods by which you can have your product accepted by the broader WITS community. That means new users should consider that your product is ready for their use and Master Station vendors should consider your product as less of an integration risk. The two methods provide a different level of assurance as to how compliant your product is; they are:
- Self Certification – You perform tests and provide the results to the WITS PSAC who check that they contain the right elements and, if they do, the PSAC will allow your devic