The idea behind a wireless mesh network is that redundancy is the savior of data loss. As with the famous Internet protocol, TCP/IP, mesh networks route signals between short distances to router-redirectors in a self-organizing, and self-healing fashion. That’s the good news. The other piece of good news is that there is a standard: IEEE 802.15.4 or Zigbee, which uses the mesh network topology.
The bad news is that, like industrial Ethernet, there is Zigbee, and there is Zigbee, and just saying your device is Zigbee enabled doesn’t mean it is interoperable.Alphabet Soup: The Standards War
The situation is further complicated by the fact that there are several axes of interoperability, not one or two. Figure 2
below shows the landscape of industrial bus networks, and notes that not all network protocols are useful for all devices and applications. Peter Fuhr, an SP100 member from Apprion
, says, “This chart could be hideously more complicated ‘cause there are over 120 different buses.”FIGURE 2: THE BUS NETWORK LANDSCAPE
Industrial bus networks are a multiheaded hydra. Source: SP100 and Apprion
Now overlay the landscape of existing wireless networking protocols and standards, from Figure 3
below. Here we have more axes: power consumption, cost and complexity vs. data transmission rate.FIGURE 3: THE WIRELESS LANDSCAPE
A hodgepodge of mutually incompatible standards litters the landscape. Source: SP100 and Apprion
As with industrial bus networks, there are turf wars, politics and other non-engineering related issues, which happen when many organizations are trying to develop standards in the same space. Figure 4
below shows the intense competition in the wireless standards-making arena.FIGURE 4: THE STANDARDS LANDSCAPE
The role of Standards, Wireless Organizations and Ind Bus Organizations is not to confuse or constrain, but that happens anyway.
Unlike other industrial standards, the eventual industrial wireless standard must achieve total interoperability with the existing IEEE series of wireless standards, including WiFi, WiMax and others. That is going to be necessary because of the growing interpenetration of the plant-floor space and the enterprise, where the IEEE standards are ubiquitous.
Drawing on the SP50 fieldbus standard experience, the SP100 committee doesn’t want to create a situation in which, in the words of committee member Tom Phinney of Honeywell: “You only co-exist if you use my spec.” It will be critical that any standard be absolutely non-proprietary.SP100: Taming the Wireless Dragon
Under the leadership of Wayne Manges, from Oak Ridge National Laboratory, and Richard Sanders, from ExxonMobil, ISA’s SP100 committee is creating a single industrial wireless standard for automation. The first deliverables for the committee will be a Wireless User Guide, currently in outline form, an Interoperability Guide, a Requirements Technical Note, and a Tutorial on the Physics of Radio. Eventually, the goal is a standard for industrial wireless networking that will permit easy specification and use of wireless sensors and controls in process automation.
The SP100 committee will host a series of technical sessions at ISA 2005 in Chicago (currently scheduled for Thurs., Oct. 27) which will be “required attendance” for anybody wanting to get up to speed on the state of wireless in industrial automation.What End-Users Want
It is already clear that users want what isn’t yet available. Figure 5
below shows a comparison between the requirements that the SP100 committee has identified and the existing wireless standards. Note that very few of the existing standards appear to be suitable to meet the SP100 requirements.
Clearly the SP100 committee has a tough and important job ahead.FIGURE 5: HOW THEY COMPARE
(Click the chart below for a .pdf version of this graphic.)
The major wireless standards, and how they rate as industrial standards. Spreadsheet courtesy of SP100 and Honeywell Inc. (Click the chart above for a .pdf version of this graphic.)