ISA SP100 wireless network committee shoot-out
These groups presented their views on the protocol requirements and submitted their recommendations for the wireless technology they favor. To further clarify the technical content, each vendor and consortium was asked to supply a white paper to the committee, but, for the most part, these are not yet available.
At individual panel meetings, attendees discussed the proposed communications layers, and, during a special session, how to harmonize IEEE 802.15.4 and the work of the ZigBee Alliance.
SP100 leaders stressed that the purpose of these presentations was not to select one of the proposed protocols as the SP100 standard, but to allow the innovation contained in each proposal to be identified, together with the user problem it solved, so that these innovative features can be considered for the SP100 standard.
Membership in the two key groups breaks down this way:
- WNSIA (Wireless Network for Secure Industrial Applications) Honeywell, 3eTI, Adaptive Instruments, Endress+Hauser, Flowserve, Omnex Controls and Yokogawa;
- WINA (Wireless Industrial Networking Alliance) Dust Networks, Apprion, Invensys, Emerson, Siemens, General Electric, Certicom, MachineTalker, Maximum, Nanotron, NewTrax, Oak Ridge National Laboratories, Sensicast, STG (Software Technologies Group), and TI/Chipcon.
Most of the proposed protocols depend on the use of IEEE 802.15.4 radios also used by ZigBee. A broad consensus of attendees agreed that the 2.4 GHz radio band currently used by Wi-Fi, ZigBee, Bluetooth, cordless telephones and microwave ovens, should be used, but with some type of protocol adjustment to allow peaceful coexistence with other wireless networks. The proposed protocols generally call for the use of mesh network topology supported by these low-power radios and the ZigBee Network layer.
Several presenters suggested that the direct sequence spread spectrum (DSS) protocol of 802.15.4 be either replaced by or augmented with some frequency- or channel-hopping in order to eliminate the effects of interference. All presenters agreed that impenetrable security, high reliability and very low power consumption were necessary elements of their proposals. Several specific recommendations were made about methods to achieve a high degree of security, usually through existing methods of encryption and authentication.
The consensus was that wireless industrial networks were too small a market to demand a dedicated frequency channel assignment or to use custom hardware. This market would best be served by adapting the use of high-volume electronics and parts made for broad market wireless services, such as those addressed by the IEEE 802.15.x standards.
- Analog Devices an original protocol using narrow-band adaptive-FHSS in the sub-GHz region (780 to 956 or 426/27 MHz) to escape the busyness of 2.4 GHz
- Emerson and Dust Networks ― 802.15.4 time-synchronized, channel-hopping, self-organizing mesh network at 2.4 GHz with a variety of wired and wireless upper level (backhaul) networks
- WNSIA Narrowband frequency-hopping spread spectrum with ARQ protocol field network at either 2.4 GHz or 800/900 MHz, connecting to a mesh-networked backbone using 802.11a/b/g to pass EDDL-based messages. Highly compatible with HART, Foundation fieldbus or Profibus. Network quality of service very similar to Foundation fieldbus using distributed time-based publish and subscribe Agreement among the WNSIA member companies that SP100 should be viewed as a wireless extension of the fieldbus networks, including HART
- Crossbow ZigBee- XMesh-compatible network at 2.4 GHz with time-synchronized slow frequency-hopping for network coexistence. Uses XServe for application layer interface, security and network management
- Siemens Analysis of application needs and recommendation of a backbone based on use of Wi-Fi with the PROFInet wireless draft specifications. Suggested that SP100 use elements of IEEE 802.15.4, but with only selected bands within the 2.4 GHz domain and use both star and mesh topologies with TDMA
- General Electric Recommendations for both 2.4 GHz and 5.0 GHz using both CSMA and TDMA protocols based on data rates and coexistence requirements. Security key management proposed for network authentication
- STG and Sensicast System based on use of 802.15.4 radios with adaptive channel-hopping using star-connected edge nodes and mesh-connected routing nodes. Use TDMA if adopted by ZigBee/802.15.4. Recommendations for using a tunneling strategy for simplification of mesh networking. Use 802.11a at 5 GHz for the backbone network
- AIN System based on the use of 802.15.4 with adaptive frequency-hopping using star-connected edge nodes and mesh-connected routing nodes. Splits the time into contention-free periods and contention-access periods to support event-driven access from edge devices. Recommends use of 802.11e specification for connection of gateways to Wi-Fi backbone network
- Nanotron Introduced IEEE 802.15.4a, an addition currently in committee, for use in SP100. Offers use of either CSS (Chirp Spread Spectrum) or ultra-wideband physical layers. Claims to improve multipath performance in highly metallic environments, better propagation through solids and increases available data rate
- Newtrax Introduced applications in underground mines and in intermodal transport where conventional 2.4 GHz signals have difficulty penetrating the ground or the container walls. Recommended the use of full mesh-network topology and use of GPSK (Gaussian Phase Shift Keying) signal modulation
- Machine Talker Proposed Kerberos as the wireless security standard for ISA-SP100
- Texas Instruments Proposed the use of the entire ZigBee stack for SP100
- Certicom Provided a tutorial on security for wireless networks and recommended improvements for use in ZigBee
- Zhejiang University and SUPCON Stressed that redundancy is often needed for wireless networks, but may be less costly in wireless than for wired redundancy. Recommended that TDMA be used to reserve time for non-contention access
- Shenyang Institute Submitted a protocol for synchronized frequency-hopping using 802.15.4 radios. Supported mesh networking at the network layer similar to ZigBee, but with advanced routing algorithms
- Oak Ridge National Laboratory ORNL recommended that IEEE 1451 be used as the basis for SP100. IEEE 1451.5 is the wireless segment of this draft standard
Individual presentations were given by Adaptive Instruments, Omnex, Yokogawa and 3eTI, but each of these deferred to the WNSIA presentation given by Honeywell. The announcement at the end of the meeting on the private agreement among sixteen of the organizations active in SP100 essentially reduces the dialog to only WINA and WNSIA.
Commenting on the SP100 meetings, [ital]Control [ital] editor Walt Boyes noted, It is clear that there are now two camps: the Honeywell camp and the Emerson camp. Pretty nearly everybody has divided themselves into those two camps. This could be very bad. It doesn't have to be, however. If we continue to look at (Emerson corporate director of technology planning) Jose Gutierrez concept for determining which proposals should ascend to become the standard, the fact that battle lines were drawn pretty clearly last week may, in fact, help to make that occur.
Gutierrez said, in an interview with Boyes, Now we need to test. Perhaps Wayne Manges at ORNL [co-chair of SP100] and another lab could test them against the RFPs requirements; then the one that is demonstrated, by a disinterested third party, to be the better proposal wins. Everybody climbs on the same bus, and we go make a market for wireless in process automation.
Boyes commented, Based on the track record of standards bodies, this sounds like a pipe dream, but it doesnt have to be. It is up to the end-user community to make sure that it doesn't become one.
SP100s next session is in Amsterdam in December.