Perceptions and realities of Ethernet use: Part 2

By Jim Taylor, VDC, and Joe Feeley, Editor in ChiefTHE ANALYSTS at Venture Development conducted a comprehensive survey of industrial machine builders, system integrators, and end users regarding their understanding and use of both wireless and wired Ethernet. The study was concluded last year and readers of Industrial Networking were among those participating in the survey.In the Spring 2005 issue of Industrial Networking magazine, we had a quick look at the overall market, identified where current activity and future growth are centered, and began to identify user preferences that emerged from the data [Network Distinctions—Part I]. Here, in Part II, we’ll explore current and emerging protocols, connectivity issues, and a host of selection, installation and operational criteria.Communication ConnectivityData transfer over wired [wireline] or wireless Ethernet networks today is possible between the general enterprise and many classes of systems and products found in industrial facilities, including supervisory control and data acquisition systems (SCADA); HMI (operator interfaces); controllers such as PLCs, motion, temperature, etc.; distributed/remote I/O; and device-level components such as actuators, sensors, etc. Data transfer over wired or wireless Ethernet networks, of course, also is possible between these systems and products within industrial facilities.Among the users of wired Ethernet, the largest use was noted in communication between the enterprise and the HMI and controllers (both were noted by 60% of respondents), between the HMI and controllers (61%), and, not surprisingly, between controllers (64%). In general, the smallest share of the surveyed participants use wired Ethernet to provide communications with distributed/remote I/O and device-level components, although the largest gains in use are expected for these types of data communication.Among the wireless Ethernet users, the largest segments use these networks in data transfer between the enterprise and HMI and controllers (both registered 41% of respondents), and between controllers and distributed/remote I/O (also 41%). The lowest stated shares were for data transfer with device-level components. More of the users expect to be using wired and wireless Ethernet as a communication network between all the classes of devices above in 2006.Performance and RequirementsRapid Response in Eye of Beholder —Users were queried about the minimum response times they require for their applications. For wired Ethernet, response times varied widely, with 10 msec being the most noted (by 17%) of respondents), followed by 500 msec, noted by 16%. The median required response was 85 msec.Required response time in a wireless configuration showed similar levels of variety. The two most noted response times were 100 msec and 1,000 msec, both garnering 16%. The median response time for wireless configurations was 100 msec. Figure 1 details the variety in both wireless and wired response times. (Click the Download Now button below to view a .pdf version of all charts and tables referred to in this article.)

Transmission Distances/Topologies — For wired Ethernet users, maximum transmission differences also showed wide variation. While the median distance was 300 ft (noted by 29% of participants), 23% of the respondents reported distances in excess of 1,500 ft, and 17% indicated their maximum distances to be 100 ft or less. Over these transmission paths, the participants indicated a median message length of 512 bytes; the smallest noted was 32 bytes, the largest 5 Mbytes. The respondents also showed a clear preference for star/hub topology use (87%), as opposed to rings/daisy chains (40%).The wireless users also summarized their topologies, showing a preference for more than one: 73% have multipoint configurations, 58% indicated point-to-point, and 42% identified peer-to-peer.Network Load — Given the stated requirements of distance and message size, users of both wired and wireless networks also were asked about the number of devices they connect to their networks. Again, given the mix of users and machine builders, the study found large variation. While a maximum of 50 devices was the wired network median response (with the high in the several thousands, and nine being the low), the respondents said the median typical number of devices on their network was 20.The wireless users, as would be expected, reported smaller numbers, with 10 being the median maximum, across a range that varied from 2 to 1,000 devices.Support Our Network TroopsThe survey participants were asked to describe the types of outside support services they’ve used in the implementation of their networks. Five services were proposed to consider: integration, testing, custom engineering, configuration development, and configuration management. Of these five, assistance in integration of the system was the top service needed by both camps. Forty-three percent of wireless network users and 37% of wired network users identified this need. Testing, at 28%, came second for the wired network users, while custom engineering (37%) was the second most-noted need of the wireless camp. Figure 2 details the findings here. (Click the Download Now button below to view a .pdf version of all charts and tables referred to in this article.)

Internal support via remote web diagnostics was identified as another need. Among the wired network users, 77% currently have this capability. Among those who don’t, some 91% of them wish they did.The wireless users show similar results. Seventy-nine percent current have remote web diagnostics tools. Among the 21% who do not, 89% of them said it would be helpful to have the capability.Product Selection Criteria: Balance Price and PerformanceUsers were asked what are their most important selection criteria in choosing wired and wireless Ethernet infrastructure products. Those most identified, ranked in order, were:

For Wired-Networking Components:
Price (31%)
Quality/Reliability (31%)
Being Industrial-Grade (29%)
Ease of Installation/Connection/Configuration (11%)
Ease of Use (10%)

For Wired-Network Analysis & Management Software:
Ease of Use (50%)
Price (44%)
Reliability (11%)
Diagnostic Capabilities (6%)

For Wireless Access Point/Networking Components:
Price (46%)
Reliability (32%)
Security Features (21%)
Being Industrial-Grade (14%)
Range (13%)

For Wireless Network Analysis & Management Software:
Price (50%)
Ease of Use (31%)
Reliability (19%)
Ease of Installation/Configuration (17%)
Diagnostic Capabilities (13%)

Changes Foreseen in Power StructureUsers were asked how the wired and wireless Ethernet networking components they purchased are powered, and how the components they will purchase in 2006 are likely to be powered. The largest share for every category purchased is for products that are AC or DC powered via cords/cables. For wired networks this still is expected to be the case in 2006, although fewer expect to be purchasing products powered in this manner; the expectation is that they’ll be powered by the equipment in which the products are installed, as well as anticipation of a significant increase in Power Over Ethernet (PoE) availability. Among the wireless users, all expect to be purchasing considerably more battery-powered units in 2006 rather than those powered by AC or DC power cords and cables, and actually expect that more device servers will be battery powered than AC or DC powered by 2006. PoE also is, across the board, expected to provide a significantly larger share of power by 2006.There might be confusion among some of these users, relative to the survey question or their understanding of PoE and its applicability. Some identified PoE as being a function of the products, and not necessarily as the method by which the products are powered. It is likely that some of these infrastructure products are and will be PoE sources for other devices (e.g., PSE-Power Sourcing Equipment), rather than being powered over Ethernet (e.g., PD-Powered Devices). It is clear, however, that there are strong growth expectations among these users regarding the purchase of both wireline and wireless Ethernet infrastructure products with PoE functionality.The survey makes clear that the need to run power cords and cables to fixed location infrastructure products and other devices is a hindrance to industrial adoption of wireless technologies for non-mobile applications. If power cabling has to be installed, it is not prohibitively expensive to also install signal cabling. Alternative power sources such as batteries and solar power eliminate the cabling need, and open up fixed location wireless applications where cabling would not be practical at all. PoE does not eliminate the cabling, but simplifies it by combining the signals and power in the same cable.Who’s Installing All This?
Design and performance considerations aside, there’s still the issue of who installs the products. Electrical contractors were cited the most as installers of the wireline Ethernet infrastructure hardware. However, a number of internal user departments were cited almost as often, as were system integrators. User maintenance departments were cited the most often as installers of the wireless Ethernet infrastructure hardware, followed by user IT departments. Figure 3 details these findings. (Click the Download Now button below to view a .pdf version of all charts and tables referred to in this article.)

It’s no contest when it comes to installing network analysis and management software for both wired and wireless network users. The IT department is easily the most often cited, with systems integrators being the second most identified. See Figure 4 for the complete list. (Click the Download Now button below to view a .pdf version of all charts and tables referred to in this article.)

Wireless Users ID Interference and Security Issues

Signal integrity is a big concern to users and potential users of wireless Ethernet networks in industrial facilities. The interference problems most cited were identified as:

• Interference from other wireless networks/products such as cell phones and other wireless LANs or networks operating in the vicinity
• Transmissions causing problems with other equipment
• RF interference from many types of devices operating in the spectrum being used or generating noise
• Signal blockage and multi-path disturbances due to walls, ceilings, buildings, equipment and metal structures

The most cited means to prevent or overcome interference problems can be summarized as:

• Add access points, antennas, and repeaters to provide better coverage
• Carefully choose type and size of antennas; e.g., directional or omni as appropriate for the site to give optimal coverage and to minimize interference
• Select channels to minimize interference
• Conduct antenna site surveys to ensure good signal reception coverage
• Employ contractors skilled in RF technology to perform the installations
• Increase transmission power where possible
• Limit transmission distances where signals create problems for other equipment
• Provide loss-of-signal alarms
• Reduce sources of RF interference if possible
• Shift to a higher frequency band (IEEE 802.11a at 5 Ghz) where there are fewer interference sources.

Security of wireless signal transmissions is a big concern regarding unauthorized persons — within or outside the facility--being able to receive and use the data. Security of wireless signal receptions is of equal concern, as receipt of unauthorized transmissions--again from within or outside the facility — appearing to be legitimate signals can result in serious consequences.

Wireless Ethernet users most identified a need for software to provide security protection by requiring log-on access codes with frequent code changes and encryption of signals. Some of the same means identified for prevention and solving interference problems also were cited as being applicable to improving security:

• Careful choice in type and size of antennas — i.e., directional or omni as appropriate for the site to give optimal coverage where desired, but to minimize coverage elsewhere.
• Conduct antenna site surveys to ensure good signal reception coverage where desired, and to minimize coverage elsewhere.
• Employ contractors skilled in RF technology to perform the installations.
• Limit power to prevent reception of signals outside the desired coverage area.

About the Authors

Jim Taylor is group manager for industrial automation at Venture Development Corp. He can be reached at[email protected]. Joe Feeley is Editor in Chief of CONTROL DESIGN magazine and ControlDesign.com.

(Click the Download Now button below to view a .pdf version of all charts and tables referred to in this article.)