Wireless Design Considerations for Industrial Applications

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Today, plants increasingly use wireless networks for critical Industrial Automation and Control System (IACS) applications that require reliable data transmission with low levels of latency and jitter. Wireless local area networks (WLANs) differ significantly from traditional wired LANs in their use of shared radio frequencies, susceptibility to interference and coverage impairments. Deploying a wireless network requires thoughtful planning and design, as well as periodic monitoring to meet expectations for bandwidth, throughput, reliability and security.

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Wireless Design Considerations for Industrial Applications

  1. 1. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. PUBLIC INFORMATION Wireless Design Considerations for Industrial Applications
  2. 2. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Introduction This presentation is an overview of the joint Rockwell Automation/Cisco® application guide ENET-TD004 “Wireless Design Considerations for Industrial Applications” Please refer to the complete guide for:  Full list of recommendations  Details of Wireless Local Area Network (WLAN) implementation  Test details and full results  Links to Cisco documentation on wireless technology
  3. 3. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 3 Agenda Wireless Application Considerations Technology Overview WLAN Design Considerations Wireless Equipment Use Cases Wireless Application Evaluation
  4. 4. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview 4 Advantages of a wireless network include:  Lower installation costs due to cabling and hardware reduction  Lower operational costs by eliminating cable failures  Ability to connect hard-to-reach, restricted and remote areas  Gains in productivity and efficiency due to equipment mobility  Higher productivity and less downtime due to personnel mobility
  5. 5. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview 5 Wireless is different from wired media  Half-duplex shared medium: only one device can transmit at a time  Wireless signal may vary with time and direction  Wireless coverage area cannot be precisely defined  Signal may reach beyond the intended area  Some packet loss compared to wired Ethernet  Less protected from interference  Dynamic network topologies due to wireless roaming Advantages > Challenges (Protocol + Device + Environment )
  6. 6. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview Wireless sensors Process Control WirelessHART ISA-100.11a 3G / 4G LTE / WiMAX FHSS 900 MHz / 2.4 GHz Wi-Fi: 802.11a/g/n Remote site connectivity Long haul SCADA Monitoring and supervisory control I/O control Peer-to-peer control Safety control Mobile HMI Performance Industrial Wireless Technologies Different characteristics and use areas
  7. 7. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview 8 Wireless Client Types WGB WGB Access Point (AP) Bridge Embedded Adapter: • Higher cost • Antenna limitations • Placement limitations Universal Bridge: • Single wired client (MAC address) Workgroup Bridge (WGB): • Multiple wired clients (MAC addresses) • Viewed as a single wireless client on the network Workgroup Bridge is the main method of connecting to WLAN
  8. 8. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview 10 Autonomous WLAN Architecture WGB Autonomous AP … SSID1 5 GHz Access Switches Distribution Switch 1 2 3 1 EtherNet/IP (Wired) 2 EtherNet/IP (Wireless) 3 AP management 1 Autonomous AP … SSID2 2.4/5 GHz 3 • Each autonomous Access Point (AP) is managed individually • Limited coordination between APs • Stand-alone IACS applications • Fixed clients and predetermined traffic
  9. 9. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Technology Overview 11 Unified WLAN Architecture • Functionality is split between lightweight APs and Wireless LAN Controller (WLC) • Centralized management of WLAN parameters • Zero-touch AP deployment • Large scale plant-wide coverage WGB Lightweight AP … SSID1 5 GHz … SSID2 2.4/5 GHz 2 3 Lightweight AP WLC EtherNet/IP (Wireless) MSE ISE NCS 1 1 EtherNet/IP (Wired) 2 3 WLC / AP management CAPWAP tunnel (Data / Control) 1 1
  10. 10. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 12 Agenda Wireless Application Considerations Technology Overview WLAN Design Considerations Wireless Equipment Use Cases Wireless Application Evaluation
  11. 11. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless use cases include…  Equipment Wire Replacement / Mobility  Hard to reach (costly)  Valuable data without system connection requirement  Moving parts on static machines  Portable or moving equipment  Personnel Mobility  Mobile HMI and operator access  Maintenance and engineering access  Wireless voice communication  Vendor guest access Wireless Equipment Use Cases 13  Asset and Personnel Tracking  Radio Frequency Identification (RFID)  Real Time Location Services (RTLS)  Remote Device Monitoring  Condition based maintenance  Instrumentation of existing machinery  Video surveillance  Long Haul SCADA Communication  Process Instrumentation
  12. 12. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 14 Single Coverage Cell (No Roaming) WGB Autonomous AP … SSID1 5 GHz WGB Fixed Position • Equipment is static while operating • Associated to the same AP • Installed in a permanent location
  13. 13. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WGB Wireless Equipment Use Cases 15 Single Coverage Cell (No Roaming) WGB Autonomous AP … SSID1 5 GHz Nomadic (Non-operational Relocation) • Equipment is static while operating • Associated to the same AP while operating • Moves to a new location in the shutdown state Autonomous AP
  14. 14. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 16 Single Coverage Cell (No Roaming) Autonomous AP SSID1 5 GHz Mobile (No Roaming) • Equipment is moving while operating • Associated to the same AP while operating • May rapidly change position and orientation WGB
  15. 15. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 17 Multiple Coverage Cells (Roaming) Lightweight AP SSID1 5 GHz Mobile (Fast Roaming) • Equipment is moving while operating • Changes association (roams) between APs while operating • Roaming delays do not cause application timeouts (target <50 ms) WLC … WGBWGB Lightweight AP
  16. 16. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 18 EtherNet/IP (Wireless) WGB AP … SSID1 5 GHz Access Switches Distribution Switch Stack 1 2 1 EtherNet/IP (Wired) 21 Coverage Cell/Area WGB Fixed PAC Mobile I/O I/O, Safety I/O Mobile I/O Wired PAC to Wireless I/O
  17. 17. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 19 EtherNet/IP (Wireless) 1 EtherNet/IP (Wired) 2 Wired PAC to Wireless PAC WGB AP … SSID1 5 GHz Access Switches Distribution Switch Stack 2 1 Coverage Cell/Area WGB Fixed PAC Mobile PAC P/C, Safety P/C, MSG 1 Mobile PAC
  18. 18. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Equipment Use Cases 20 EtherNet/IP (Wireless) 1 EtherNet/IP (Wired) 2 Wireless PAC to Wireless PAC or I/O WGB AP … SSID1 5 GHz Access Switches Distribution Switch Stack 1 Coverage Cell/Area WGB Fixed PAC Mobile I/O 1 Mobile PAC WGB 1 Mobile PAC 2 2 Not recommended: x2 bandwidth, higher latency
  19. 19. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 23 Agenda Wireless Application Considerations Technology Overview WLAN Design Considerations Wireless Equipment Use Cases Wireless Application Evaluation
  20. 20. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Evaluation 24 Preparing for WLAN Implementation 1. Identify Site Requirements:  Number of wireless channels available and in use  IT policy regulating wireless spectrum in the facility  Existing and potential sources of wireless interference in the area  Locations, dimensions, material compositions of required coverage areas  Environmental characteristics of the site  Any obstructions that may enter and leave the coverage areas  Installation limitations for the antennas, APs, and cabling  Has a site survey been done? What was the survey equipment and parameters? Proper RF design and comprehensive site survey are crucial
  21. 21. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Evaluation 25 Preparing for WLAN Implementation 2. Identify Network Requirements:  WLAN architecture (Autonomous or Unified)  Existing WLAN and switch infrastructure  Who is responsible for managing WLAN?  Required WLAN security  Required network redundancy  IP addressing, DHCP, VLAN requirements Early collaboration with IT personnel is critical
  22. 22. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Evaluation 26 Preparing for WLAN Implementation 3. Identify Application Requirements:  Number and type of wireless and wired devices  Type of CIP and non-CIP protocols required by the application  Packet intervals, size, and packet per second (PPS) rate for each type of traffic  Explicit Messaging  Standard P/C and I/O  Safety P/C and I/O  Motion P/C (Virtual Axis), CIP Sync  Directional flow of the traffic per protocol  Total PPS per wireless channel Is wireless technology appropriate for your application?
  23. 23. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Evaluation 27 Preparing for WLAN Implementation 3. Identify Application Requirements:  Application timeout requirements per protocol  Maximum tolerable latency and jitter per protocol  Handling of lost or late data packets by the application  Time synchronization requirements  Equipment mobility requirements  Does it require fast roaming?  If multiple identical applications need to operate throughout the plant  Number of installations and distance between each operation area Is wireless technology appropriate for your application?
  24. 24. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 28 Agenda Wireless Application Considerations Technology Overview WLAN Design Considerations Wireless Equipment Use Cases Wireless Application Evaluation
  25. 25. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 29 Packet Rate Limitations Total packet rate in a wireless channel is the main factor that determines application performance  Do not exceed 2,200 PPS in a wireless channel  Reduce packet rate in environments with RF issues and interference  Reserve 20% of bandwidth for HMI and maintenance traffic  All communication should be accounted for, including non-CIP packets and traffic from neighboring WLAN sharing the same channel  Use rack-optimized I/O (vs. direct) connections when possible. Minimize the number of individual connections by using produce/consume tags, large arrays, data aggregation and other techniques  Direct communication between wireless clients should be limited, since each packet is transmitted twice (upstream to the AP and downstream from the AP) Use techniques to reduce packet rate as much as possible
  26. 26. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 30 Wireless Node Limitations  Number of wireless clients in the cell affects the performance, especially in the heavily loaded channel  Do not exceed 20 wireless nodes (WGBs or embedded adapters) per AP  Number of nodes may need to be smaller with high packet rate  Do not exceed 19 wired clients per WGB  Total number of Ethernet devices on a single VLAN (wired or wireless) should be below 200 to restrict the amount of broadcast traffic
  27. 27. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 31 Latency and Jitter  Average wireless latency and jitter should meet the requirements of many applications with these conditions:  A channel is loaded below the limit  Proper Quality of Service (QoS) policy is applied  Very small percentage of packets are delayed significantly. An application should be able to handle delayed packets.  Requested Packet Intervals (RPIs) faster than 5ms may not be useful  Overloading the channel will quickly lead to excessive latency and timeouts  Larger number of wireless nodes increases maximum latency  Certain events can also cause significant delays and packet drops:  Wireless roaming  Periodic RF monitoring of channels, if enabled  Persistent interference in the channel
  28. 28. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 32 Packet Loss and Reliability  If a wireless frame is not received, it will be retransmitted until retry limit is reached  An application should be able to tolerate occasional packet loss  With normal channel load, RF conditions, and recommended QoS configuration, the expected application-level packet loss is very small  Excessive packet rate causes high packet loss and application timeouts  Large number of wireless nodes may increase chance of timeouts  Multicast and broadcast traffic is much less reliable than unicast traffic  Changes in RF environment, interference, or unauthorized channel transmissions may decrease reliability or even completely disrupt wireless communication. This risk should always be considered for the application. Wireless is not lossless but can be sufficiently reliable
  29. 29. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 33 Unicast vs. Multicast  Multicast wireless frames are not acknowledged and not repeated if lost.  Use only unicast EtherNet/IP connections with I/O or Produced / Consumed  Do not use ControlLogix® Redundancy System with wireless communication  CIP Sync uses multicast at a low rate  Configure IGMP snooping and querier in the network infrastructure Traffic Type Unicast Support / RSLogix™ version Standard I/O v18 (ControlLogix Redundancy - multicast only) Standard Produced / Consumed v16 (ControlLogix Redundancy – multicast only for consumed tags) Safety I/O v20 Safety Produced / Consumed v19 CIP Sync Multicast only (as of v21)
  30. 30. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 34 Application Protocols with 802.11 IACS Protocol Type CIP Standard Use with Wireless Constraints Information and diagnostics; Peer to peer messaging CIP Class 3 (HMI, MSG) Yes Peer to Peer Control; I/O Control CIP Class 1 (P/C, I/O) Yes Higher latency and jitter may be an issue if an application depend on exact timing of updates Safety Control CIP Safety Yes Very fast safety reaction times may not be supported Time Synchronization (IEEE 1588 PTP) CIP Sync Limited Accuracy of ~150 µs can be achieved; suitable for Sequence of Events (SoE) and event logging applications; Motion Control CIP Motion; Produce/Consume Virtual Axis Caution: Experimental Position accuracy depends on CIP Sync performance; Direct CIP Motion control is not feasible; Virtual Produce/Consume axis may be possible for low performance applications Additional detail on protocol characteristics see Application Guide
  31. 31. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 36 CIP Safety & Standard over wireless Based on Reference Architecture lab testing:  Safety RPI as low as 15ms can be supported (Produced / Consumed)  Standard RPI of 20ms can be supported  As low as 10ms depending on the application sensitivity to jitter and delay  Connection Reaction Time Limit (CRTL) for a CIP Safety connection over wireless should be at least:  60 ms for Safety Produced / Consumed  72 ms for Safety I/O  CRTL should be x4 greater than the RPI value (can handle 2 lost packets in a row).  CRTL may need to be increased further to prevent safety connection timeouts by changing Safety multipliers. Assuming packet rate below the limit and proper QoS policy
  32. 32. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 37  8 WGBs  Min. 6,000,000 samples  Avg. latency <2ms vs. 0.3ms wired  99.99% samples <10ms latency  No connection timeouts Test results example: Wireless Latency I/O or P/C Packet rate, pps Total Packet rate, pps Std I/O or P/C RPI, ms Safety Input RPI, ms Safety Task Period, ms Measured Network Latency AP to WGB / WGB to AP, ms Avg. Max. 99.99% samples Max. 100% samples 2,222 (I/O) 2,375 20 18 30 0.7 / 1.2 2.5 / 6.8 12.5 / 20.8 2,133 (P/C) 2,723 15 15 15 0.7 / 1.5 2.2 / 7.5 27.1 / 16.8 For complete test results see Application Guide WGB to AP, msAP to WGB, ms
  33. 33. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Wireless Application Considerations 38  8 WGBs  Min. 1,000,000 samples  Measured screw-to-screw time  Up to 14 days continuos run with no connection faults  99.99% samples < No-fault theoretical worst case SRT Test results example: Safety Reaction Time I/O or P/C Packet Rate, pps Total Rate, pps Safety Input RPI, ms Safety Task Period, ms Input I/O or P/C CRTL, ms Theoretical SRT, ms No fault / Single fault Observed SRT, ms Avg. Max. 99.99% samples Max. 100% samples 2,222 (I/O) 2,375 18 30 72 117 / 171 52 79 152 2,133 (P/C) 2,723 15 15 60 125 / 158 58 78 89 Wired Wireless
  34. 34. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 39 Agenda Wireless Application Considerations Technology Overview WLAN Design Considerations Wireless Equipment Use Cases Wireless Application Evaluation
  35. 35. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 40 Radio Spectrum  5 GHz frequency band is recommended for critical applications  Channel availability:  2.4 GHz band: 3 non-overlapping channels (1, 6, 11)  5 GHz band: based on regulatory domain  Rules are subject to change  Use non-DFS (Dynamic Frequency Selection) channels when possible  Weather / military radars cause disruption of service in DFS channels  If DFS channels are used, site survey and monitoring is required  Particular caution when operating near airports, sea ports, or military bases.  Exclusive use of a channel bandwidth is expected in most cases  Early dialogue and collaboration with the IT department is important Country examples Available 20 MHz Channels in 5 GHz No DFS DFS U.S., Canada, Australia 9 12 Europe 4 15 China 5 0 Wireless spectrum management policy is critical!
  36. 36. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 41 Site Survey Recommendations  Thorough RF spectrum survey is critical  Prolonged monitoring for interference in various locations  Active survey type is required  Evaluates link performance at the actual data rate  Survey conditions must match production environment  AP and antenna type, RF channels, transmit power  Installation restrictions, moving obstacles  Complete walk-through of the coverage area  Changes in the environment may require a follow-up survey  Adequate signal level and cell overlap should be maintained (see App. Guide)  Survey for performance, not just coverage Survey experience in industrial environment is important
  37. 37. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 42 Antenna Recommendations  An accurate site survey is necessary to determine appropriate antenna type and placement  Follow manufacturers‟ recommendations about antenna orientation, mounting hardware, and installation procedures  Set the correct antenna gain in the AP/WGB configuration  Antennas should be mounted clear of any obstructions, particularly metal obstacles  Length of the antenna cable should be minimal  High ceilings may present problems in coverage  Low-gain omnidirectional antennas are typically appropriate for most applications
  38. 38. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 43 Channel Re-use  Wireless cells using the same channel can interfere at a great distance  Must defer transmission as long as can detect valid Wi-Fi signal  Co-channel Interference (CCI) can be decreased but hard to eliminate  Channel bandwidth may be essentially shared between applications  Do not reuse channels with high utilization and client count, unless complete signal separation can be reliably achieved Ch. 36 WGB AP Ch. 36 WGB AP Ch. 40 Tx Power + Antenna Gain – Attenuation > Rx Sensitivity Just an example: free space signal propagation Receive sensitivity at 6 Mbps (5 GHz radio) -92 dBm Transmit power 0 dBm Transmit antenna gain 4 dBi Receive antenna gain 4 dBi Attenuation needed -100 dB Distance with free space loss (5180 MHz) 460 meters
  39. 39. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 47 QoS Recommendations  802.11 wireless uses statistical QoS mechanism to give preference to certain classes of traffic  Still half-duplex media: cannot transmit while someone is using the channel  Traffic is placed into one of the queues based on selected criteria  DSCP (L3 QoS) is recommended  TCP/UDP port numbers can be used  Transmission parameters are adjusted for each queue (see App. Guide)  Backoff time  Number of retries  Packet timeout Traffic Type DSCP Queue PTP event 59 Voice PTP management 47 Video CIP class 0 / 1 (I/O, P/C, Safety, Motion) 55 47 43 31 CIP class 3 (MSG, HMI) 27 Best Effort Unclassified 0 Media contention between stations BK Classification BE VI VO Internal contention between queues
  40. 40. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. WLAN Design Considerations 48 Security Recommendations  WPA2 security with AES encryption is the only mechanism recommended for IACS wireless applications.  Hardware AES encryption does not significantly affect application performance  WPA2-PSK (pre-shared key) is a common method of authentication in WGB-based topologies, but it has limitations:  No user-based authentication  Does not provide fastest roaming time  May not satisfy organization requirements  802.1X/EAP-based authentication is most secure  May require additional infrastructure support  EAP-FAST is recommended (reduced complexity, local authentication support)  MAC address authentication is not a secure method by itself Security is organic to the standard….USE IT!
  41. 41. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. Industrial IP Advantage  A „go-to‟ resource for educational, technical and thought leadership information about industrial network communication  Receive monthly e-newsletters with the latest articles and video  Networks Mythbusters launching next month  Basic and Advanced Training courses will be available at the end of 2014 Don’t miss the latest news and discussions – Register at http://www.industrial-ip.org to become part of a community today.
  42. 42. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. We care what you think!  On the mobile app: 1. Locate session using Schedule or Agenda Builder 2. Click on the thumbs up icon on the lower right corner of the session detail 3. Complete survey 4. Click the Submit Form button 50 Please take a couple minutes to complete a quick session survey to tell us how we’re doing. 2 3 4 1 Thank you!!
  43. 43. Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. www.rsteched.com Follow RSTechED on Facebook & Twitter. Connect with us on LinkedIn. PUBLIC INFORMATION Thank You.

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