Enhancements to EtherNet/IP for Constrained
Devices and Networks
David D. Brandt
Senior Principal Engineer
Rockwell Automation, Inc.
Dayin Xu
Senior Research Engineer
Rockwell Automation, Inc.
Dr. Jörg Hähniche
Head of Development & Integration Services
Endress+Hauser Process Solutions AG
Matthias Dietrich
Software Engineer
Endress+Hauser Process Solutions AG
Presented at the ODVA2018 Industry Conference & 18th Annual Meeting
October 10, 2018
Stone Mountain, Georgia, USA
Abstract
Industrial Ethernet has exhibited rapid growth, with EtherNet/IP emerging as a leader. The reality is thatfieldbuses and sensor networks still retain a large position and many potential network nodes remain
hardwired. End users understand and seek the advantages of a harmonized network - based on Ethernet,
IP, and the related open ecosystem. Benefits include: reduced complexity and cost by minimization of
gateways and elimination of hardwiring; expansion of the qualified labor pool; and improved optimizationand maintenance opportunities via Cloud connectivity and analytics. Unfortunately there remain barriers
to the single network vision. The mix of EtherNet/IP, fieldbuses, and hardwired nodes persists due toapplication constraints near the network edge. Fortunately, the open market is bringing new techniques tobear. Unprecedented IoT opportunities led IETF to create IP-stack optimizations for constrained devices
and networks (RFC 7228). Enhancements are applicable to both low power wireless (6TiSCH) and wired
networks, eliminating TCP overhead (UDP-only), compressing messages (6LoWPAN), expanding theaddress space (IPv6), optimizing security (OSCORE), and shrinking the Web server (CoAP). Numerous
industries flooded into IEEE to develop enhancements for enabling Ethernet to displace other networks at
the edge. The resulting Single Pair Ethernet suite offers reduction in wiring, node cost, size, and power
consumption, delivering communication and power over a single pair. A 1000 meter variant targets
process plants and other large sites. A deterministic Ethernet bus variant targets very constrained
devices, such as in-cabinet components. This paper proposes a set of enhancements, adopted from orinspired by IETF and IEEE, to extend EtherNet/IP into constrained applications, further enabling thesingle network vision.

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Keywords
EtherNet/IP, Constrained-Node Networks, APL, In-cabinet, 6TiSCH, Ethernet, IEEE 802.3, IEEE 802.3cg,
Single-pair, Industrial Automation, Process Automation, Fieldbus, NAMUR, ODVA,Definition of terms (optional)
Industrial Automation
NAMUR
APL
IETF
IP
6TiSCHIEEE P802.3cg
PHY
MAC
SPE
PoDL
Fieldbus
Industrial Ethernet
Edge
Gateway
SwitchIT
OT
MES
Purdue Model
IIoT
Intrinsic safety
Point-to-point
Multi-drop
PLCA
Full-duplex
Half-duplex
CAN
MCU
ASIC

-

Discrete, Process, and Hybrid (Batch) Automation
Process Automation user group, Germany
Advanced Physical Layer, organization bringing Ethernet to Process
Internet Engineering Task Force, standards body for IP-related protocols
Internet Protocol
IETF standards and drafts for low power wireless supporting IP
Ethernet project, including 10BASE-T1L and 10BASE-T1S PHYs
PHYsical layer connecting a link layer to a physical medium
Medium Access Control layer (IEEE)
Single Pair Ethernet
Power over Data Line (IEEE single pair power)
Industrial network protocol for real-time control
Fieldbus protocol operable over Ethernet
Leaf nodes attached to a network core, i.e., sensor and actuators
Network protocol converter spanning ISO model layers
IEEE 802.3 bridge, forwarding based on MAC addresses
Information Technology
Operational Technology
Manufacturing Execution Systems
Layered functional automation model
Industrial Internet of Things
Method to allow safe equipment operation in explosive environments
Communication link with a single device at each end
Communication link with multiple devices sharing the same link
PHY-level Collision Avoidance, multidrop determinism protocol
Simultaneous communication in both direction on a link
Communication in a single direction at a time on a link
Communication protocol, Controller Area Network
Micro Controller Unit
Application-Specific Integrated Circuit

Trademarks
DeviceNet™, CompoNet™, and EtherNet/IP™ are trademarks of ODVA, INC.
HART®, HART-IP™, and FOUNDATION™ are trademarks of the FieldComm GroupPROFIBUS, PROFINET, and IO-Link are trademarks of PROFIBUS Nutzerorganisation e.V. (PNO)CANOpen® is a trademark of CAN in Automation
Modbus® is a trademark of SCHNEIDER ELECTRIC USA, INC.
CC-Link and CC-Link IE are trademarks of MITSUBISHI ELECTRIC CORPORATION
AS-Interface is a trademark of Verein zur Forderung busfahiger Interfaces fur Binare Aktuatoren und
Sensoren e. V.
INTERBUS is a trademark of Phoenix Contact GmbH & Co.

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Purpose of Paper
This paper presents a set of proposed enhancements, many adopted from or inspired by IETF and IEEE,
making it possible to use EtherNet/IP on constrained devices and networks, thus enabling the singlenetwork vision - where all devices in an industrial plant can communicate with the same set of protocols.
It is assumed the reader had familiarity with EtherNet/IP implementation concepts.

Industrial Network Convergence

Source: HMS networks, Feb 2018
(Parentheses indicate 2017 numbers)
Figure 1: Market share for industrial automation networks

As shown in Figure 1 Industrial Ethernet solutions have been growing rapidly, with EtherNet/IP emerging
as a leader. However, traditional fieldbus solutions and sensor networks still have advantages, retaining alarge position. Additionally, many potential network nodes remain hardwired.

The Single Network Vision
Many end users understand and are seeking the advantages of a harmonized network - based on
Ethernet, IP, and the related open ecosystem. This desire is expressed within organizations across manyindustries. Some examples are referenced in Figure 2.

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Figure 2: Organizations promoting expansion of Ethernet and/or IP at the edge

The Automotive industry has been working toward an all-Ethernet vehicle. Multiple, incompatible
networks (including Ethernet) were added to vehicles, until finally the cable harness became the third
heaviest component in a vehicle – adversely affecting the mileage. The industry formed the OPEN (OnePair EtherNet) Alliance to promote a variety of Single Pair Ethernet (SPE) solutions, first creating a
specification around a proprietary solution and the later developing open standards solutions within theIEEE. Automotive continues to push SPE solutions to both higher rates (e.g., LIDAR and radar) and low
bit rates (e.g., door switch and headlamp assemblies). Ethernet now pushes to the edge to displace othernetworks in the vehicle.
The Digital Ceiling is a partner ecosystem promoting smart LED lighting and associated applications. The
transition to LED enables recent Power over Ethernet to both power the lighting and to communicate withthe lighting over a single cable. Once smart lighting is in place, sensors (occupancy, security, etc.) can be
integrated, and wireless communication can be added, to service both the room and the occupants.
Process Automation end users from NAMUR promoted Ethernet (and IP-based automation protocols
including EtherNet/IP) for instruments and related devices. Vendors have responded to deliver thetechnology, organizing in the Advanced Physical Layer organization, and involving ODVA and their peerorganizations. Work in IEEE on Single Pair Ethernet (SPE) is anticipated to deliver Ethernet
communication and power over cables as long as 1000 meters (including many installed cables) into
intrinsically safe environments. See: https://www.slideshare.net/FieldCommGroup/press-conference-jointfcg-odvapi-20171108-draft-201711041
These initiatives exist due to compelling advantages of a single network: Higher performance for a similar cost (compared to the displaced networks)
 Elimination of costly application-specific gateways
 Leverage of a large existing ecosystem (protocols, security, network switches, etc.)
 Reduced installation, maintenance, and management complexity
 Simplified integration with cloud applications
 Reduced interoperability issues

Barriers to the Single Network Vision
The mix of Industrial Ethernet, fieldbuses, and hardwired nodes persists due to application constraints
near the network edge.
Many of the edge devices are constrained by very low cost. It does not make economic sense to have the
network cost more than the rest of the device.
Some devices are constrained by size. They are very small (photo-sensors) and the network components
must fit.
Other devices are constrained by power. They are either densely packed or battery powered. Low power
consumption becomes a requirement.
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Total system cost may be constrained by the amount of wiring, which includes running bothcommunication and power wiring. Wiring cost may exceed the cost of certain devices. Delivery ofadequate power plus communication over a single cable becomes a necessity. Certain applications areconstrained by the disadvantages in having any wiring at all. Low power wireless solutions exist, but notas part of a harmonized system.
For other applications, long cable distances are required (1000 m or more for industrial fieldbus) andconstrained by existing Ethernet length limitations. This may be associated with a requirement forcompatibility with Intrinsic Safety for explosive environments.

Addressing the barriers
These barriers are in part addressed with the development of new constrained Ethernet and IP
technologies, for wired and wireless usage, emerging from standards organizations such as IEEE andIETF.
This does not automatically imply that Industrial Ethernet protocols can be used on such technologies.
The industrial Ethernet protocols have assumed operation over traditional platforms. Thus protocols suchas EtherNet/IP must be adapted to match with new constrained devices.

IETF contributions
The IETF introduced “Terminology for Constrained-Node Networks” in https://tools.ietf.org/html/rfc7228.
We adopt this terminology in this paper. The nodes and the networks have separate characteristics thatmake them constrained.
Constrained Node characteristics:
 Low cost
 Small size Limited memory [Flash, RAM], and processing resources
 Limited power and energy [battery size or scavenging] Limited upper layer services
 Low weight
Constrained Network characteristics:
 Low bitrate or throughput
 High packet loss Variability delivery rate Asymmetric traffic Small packet size Limited availability [device sleeps]
 Limited upper layer services
The IETF has introduced a number of related standards and drafts for constrained nodes and networks.
These include RFC 7252 (CoAP), RFC 7400 (6LoWPAN), and derivative documents. Techniques are
introduced and are applicable to both low power wireless and wired networks, and include: Elimination of TCP overhead (UDP-only) Compression of message headers Expansion of the address space (IPv6)
 Optimization of security (OSCORE) Shrinking the Web server (CoAP)

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The IETF suite of IP standards is intended to solve IoT needs, but these needs are similar to Fieldbus
needs.

IEEE contributions
Within IEEE, a family of Single Pair Ethernet (SPE) standards have been developed. These enablecommunication and optional power over a single pair, facilitating reduction in wiring, node cost, size, andpower consumption. A number of the standards are already complete, including 100BASE-T1 (100 Mb/s),
1000BASE-T1 (1000 Mb/s), and optional power known as PoDL.
Another family member, IEEE P802.3cg, is in development and has estimated completion in late 2019.
The new standard will introduce a pair of 10 Mbit/s SPE PHYs that are targeted for constrained
applications. Numerous industries, illustrated in Figure 3, sought Ethernet enhancements to displaceedge networks and are contributing to the standard.

Figure 3: Industries seeking Ethernet enhancements to help displace other edge networks

IEEE P802.3cg includes the following 2 PHYs.
10BASE-T1L:
 Addresses long distance Targeted at process automation instruments
 1000 m, intrinsic safety compatible, legacy wiring
10BASE-T1S:
 Addresses low cost control
 Targeted at replacing:o CAN, CAN FD, MOST, and FlexRay protocols in automotive
o Hardwired components for in-cabinet industrial automationo I2C and SPI in data centers 25 m multidrop option
 Determinism by PHY-level Collision Avoidance (PLCA) protocol

Constrained EtherNet/IP application areas
Figure 4 shows several new application areas for EtherNet/IP at the network edge. These are constrained
applications for field devices. From basic control, up through the enterprise, 100BASE-TX Ethernet andemerging 1000BASE-T Ethernet is suitable and likely to remain in place. At the field level, these are notwell suited to meet the listed constraints.
One important application area is Process Automation. Users are requesting Ethernet to the instruments.
Constraints include achieving long distance communication and power over single pair cables while
maintaining compatibility with intrinsic safety.
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A related application area is Low-power Wireless. This is complementary for Process Automation, but has
wider usage in Discrete and Batch. The constraints are related to achieving long battery life and therelated constraint of fitting into small packet sizes.
Another important application is In-cabinet components. Here the transition is from hardwiring to
networked devices. Very strict constraints exist for low cost, small size, and low power.
Another potential application area is On-machine components. The challenge is to reduce the number ofcables, while delivering adequate power. Often the component constraints are low cost and small size.
Higher performance SPE may be applicable. This application is not discussed further in this paper.

Figure 4: Candidate constrained application areas for EtherNet/IP

UDP-only option
EtherNet/IP currently requires the use of both TCP and UDP in the network stack of a device. While TCP
does have advantages e.g. when it comes to the guaranteed delivery of messages, it also adds additional
resource requirements. TCP being connection-oriented, the stack needs to keep track of each single
client connected to the device and needs to buffer messages in case packets are lost on the network andneed to be retransmitted. This means TCP needs additional memory and processing compared to UDP.
Using UDP-only can result in a substantial reduction in stack complexity and messages. A UDP-only
prototype demonstrated about 30% savings in Flash and RAM in a constrained device. Such a reduction
can mean a device uses one size smaller MCU, reducing cost, size, and power.
Figure 5 shows the elimination of TCP-based connected messages. It also shows the elimination of theassociated encapsulation session. Besides the reduction in stack size, the reduction in messages
benefits low power wireless applications by extended battery life.

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Figure 5: Simplification of EtherNet/IP messaging

Note that other constrained stacks, such as CoAP from IETF, also implement and rely on UDP
exclusively. Support of UDP-only would align EtherNet/IP with IoT requirements and evolution.
We propose to add optional support into the EtherNet/IP adaptation for UDP-only. Since CIP Security
requires both TLS and DTLS, we also propose to add optional support for into the EtherNet/IP adaptation
for DTLS-only. This is illustrated in Figure 6. It is also proposed that ListServices be extended to identify
the capabilities of UDP-only, TCP+UDP, or both.

Figure 6: Simplification of EtherNet/IP stack by optional UDP-only and related DTLS-only

A number of implementation options exist. One option is to base the solution on the existing Volume 8 Secure UDP-only. Extension would be necessary to support both secure and standard UDP-only, and tosupport a more complete set of services via UCMM. It would also be beneficial to support a unified
capability discovery method. Figure 7 shows an example stack for this implementation option.

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Figure 7: Example UDP-only stack

Encapsulation and CPF Header Compression option
In relation to typical CIP application payloads, the encapsulation and CPF headers create a significant
overhead in EtherNet/IP messages. Low power wireless networks, such as IETF 6TiSCH, haveconstrained packet size, which is not able to carry the existing encapsulation header in a single wirelesspacket. Extra messages (multiple per message) substantially reduce battery life.
The EtherNet/IP encapsulation and CPF headers can be compressed by adopting the same technique as
is used in 6TiSCH. The process is called “eliding”. Many of the header fields are options that rarelychange. Addition of bit fields to indicate the optional presence of byte or word fields allows a compression
on the order of 8 to 1. Eliding is lossless in function and backward compatible.
Prototyping (Figure 8) has shown excellent compression for ListIdentity, ListServices, General UCMM,
and Class 0/1. Note the ability to compress multiple headers in a single message.

Figure 8: Prototype header compression results

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Existing Volume 8 - Secure UDP-only introduced the “CPF for UCMM” to replace and reduce theEncapsulation header from 40 bytes to 16 bytes. The proposed compression could reduce this evenfurther.
It is proposed to evaluate compression options for:
 Encapsulation header
 CPF for Class 0/1
 CPF for UCMM
 CPFs used within CIP services

Constrained EtherNet/IP physical layers
EtherNet/IP does not support appropriate physical layers for several constrained domains: Process Automation wired instruments for APL
 Process Automation companion wireless instruments
 In-cabinet components
We suggest to reference and extend 3 new PHYs:
 IEEE P802.3cg 10BASE-T1L PHY for Process Automation wired instruments
 IEEE P802.3cg 10BASE-T1S PHY for In-cabinet component usage
 IEEE Std 802.15.4-2015 PHY for Process Automation wireless instruments

Constrained EtherNet/IP Communication Profile
Current EtherNet/IP communication does not support constrained device and network requirements.
It is proposed to develop a constrained EtherNet/IP communication profile as shown. Note that this differsfrom the concept of a device profile.

Figure 9: EtherNet/IP Communication Profile for constrained nodes

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The minimum device object model uses the same base objects for constrained EtherNet/IP, but
minimizes the implementation of the base objects. There is optional compression of Encapsulation and
CPF headers. There are minimized CIP transports over UDP, supporting only UCMM + Class 1.

Figure 10: EtherNet/IP Base Device Object Model

As part of reducing the overhead in a device, the objects are minimized by limiting the optional features.
The Connection Manager is shown as an example. Attributes and services are minimized. The
communication methods are minimized. The simplifications still retain the required interoperability.

Figure 11: Object minimization example for Connection Manager

A new “Constrained EtherNet/IP Capability” CPF item is proposed. This allows discovery of a constrained
device’s EtherNet/IP capability using ListIdentity. Paired with this is a new EDS entry [Constrained
EtherNet/IP Capability], to describe constrained device’s EtherNet/IP Capability.
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Figure 12: EtherNet/IP Capability CPF Item for constrained nodes

Constrained EtherNet/IP over 6TiSCH network
Quoting the EtherNet/IP adaptation of CIP:
9-2 Data Link Layers
Though this specification is called “EtherNet/IP”, Ethernet is technically not required. The
EtherNet/IP protocol may be used on any media that supports the transmission of the Internet
Protocol.
Wired EtherNet/IP for Process Automation (under APL) calls for a complementary low power wirelesssolution. Best suited is IETF 6TiSCH with its open UDP support. EtherNet/IP over 6TiSCH requires
constrained features and 802.15.4 link support. EtherNet/IP lack of IPv6 complicates 6TiSCH solutions,and precludes other usage.
We suggest to specify necessary enhancements for EtherNet/IP over 6TiSCH. We can leverage theConstrained EtherNet/IP enhancements:
 Add 802.15.4 MAC and PHY
 Add 6TiSCH router and network management
 IPv4/6 mapping to integrate 6TiSCH devices into IPv4
A full support of IPv6 requires substantial changes. Hence we suggest revisiting full IPv6 EtherNet/IP
enhancements and security additions at a future date.
There is good motivation for adopting the IETF 6TiSCH stack (Figure 13) for EtherNet/IP. It is an open
(not industry specific) wireless standard, supporting IP-based communication. It provides a self-organizing
mesh network that is robust, reliable, and reduces engineering. Furthermore it is based on IEEE Std.
802.15.4 radio hardware, which leads the market.

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Figure 13: IETF 6TiSCH stack supporting EtherNet/IP

Several enhancements are important for integration of constrained EtherNet/IP over 6TiSCH. These areillustrated in the Figure 14. The physical layer needs to be converted between Ethernet and 802.15.4e.
The network and transport layers need to be converted between IP/UDP and 6LoWPAN. The addressing
needs to be converted between IPv4 and IPv6.

Figure 14: Enhancements simplifying integration of EtherNet/IP over 6TiSCH

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Security is required for constrained EtherNet/IP over 6TiSCH. Figure 15 illustrates security options for
6TiSCH.
One option is to utilize two separate security systems. Link layer security is mandatory for 6TiSCH.
Additionally, 6TiSCH requires IETF OSCORE security for network join. CIP Security can provide optional
security terminating at the 6LBR. Note that CIP end-to-end security is precluded by any 6LBR processingof the application layer (Encapsulation Layer compression).
While CIP Security could operate end-to end, DTLS increases the wireless node overhead. Double
processing would have a negative impact on battery life.

Figure 15: Security options for EtherNet/IP over 6TiSCH

Two new objects are required for support of 6TiSCH networks.
804.15.4 Link Object
 Utilized in both 6LBR and WSNs
 Similar to Ethernet: Interface Speed, Flags, Counters, State, Label, Capabilities, Physical
Address…
 New: RF characteristics
6TiSCH Wireless Network Management Object
 Utilized in 6LBR
 Includes:o Network status informationo Network topology informationo Network routing informationo Device join and leave

Stack Summary
Figure 16 summarizes the constrained EtherNet/IP proposal. Features shown in red are eliminated.
Features shown in green are new additions. Features shown in yellow are modified (reduced).

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Figure 16: Stack modification summary for EtherNet/IP for constrained nodes and networks

References
NAMUR, “Position paper An Ethernet communication system for the process industry”,
http://www.namur.net/fileadmin/media_www/Dokumente/Anforderung_Ethernet-NAMUR_2016-0225_EN.pdf
IEEE 802.3 CFI, “10 Mb/s Extended Reach Single Twisted Pair Ethernet PHY”,
http://www.ieee802.org/3/cfi/0716_1/CFI_01_0716.pdf
IEEE 802.3 SG, “10SPE” (10 Mb/s Single Pair Ethernet),
http://www.ieee802.org/3/10SPE/index.htm
IEEE 802.3cg (10SPE) – 10 Mb/s Single Pair Ethernet Meeting Industrial Automation Objectives : 2017ODVA-Conference_Brandt Xu Haehniche_IEEE-802-3cg-10SPE_R0_FINAL
DeviceNet of Things - Use Cases, Value Proposition and Status of Specification: 2017-ODVAConference_Caspers_DOT_FINAL
Resource-constrained Industrial Things - Proposal for the Adaptation of CoAP to EtherNet/IP: 2017ODVA-Conference_Green Otterdahl_CoAP_FINAL
EtherNet/IP to the Edge – A Concept for "Low-complexity Ethernet” : 2017-ODVAConference_Alsup_Weingartner_Low-complexity_Ethernet_FINAL
Extending EtherNet/IP™ to Resource-Constrained Industrial Things: 2015_ODVA_Conference_XuBrooks_Extending-EtherNetIP-to-Resource-Constrained-Industrial-Things-FINALCIP over 6LoWPAN: Expand CIP to IPv6-based Field Wireless Network:
2014_ODVA_Conference_Xu_Brooks_Yu_Brandt_CIP_over_6LoWPAN_FINAL******************************************************************************************************************************************************The ideas, opinions, and recommendations expressed herein are intended to describe concepts of the author(s) for the possible useof ODVA technologies and do not reflect the ideas, opinions, and recommendation of ODVA per se. Because ODVA technologies
may be applied in many diverse situations and in conjunction with products and systems from multiple vendors, the reader andthose responsible for specifying ODVA networks must determine for themselves the suitability and the suitability of ideas, opinions,2018 ODVA Industry Conference

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and recommendations expressed herein for intended use. Copyright ©2018 ODVA, Inc. All rights reserved. For permission to
reproduce excerpts of this material, with appropriate attribution to the author(s), please contact ODVA on: TEL +1 734-975-8840
FAX +1 734-922-0027 EMAIL odva@odva.org WEB www.odva.org. CIP, Common Industrial Protocol, CIP Energy, CIP Motion, CIP
Safety, CIP Sync, CIP Security, CompoNet, ControlNet, DeviceNet, and EtherNet/IP are trademarks of ODVA, Inc. All othertrademarks are property of their respective owners.

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