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Single-pair Ethernet: The Infrastructure for IIoT

Matthias Fritsche, Jonas Diekmann & Rainer Schmidt | 01/04/2022

Single-pair Ethernet: The Infrastructure for IIoT


HARTING Inc. of North America

July 20, 2021



The Internet of Things (IoT) describes the networking of virtual and real physical objects to make them work together using information and communication technologies. Objects in our daily lives acquire digital skills. Thus, these physical objects can also participate in digital networks. This process also takes place in industrial applications, where it is called the Industrial Internet of Things (IIoT).


More and more industrial components are also becoming smart, intelligent participants. These connections are no longer limited to internal company networks, but devices are also becoming part of the Internet. The increased collection, evaluation, and use of data creates the need for more powerful infrastructure. At the same time, this infrastructure is expected to take up less space and use fewer resources. Efficiency is the key word here, as more sensors with their increasing bandwidth requirements become network participants. New technologies are required.


In the automation world, the phrase “automation island” was coined to refer to the entire range of independent and proprietary (yet analog) networks that dominate the field level. This classic system schism between Ethernet/Internet and analog fieldbus systems should now be broken up and eliminated. The goal is to extend Ethernet from the cloud to every sensor. Each sensor will be smart and capable of being evaluated individually—and therefore an essential step on the road to IIoT.


The appropriate infrastructure is still missing, however. Current networks are based on two-pair or four-pair cables and connectors. This conventional infrastructure is too large and too expensive when you think about the sheer number of sensors and actuators that have to be connected in the field. Bus cables are designed to be space saving and economical for a reason.


The solution for a high-performance Ethernet infrastructure is From the cloud to the sensor: this is a based on a single pair of twisted copper wires: single-pair Ethernet (SPE).



One pair is enough – SPE makes the field level smart


From the cloud to the sensor: this is a claim that has recently been heard more often in the automation environment. This claim is normally made in connection with megatrends such as IIoT and Industry 4.0 (I4.0). It refers to continuous TCP/IP–based communications based on Ethernet, which currently mostly ranges from cloud applications down to the distribution level in manufacturing. Where previously there was a classic break in communication systems between Ethernet and bus systems, modern components can now bring fast Ethernet (up to 1 GBit/s) to the smallest application using just one twisted wire pair. Thus, SPE enables consistent usage of TCP/IP for the first time. And that drives the development of new devices and application fields, especially for sensor/actuator networks. The sensor becomes “intelligent” and a part of the overall network. This speeds up parameterization, initialization, and programming. When using SPE—whether with a simple state sensor or a modern vision system consisting of a highresolution camera—the Internet of Things becomes reality, and the field level becomes smart.



The roots


After the automobile industry, which needed a replacement for the CAN bus, identified this new TCP/IP–based transmission method, the IEEE 802.3 working group released the first SPE standard as the standard 100BASE-T1 in IEEE 802.3bw-2015 clause 96. Self-driving or semi-autonomous driving, however, requires even higher data rates. So, after the first SPE standard for 100Mbit/s, a gigabit version followed quite quickly. Ethernet technology based on IEEE 802.3bp 1000BASE-T1 is already available today and delivers 1 Gbit/s transmission speeds using only one pair of copper wires.


IEEE published a standard in 2021 for up to 10 Gbit/s (IEEE 802.3ch), which is required for high-resolution sensors and video transmissions. A standard for only 10 Mbit/s (IEEE 802.3cg) was published in February 2020. This standard is very relevant for many industry sectors, as it allows transmission distances of up to 1,000 meters and can therefore replace almost all fieldbuses. Another working group was set up in March 2019 to deal with transmission rates above 10 Gbit/s. Their targets are 25 Gbit/s and 50 Gbit/s. These high-data rates are the technology required for autonomous driving and new zonal computer architectures within vehicles. SPE is the ideal technology for this.



Industrial automation recognizes this potential


The production and automation industry has a similar problem as the automotive industry in that it demands integrated industry, meaning the integration of the field level (sensor/actuator networks) down to the tool and workpiece within automated production. It requires a network strategy that can be used universally while also being sustainable well into the future. In other words, IT solutions are needed that are not proprietary and provide the availability and security standards that are common in the industry. SPE is the right technology for this. It offers many advantages:


  • end-to-end TCP/IP communications as an alternative to proprietary bus or power interfaces
  • high security and 100 percent availability
  • enormous range from a few meters up to more than 1000 meters
  • minimal space required for cables and distributors
  • easy to install
  • simultaneous power supply for end devices and sensors using power over data line
  • rechargeable and nonrechargeable batteries are not needed, which is an important environmental consideration.
  • reduces costs with better operational reliability


Thus, SPE is a technology that removes most of the restrictions of wired communications. It also compensates for the disadvantages of cable compared to other technologies (such as wireless)—based on the types of applications considered here. In summary, SPE highlights the advantages of copper fiber optics as a transmission medium. Wireless communication is also facing new competition.



Power over data line


Like multipair cabling, there is a new standard for remote power supply for SPE that is analogous to Power over Ethernet (PoE); it is called power over data line (PoDL) (IEEE 802.3bu). This combination of data and power using very small plug-in connectors and single-pair cables helps to support the trends toward miniaturization, higher data rates, and modularization for more complex systems. These are all prerequisites for the rapid development of nonvehicle SPE applications in industry, smart cities, buildings, etc.


Ethernet over copper for over 1000 meters? SPE technology has already achieved the same performance as today’s predominant “multipair Ethernet” (MPE) within a very short period of time. Currently, the only limitation is the limited range for 100 Mbit/s and gigabit SPE (15 m and 40 m respectively), which results from the requirements of the main target group in the automotive industry.


Experts agree that greater transmission lengths can also be achieved. The chart shows the extended transmission lengths that are technically possible. However, for these extensions of the SPE standards to be covered by IEEE 802.3 and, in particular, for the semiconductor industry to invest in the development of these new chip sets, it is necessary to define the new target applications and suitable market potential. This requires the open cooperation of all interested parties for the extended SPE ranges. The first presentations at IEEE 802.3 have already been published and were well received. Further supporters for these target standards are very welcome.



T1 industrial style: All standards united in support


There is still a long way to go before the SPE infrastructure and its associated potential are firmly established. Currently, several solutions and different standards are being discussed on the market, with a particular focus on the interfaces for SPE. Users are now rightly asking whether manufacturers will develop a consistent and compatible solution based on a uniform standard, or whether there will be multiple solutions and incompatible mating faces. Thus, it is necessary to take a closer look at the cooperation of various standards committees and their work relating to Ethernet communication.


ISO/IEC SC25 WG3: ISO/IEC JTC 1/SC 25/WG 3 plays a central role in the standardization. This is where the cabling standards in compliance with ISO/IEC 11801 are created and maintained.

IEC SC46C: Committee for cabling components: copper data cables

IEC SC48B: Committee for cabling components: connectors

IEEE 802.3: Cable-based Ethernet protocol standards



IEC 61156-x – Standardization of single-pair Ethernet cables


Within the IEC SC46C working group for the standardization of data cables as bulk goods, the following standards are currently in progress:


  • IEC 61156-11: SPE data cable up to 600 MHz bandwidth for fixed installations (final published)
  • IEC 61156-12: SPE data cable up to 600 MHz bandwidth for flexible installations (CD available)
  • IEC 61156-13: SPE data cable up to 20 MHz bandwidth for fixed installations (CD available)
  • IEC 61156-14: SPE data cable up to 20 MHz bandwidth for flexible installations (planned).


Further standards projects, for example for higher bandwidths to support data rates above 1 Gbit/s, will be processed in the future.



IEC 63171-6 – Standardization of single-pair Ethernet connection technology


HARTING submitted the first draft standard for the SPE connector to SC48B as early as 2016, and it was published as IEC 61076-3-125 up to the CD document. In 2017, the company CommScope submitted another SPE mating face for standardization and decided to create the IEC 63171 series of standards for all SPE connectors. Accordingly, the project team PT63171 was set up at SC48B and commissioned with the task of preparing this new series of standards. The standards already in process up to this point will be completed as self-contained documents and later integrated into this new series of standards as revisions.


The following standards projects are currently in progress:


  • IEC 63171: Base standard with all necessary specifications and test sequences (CDV available)
  • IEC 63171-1: SPE connectors from CommScope based on LC interlock, for M1I1C1E1 applications published
  • IEC 63171-2: SPE connectors from Reichle & De-Massari for M1I1C1E1 applications published
  • IEC 63171-3: SPE connectors from Siemon based on a pair of the well-known Tera connectors for M1I1C1E1 applications (withdrawn)
  • IEC 63171-4: SPE connectors from BKS for M1I1C1E1 applications (CD available)
  • IEC 63171-5: SPE connectors from Phoenix Contact based on the IEC 63171-2 mating face for M2I2C2E2 and M3I3C3E3 applications (second CDV in preparation) 
  • IEC 63171-6 (previously IEC 61076-3-125): SPE connectors from HARTING and TE Connectivity for M2I2C2E2 and M3I3C3E3 applications published since 23 January 2020, second edition in work.


Note: IEC 63171-1 (LC Style) and IEC 63171-6 (Industrial Style) are complete standard documents with all necessary specifications and test sequences. All standards started after this refer to the base standard IEC 63171 and describe only the different mechanical versions.



The cabling standards for SPE


SPE and its standardized connectors are incorporated into the current cabling standards. Internationally, this applies primarily to the series of standards for structured cabling according to ISO/IEC 11801:2017 and, in a similar way, to the European series of standards in CENELEC according to EN 50173. Here, SPE is included in part 3 of industrial cabling in the annex (amendments). The central document for these annexes is the ISO/IEC TR 11801-9906, Balanced single-pair cabling channels up to 600 MHz for SPE.


The implementation of SPE in the ISO/IEC 11801 documents is very important. It is the only standard to describe the cabling channels with all the necessary parameters (length, number of connections, bandwidth, and the complete set of technical transmission-related parameters including NEXT, FEXT, and shielding properties) in relation to the MICEspecified environment, so that this can be tested with measurements after the installation parallel to this. The industrial installation standards will be adapted as a basis for the cabling of automation solutions according to IEC 61918 (IEC SC65C). It remains to be seen to what extent this will affect the automation profiles themselves. What is certain is that PI (with PROFINET according to IEC 61784-5-3) and ODVA (with EtherNet/ IP according to IEC 61784-5-2) are actively involved in the further development and implementation of standards for SPE.


In conjunction with the component standards for connectors and cables, all users of SPE can receive clear guidelines for the construction and testing of appropriate transmission paths. For 1 Gbit/s SPE, this cabling is initially limited to a range of 40 m. For the 10 Mbit/s variant, ranges of 1000 m and beyond can be implemented.


Further documentation on SPE cabling relevant to the U.S., Canada, and Mexico are being prepared at ANSI/TIA-568.5 and TIA TR-42.7. This is updated in the TIA-42 documents as an addendum: TIA-1005-A-3. The content of all these additions is largely identical.


These cabling standards provide the user with information about the structure of the cabling, the cabling components that should be used to achieve the performance specifications, and the limit values for testing the cabling. Thus, they are the most important instrument for setting up and commissioning SPE cabling systems. They also ensure compatibility between devices and cabling by providing references to component standards (e.g., connectors according to IEC 63171-6). This compatibility is a basic prerequisite for the proper functionality of networks and connections based on SPE and, thus, the foundation of IoT/IIoT. The use of cabling components other than those specified in ISO/IEC 11801-3 Amendment 1 would be theoretically possible. However, these would no longer conform to the standard and would risk incompatibilities and loss of functionality.


For this reason, at the start of 2018, ISO/IEC JTC 1/SC 25/WG 3 and TIA-42 started international selection processes to define uniform interfaces. These two selection processes were co-initiated by IEEE 802.3, which requested a recommendation for a SPE MDI (SPE device interface) from ISO/IEC and TIA.


More than 20 national expert panels participated in this selection process. Two connector-mating profiles emerged from this selection process as the preferred choices:


  • For building wiring, the mating face according to IEC 63171-1. This mating face is based on the proposal by CommScope.
  • For industrial and applications adjacent to industry (M2I2C2E2 and M3I3C3E3), the mating face according to IEC 63171-6 (formerly IEC 61076-3-125). This mating face is based on the proposal made by HARTING T1 Industrial.


The selection process at TIA-42 has confirmed the results of ISO/ IEC, and as such there is significant global consensus on the SPE interfaces. These selected mating faces are now being incorporated into the corresponding international cabling standards. IEEE 802.3 has also specified these SPE interfaces in the IEEE 802.3cg as the recommended media dependent interface (MDI).


This is required for large-scale usage. Thus, it is also required to successfully market SPE technology along with the consistent compatibility of devices, cables, and connectors throughout different types of applications. This provides planning security for all market participants.


Note that MICE describes environmental conditions for installations. It also provides planners and users with valuable information for specifying technical equipment and cabling. The requirements for mechanical robustness (M), IPxx degree (I), chemical and climatic resistance (C) and electromagnetic safety (E) are described. In the broadest sense, M1I1C1E1 describes an environment similar to that inside an office building. M3I3C3E3 describes a fairly extreme environment such as that found in industry or outdoors.



Deep-dive into technology


Even if twisted pairs of wires are required for existing four-pair data cabling as well as for SPE, the requirements for cabling and connection technology are quite different. This is especially the case for transmission lengths with the currently available SPE transmission standards, as well as the radio frequency (RF) requirements, which are particularly evident for these required bandwidths.



Migration from multipair cabling (MPE) using SPE (cable sharing)


High data rates are possible over one pair of wires—so why not combine four SPE paths in your existing infrastructure? This idea of using four-pair cabling for SPE by means of “cable sharing” is quite straightforward. This is possible for special cases, but it does not really make sense technically and economically. On the one hand, SPE cabling requires higher bandwidths compared to MPE, especially for cross talk. Also, compared to MPE with 100 meter transmission length, so far SPE has only shorter transmission lengths of 40 meters at 1000BASE-T1 for shielded cables. For this migration scenario, the user must check each path of the installed cabling for SPE. Thus, the actual economic viability of such usage strategies is questionable. For example, for an installed Cat. 6A cabling to qualify for 1000BASE-T1, the transmission length must not exceed 40 meters, and the corresponding RF parameters must be qualified for up to 600 MHz. If all this matches perfectly, you could then transmit four times 1 Gbit/s over SPE, even though this Cat. 6A cabling path could also support 10 Gbit/s MPE.



The connection technology for SPE


Individual connector types are inseparably linked to a specific application and have been, of course, internationally standardized. Well-known examples of this are the RJ45 connectors for Ethernet and the concise HDMI or DVI connectors for video transmission. Thus, standardized interface connectors are required in order to have a successful market launch for new network technologies such as SPE. This is because only with standardized interfaces is it possible to network a wide variety of devices in a uniform data network. The design of the SPE connectors (according to IEC 36171-6) was based on the specifications of the associated IEE 802.3 standards and other market requirements.



Overview of the electrical characteristics


Nominal voltage


A differential voltage signal of ±1 V is usually used for pure Ethernet transmissions. When determining the nominal voltage of an SPE connector, however, the parallel use of the two wires must also be considered for the remote power supply. The method used for this in SPE is power over data line; it is standardized according to IEEE 802.3bu. Similar to PoE, the maximum rated voltage is 48 VDC, resulting in a maximum supply voltage of 60 VDC to the power sourcing equipment (PSE). In contrast to PoE, PoDL defines additional typical onboard voltages of 12 V and 24 VDC, which are used in vehicles


Insulation voltage


Even though the IEEE 80.3 SPE standards do not define explicit specifications for insulation requirements pertaining to the largest group of users in the automotive industry, the same requirements are applied for normal applications in building and industrial cabling as exist for four-pair Ethernet with 1.5 kV (rms) contact–to-shield and 1.0 kV (rms) contact-to-contact (refer to Section 126.5.1 IEEE 802.3cr).


Rated current


The PoDL requirements are also decisive when determining the rated current. In the current standard, Table 104-1 IEEE 802.3bu specifies the maximum feed-in power as 63.3 W, which corresponds to a maximum supply power at the powered device of 50 W. This results in 1.36 A at 48 V at the minimum permissible supply voltage. However, a rated current of 4 A DC has been selected to maintain a sustainable interference level into the future.


Background: According to the National Electric Code (NEC) for the North American market, the maximum power for NEC Class 2 devices is limited to 100 W; this is also the maximum remote power supply power for the PoE standard IEEE 802.3bt. This means that future PoDL expansions will remain below 100 W and the 24 V supply voltage used in industrial automation will result in a rounded maximum-rated current of 4 A.



RF transmission parameters


For transmitting data, SPE uses a full-duplex connection on a differential wire pair with an impedance of 100 ohm. To achieve lower interference sensitivity (especially for use in electric vehicles), a lower coding with PAM3 up to 1000BASE-T1 and PAM4 for 2.5/5/10GBASE-T1 was chosen for SPE. This increases the bandwidth requirement enormously compared to the multipair Ethernet standards. For example, IEEE 802.3ch for multi-gigabit SPE up to 4 GHz at 10GBASE-T1 (compare with 10GBASE-T of only 500 MHz) is currently being discussed. Therefore, the RF requirements for cable and connection technology are increasing, and a very symmetrical connector design is necessary to reliably meet these stricter RF requirements. For this reason, the contacts of the T1 Industrial connector are arranged symmetrically in a completely closed shield housing.


The coupling capacitances and inductances of both conductors to the shielding or the printed circuit board are identical. There is no interference with the differential data transmission. This means that the signal path is identical in both conductor paths, and differences in the signal propagation time are avoided.



Technical design of the SPE connection technology in compliance with IEC 63171-6


The aim of the design for the SPE interface was to consider all the electrical parameters already explained above with sufficient reserve for future higher bandwidths, the requirements regarding a remote power supply (PoDL), and the variety of housing designs already accepted and widely used on the market. Multiple factors were important: a balanced relationship between the market demands for miniaturized interfaces and high robustness, as well as good handling and a well-designed termination area to match the wire and cable diameters to be used.


Following these design objectives, 0.5 mm contacts with a contact gap of 2.8 mm were chosen for the contact system. The contact spacing is matched to fit with the cable cross-sections to be connected. For the short transmission distances with 100BASE-T1 and 1000BASE-T1, AWG 26 or AWG 22 conductors with wire core diameters of approximately 1 mm or 1.6 mm diameter can be used. For the 10BASE-T1L 1000 m with longer range, however, AWG 16/18 conductors with a typical wire core diameter of approximately 2 mm are required; thus, a 2.8 mm contact distance is optimal.


According to the IEEE 802.3 standards, longer ranges can only be achieved with shielded transmission paths. For this reason, and to ensure secure transmission even in harsh industrial environments, a shielded design has been consistently implemented. At the same time, these shielding plates also provide the robust mechanical interlocking for the IP 20 version. The metallic latch lever eliminates the problem of the broken latching mechanism—a common criticism with RJ45. M8 and M12 circular connectors have established themselves for usage in industrial applications.


Accordingly, screw-type, snap-in, and push-pull interlocks have been added for the M8 construction types of the new SPE mating face to make them a uniform “data container.” The M12 designs with screw and push-pull interlocks are also standardized, to accommodate the large cable cross-sections for the 1000-m 10BASE-T1L channel. This means that the same mating face is used in all designs, and IP20 connectors can also be connected to the IP65/67 interfaces for parameter configuration or testing.


Usage of the widely accepted M8/M12 types ensures good market acceptance while also reducing the necessary investment costs, since many suppliers have the corresponding housing designs already available. The use of identical socket and plug-in connector inserts (“data containers”) throughout all construction types guarantees that there are uniform technical characteristics in all the product series. This makes it easier to implement cost-efficient production through economies of scale. Thus, the SPE interfaces according to IEC 63171-6 provide an internationally standardized mating face that optimally supports the future usage of SPE in industrial applications. By using this standardized SPE data container, it is also easy to integrate this IEC 63171-6 mating face into other designs, such as the connector system with internal M12 push-pull interlock that is currently being developed as a new standards project.



An ecosystem of strong partners


Industrial Ethernet is becoming widespread in automation and I4.0 applications. More and more devices and solutions from a wide range of sectors are becoming “smart”—for this, they need the right Ethernet infrastructure. The SPE ecosystem shows us how technology, standards, infrastructure components, devices, and test equipment logically build on and support each other. They ultimately provide a solid foundation for the digitization of multiple different markets.


That is why HARTING has worked actively in the field of standardization and developed an infrastructure suitable for industrial usage. HARTING now actively supports device manufacturers as they implement SPE.


All partners together wish to provide the building blocks for the SPE ecosystem. They see themselves as partners for the industrial Ethernet user groups, since SPE can provide a new infrastructure for these protocols (such as PROFINET), which would enable IP-based communications all the way down to the field level. Just as the slogan promises: “SPE – the infrastructure for IIoT.”


This means that SPE will not only support many applications in a more efficient and environmentally friendly manner, SPE will also enable many new applications. In addition to the currently predominant discussion of the technical side of digitization, the social challenges and effects of digitization on our democratic societies, which were only formed at the beginning of the first industrial revolution, must also be discussed throughout society. In his book The Web of Digitization: Humanity in Upheaval – on the Way to a New Worldview, published in 2018, Ulrich Sendler gives a detailed overview of the development of industry, technologies, and society. This is a book that is worth reading, with many suggestions about the steps required to ensure that digitization succeeds socially and serves the well-being of humankind.



Where are we headed?


New applications fields—such as autonomous driving, IoT, and IIoT— require new and more powerful network technologies. SPE is one such technology. The ability to simultaneously supply power and data to devices with only one connection is a huge advantage over wireless solutions. The remote power supply via PoDL makes batteries and accumulators superfluous—a big advantage for environmental compatibility and sustainability. Cable-based transmission methods have the additional advantage of no regulatory restrictions regarding the usable frequency ranges, so no license fees are incurred for the necessary frequency bands. Because frequency bands are not allocated uniformly (even internationally), equipment with radio interfaces must always be adapted to different market requirements. This is not necessary for cable-based transmission methods. Thus, uniform devices can be developed that can be used globally.


Together with the time sensitive network (TSN) standards developed in IEEE 802.1, Ethernet technology is being expanded along with all necessary mechanisms in order to implement determinism for data communications—this is a prerequisite for all real-time applications.


SPE, therefore, qualifies as a perfect infrastructure solution and “enabler” for IoT and IIoT, making it an important building block for integrated industry.


For SPE to fully develop this potential within an ecosystem, the partners from different industrial sectors must work together intensively and make this vision possible. This starts with the joint international standardization in IEEE 802, ISO/IEC, and TIA. It continues with the development and production of the necessary components starting with semiconductors, magnetic components, connectors/ cabling components, and measurement technology. Only when the standards and components are available (at least in initial sample quantities) will users be able to equip their multitude of possible devices with SPE transmission technology and open up a wide range of new applications.


This article comes from the IIoT & Industry 4.0 eBook.

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