Single Pair Ethernet - Standardization landscape

With Single Pair Ethernet, a new physical layer is entering the world of Ethernet communication. Born out of the automotive industry, SPE is also developing into a key technology for the coming steps of digitization in industrial automation. Ethernet IP can finally be transmitted continuously from the cloud to the field level via just one pair of copper wires.

In industry, communication protocols and the infrastructure are subject to strict rules. To ensure interoperability and interchangeability, standardization is a high priority. This also applies to Single Pair Ethernet.

This article shows the work of international committees, the current status of standardization around the new physical layer SPE, and explains to users how and with which standards the path to the IIoT will be successfully taken.

The IEEE 802.3 specifies the primary transmission method and must also specify the transmission channel, such as the transmission length and number of connectors. The cabling committees ISO/IEC and TIA consider the transmission channel and access the corresponding IEC groups for connectors and cables. There is close cooperation between IEEE802.3 and ISO/IEC and TIA.

For even higher speeds, especially in vehicles, the 25GBASE-T1 protocol for 25 Gbit/s up to at least 11 m channel length was published in June 2023. This SPE standard will primarily be used as a backbone in vehicles.

In addition to the "classic" point-to-point (P2P) SPE protocols described above, a type of BUS standard 10BASE-T1S is also available. The 10BASE-T1S standard is a point-to-multipoint (P2MP) or, as IEEE802.3 calls it, a MultiDrop transmission system and therefore functions like an Ethernet bus over a minimum 25 m long, unshielded cable with at least 8 devices. With the exception of 10BASE-T1S, all SPE protocols are compatible with Power over DataLine (PoDL) remote power supply technology. The IEEE802.3da working group has set itself the goal of increasing the number of bus participants to at least 16 nodes and the transmission length to at least 50 m and enabling remote power.

The origin

The IEEE 802.3cg was approved in November 2019 and there the “LC Style” according to IEC 63171-1 and the T1 Industrial according to IEC 63171-6 are listed as optional MDI ("...may be used..."). This formulation was chosen in order to be able to use other connectors, in particular special types for automotive applications or also PCB terminals, provided they meet the defined requirements. However, for cabling in buildings, data centers and industry, the LC style connectors selected in the ISO/IEC 11801 and TIA sets of standards according to IEC 63171-1 and the "T1 Industrial Style" according to IEC 63171-6 must be used.

In March 2021, the IEEE802.3de working group for the extension of point-to-point protocols was founded to add TSN functionalities for 10BASE-T1L. This working group "Time Synchronization for Point-to-Point Single Pair Ethernet Task Force" specified an extension of the MAC merge function and the Time Synchronization Service Interface (TSSI).

The 802.3dg working group will close the first gap in the transmission length with 100BASE-T1L, a new protocol for 100 Mbit/s over at least 500 m transmission length. As of January 2024, final results are expected by the end of 2024 and the location should be published in mid-2025. Information on the IEEE802.3 projects can be found here:

www.ieee802.org/3/index.html.

The IEC 63171-6 for the T1 Industrial connector family is the world's first available standard for SPE connectors and covers all versions from IP20 to IP 65/67 including the T1 Industrial M8 Hybrid with 2 contacts each for SPE and Power.

sPE CABLING STANDARDS

In parallel, the installation standard IEC 61918 (IEC SC65C) for industry as a basis for the cabling of automation solutions was also adapted and supplemented by SPE. The new amendment to IEC 61918 addresses the new 1-pair cabling structures for Single Pair Ethernet (SPE) and the associated remote power supply PoDL (Power over Data Line). This closes the gap between classic IT infrastructure and industry, IoT/IIoT. SPE has a special significance for industry and the automation island. For the first time, it enables the universal application of TCP/IP-based automation protocols even for long distances, as in process automation or for the simple connection of sensors and actuators up to the industrial field level.

To what extent this will then also influence the automation profiles themselves remains to be seen. 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 and are working on corresponding profile-specific standard documents. A similar approach will certainly be taken with Advance Physical Layer (APL), based on 10BASE-T1L, for the process industry and a new profile will also be developed for this in IEC 61784-5-x. In conjunction with the component standards for connectors and cables, all users of SPE receive clear guidelines for the construction and testing of corresponding transmission links. For 1 Gbit/s SPE, these cablings are initially limited to a range of 40 metres. For the 10 MBit/s variant, ranges of 1,000 m and beyond are realised.

Other papers on SPE cabling relevant to the USA including Canada and Mexico, such as ANSI/TIA-568.5, are being prepared at TIA TR 42.9. In the TIA 42.9 papers, this is realised via a revision: ANSI/TIA-568.7 (industrial cabling without SPE). In terms of content, all these additions are largely congruent.

These cabling standards provide the user with information on the structure of the cabling, the cabling components to be used to achieve the performance specifications and the limit values for checking the cabling. Thus, they are the most important instrument for the construction and commissioning of SPE cabling. At the same time, they ensure compatibility between devices and cabling via the references to the component standards (e.g. connectors according to IEC 63171-6). This compatibility is a basic prerequisite for the function of networks and connections based on SPE and thus the basis for IoT/IIoT. The use of other cabling components is possible in principle, but then no longer complies with the standard and carries the risk of incompatibilities and functional losses.

OUTLOOK - INDUSTRIAL ETHERNNET USER GROUPS

In addition to the completion of the cabling standards at ISO/IEC and TIA, the focus of SPE standardization will now be on the integration of SPE into the Industrial Ethernet standardization groups such as PI (PROFINET International), ETG (EtherCAT), IDA (Modbus), CLPA (CC-Link IE), ODVA (EtherNet/IP™) and other user groups. 
However, depending on the strategic orientation and skill of these user groups, the implementation of SPE in the individual automation profiles will probably be more from the device side (sensor/actuator networks) and will not automatically affect communication in the automation network above. Fast Ethernet (e.g. PROFINET) and Gigabit Ethernet (e.g. EtherNet/IP™) will still predominate here for the time being. 

For PROFINET, hybrid interfaces for field cabling have been added to the current guideline for cabling and connection technology. In the new version, the T1 Industial M8 Hybrid according to IEC 63171-6 and the M12 Hybrid Type II and Type VI according to IEC 63171-7 have been newly defined as PROFINET interfaces for SPE and power supply. The ODVA is also discussing SPE as a new physical layer and is working on the corresponding documents.