Single Pair Ethernet (SPE) in Industrial and Edge AI Computing

Single pair Ethernet (SPE) is Ethernet over one twisted pair of wires, instead of the two pairs used by 100BASE-TX or the four used by 1000BASE-T. IEEE 802.3 defines it as a family of physical layers whose names end in T1, for one pair: 100BASE-T1 (IEEE 802.3bw), 1000BASE-T1 (802.3bp), 10BASE-T1L and 10BASE-T1S (802.3cg) and the multi-gigabit 2.5G, 5G and 10GBASE-T1 (802.3ch). Above the physical layer nothing changes: frames, MAC addresses, VLANs, IP and industrial protocols work exactly as they do on any other Ethernet link.

SPE grew from two directions. In vehicles, it replaces heavy multi-pair harnesses with light cabling between cameras, radar, displays and zonal controllers, which is where 100BASE-T1 and 1000BASE-T1 began. In factories and process plants, 10BASE-T1L brings Ethernet over a single pair to field instruments up to 1,000 m away, the job that 4–20 mA loops and fieldbuses such as PROFIBUS PA and HART have done for decades, and Ethernet-APL builds on it for hazardous areas. Power can travel on the same pair using Power over Data Lines (PoDL, IEEE 802.3bu), the single-pair counterpart of PoE.

This guide builds on that definition. It compares the T1 standards, explains the difference between 10BASE-T1L and 10BASE-T1S, sets out how Power over Data Lines works and which connectors are used, covers Ethernet-APL for process plants and automotive-grade SPE on edge AI computers, and compares SPE with standard Ethernet and fieldbus. It ends with a checklist, products from our range and answers to the questions engineers ask most.

The T1 standards differ in speed, reach and whether several devices can share one pair. Reach figures are the IEEE link segment lengths; real installations depend on the cable and connectors.

Connectors are standardized separately. Vehicles use automotive connectors such as H-MTD and MATEnet, while industrial equipment uses the IEC 63171 family, with IEC 63171-6 in M8 and M12 housings for IP67 field connections. The variants do not interwork: a 1000BASE-T1 port will not link to a 10BASE-T1L instrument, and neither plugs into an RJ45 port without a converter or a switch with matching ports.

To bring automotive Ethernet into an industrial computer, we supply PCIe cards such as the Neousys PCIe-AE304bp, with four 100/1000BASE-T1 ports on H-MTD connectors, and the Vecow AE-1004, with four 1000BASE-T1 ports on MATEnet, as well as in-vehicle edge AI computers with a built-in 100/1000BASE-T1 port, such as the Sintrones IBOX-650P-T1 series.

Both run at 10 Mbit/s and both are defined in IEEE 802.3cg, but they solve opposite problems. 10BASE-T1L, the L for long reach, takes Ethernet a long way to one device. 10BASE-T1S, the S for short reach, connects several devices along a short shared cable.

10BASE-T1S takes over much of the role that CAN bus plays today: many small nodes on one cable, but with Ethernet addressing and no gateway between the sensor network and the rest of the system. Multidrop wiring is a form of bus topology, which is unusual for Ethernet and is what PLCA makes deterministic.

Yes. Power over Data Lines (PoDL) puts DC power on the same pair that carries the data, which is the single-pair counterpart of Power over Ethernet. PoE uses two or four pairs and separates power from data with transformers; PoDL couples the DC onto the single data pair with inductors and filters it off at the far end.

The class tables in the standards set the exact voltage and power per class, so check them against the device. Like PoE, PoDL lets a sensor take power and data from one cable; our guide to industrial Power over Ethernet covers the multi-pair side.

Connectors are standardized separately from the IEEE physical layers, and the vehicle and industrial worlds use different families. Two groups of companies promote different industrial connector designs: the SPE Industrial Partner Network around the IEC 63171-6 design, and the Single Pair Ethernet System Alliance around the IEC 63171-2 and IEC 63171-5 designs. Both are IEC standards; choose one family per installation and keep to it.

M12 is already the rugged connector for multi-pair industrial Ethernet, as our guide to M12 connectors explains, and SPE versions follow the same circular format. In our range, the Sintrones IBOX-650P-IP66-T1 uses a Phoenix Contact IEC 63171-5 connector for its SPE port, while the automotive Ethernet cards use H-MTD or MATEnet.

Ethernet-APL (Advanced Physical Layer) is 10BASE-T1L adapted for process plants and hazardous areas. It carries Ethernet and power over the two-wire cable that instrument loops already use, with a trunk of up to 1,000 m and spurs of up to 200 m to each instrument. For hazardous areas it uses the 2-WISE concept, described in IEC TS 60079-47, so intrinsically safe instruments can be connected and checked without detailed loop calculations.

The aim is to replace 4–20 mA and HART at the instrument with full Ethernet: higher bandwidth for diagnostics and configuration, direct IP access to every device, and PROFINET, EtherNet/IP, HART-IP or OPC UA running end to end. Our FAQs on ATEX and intrinsically safe vs non-incendive protection explain the hazardous-area rules that APL is designed around. Power on intrinsically safe spurs is limited, typically to well under a watt per instrument.

Single pair Ethernet was first standardized through work promoted by the OPEN Alliance, a group of automotive makers and semiconductor vendors set up to make in-vehicle Ethernet interoperable. That work led to 100BASE-T1 and 1000BASE-T1, and IEEE has since added the multi-gigabit 802.3ch and faster automotive standards. To take SPE beyond vehicles, the SPE Industrial Partner Network brought together connector, cable and system makers focused on industrial use.

In vehicles and mobile machines, LiDAR, radar, cameras and zonal controllers increasingly connect over 100BASE-T1 or 1000BASE-T1. An AI computer that has to join that network needs a matching port, or a card or media converter for each link. For rugged box PCs and edge AI computers, a growing industrial supplier base means SPE is available with IP-rated connectors, long-lifecycle supply and the reliability needed in factory, energy and transport environments.

The PCIe-AE304bp also provides hardware timestamping for IEEE 1588 and 802.1AS, so LiDAR points, radar returns and camera frames can be lined up in time. The IBOX-650P-T1 computers run on NVIDIA Jetson AGX Orin. We fit and test the cards in the host and install the drivers before shipping.

Where SPE links carry time-critical control or sensor traffic, how Time-Sensitive Networking bounds latency on standard Ethernet is the companion topic. Cameras with very high data rates often use GMSL rather than Ethernet; our guide to GMSL technology compares the approach.

Take an autonomous mobile robot with two LiDAR sensors and two radars on 1000BASE-T1 and 100BASE-T1, a 10BASE-T1S bus linking six bumper, door and lamp controllers, and four cameras on standard Gigabit Ethernet. The robot’s AI computer has to receive all of it, keep it time-aligned and act on it. The device mix is illustrative; check each sensor’s interface and data rate.

The T1 card replaces four media converters and their power supplies, and the shared clock lets LiDAR points, radar returns and camera frames be fused at the right instant. Our robot computer guide covers the rest of the onboard compute decision.

Each T1 standard defines a link segment: the cable, connectors and inline connections that the physical layer must work across. The reach figures below are those link segments. Real links depend on cable gauge, the number of inline connectors and the electrical noise along the route.

Where a run is longer than the T1 reach, a switch extends it, or the link changes to fiber between switches. For field instruments the 1,000 m reach of 10BASE-T1L is usually enough to reach the control room or a field junction box directly.

SPE sits between the multi-pair Ethernet used for computers and cameras and the fieldbuses and analog loops used for instruments and sensors.

EtherNet/IP and OPC UA are two of the protocols that run unchanged over it.

Is SPE replacing fieldbus?

Over time, at new installations. 10BASE-T1L and Ethernet-APL let new process instruments use Ethernet directly, and 10BASE-T1S offers an Ethernet alternative to low-speed sensor buses. Installed fieldbus networks will run for many years, and gateways will connect the two. The practical gain is one protocol stack from the sensor to the cloud, without translation at every layer.

Compared with multi-pair Ethernet, SPE is optimized for weight, distance and connecting small devices.

Where multi-gigabit links are needed between cameras and AI computers, our white paper on 10 Gigabit Ethernet for edge AI covers the multi-pair side.

Products from our catalog with single pair Ethernet ports. Figures are from each product’s page.