Comprehensive Guide to IEEE Single-Pair Ethernet Standards

Eight IEEE Single-Pair Ethernet (SPE) standards exist, and a ninth is expected to be announced next year. Current standards include 802.3bw (100BASE-T1), two types of 802.3bp (1000BASE-T1), 802.3ch (10BASE-T1) optimized for automated environments, three versions of 802.3cg (10BASE-T1S, 10BASE-T1L, and 10BASE-T1M), and the 802.3da single-pair multidrop segments enhancement standard approved in 2023.

This article reviews the eight existing SPE standards and closes with a preview of 802.3dg, which is expected to be published by the end of 2025. The following article in this five-article series will begin a deep dive into multidrop SPE by answering the question, “How does multidrop SPE work?” Other articles in the series will examine multidrop SPE architectures, PHY implementations, and technical requirements for interconnects.

SPE is designed to simplify Ethernet implementation. It builds on Fast Ethernet, which uses two cable pairs, and Gigabit Ethernet, which requires four cable pairs (Figure 1). Some SPE standards can transmit power and data using Power over Dataline (PoDL) technology.

Figure 1. The three types of Ethernet cabling. (Image: CAE Group)

Eight ways to use a single pair

SPE technology has been embodied in many standards to support specific application needs. The first IEEE SPE standard was 802.3bw (100BASE-T1). It was released in 2015. Designed for use in automotive environments, it can support up to four series connections in a point-to-point (P2P) architecture with two mating connections with transmission rates of up to 100 Mbps over a total distance of up to 15 m. Subsequent SPE standards (in the order of release) include:

802.3bp (1000BASE-T1) consists of two types and was released in 2016. Both support data rates up to 1 Gbps and P2P architectures. Type A is for automotive systems using unshielded cables over distances up to 15 m. Type B uses shielded cables for industrial applications and has a reach of up to 40 m.

The 802.3cg sub series, including 10BASE-T1S, 10BASE-T1M, and 10BASE-T1L, was released in 2019. 10BASE-T1S is for short-reach P2P and multidrop applications up to 15 m, while 10BASE-T1M is for multidrop applications with a reach of at least 25 m. Both support transmission speeds up to 10 Mbps and are designed for automotive applications like zonal architectures and industrial Internet of Things (IIoT) applications.

10BASE-T1S specifies that at least eight nodes be supported, while 10BASE-T1M requires support for at least 16 nodes. In addition, while the T1S standard supports PoDL, T1M supports an enhanced version of PoDL.

10BASE-T1L is for long runs up to 1 km in P2P networks, handles data rates up to 10 Mbps, and is compatible with PoDL. It supports industrial and building automation protocols like PROFINET, Modbus, BACnet, KNX, and LON. It specifies using a balanced pair of conductors and requires a shielded cable in electrically noisy environments.

802.3ch Multi-Gigabit Ethernet (10G/5G/2.5GBASE-T1), optimized for automotive environments, includes data rates of 2.5 Gbps, 5 Gbps, and 10 Gbps on a single balanced pair and a reach of 15 m. It was added in 2020. 802.3ch is designed to act as the in-vehicle network backbone to link various slower zonal functions and support Advanced Driver Assistance Systems (ADAS), such as high-resolution, high-frame-rate, uncompressed video transmission for autonomous driving.

802.3da, released in 2023, enhances 10BASE-T1M multidrop technology. It doubles the reach to 50 m and supports regular PoDL powering instead of requiring enhanced PoDL. 802.3da adds a definition of the noise environment characterized by impulse and RF noise, as defined in IEC61000-4-4, IEC61000-4-6, and CISPR25. It is intended to support operations in industrial, building, and transportation applications. It also adds the option for using dynamic physical layer collision avoidance (D-PLCA) node identification allocation.

Table 1. Summary of current SPE standards, except 802.3ch (10BASE-T1) optimized for automotive environments with a data rate of 10 Gbps and a reach of 15 m. (Table: CAPIEL)

What will number nine be?

The ninth SPE standard will be 802.3de — Time Synchronization for Point-to-Point SPE. It will add time-sensitive networking (TSN) capabilities to 10BASE-T1L P2P networking. It will support data rates up to 10 Mbps over at least 500 m and is expected to be published in mid-2025.

Summary

SPE is not a single technology. It’s a diverse series of standards optimized for various applications, such as transportation (including automotive ADAS), industrial, and building automation. Various standards can support data rates from 10 Mbps to 1 Gbps and transmission distances up to 1 km. The next step in developing SPE standards is expected to be the addition of TSN capability.