10BASE-T1S
IEEE 802.3cg single-pair Ethernet.

10BASE-T1S is defined in IEEE 802.3cg-2019 as part of the Single-Pair Ethernet (SPE) family. The "T1S" suffix decodes as Twisted-pair 1, Short reach — a single twisted pair (rather than the four pairs used by 100BASE-TX) over short distances.

Unlike most prior Ethernet variants, which use point-to-point links into a switch, 10BASE-T1S supports a multi-drop bus topology: up to 8 nodes can share a single mixing segment up to 25 m long, terminated at both ends. This makes it a direct replacement for legacy buses (CAN, LIN, RS-485) in vehicles and industrial systems that need IP-based diagnostics or higher payloads without a switch infrastructure.

Media access on the shared segment is governed by PLCA — Physical Layer Collision Avoidance — a token-passing scheme defined in IEEE 802.3cg Clause 148. Each node gets a guaranteed transmit opportunity per cycle, giving the bus deterministic latency suitable for control traffic, unlike classical CSMA/CD Ethernet.

Common applications today are automotive zonal architectures, factory-floor sensor networks, and building automation.