The 802.3cg Ethernet standard uses a single pair of wires, and it manages data flow without switches, making it suitable for industrial networks at a lower cost than traditional Ethernet.
Industrial plants have long used digital data to monitor and control their production facilities. Networks in factories, data centers, and commercial buildings push the edges of their networks ever closer to the physical world. Sensors convert temperature, pressure, proximity, and light into digital information that systems use to control physical actions for valves, fans, power supplies, indicators, and so on.
In automation’s early days, systems used specialized buses for communication, requiring gateways to translate protocols from one hardware system to another. Today, Ethernet connects many of those systems, but that often requires switches to manage transmissions and eliminate data collisions. Those switches increase costs. Ethernet’s utility comes from using one software stack and one frame format across different hardware physical layers.
Process-control devices typically need small amounts of data. The cables need to be simple and easy to install. 10BASE-T1S serves these applications and brings Ethernet to simple devices. Figure 1 shows this trend.
10BASE-T1S technology is based on the simple mechanisms first used when Ethernet became an IEEE standard in 1980 but utilizes all available bandwidth more effectively. The 10BASE-T1S specifications require a reach of at least 25 m, but practical implementations far exceed that minimum requirement. Microchip has demonstrated 50 nodes connected with 100 m of cable.
At first, Ethernet used a single coaxial cable onto which multiple devices connected directly. The switches in wide use today were developed later to eliminate the shortcomings caused by the multidrop nature of the original scheme. Unfortunately, they introduced complexity and cost and resulted in the requirement of single point-to-point connections between a device and a switch.
The original Ethernet worked by various devices sensing the line they were connected to and then trying to transmit data. If only one device started transmitting, it could send a whole packet of information. If multiple devices tried to transmit at the same time, there would be a collision on the line that all devices would sense. The devices would then shut off and try again after a random amount of time. This technology was called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Its major shortcoming was that as more devices were connected to the single-wire backbone, more collisions would occur. That resulted in an increasing amount of time wasted backing off and trying again. The effective bandwidth of the link became very limited.
10BASE-T1S Ethernet solves this problem by introducing an arbitration mechanism called Physical Layer Collision Avoidance (PLCA). PLCA is designed for half-duplex, multidrop networks such as 10BASE-T1S, and it eliminates the problems with CSMA/CD in multidrop mixing segments.
With PLCA, the transmission cycle begins with a beacon sent by a coordinator node (Node 0) that the network nodes use to synchronize. After the beacon is sent, the transmit opportunity passes to Node 1. If that node has no data to send, it yields its opportunity to Node 2, and so on, with the process continuing until each node has been offered at least one transmit opportunity. A new cycle is then initiated by the coordinator node, which sends another beacon.
To prevent a node from blocking the bus, a jabber function interrupts a node’s transmission if it exceeds its allotted time, allowing the next node to transmit. The result is that there is no impact on data throughput and no data collisions on the bus. CSMA/CD can, however, exhibit random latencies caused by data collisions. PLCA provides guaranteed maximum latency and other characteristics that overcome these limitations. Figure 2 illustrates how PLCA works.
After the data gets recovered from the wire that carried them, they are given to higher software layers in a standard Ethernet packet format. This format has a destination address, a source address, some administration bits, and a payload. The format doesn’t change with changes in the physical layer. That means the software layer remains constant even as network speeds change when more and more data is aggregated for processing by a computer system. Figure 3 shows the overall concept.
Instead of having various field buses and protocols at the endpoints of a network, Ethernet mechanisms can attach to these devices. They can all be addressed using well-understood Ethernet protocols such as security to prevent intrusion or snooping of the data, or worse, interference with the physical systems using the data. Ethernet is used in very high security applications such as banking because of its well-developed cyber resilience. Other dedicated communication technologies may have little or no cybersecurity features. They would have to be developed and then maintained. The logistics for provisioning these features would also have to be put in place. These logistics can be more complex than the design and manufacture of a hardware product. Controlled-access facilities are needed, and breaches in the chain of trust can happen anywhere in the supply chain.
Using standardized technology such as Ethernet also simplifies the development of systems that are functionally safe. Functional safety means that when something in a system fails, the system can react in a predictable manner to safely avoid causing more problems. Different industries have different standards. For example, the automotive industry has ISO26262. Industrial applications use IEC61508. Medical, consumer, and other applications have their own standards. However, they are all similar. Functional Safety applies to complete systems, but system designers need to make sure the components they use are functional safety-ready to certify the complete system.
Semiconductor components, for example, need functional safety manuals that analyze and diagnose the effects of failure modes. This is known as Failure Modes Effects and Diagnostic Analysis (FMEDA) and is a method to determine causes of failure and their Impact on the system. It is applied in the early phases of the system development to detect and correct any weaknesses.
10BASE-T1S Ethernet connects sensors, networks, and equipment that require interoperability and security. Data can reside in nodes at the network edge and can enable new smart predictive services, asset tracking, and more informed management decisions.
The network technology reduces costs through simpler components, software design, and wiring because it eliminates costly gateways. The number of switch ports used is reduced as multiple devices attached to a single bus line over single-pair cabling.
Furthermore, 10BASE-T1S reduces risk by using unified interfaces and well-established security mechanisms. It complements legacy installations at the edge of IIoT networks, enabling unified design, software development, testing, and maintenance at all network levels. Simpler architectures with enhanced security reduce risk for designers and enable functionally safe systems.