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Single Pair Ethernet (SPE) and Industrial IoT

Martin Keenan | 05/03/2022

Although Single Pair Ethernet (SPE) has been around for some time, the road to adoption has not been entirely smooth despite the potential benefits of the technology.


SPE is a growing force in networking circles for various practical and technical reasons and has particularly relevant attributes for IIoT implementations. At the heart of the value proposition of SPE is that it delivers considerably better performance than existing deployments of 4-pair cabling and traditional IEEE 802.3 Ethernet standards.


SPE operates over a single twisted pair and can deliver up to 10mbps speeds at distances of up to 1km, a significant upgrade over the 100-meter maximum possible under 10/100/1000BASE-T Ethernet standards. This is via the IEEE 802.3cg Ethernet standard, also known as 10BASE-T1L. The initial market for the BASE-T1 standard was initially the automotive market, but the more recent 802.3cg made the standard applicable to smart building and IIoT markets.



Power and Distance with SPE


A 1km operating distance makes SPE ideal for IIoT implementations over larger areas, needing far less convoluted networking equipment to achieve coverage of a large factory or complete industrial site. SPE has another trick, though, as it uses single-pair powering technologies, not dissimilar to PoE, to deliver power to devices. While only relatively low wattage can be delivered via PoDL (power over data line), around 50W over short distances, and incrementally less over the full 1km, it is still beneficial for IIoT devices designed to operate within low power footprints.



Lighter, Thinner, Cheaper


The benefits of CAT6 cabling are also significant. A new IIoT project might anticipate installing a considerable amount of new cable. Still, because SPE only requires a quarter of the overall physical cable (one pair instead of four-pair), costs can be decreased significantly. The SPE cable is also a quarter of the weight and diameter, enabling better use of existing conduit space and reducing the weight support requirements. Finally, SPE can often operate over repurposed existing 4-pair copper cabling, further lowering installation costs.



Network Topography Standardization


A key reason for industry interest in SPE is that it offers the opportunity to standardize the network protocol across the entire network. Previously, ethernet has been the de facto standard for the vast majority of enterprise networks, but not at the so-called ‘field’ level, where various BUS systems have been commonplace.


Traditionally, one reason for this is that BUS systems only require twin-pair cables instead of the older ethernet 4-pair, resulting in a major cost saving when considering thousands of sensors and actuators across an industrial installation. That standardization means the current array of gateways needed to bridge the ethernet-BUS gap will no longer be required, much to the relief of those maintaining this often-bespoke legacy software.



Standardization: Security Risk?


Standardization does raise a new consideration for future SPE IIoT deployments––security. Those legacy industrial automation systems running serial bus technologies effectively isolate the field-level devices from the rest of the network. Switching to SPE means that field-level devices will have to be subject to the same scrutiny as any other connected enterprise hardware, inevitably requiring occasional OTA (over the air) bug fixes, protocol updates, and the like.


Fortunately, with the bandwidth and power delivery of SPE, newer SPE-compliant devices shouldn’t be technically restricted by the two traditional IIoT OTA hurdles. Still, any legacy equipment might not be so tractable. Pure ethernet also has the benefit of avoiding many of the security challenges of wireless alternatives, although mainly from a local interception standpoint.



Disconnected Connector Standards


There are other barriers to SPE adoption, too, in the familiar shape of standardization. Although the SPE and IEEE 802.3cg Ethernet standards are well established, the problem arises at the connector end, with two differing connector implementations already on the market. Both are standards-based. The SPE Industrial Partner Network promotes the T1 interface defined in IEC 63171-6, while the SPE System Alliance is currently backing IEC 63171-2. What the future holds is still very much up in the air – will one connector become accepted by the whole industry, or will the two continue to co-exist, perhaps in specific vertical niches, are questions that will be answered over the coming months.


The SPE Industrial Partner Network members include Harting, TE Connectivity, Hirose, Amphenol ICC, and Molex. Simultaneously, the SPE System Alliance counts Phoenix Contact, Weidmüller, and SICK among its backers. The two groups have varying focus, too, with the Network zeroing in on industrial applications and the Alliance taking a broader view across various sectors, including automotive and smart buildings.



Bright Future for SPE


Clearly, SPE has much to offer IIoT deployments, as well as the automotive and avionics sectors. While connector confusion may inhibit adoption in the short term, the longer-term future looks bright. Looking forward to the requirements of increasingly connected manufacturing and infrastructure supply chains, it’s clear that a unified ethernet network providing robust connectivity and power to IIoT devices will be a highly potent concept in IIoT deployments for some time to come.


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