Reversing course – single-pair Ethernet cabling is the future

For more than 25 years structured cabling systems for voice and data applications have been standardized as 4-pair, balanced UTP, ScTP or Sc/FTP cable that now supports up to 40 Gb/s on 30 meters of category 8. The driving force has been requirements for ever more bandwidth to meet a variety of customer needs.

Suddenly, interest in building automation, “smart” systems and the “Internet of Things” (IoT) is changing the scope of the next generation of cabling systems. Sensors for lighting, HVAC, occupancy, access control and other smart systems require very little bandwidth compared to typical data applications. A sensor transmits just a few bytes of data when polled by a controller or triggered by an external event. 

The lack of bandwidth required for this wave of network enabled devices has led the IEEE to develop a new ethernet protocol that is designed to operate over a single pair of UTP/STP cable. 100Base-T1 and 1000Base-T1 have been available for a few years, though the intended application was to increase total bandwidth available through existing four-pair cables in primarily industrial installations.

A new ethernet option

In March 2018 the IEEE 802.3cg Single Pair ethernet Task Force met near Chicago to continue defining the electrical requirements for 10Base-T1 (the presumed name). The Task Force expects the standard to be approved in June 2019.

802.3cg objectives:

• 10Base-T1s – 15m link segment with up to 4 in-line connectors operating from 0.3-200MHz
• 10Base-T1L – 1,000m link segment with up to 10 in-line connectors operating from 0.1-20MHz.
• 25m mixing segment with 8 or more nodes (network devices)
• Support for 802.3bu 1-Pair Power over Data Lines in point-to-point and powered trunk applications.
• Support for both automotive and industrial installations

A big change from the installation requirements that LAN installers are familiar with is the number of connectors allowed in a link. The industrial environment is a key target market for 100Base-T1 and cables in those installations penetrate sealed enclosures and cable pathways to access the equipment protected within.

With electronics that are low cost, small and consume very little power, 10Base-T1 provides numerous advantages over existing single-pair ethernet options and is expected to be the preferred choice when cabling for sensors, actuators and other low data consumption devices in the near future.

As networks become increasingly ubiquitous, the applications for this new system will also extend far beyond just building cabling. Vehicles, for example, are also becoming “smart,” presenting future automotive applications.

Cable considerations

Cables supporting 10Base-T1 applications will be either very small and compact or large and rugged. In commercial installations, designers will need to deal with hundreds or thousands of devices and sensors. With so many cables to manage and route smaller is definitely better. Here we can expect to see 24 AWG conductors sheathed in thin jackets that reduce the cross-sectional size of the cable. At a maximum frequency of just 200MHz there are no alien crosstalk concerns, so cables can be bundled tighter without fear of signal interference. Cat 6A UTP cable is often constructed with thick jackets to increase the spacing between the conductors of cables in a bundle to reduce the effects of alien crosstalk at 500MHz.

For industrial installations where 1,000-meter links are allowed the considerations are quite different. The long links suffer increased insertion loss (attenuation) which is being solved in two ways. First is that the 1,000m link topology of 10Base-T1 will utilize a PHY (ethernet transceiver) that operates at 20MHz compared to 200MHz for the 15m PHY. Attenuation is proportional to length and frequency. Therefore, the longer cables will increase attenuation and limiting the frequency to 20MHz will reduce it. But this is not enough. Cabling conductors for 1,000m link segments can be up to 18AWG in diameter, further reducing attenuation.

The ANSI/TIA and ISO/IEC standards groups are now entering the picture to define cabling and connectors for 802.3cg/10Base-T1.

Single-pair cabling standards in development

Both the ANSI/TIA and ISO/IEC structured cabling standards groups are developing specifications for single-pair cabling in commercial and industrial installations with a range of supported data rates and distances.

TIA has started work on a new single-pair cabling standard that will be published as the TIA-568.5. The standard will define single-pair cabling to support 10 Mb/s to 100 meters, 100 Mb/s to 15 meters and 1 Gb/s to 15 and 40 meters. The cable will also support an alternative to PoE called Power over Data Line (PoDL – pronounced “poodle”). PoDL will provide up to 50 watts of power over a single 24 AWG pair.

The TIA is also starting work on an amendment to the TIA-1005 Industrial Cabling standard that will define cabling to support 10 Mb/s to 1,000 meters. To counteract the signal loss on such long cables, the conductor size will be increased to 18 AWG for this application.

ISO has similar works in progress. ISO 11801-9906 Ed. 1 and 11801-6 Ed.1/Amd.1 standards will cover the commercial cabling specifications for 10/100/1,000 Mb/s single-pair cabling, and the 11801-3 Ed.1/Amd.1 will define the cabling for industrial applications.

The end of the RJ45?

Both TIA and ISO are in the process of selecting a new single-pair connector that will be used to support these applications. The desire is to have a connector that has one-half to one-third the frontal area size of an RJ45, supports conductor sizes from 18-26 AWG, supports 1 amp of current and can be shielded or unshielded. Five manufacturers presented their first proposals at the most recent TIA TR-42.7 meeting in February 2018 and ISO SC25/WG3 meeting the following month.

The form factors range from an LC-style connector with metal contacts in place of the fiber optic ferrules, to single-pair variants of existing 4-pair “cat 7” connectors.  Both committees expect to select a connector through a series of votes by October 2018.

The companies presenting their proposed connectors stated that they will waive any intellectual property rights on the interface between the “plug” and “jack” portions, allowing any company to make connectors that are compatible with the selected design. Intellectual rights are expected to be preserved on the interface between the cable and the connector. This is where companies can innovate on the speed, integrity and simplicity of field-terminating the new connector.

Field testing specifications for single-pair cabling are still a long way off. We do know that the cable for the 1 Gb/s applications will be tested at up to 600MHz and most existing cable certifiers can test up to 1 GHz. What is known at this time are which tests will be required and what the pass/fail criterion will be, and that at frequencies above 400MHz, alien crosstalk becomes an issue. While the applications are expected to allow UTP cable, wise integrators may decide to opt for STP to eliminate any concerns over alien crosstalk.