Figure 1: The Ethernet transmission methods Fast Ethernet, Gibabit Ethernet and Single Pair Ethernet.

© Harting

Generations of network technicians, planners, installers and users have learned that cabling with two wire pairs is required for Fast Ethernet (10/100 Mbit/s) and all four wire pairs for Gigabit Ethernet. With the new Single Pair Ethernet (SPE), a technology is now entering the market that can also transmit these TCP/IP-based data streams via just one wire pair.

How it all began

The starting point for the development of SPE is the BroadR-Reach standard, which was developed by the Broadcom Corporation. After the automotive industry identified this new TCP/IP-based transmission method in its search for a successor to the CAN bus, the first SPE standard was published by IEEE 802.3 as the 100BASE-T1 standard in IEEE 802.3bw-2015 Clause 96.

However, piloted or semi-autonomous driving requires even higher data rates and so the gigabit version followed quite quickly after the first SPE standard for 100 Mbit/s.

The Ethernet technology already available today in accordance with IEEE 802.3bp 1000BASE-T1 delivers 1 Gbit/s transmission speed over just one pair of copper wires. The IEEE is currently working on a further standard for even higher data rates of up to 10 Gbit/s (IEEE 802.3ch), which is required for high-resolution sensors and video transmissions. A standard for only 10 Mbit/s (IEEE 802.3cg) is also in the development phase. This standard is also particularly relevant for many areas of industry, as it allows transmission distances of up to 1000 m and can therefore replace almost all fieldbuses.

Figure 3: The range and transmission speed for the future possible IEEE 802.3 SPE standards - Extended Reach.

© Harting

Since March 2019, there has also been another working group that deals with transmission rates above 10 Gbit/s. The target here is 25 Gbit/s and 50 Gbit/s. These high data rates are the basic technology for autonomous driving and new zonal computer architectures in vehicles. As with multi-pair cabling, there is also a new standard for remote power supply for SPE, similar to Power over Ethernet (PoE), called PoDL = Power over Data Line (IEEE 802.3bu). This means that SPE technology has already achieved the same performance as today's predominant 'multi-pair Ethernet' (MPE) within a very short period of time. The only limitation is the currently shorter range for 100 Mbit/s and Gigabit SPE (15 m and 40 m respectively), which results from the requirements of the main target group in the automotive industry.

However, the experts assume that longer transmission lengths can also be achieved here. Figure 3 shows which extended transmission lengths are technically possible. However, in order for these extensions to the SPE standards in IEEE 802.3 to be tackled and for the semiconductor industry in particular to invest in the development of these new chipsets, the new applications and market potential suitable for this need to be defined. This requires open cooperation between all interested parties for the extended SPE ranges. The first presentations at IEEE 802.3 have already been published and have been well received.

Overview of the standards committees

The central role in standardization is played by ISO/IEC JTC 1/SC 25/WG 3. This is where the cabling standards according to ISO/IEC 11801 are created and maintained based on the IEEE 802.3 standards.

To this end, there is a close exchange and intensive cooperation with IEEE 802.3 and the committees for cabling components. Four standards projects are in progress within the IEC SC46C working group for the standardization of data cables in bulk.

The standardization of SPE connection technology

Figure 4: Overview of the relevant standards committees around ISO/IEC JTC 1/SC 25/WG 3

© Prof. Dr. Oehler

The first SPE connector draft standard was submitted by Harting to SC48B back in 2016 and published as IEC 61076-3-125 up to the CD document. CommScope submitted another SPE connector face for standardization in 2017. As a result, the decision was made to create the IEC 63171 series of standards for all SPE connectors. Accordingly, the PT63171 project team was set up at SC48B and tasked with creating this new series of standards. The standards already in progress at this time will be completed as self-contained documents and later integrated into this new series of standards as part of revisions.

The following standards projects are currently in progress:

• IEC 63171 - basic standard with all necessary specifications and test sequences (CD available)
• IEC 63171-1 - SPE connectors from CommScope based on the LC latch for M1I1C1E1 applications (CDV approved, FDIS in preparation and final publication in 2020)
• IEC 63171-2 - SPE connectors from Reichle & De-Massari for M1I1C1E1 applications (CD available)
• IEC 63171-3 - SPE connectors from Siemon based on a pair of the well-known Tera connector for M1I1C1E1 applications (withdrawn)
• IEC 63171-4 - SPE connector from BKS for M1I1C1E1 applications (CD available)
• IEC 63171-5 - SPE connectors from Phoenix Contact based on the IEC 63171-2 mating face for M2I2C2E2 and M3I3C3E3 applications (CD available)
• IEC 63171-6 (previously IEC 61076-3-125) - SPE connectors from Harting and TE Connectivity for M2I2C2E2 and M3I3C3E3 applications (CDV approved, FDIS in preparation and final publication 2020)

Comparison of MPE and SPE

© Harting

Even if twisted wire pairs are required for existing 4-pair data cabling as well as for SPE, the requirements for the cabling and connection technology are quite different, especially with regard to the transmission length with the currently available SPE transmission standards and the RF requirements, which is particularly evident in the required bandwidth(see table).

Migration of MPE from SPE

High data rates via one wire pair - so why not combine four SPE routes in an existing 8-wire infrastructure? This idea of using quasi 4-pair cabling for SPE by means of 'cable sharing' is almost a logical one. And indeed: in special cases, this is certainly possible, but technically and economically not really sensible. On the one hand, SPE cabling requires higher bandwidths compared to MPE, especially in terms of crosstalk, and compared to MPE with 100 m transmission lengths, SPE only has shorter transmission lengths of 40 m at 1000BASE-T1 for shielded cables. In this migration scenario, the user must therefore check the installed cabling section by section for SPE. The economic viability of such utilization concepts is therefore also questionable. For example, in order to qualify an installed Cat. 6A cabling for 1000BASE-T1, the transmission length must not exceed 40 m and the corresponding RF parameters must be qualified up to 600 MHz. Even if everything fits perfectly, only 4 x 1 Gbit/s can be transmitted with SPE, although these Cat. 6A cabling links can now be used with 10 Gbit/s MPE.

The connection technology for SPE

The design of the SPE connectors in accordance with IEC 63171-6 was based on the specifications of the relevant IEE 802.3 standards and other market requirements. The following electrical parameters are precisely defined: The rated voltage, the insulation voltage, the rated current and the RF transmission parameters.

The aim of the design for the SPE interface was to take into account the electrical parameters mentioned with sufficient reserve for future higher bandwidths and the requirements regarding remote power supply (PoDL) as well as the selection of housing designs already accepted and widely used on the market. Great importance was also attached to a balanced relationship between the market trend towards miniaturized interfaces and high robustness on the one hand and good manageability and optimum design of the connection area to suit the wire and cable diameters to be used on the other.