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Industrial Ethernet Book Issue 103 / 13
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Single-pair balanced Ethernet transmission for IoT applications

The mega trends in communication technologies, and their impact on associated cabling philosophies, are being influenced and driven in no small way by the emergence of the IoT, Industry 4.0 (I4.0), cloud computing and smart technologies -- ultimately leading to new connector and cabling solutions.

ETHERNET IS THE LEADING NETWORK PROTOCOL in LAN applications and is increasingly gaining ground in new areas. At the start of the Ethernet "era" in the early 1980s, coaxial cabling dominated (thick Ethernet - yellow cable, thin or cheap Ethernet), from the 1990s the focus shifted to cabling solutions based on symmetric cabling (twisted pair) and fibre optics.

Initially, twisted pair cabling relied on two-pair cables. This utilized a wire pair as a transmission and reception line (100Base-TX). This principle, limited to a transfer rate of 100Mbit/s, still represents the main transfer principle in industry and automation systems technology today and is often achieved using star-quad cable designs.

In order to achieve higher transfer rates of 1 Gbit/s and 10 Gbit/s, a transfer technique was selected, which requires four symmetric pairs in connection with 8-pole connectors.

Now, let′s discuss the transfer of Ethernet with a single strand pair, in other words, a solution that quite obviously runs contrary to the technical development of Ethernet and its associated cabling.

This article deals with the background of these developments, with the technical details and the normative activities as well as the applications for single-pair Ethernet. We consider the performance of new chipsets and discuss the classification of single-pair cabling with respect to existing two and four-pair versions as well as future n-pair cabling.

Overview of co-action of standardization bodies to strengthen cabling guidelines and technology.

Mega trends in communications

The development of new communication technologies and their associated cabling philosophies, are influenced and driven in no small way by the current ICT mega trends, such as IoT, Industry 4.0 (I4.0), cloud computing and smart technologies.

This leads to new demand profiles regarding communications technology and the network infrastructure behind it, based on cables and connectors.

Demands include: high availability, short access times including distributed data and fast transport of this data from A to B. Secure transfer of large datasets in different application areas up to determinism (real-time transfer and, for example, guaranteed data transfer within a defined timeframe).

At the same time, data transfer should remain cost-efficient. For devices, cables and connecting hardware this means they must achieve higher performance, be smaller and stronger as well as possess a high degree of modularity and compatibility (exchangeability and plug-compatibility). These demands can only be fulfilled through innovation, i.e., new development of products with consistent international standardization.

Another trend in network technology and cabling is the increasing use of Ethernet protocols in new application areas. This includes many automation protocols and, increasingly, sensor/actuator applications. Numerous traffic and transport platforms such as rail, tram, bus, ship and aircraft, are fitting their fleets with Ethernet.

While Ethernet has been successfully employed, in particularly for passenger information systems and for WLAN services for many years now in the methods of transport mentioned above, it remained more or less unused in the private car/truck market for a long time. The automobile industry has now recognized the advantages of Ethernet and started an initiative to develop Ethernet protocols for short-distance transmission routes in vehicles. The solution is called: single-pair Ethernet for transmission distances up to 15 m or 40 m.

This Ethernet technology has since been published in the standards (Gigabit Ethernet over single-pair balanced copper cabling) and 802.3bw 100Base-T1 (100 Mbit over single-pair balanced copper cabling).

To achieve simultaneous transmission of data and energy, PoDL was also defined under IEEE 802.3bu (Power over Data Lines = a principle suitable for single-pair transmission for remote powering).

On the basis of these standards chipsets, devices, cables and connecting hardware are now being designed, developed and produced for integration in private cars.

Cabling for private cars focuses on a transmission distance of up to 15 m and, in general, needs to be produced in unshielded form due to weight and spatial constraints.

Larger vehicles such as trucks and buses require longer transmission distances of up to 40 m and, due to the associated higher EMC requirements, need to be fully shielded.

In fact, the latter single-pair shielded transmission distance also has other "non-automotive" application groups and has piqued the interest of manufacturers. This is because, in general, shielded single-pair Ethernet cabling offers all of the features required to fulfill the mega trend described above. They are fast, space-saving, cheap and simple to implement.

For this reason, industry, whose automation profile is now largely based on 1000 Mbit Ethernet (100BASE-TX), is showing increasing interest in solutions with single-pair Ethernet. In fact, within building automation developers are actively considering the different possibilities provided by integrating single-pair Ethernet within the hierarchy and structure of contemporary building cabling. Then there are also numerous other application areas, which present attractive opportunities for the development of single-pair Ethernet.

The interest in single-pair Ethernet also reflects a general trend in standardised network cabling, and diversification of structured cabling for specific application areas.

ISO/IEC JTC1 SC25 WG3 currently includes activities or projects which deal with the realisation and implementation of the technical results of IEEE 802.3 within structured building cabling.

Single-pair transmission channels

What do the standards activities look like for single-pair Ethernet communication?

First of all, standardisation is a continuous, dynamic process, which develops and publishes new standards, revokes existing papers or updates and launches new standards projects. Therefore, this white paper is just intended to be a snap shot of the state of standardisation.

Standards activities in IEEE802.3 define the Ethernet transmission protocol and define the minimal requirements for link segments (link segments are not identical but similar to the transmission channel of cabling). ISO/IEC JTC1 SC25 WG3 defines the required cabling and in doing so relies on the component standards for cables and connectors, which are given in the IEC standards groups.

As already mentioned, the following IEEE 802.3 standards have already been published: IEEE 802.3bp 1000 BASE-T1 "Physical Layer Specifications and Management Parameters for 1 Gb/s Operation over a single Twisted Pair Copper Cable".

In this, single-pair Ethernet transmission via a 15 m UTP channel (Type A, unshielded) and a 40 m STP channel (Type B, shielded) is defined. Both channels are specified for a bandwidth of 600 MHz, may contain up to four connections and guarantee a transmission capacity of 1 Gbit/s.

IEEE 802.3bu "Physical Layer and Management Parameters for Power over Data Lines (PoDL) of Single Balanced Twisted-Pair Ethernet"

Analogously to PoE (Power over Ethernet), this also specifies the parallel provision of energy up to 50 W via single-pair Ethernet channels.

ISO/IEC JTC1 SC25 WG3 currently includes activities or projects which deal with the realisation and implementation of the technical results of IEEE 802.3 within structured building cabling.

Therefore, a technical report is being prepared under the title "TR ISO/IEC 11801-99xy, One Pair Channels up to 600MHz", which describes shielded single-pair transmission channels. The target applications are the so-called "non-automotive" segments or Industry 4.0, IoT and smart lighting in the style of IEEE 802.3bp.

These transmission channels allow bidirectional transfer of 1 Gbit/s by using a balanced pair up to 40 m with simultaneous energy supply of end devices.

The transmission channels typically consist of a permanent link 36 m in length which incorporates up to four connections and two 2 m long patch cords. This document is scheduled for completion in 2018.

As part of the restructuring and updating of ISO/IEC 11801 standards series (as 3rd edition) it will also be determined in which application-specific parts an addition with single-pair shielded balanced cabling is technically and economically feasible.

Initial consideration seems to suggest this is so for ISO/IEC 11801-3 (industrial applications) and ISO/IEC 11801-6 (building automation). Publication is expected in 2018.

At the same time, the cabling specifications allow the requirements for the components, cables and connectors to be derived. This is performed for cables in the IEC SC46C standards committee and for connectors in the IEC SC48B standards committee (SC = subcommittee).

New designs offer the ability to transmit Ethernet according to 1000Base T1 over a single-pair cabling channel.

Cables for 1 Gbs over one pair

These international standards titles describe cables that are suitable for transferring 1 Gbit/s over a balanced pair. Application areas include office, home and industry.

The use of 4-pair data cables should also be possible, which are capable of operating 4 single-pair transmission channels. This feature is also known as so-called "cable sharing". The transmission parameters should be defined for a frequency of up to 600 MHz. This international standard should be published by 2018/2019.

IEC 61076-3-125: "Connectors for electronic equipment - Product requirements - Detail specification for 2-way, free and fixed connectors for data transmission up to 600MHz with current carrying capacity Following the application areas and performance of the single-pair cables, the two-pole connectors are being standardised up to min. 600 MHz. Standardisation of the connector means that the mated interface will be fully defined. Definition of the interface ensures plug compatibility and guarantees that products from different manufacturers can be used. It is expected that various designs of single-pair connectors will then be available in safety class IP20 to IP65/67. The publication of this standard is also scheduled for 2018/2019.

Cabling design standards on European and international level scheduled for 2018/19.

Balanced transmission channels

he theoretical basis for designing a 40 m channel with single-pair cabling has already been worked out. This means that the interested manufacturers of electronics and cabling have all the necessary information on the development and design of chipsets, cables and connectors at their disposal.

The first chipsets are already available on the market. However, a range of new products, which offer optimal support for the individual applications, are still expected. Accordingly, devices fitted with "single-pair Ethernet" are expected within two to three years. There are basically two ways to transmit Ethernet according to 1000Base T1 over a single-pair cabling channel.

On the one hand, this protocol can be transferred using existing four-pair cabling according to category 7 / transmission class F (specified up to 600 MHz) or according to category 7A / transmission class FA (specified up to 1000 MHz) according to the relevant qualification and with consideration of the length restriction of 40 m. This opens up the option of "cable sharing", which allows several single-pair Ethernet services to be transferred using a four-pair cable.

On the other hand, and this is generally the case, new single-pair cable and connector products are created to serve new single-pair cabling structures on the basis of single-pair Ethernet. Important points for the design of the cabling components include:

  • Impedance 100 Ω, bandwidth 600 MHz and the associated fixed parameters, such as insertion loss, return loss, alien cross-talk etc.
  • Complete shielding to ensure transmission quality under extreme EMC conditions
  • Single-pair cable with the smallest possible outer diameter (space and weight savings) for fixed and flexible installation
  • Two-pole connectors in the smallest possible design form for use in IP20 and IP65/67 environments - mutually compatible plug interfaces.

IP20 and IP67 T1 connector design studies for SPE.

Conclusion and outlook

The increasing network requirements driven by the demands of I4.0 and IoT rely on innovative and application-specific solutions. Single-pair Ethernet offers a solution for cable-based communications infrastructure. Particularly for application areas in industry and building management, this represents a smart addition to the communications landscape, which combine Gigabit Ethernet performance, transmission reliability, optimal handling and remote powering as well as space and weight savings.

The normative basics have already been defined in IEEE 802.3 Standards for applications within the automotive and non-automotive sectors. For the respective non-automotive applications, the planning orientation incorporated within the international standards of ISO/IEC and IEC is used. The respective standardisation projects have been started.

The compact design of the device connectivity and the Ethernet compatibility according to IEEE802.3 offer device development, e.g. within automation as well as sensor and actuator production, a networking concept that represents a simple change from bus- to Ethernet technology. This allows Ethernet to penetrate further into the field level, reduces enormously times for parameterisation, initialisation and programming and expands the range of functions of devices.

Single-pair cabling saves space, installation time and costs. At the same time new applications are tapped, which were previously reserved for cable-based infrastructure. After the Internet and Ethernet have connected people, computers and machines both in terms of space and time, this is now also happening with objects and things. The backbone of this new technology is provided by, amongst others, single-pair balanced copper cabling. With this it becomes clear that the connection between single-pair Ethernet technology and is more prevalent within the mega trends of IoT and I4.0 than in cloud computing and big data.

Single-pair Ethernet represents an important technological progression, but is still only an addition to existing Ethernet technologies that use multi-pair copper cables or fibre optics and will not replace them.

Final thoughts

Single-pair Ethernet cabling opens up new application areas, such as in industry and represents a useful addition to existing four-pair cabling systems. Therefore, single-pair Ethernet particularly supports trends such as IoT and I4.0. In particular, single-pair Ethernet can provide an important technological basis to the further development of multi-pair cabling within the development of cloud computing.

Matthias Fritsche, Product Manager Device at HARTING, Rainer Schmidt, Business Development Manager for HARTING and Yvan Engels, Strategic Market Development / Standardization BU Datacom, LEONI Kerpen GmbH.

Source: Industrial Ethernet Book Issue 103 / 13
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