Advancing Aircraft Connectivity With Single Pair Ethernet (SPE) Solutions

The Ethernet physical (PHY) layer has evolved, significantly, changing as it moved from offices to automobiles to aircraft. First published in 1983, the initial Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard—also known as 10BASE5—employed a PHY layer nicknamed “thicknet” for its hefty cable size that supported 10 Mbs transmission. Subsequent developments resulted in much thinner cable using two pairs of unshielded twisted wire in the 10BASE-T standard (published in 1990 as IEEE 802.3i).

The successors of 10BASE-T—100BASE-TX (100 Mbs), 1000BASE-T (1 Gbs), and 10GBASE-T (10 Gbs)—still contain four unshielded twisted wire pairs (UTP). Cable design evolved from Category 3 (a voice-grade UTP cable for telephone wiring and 10BASE-T Ethernet) to Category 6 (using four pairs of wire) and beyond. To fit automotive and aircraft needs, engineers have continued to shrink the Ethernet PHY layer.

In 2011, Broadcom Corporation released its BroadR-Reach standard allowing automotive manufacturers to standardize on an open, scalable 100 Mb/s Ethernet-based network protocol. The goal was to accommodate multiple electronic systems, such as advanced driverassistance systems (ADAS) for rear-view cameras and infotainment devices. A BroadR-Reach link offers two-way (full-duplex) operation at a 100 Mbs data rate over a single twisted pair of wires in cable lengths up to 15 m (49 ft). The two-wire design cuts connectivity costs and reduces cable weight nearly in half compared to four and eight wires in commercial-grade Ethernet cables.

The development of BroadR-Reach technology inspired the OPEN Alliance working group, a non-profit, open industry alliance of mainly automotive industry and technology providers, to define 100BASE-T1 as an “Automotive Ethernet” standard. (Broadcom is a promoting member of the OPEN Alliance that developed 100BASE-T1; TE is an adopting member.)

TE implemented 100BASE-T1 in a range of products developed specifically for Automotive Ethernet. The only differences between the BroadR-Reach and 100BASE-T1 standards are the types of PHY chips used at both ends of the link to transmit data. Published as IEEE 802.3bw in 2015, the 100BASE-T1 specification also supports 100 Mbs operation over a single balanced twisted pair cable.

The advantages of adapting Automotive Ethernet for aircraft are readily apparent. 100BASE-T1 standard defines a robust interconnection technology for rugged operating environments where temperature changes and vibration are encountered. It enables cost-efficient, in-vehicle network links and a distributed network architecture for mid-size data volumes and low latencies. It is also scalable up to the 1 Gbps performance of the 1000BASE-T1 specification, with future potential for 5 Gbps using alternative technologies.

As further evidence of robustness, the 100BASE-T1 standard is among several IEEE 802.3 SPE standards positioned as a platform for the Industrial Internet of Things (IIoT). Developments aim to enable Industry 4.0 connectivity by simultaneously delivering data (Ethernet) and remote power (Power-over-DataLine) over a two-wire cable.

Given the technological momentum, transferring the benefits of 100BASE-T1 from automobiles to aircraft was a “no brainer.” Accordingly, the recent ARINC 854 Cabin Equipment Network Bus specification developed by the Cabin Systems Subcommittee (CSS) references the 100BASE-T1 standard. CSS is organized under the Airlines Electronic Engineering Committee (AEEC)—itself operating under ARINC Industry Activities (ARINC IA), a program of SAE Industry Technologies Consortia (SAE ITC).

As a member of the CSS, TE developed a family of 100BASE-T1 products to meet ARINC 854 specifications. The result is the Mini-ETH interconnection system—an end-to-end, pointto-point, SPE solution with significant SWaP and performance advantages for networks in jet airliners and light aircraft.

The same TE expertise that developed MATEnet automotive interconnects—and a host of ARINC compliant interconnects for aircraft—is embodied in Mini-ETH technology. The result is an SPE platform that enables aircraft to fly smarter and lighter.

Mini-ETH interconnects are described under ARINC 854 specifications for the Cabin Equipment Network Bus. Compatible connectors and cables are described under ARINC Part Two and Part Three specifications, respectively.

A Mini-ETH interconnection solution reduces SWaP in next-gen aircraft network architectures without compromising signal integrity or network reliability. It provides electrical-wiringinterconnect-systems (EWIS) compliance along with significant SWaP, performance, and implementation advantages.

How much could a Mini-ETH interconnection solution contribute to aircraft weight reduction? Let’s look at the earlier example about wiring weight and focus on the Ethernet portion of wiring in a widebody commercial jet. If a Mini-ETH cable/connector solution reduces Ethernet wiring weight by 50 percent, that would reduce the load by 50 kg (110 lbs). If that much weight was eliminated, then annual fuel costs would be cut by $3,185 per aircraft⁷.In the future, if avionics design moves to a distributed and modular approach as is currently being discussed, a Mini-ETH interconnection solution will also support and enable savings for those developments.

The following advantages provided by MiniETH technology apply to present-day cabinnetwork design:

• Connector Weight and Performance: The design of Mini-ETH connectors is based on the success of TE’s DEUTSCH 369 series connectors, a family of EWIS-compliant rectangular connectors that provide a robust solution in a small envelope. The 369 series connector design was itself based on TE’s DEUTSCH DMC-M series connectors, the classic modular cabin and avionics design used in aerospace applications for nearly three decades. In addition to compactness, the 369 series connector design also provides internal latching and an ergonomic push-button feature that reduces installation time and damage to both the connector and aircraft during installation. The design also offers additional security features that provide extra layers of protection to aircraft systems. Mini-ETH connectors offer as much as 41 percent weight savings compared to typical D-sub connectors. This reduction can eliminate up to 20 kg (44 lbs) or more per plane depending on the configuration and requirements of the network and other aircraft applications. 
• Cable Weight and Size:  Compared to 4-wire quadraxial cable commonly used for 100 Mbs Ethernet or octal cable with eight 24 AWG wire used in common Category 5e and 6a cable, two-wire Mini-ETH cable is up to 73 percent lighter (Figure 1). The smaller dimensions of Mini-ETH cables with 26 AWG wire improve space utilization. For example, switching from a quadraxial cable with four 24 AWG wires to a Mini-ETH cable with two 26 AWG wires shrinks the cable’s diameter by approximately 15 percent. The jacket construction of Mini-ETH cables is based on TE’s long experience with Raychem precision extruded high-temperature foamed dielectrics. Jacket materials are low smoke, meet the flammability requirements of FAR Part 25, and the toxicity requirements imposed by major aircraft manufacturers. Mini-ETH cabling is described under ARINC 800 Part 3 Specification of Cables. Anticipating further development of ARINC standards, Mini-ETH cables are also provisioned for future operation up to 1,000 Mbs. 
• Link Length: Mini-ETH links are certified for 100 Mbs operation at 15 m (49 ft) lengths. Future provisions will enable 40 m (131 ft) lengths and speeds up to 1,000 Mbs. 
• Robust Contacts and Lightweight Shells: Mini-ETH connectors employ standard Mil-Spec AS39029 contacts—a high-performance design suitable for harsh environments. These miniaturized contacts are particularly robust against vibration. The connector shell is constructed from rugged materials with strength similar to steel but 40 percent lighter. The combination of composite materials and machined contacts allows for operation in temperatures between -55 °C (131 °F) and up to 175 °C (347 °F)—suitable for aircraft cabin environments.