With larger bandwidth, lower latency, and lighter weight, this is the Übersystem; it’s the OPEN (One-Pair Ether-Net) Alliance Ethernet for automotive, aerospace and more! On June 12th, 2018 I talked to Stephen Jackson (Steve) of Keysight’s Ixia Solutions Group about why Automotive Ethernet is the best solution for Advanced Driver Assistance Systems, ADAS, power train, body electronics, and Infotainment – and its evolution to be the best with the help of TSN, Time-Sensitive Networking! (Steve was involved with the original IEEE power over Ethernet standard 802.3af; for Automotive Ethernet the limit is about 5 Watts, IEEE 801.3bu.) [1].
Automotive Ethernet is the IEEE standard 802.3bw, often called BroadR-Reach or BRR based in part on its Broadcom roots in the OPEN Alliance Special Interest Group. BRR uses a SINGLE unshielded twisted wire pair instead of the FOUR twisted pairs found in most other Ethernet versions. If all the signal wiring in a vehicle went with the BRR standard, it would save an estimated 80% of the wiring harness weight [1] and a large portion of the labor [2]. This standard allows for multiple vendors to make this ubiquitous across many platforms: security systems, vehicles, industrial equipment, drones, even airplanes. BRR has a limited length, 10m compared to typically 100m for traditional wired Ethernet, but Steve said that is not a problem because a typical vehicle fits within these distances.
Steve said although BRR is applicable for many vehicle systems, the first area for it to be popularly accepted in is infotainment. Legacy technologies are in widespread use for the areas of vehicle control that are mission-critical, even though Automotive Ethernet can ultimately work better and faster! Due to the cost benefits, Automotive Ethernet has now started to move into areas that had been dominated by CAN, LIN, FlexRay and Most. [1]
CAN is an example of a deterministic system. Like FedEx, you know when a message arrives in a deterministic system [1]. A deterministic system, given a certain input, always has a predictable output, i.e. there is a unique input-event, output-event pair [1,3]. With Ethernet standards that implement TSN (Time Sensitive Networking), Ethernet can be made deterministic. TSN is implemented in layer 2 of the OSI, Open Systems Interconnection, model (Figure 1) [4-6]. TSN is scalable, and can be used for almost any vehicle function [10]! But, there are still millions of lines of code in LIN, CAN, Flexray, Most and others [7]. Industry can’t change quickly because of the inertia of coding and the need for deployed systems to be fully vetted for scale production use [1]. Steve said the deterministic technology will whittle away the perceived advantage of the legacy automotive components. This has to happen over time because of the great inertia of the legacy technology in volume manufacturing. Economics will drive implementation of an Ethernet-enabled wiring harness with TSN, Time-Sensitive Networking. [1]
Figure 1. Open Systems Interconnection Model
Steve Jackson mentioned how TSN is the next evolution from AVB, Audio Visual Bridging, which helps schedule information packets, implement lower latency and determinism in the automotive Ethernet. (The word time in this sense references the worst-case delay or latency, not the average [1,17,18]). Time is very important in a deterministic system. Steve told me that the IEEE AVB group had become the IEEE TSN group in 2012 [8], since AVB does not imply a time aware network. He guided me to some of the articles that Volker Goller of Analog Devices, the IEEE TSN group, the University of New Hampshire Interoperability Lab, Broadcom, and others wrote on TSN [9-18]. TSN is implemented in the second layer of the OSI (Figure 1), allowing scheduling of the data so there can be an absence of collisions and the data is received by the correct switch at the right time. There are a set of IEEE 802.1 sub-standards that can be used to implement TSN, but not all have to be implemented [1,12,16].
Data packets can be redundant so the information always arrives (IEEE 802.1CB). Seamless Redundancy insures that the same message is sent by two or more different paths [16-18]. When the second message arrives, the redundant message is discarded. By sending multiple messages, there are less frames that are lost due to congestion and device failures [9,15-18] (Figure 2).
Figure 2. 802.1CB Frame Replication and Elimination for Reliability
TSN allows for a Grand Master Clock and multiple grand master clocks IEEE 802.1AS (REV) a subset of IEEE 1588, Precision Time Protocol, PTP [18]. To select the best Grand Master clock, a Best Master Clock Algorithm is used. One of the ways components become a better value commodity is to reduce the cost of the clock, so having time that is constantly checked across the network is essential [9].
Bob Noseworthy of the University of New Hampshire Inter-Operability Laboratory when talking about the TSN said, “To achieve the absolute lowest possible latency, IEEE 802.1Qbv defines a Time Aware Shaper, which defines timed traffic gates which act as stop-lights on different priorities of traffic flowing through a switch. “[13]. Volker Goller said that the purpose of the Time Aware Shaper is to avoid traffic interference by dividing Ethernet traffic into separate classes. This makes sure that each traffic class has a set time that it uses the network [9]. Thus, the switches must know what class of traffic can use the network at a given time. Implementing Time Aware Shaper demands highly sophisticated algorithms such as the algorithms used in Siemen’s Profitnet [15].
TSN involves scheduling, this is a big part of its time sensitivity, it makes sure express frames are where they need to go before they have to arrive! When the car in front of you stops, the ADAS needs to stop your car, before you hit the stopped vehicle. To allow the stream of data frames to flow smoothly, cyclic queuing and forwarding keeps the frames moving (IEEE 802.1Qch) [17,18]. Each queue has an associated gate. The queue transmits frames according to a set timescale (IEEE 802.1Qbv) [17,18]. Interjecting express messages between preemptible frames is specified by (IEEE 802.1Qbu and 802.3br). The express fames can suspend a preemptible frame in the middle of its transmission as shown in Figure 3 (IEEE 802.3br) [17,18].
Figure 3. Express Frame Preempting Preemptable Frame IEEE 802.1br
TSN, Time Sensitive Networking has other possible implementations. Just look at all the IEEE 802.1 standards [16-18]. As Steve Jackson said, TSN enables Automotive Ethernet to be dynamic and deterministic. Since the messages always arrive in time sensitive manner, it is by definition reliable. It commands the needed economic benefits that automotive Ethernet may soon replace the entire wiring harness [1]. The conversion will be fun to watch!
The governing bodies for the Automotive Ethernet are the IEEE [19], the OPEN Alliance [20], the AVNU Alliance [21], and the University of New Hampshire Inter-Operability Laboratory [22]. The IEEE standards that pertain to the OPEN Alliance are free. Membership in the OPEN Alliance is gratis as of July 16, 2018. Membership in the AVNU Alliance is not gratis. The University of New Hampshire Interoperability Laboratory developed the basic tests for the Automotive Ethernet.
Figure 4. Governing Bodies for Automotive Ethernet
Experts say the Automotive Ethernet 100BASE-T1 is less susceptible to EMI than 10BASE-T and 100BASE-TX [23], but how can it be that an unshielded twisted two-wire pair does so well and is able to pass stringent testing? Texas Instruments Donovan Porter wrote, ‘By using the basic principles of superposition and specific encoding and scrambling schemes, 100BASE-T1 reduces electromagnetic interference (EMI), cabling weight, cost and footprint size compared to Ethernet standards 10BASE-T and 100Base- TX.’[23]. Basic test protocols for the Automotive Ethernet have been defined by the University of New Hampshire Interoperability Laboratory and Original Equipment Manufacturers (OEMs), to determine if components will meet the standards. The tests look at how signals can degrade and how injected noise affects the frames. Test manufacturers have developed test packages [24-27] for test protocols and have great decode programs for the Pulse Amplitude Modulation 3 – PAM 3- (Figure 5) signals on the Automotive Ethernet [24-27] to help trouble- shoot problems that come up in testing. The Automotive Ethernet uses PAM3 to reduce the bandwidth needed to operate over a twisted pair channel [28], and according to Broadcom, using PAM 3 reduces EMI allowing a more aggressive EMC filtering with lower cost, even over a low-quality transmission line [28].
Figure 5. Pulse Amplitude Modulation 3 (PAM 3) signals on the Automotive Ethernet
Our next article examines the tests used to stress test Automotive Ethernet and its protocols.
There are many people I need to thank for their help in writing this article! I am indebted to Stephen Jackson for spending his time to explain to me how amazing a deterministic Ethernet is to the automotive market. Thank you, Steve. Thank you, David Paul, of Keysight Technologies for making Stephen Jackson available for the interview. Special thanks to Jackie Mancini of Rhode and Schwartz for encouraging me to understand the scope of change the automotive Ethernet involves.
[1] Interview with Stephen Jackson, Solutions Architect Ixia Solutions Group, Keysight Technologies, June 12, 2018, Novi, Michigan.
[2] https://www.wired.com/2012/10/in-car-ethernet/ (Damon Lavrinc 10.16.12 01:00 pm) Retrieved July 1, 2018 9pm ET .
[3] https://en.wikipedia.org/wiki/Deterministic_system Retrieved July 1, 2018 9pm ET .
[4] https://www.cisco.com/c/dam/global/fi_fi/assets/docs/SMB_University_120307_Networking_Fundamentals.pdf Retrieved July 2, 2018 7:50pm ET.
[5] http://ru6.cti.gr/bouras-old/WP_Simoneau_OSIModel.pdf (Paul Simoneau 2006) Retrieved July 9, 2018, 4:15pm ET.
[6] https://www.computernetworkingnotes.com/ccna-study-guide/osi-seven-layers-model-explained-with-examples.html Retrieved July 9, 2018, 4:17pm ET.
[7] Comment by Ali Ranjbar, LHPES, June 12, 2018, Novi Michigan.
[8] http://www.ieee802.org/1/pages/avbridges.html (November 2012) Retrieved July 1, 2018 9pm ET.
[9] http://www.analog.com/media/en/Other/electronica/Time-Sensitive-Networking-for-Industrial-Applications-Volker-Goller.pdf (Volker Goller, Analog Devices, 2016) Retrieved July 1, 2018 9pm ET.
[10] http://www.electronicdesign.com/industrial-automation/what-s-difference-between-ethernet-and-time-sensitive-networking (Volker Goller May 21, 2018) Retrieved July 2, 2018 3pm ET.
[11] http://www.analog.com/ru/technical-articles/a76950-what-role-will-opc-ua-tsn-and-classic-industrial-ethernet-systems-play-in-the-future.html (Volker Goller, Analog Devices ) Retrieved July 2, 2018 3:07pm ET.
[12] https://www.electronicsweekly.com/news/embedded-world-video-interview-analog-devices-tsn-real-time-comms-2017-03/ (Volker Goller, Analog Devices, March 15, 2017) Retrieved July 2, 2018 3:11pm ET.
[13] https://www.networkworld.com/article/3189131/lan-wan/the-growing-importance-of-time-sensitive-networks.html (Bob Noseworthy, University of New Hampshire Inter-Operability Laboratory) Retrieved July 2, 2018 3:20pm ET.
[14] https://www.sensorsmag.com/components/how-emerging-technologies-are-driving-inside-next-gen-cars (Curtis Donahue, University of New Hampshire Inter-Operability Laboratory, May 31, 2018 12:00am) Retrieved July 2, 2018 3:29pm ET.
[15] https://www.iol.unh.edu/sites/default/files/knowledgebase/UNH-IOL_TSN-Overview.pdf (Bob Noseworthy, University of New Hampshire Inter-Operability Laboratory, November 24, 2015) Retrieved July 2, 2018 3:50pm ET.
[16] http://www.ieee802.org/1/pages/tsn.html Retrieved July 3, 2018 9:40pm ET.
[17] http://www.ieee802.org/1/files/public/docs2017/tsn-farkas-intro-0517-v01.pdf (Janos Farkas of Ericsson May 15, 2017) Retrieved July 3, 2018 9:50pm ET.
[18] https://drive.google.com/file/d/0B6Xurc4m_PVsZ1lzWWoxS0pTNVE/view (Michael Johas Teener of Broadcom for ISPCS 2015) Retrieved July 15, 2018 10:30pm ET.
[19] www.ieee.org Retrieved July 16, 2018 3:50pm ET.
[20] http://www.opensig.org/ Retrieved July 16, 2018 3:40pm ET.
[21] http://avnu.org/ Retrieved July 16, 2018 7:50pm ET.
[22] https://www.iol.unh.edu/ Retrieved July 16, 2018 8pm ET.
[23] http://www.ti.com/lit/wp/szzy009/szzy009.pdf (Donovan Porter, Systems Engineer ,Texas Instruments 2018) Retrieved July 25, 2018, 4:30pm ET.
[24] Rhode and Schwartz Seminar on Automotive Ethernet Testing presented by Dr. Ernst Flemming, Manager of Oscilloscopes and Alyssa Harder, Oscilloscope Sales Specialist, May 18th, 2018 Southfield, MI.
[25] Teledyne LeCroy Seminar on Automotive Ethernet Testing presented by Mike Hertz, Field Applications Engineer with Teledyne LeCroy May 23, 2018, Farmington Hills, MI.
[26] Keysight Technologies Tech Day & Open House, June 12th 2018, Novi, Michigan.
[27] Tektronix Webinar on Automotive Ethernet Testing presented by Darshan Mehta, Product Manager, Tektronix automotive segment with Tektronix Automotive Solutions group.
[28] http://ieee802.org/3/1TPCESG/public/BroadR_Reach_Automotive_Spec_V3.0.pdf Retrieved July 20, 2018, 10pm ET.
