Time-Sensitive Network (TSN) Experiment in Sensor-Based Integrated Environment for Autonomous Driving - MDPI

 
sensors
Article
Time-Sensitive Network (TSN) Experiment in
Sensor-Based Integrated Environment for
Autonomous Driving
Juho Lee      and Sungkwon Park *
 Both are with Department of Electronic and Computer Engineering, Hanyang University, Seoul 04763, Korea;
 ljh0122@hanyang.ac.kr
 * Correspondence: sp2996@hanyang.ac.kr; Tel.: +82-2-2294-0367
                                                                                                     
 Received: 2 January 2019; Accepted: 27 February 2019; Published: 5 March 2019                       

 Abstract: Recently, large amounts of data traffic from various sensors and image and navigation
 systems within vehicles are generated for autonomous driving. Broadband communication networks
 within vehicles have become necessary. New autonomous Ethernet networks are being considered
 as alternatives. The Ethernet-based in-vehicle network has been standardized in the IEEE 802.1
 time-sensitive network (TSN) group since 2006. The Ethernet TSN will be revised and integrated into
 a subsequent version of IEEE 802.1Q-2018 published in 2018 when various new TSN-related standards
 are being newly revised and published. A TSN integrated environment simulator is developed in this
 paper to implement the main functions of the TSN standards that are being developed. This effort
 would minimize the performance gaps that can occur when the functions of these standards operate in
 an integrated environment. As part of this purpose, we analyzed the simulator to verify that the traffic
 for autonomous driving satisfies the TSN transmission requirements in the in-vehicle network (IVN)
 and the preemption (which is one of the main TSN functions) and reduces the overall End-to-End
 delay. An optimal guard band size for the preemption was also found for autonomous vehicles in
 our work. Finally, an IVN model for autonomous vehicles was designed and the performance test
 was conducted by configuring the traffic to be used for various sensors and electronic control units
 (ECUs).

 Keywords: autonomous driving; vehicle sensors; time-sensitive network; in-vehicle network

1. Introduction
     As autonomous vehicles are emerging, technologies including next-generation vehicle
communication, vehicle to everything (V2X), and the advanced driving assistant system (ADAS),
are also advancing. An autonomous vehicle communicates with traffic infrastructures, such as a nearby
vehicle or RSU (roadside unit). The long-term evolution (LTE) and 5G communication technologies
can be used as external communication technologies for autonomous vehicles. Dedicated short-range
communication (DSRC) protocols are also used as external communication means for providing
intelligent transport system (ITS) services. But, in order to exchange data between various sensors,
processors, and ECUs (electronic control unit) in real time within a vehicle, in-vehicle networks
(IVNs) also need proper broadband communications. Traditional IVNs include controller area network
(CAN), local interconnect network (LIN), media-oriented systems transport (MOST), and FlexRay [1–4].
Recently, as traffic for autonomous driving increases, the application of Ethernet communication
technology to vehicles is underway. This standardization work for autonomous vehicles has been
going on since 2006 in the IEEE 802.1 TSN (time-sensitive network) [5]. The Ethernet TSN is still in
the process of being developed. IEEE 802.1Q-2018 was completed in July 2018 [6]. A new version of
802.1Q will follow, and standard technologies for autonomous driving will continue to be reflected on.

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      IEEE 802.1Qbv and 802.1Qbu were published in 2015 and 2016, respectively. However,
new contributions have been steadily emerging due to functional interoperability with linked standards
and physical link scalability (IEEE P802.1ch Multi-Gig Automotive Ethernet PHY Task Force) when
integrated into the 802.1Q standard [7–9]. The functions of these standards should be considered in
the integrated environment to reconsider the parameters and requirements for the TSN environment
in IEEE 802.1Q. Several studies have been conducted on performance testing on the IEEE 802.1
TSN through simulations and theoretical studies [10–12]. These studies have been conducted in an
independent environment, which generally constitutes basic partial traffic in the TSN standards. Each
of the standards being developed is independently published, and only the interworking of some of
the most highly relevant standards are considered. Therefore, when integrating different standards
into a single standard such as IEEE 802.1Q, there may be a lack of interworking and scalability between
the main TSN functions in the standards. In some cases, some parameter values in the TSN standards
may need to be changed.
      Our contribution in this paper is the development of a TSN integrated environment simulator
applying the main functions of the TSN standards such as IEEE 802.1AS, Qbv, Qcc, Qca, Qbu,
and 802.3br that are in the early stage of standardization. Considering the upcoming revision of 802.1Q,
in order to minimize the performance gaps that can occur when the functions of these standards
operate in an integrated environment, we analyzed whether the traffic for autonomous driving satisfies
the TSN transmission requirements in IVNs and whether the preemption function reduces the overall
E2E (End-to-End) delay or not. Moreover, since there are so many different standards involved,
as explained above, it is hard to predict whether a combined architecture with so many different
parameters and configurations satisfy the requirements underlying autonomous vehicles. Software
simulations enabled us to test many different possible scenarios with ease. This significantly saved
us time and cost. In addition, as part of our analysis process in simulations, we derived a parameter
for the preemption to work optimally. Finally, an IVN model to be used for autonomous vehicles was
designed, and the performance test was conducted by configuring the traffic to be used in various
sensors and ECUs. Actual data were provided by a major motor company in Korea.
      The rest of the paper is structured as follows. Section 2 contains the overall trends in the
development of TSN standards and a description of the two standards that will be one of the
main focuses of this paper. Section 3 describes the TSN simulator in the developed integrated TSN
environment and the main functions that can be changed through parameters. Section 4 deals with the
traffic expected to be used in autonomous vehicles, and the simulation tests that were performed to
check if the traffic would satisfy the TSN transmission requirements. Lastly, we conclude the paper
and talk about future work in Section 5.

2. Background
      The IEEE 802.1 TSN Task Group (TG) is part of the IEEE 802.1 Working Group (WG). The TSN TG
evolved from the former IEEE 802.1 Audio Video Bridging (AVB) TG. The original work on AVB was
completed in 2005. TSN standards have been newly published or revised based on the AVB standards
since 2006, and the development status of major standards are shown in Table 1.
      There are two representative standards that redefine the queuing process for time-sensitive
traffic transmission. The first is IEEE 802.1Qbv-2015. The IEEE 802.1Qbv standard has extended the
time-based scheduler for time-sensitive traffic transmission and its queuing procedure over AVB traffic
transmission structure [7]. The transmission method of existing AVB streams was an event trigger.
However, in a TSN, a time-aware scheduler is applied in addition to the existing method to transmit
scheduled traffic (ST) by a time-trigger transmission method. ST is transmitted at regular intervals in
the vehicle as important data related to vehicle control and safety. If the transmission requirement of
the existing AVB stream is to deliver within the maximum 2 ms time delay when passing seven hops,
the transmission requirement of the ST is to deliver within 100 µs time when passing five hops. A hop
represents a switch. All nodes (switches, gateways, sensors, or ECUs) must be synchronized to the
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           Standard             Status                                             Functionality
     IEEE P802.1AS-Rev         Ongoing                   Timing and Synchronization for Time-Sensitive Applications
same clock with almost no error in order to transmit the ST properly based on the transmission time.
      IEEE P802.1Qcc   Ongoing   Stream Reservation Protocol (SRP) Enhancements and Performance Improvements
Therefore,  a time-aware scheduler  should be applied with the time synchronization function of the
    IEEE P802.1AX-Rev  Ongoing                                  Link Aggregation
IEEE 802.1AS-rev standard [13]. In this paper, we refer to this standard and implement these functions
      IEEE P802.1Qcr   Ongoing                            Asynchronous Traffic Shaping
in the simulator.
        There are two       representative
                        Table   1. Development  standards
                                                    status ofthat  redefine the
                                                               time-sensitive         queuing
                                                                                  network         process
                                                                                              (TSN)           for time-sensitive traffic
                                                                                                      standards.
  transmission. The first is IEEE 802.1Qbv-2015. The IEEE 802.1Qbv standard has extended the time-based
  scheduler Standard                     Statustransmission and its queuing
                for time-sensitive traffic                                           Functionality
                                                                                       procedure over AVB traffic transmission
        IEEE 802.1Qbv-2015
  structure     [7]. The transmission Published
                                             method of existingEnhancements
                                                                      AVB streamsfor       was Scheduled
                                                                                                  an eventTraffic
                                                                                                               trigger. However, in a
        IEEE    802.1Qca-2015         Published                          Path    Control    and
  TSN, a time-aware scheduler is applied in addition to the existing method to transmit scheduledReservation
        IEEE 802.1Qbu-2016            Published                                  Frame Preemption
  traffic  (ST) by a time-trigger
        IEEE 802.1Qch-2017
                                          transmission method. ST
                                      Published
                                                                           is transmitted at regular intervals in the vehicle
                                                                       Cyclic Queuing and Forwarding
  as important       data related to
         IEEE 802.1Qci-2017               vehicle control and safety.
                                      Published                              If the transmission
                                                                       Per-Stream                       requirement of the existing
                                                                                       Filtering and Policing
  AVB IEEEstream     is to deliverPublished
                 802.1CB-2017           within the maximum            2 ms timeand
                                                             Frame Replication          delay     when passing
                                                                                            Elimination                seven hops, the
                                                                                                            for Reliability
        IEEE 802.1CM-2018
  transmission       requirement Published
                                       of the ST is to deliver   Time-Sensitive
                                                                    within 100 μs     Networking
                                                                                          time when   for passing
                                                                                                           Front Haul five hops. A hop
        IEEE P802.1AS-Rev              Ongoing        Timing and Synchronization for Time-Sensitive Applications
  represents a switch. All nodes (switches, gateways, sensors, or ECUs) must be synchronized to the
                                                          Stream Reservation Protocol (SRP) Enhancements and
  same clockIEEE with
                   P802.1Qcc
                         almost no Ongoing
                                       error in order to transmit the          ST properly        based on the transmission time.
                                                                          Performance        Improvements
  Therefore,      a time-aware scheduler
        IEEE P802.1AX-Rev              Ongoing should be applied withLink           theAggregation
                                                                                         time synchronization function of the
            IEEE P802.1Qcr
  IEEE 802.1AS-rev          standard   Ongoing
                                           [13]. In this paper, weAsynchronous
                                                                             refer to thisTraffic     Shaping
                                                                                                 standard      and implement these
  functions in the simulator.
        Thesecond
      The      secondstandard
                         standardisisIEEE IEEE802.1Qbu-2016
                                                 802.1Qbu-2016[7].   [7].IEEE
                                                                           IEEE802.1Qbu
                                                                                    802.1Qbuisisthe  thestandard
                                                                                                           standardthat thatdefines
                                                                                                                               definesthethe
  preemptionmechanism.
preemption          mechanism. In   In the
                                        the existing
                                              existing transmission
                                                        transmissionpolicy, policy,ififthere
                                                                                          thereisisa aframe
                                                                                                         frame being
                                                                                                                  being transmitted,
                                                                                                                           transmitted,  the
  frame    is designed    to wait    until  the  ongoing   transmission        is finished,     even
the frame is designed to wait until the ongoing transmission is finished, even if there is a frame thatif there  is a  frame    that needs
  to betotransmitted
needs        be transmittedurgently.
                                 urgently.However,
                                               However,with   thethe
                                                           with    preemption
                                                                       preemption     technique,
                                                                                          technique,   high-priority
                                                                                                          high-priority   frames
                                                                                                                             frames can
                                                                                                                                      canbe
bepreferentially
    preferentiallyprocessed.
                        processed.The   Thepreemption
                                              preemptionmay  may interrupt
                                                                    interrupt the       transmission of
                                                                                   the transmission          ofaalow-priority
                                                                                                                   low-priorityframe frame
  (AVB)     during    transmission       to preferentially    process    a  time-sensitive       frame
(AVB) during transmission to preferentially process a time-sensitive frame (ST). After processing the      (ST). After    processing     the
  high-priority      frame,  it resumes      transmission     of the  low-priority       frame     and  receives
high-priority frame, it resumes transmission of the low-priority frame and receives it in the full frame.           it in the  full frame.
  Whenswitching
When       switchinggatesgatesforfortransmission
                                      transmissionbetween
                                                       betweenST   STand
                                                                       andAVB, AVB,a a“guard
                                                                                          “guardband”
                                                                                                    band”isisset setfor
                                                                                                                      fora acertain
                                                                                                                             certaintime
                                                                                                                                       time
window to prevent frame collision (see Figure 1). Low-priority frames can be divided into two or moreor
  window       to  prevent   frame      collision  (see  Figure    1). Low-priority          frames    can    be  divided     into  two
  more frames
frames    as needed. as needed.

                                                                    ST's transmission cycle

                                                                         ST
                           Frame arrivals
                                                                      AVB

                           Frame transmission
                                                                      AVB                   ST
                           (Without preemption)

                           Frame transmission
                                                           Frag1         ST               Frag2
                           (With preemption)
                                                                                                             t
                                                                                    IFG
                                                                              Guard band

                                 Figure1.1.Example
                                Figure      Exampleofofframe
                                                         frametransmission
                                                                transmissionwith
                                                                             withpreemption.
                                                                                  preemption.

       In order to transmit the ST at the reserved time, there is another method of blocking the frame
        In order to transmit the ST at the reserved time, there is another method of blocking the frame
(1500 bytes of maximum frame size) from entering before the transmission cycle of the ST. However,
  (1500 bytes of maximum frame size) from entering before the transmission cycle of the ST. However,
it is inefficient in utilizing network resources and also increases the delay time of non-ST frames.
  it is inefficient in utilizing network resources and also increases the delay time of non-ST frames.
Therefore, the preemption is required to increase network efficiency and reduce overall delay time. The
  Therefore, the preemption is required to increase network efficiency and reduce overall delay time.
standard technologies mentioned above have been consistently conducted with the standardization
  The standard technologies mentioned above have been consistently conducted with the
work. In general, theoretical analysis of the time-aware scheduler of a TSN and experiments measuring
  standardization work. In general, theoretical analysis of the time-aware scheduler of a TSN and
IVN performance through simulation are the main subjects. Recently, there have been studies analyzing
  experiments measuring IVN performance through simulation are the main subjects. Recently, there
the performance of the preemption [14–18].
  have been studies analyzing the performance of the preemption [14–18].
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3.
3. TSN
   TSN Simulator
       Simulator Development
                 Development
     In
      In order
          ordertotodevelop
                     developthetheintegrated
                                     integratedIEEE   802.1Q
                                                   IEEE        standard
                                                          802.1Q   standardsimulation,  we implemented
                                                                                simulation,   we implementedthe main
                                                                                                                   the
TSN
mainfunctions     in the published
       TSN functions                   standards
                          in the published          such assuch
                                               standards      IEEEas802.1AS,    Qbv, Qcc,
                                                                       IEEE 802.1AS,        Qca,
                                                                                         Qbv,     Qbu,
                                                                                               Qcc,     andQbu,
                                                                                                     Qca,    802.3br.
                                                                                                                  and
Section
802.3br.3Section
           introduces   the time-aware
                    3 introduces            schedulerscheduler
                                    the time-aware      functionsfunctions
                                                                    of IEEE 802.1Qbv-2015      (which are(which
                                                                               of IEEE 802.1Qbv-2015        the main
                                                                                                                   are
TSN   functions
the main    TSN of   a TSN) of
                  functions   and   the implementation
                                 a TSN)                     issues of the
                                          and the implementation            frame
                                                                         issues  ofpreemption    of IEEE 802.1Qbu-
                                                                                    the frame preemption      of IEEE
2016  and 802.3brand
802.1Qbu-2016        and802.3br
                          describesandthe  configuration
                                        describes           of each variable
                                                     the configuration          operation
                                                                           of each          parameter
                                                                                     variable  operationrelated  to it.
                                                                                                          parameter
The  simulator
related          hassimulator
         to it. The   been developed
                                 has been based   on OMNET
                                             developed    based++ onversion
                                                                     OMNET    5.0++
                                                                                  and  inet-3.3.0,
                                                                                     version       andinet-3.3.0,
                                                                                             5.0 and   some related
                                                                                                                  and
studies  that have
some related         beenthat
                studies    conducted
                               have been canconducted
                                              be found can
                                                         in References
                                                              be found in [10,11,14,19].
                                                                             References [10,11,14,19].

3.1. Time-Aware
3.1. Time-Aware Scheduler
      The time-aware
      The   time-aware scheduler
                            scheduler acts
                                        acts as
                                             as aa timetable
                                                    timetable for
                                                                for transmitting
                                                                     transmitting data
                                                                                     data at
                                                                                           at fixed
                                                                                               fixed intervals
                                                                                                      intervals without
                                                                                                                    without being
                                                                                                                               being
 influenced    by  the  transmission
influenced by the transmission of AVB   of  AVB   or  BE  (best  effort)  traffic. To
                                                                 effort) traffic. To  achieve     this,  it is important     to
                                                                                                        it is important to set   set aa
 cyclefor
cycle   foreach
            eachstream
                   streamand andappropriately
                                  appropriatelyplace  place the
                                                          the  STST   within
                                                                   within    thethe cycle.
                                                                                  cycle. ForFor
                                                                                              thisthis  purpose,
                                                                                                    purpose,           a parameter
                                                                                                                  a parameter     for
 for specifying
specifying         a period
              a period        for each
                          for each       stream
                                    stream   andand     a parameter
                                                   a parameter           for allocating
                                                                    for allocating        a transmission
                                                                                     a transmission        startstart
                                                                                                                  timetime   of each
                                                                                                                         of each   ST
 ST  within   the   period   were   separately     configured.     Since    this  series of  operations
within the period were separately configured. Since this series of operations was based on the                 was   based    on  the
 assumption that
assumption      that all
                      all nodes
                           nodes in
                                  in the
                                     the vehicle
                                          vehicle areare synchronized,
                                                         synchronized, aa periodic
                                                                               periodic synchronization
                                                                                          synchronization was     was performed
                                                                                                                         performed
 by designating
by   designatingaaspecific
                       specificnode
                                nodeas  asaamaster,
                                             master, which
                                                        which follows
                                                                 follows the
                                                                           the IEEE
                                                                                 IEEE 802.1AS-rev
                                                                                       802.1AS-rev operation.
                                                                                                         operation. Each Each node
                                                                                                                                node
was
was   designed     to have   eight queues—five        for ST, two    for AVB    (Class  A, B)   traffic,
                    to have eight queues—five for ST, two for AVB (Class A, B) traffic, and one for BE    and   one   for BE   traffic
(see Figure
traffic        2).
         (see Figure    2).

                                 1
                                 2          Time
         Time-triggered                    Aware
                                 3                                                                 Transmission cycle
        Scheduled Traffic                 Scheduler
                                 4
                                                                    Clock           Port       5     8     6    ...    5    7
                                 5
                                                            Schedule
        AVB
      Class A 6                             Time
        AVB                                                                                                Dataflow
                 7                          Aware
       Class B
                                             CBS                                                         Controlflow
     Best-Effort 8

          Figure 2.
          Figure    Time-aware scheduler
                 2. Time-aware scheduler and
                                         and queuing
                                             queuing structure
                                                     structure in
                                                               in the
                                                                  the in-vehicle
                                                                      in-vehicle network
                                                                                 network (IVN)
                                                                                          (IVN) nodes.
                                                                                                nodes.

 3.2. Frame Preemption
3.2. Frame Preemption
       The principles of the frame preemption and development issues in implementation are as follows.
       The
 In order toprinciples
                start theoftransmission
                              the frame preemption
                                            through the    and    development
                                                               time-aware           issues inthe
                                                                               scheduler,       implementation        are as follows.
                                                                                                   ST stops transmission         of the
In  order
 frame      to was
         that   startbeing
                      the transmission
                             transmitted through
                                            and splitsthe  thetime-aware
                                                                 frame up atscheduler,       the ST stops
                                                                                the transmission               transmission
                                                                                                       stop point     to transmitof the
                                                                                                                                     the
frame    that
 ST first.  Whenwas the
                     being    transmittedofand
                          transmission         the splits    the frame up
                                                     ST is completed,        theatframe
                                                                                   the transmission
                                                                                            preemptionstop       point to
                                                                                                            functions     to transmit
                                                                                                                              transmit
the
 the ST  first.that
      frame      When
                    the the   transmission
                         ongoing              of the ST
                                     transmission           is completed,
                                                        interrupted.      Whenthetheframe    preemption
                                                                                         transmission     offunctions
                                                                                                              the ST is to    transmit
                                                                                                                          completed,
the  frame   that  the  ongoing    transmission      interrupted.     When     the  transmission
 the frame preemption successively transmits the interrupted frame and restores the original frame.  of  the  ST  is completed,     the
frame    preemption      successively     transmits      the  interrupted     frame     and   restores
The key point of the frame preemption is to stop the non-ST frame in transit and to combine the whole    the   original   frame.   The
key   point
 of the      of theframe.
         divided      frameThe preemption
                                   guard band is toisstop   the non-ST
                                                       the interval         framethe
                                                                       between       in transit
                                                                                          non-STandframeto combine      the wholeand
                                                                                                            to be interrupted         of
the  divided     frame.   The   guard    band   is  the   interval    between     the   non-ST
 the ST frame to be transmitted (see Figure 1). The guard band is processed in units of data size.frame    to  be  interrupted     and
the ST Inframe
           ordertotobeapply
                         transmitted     (see Figure
                                 the frame     preemption,1). Theframe
                                                                    guarddivision
                                                                             band is processed
                                                                                          and merging in units   of data should
                                                                                                             processes      size. be
       In order to
 implemented        by apply
                        referringthetoframe
                                        IEEE preemption,
                                               802.3br standards   frame[20].
                                                                            division      and merging
                                                                                 The preemption             processes
                                                                                                        process            shouldand
                                                                                                                    of dividing       be
implemented        by  referring    to IEEE    802.3br     standards     [20].   The    preemption
 merging the frames is performed in Layer 2 because the PHY (Physical) layer cannot recognize the      process     of  dividing    and
merging
 operationthe     frames
              of the        is performed
                      preemption.            in Layer
                                       Therefore,          2 because
                                                      logical            the PHY (Physical)
                                                                layer processing       is requiredlayer
                                                                                                     in thecannot      recognize
                                                                                                              MAC (Media            the
                                                                                                                                Access
operation     of  the preemption.      Therefore,    logical    layer  processing     is  required
 Control) merge sublayer when going up to Layer 2 (see Figure 3). In Layer 2, MAC is divided into   in  the  MAC      (Media    Access
Control)   merge sublayerand
 eMAC (expressMAC)              whenpMACgoing   up to Layer 2 (see Figure
                                             (preemptableMAC)                     3). InThe
                                                                          logically.      Layer
                                                                                             eMAC2, MAC     is divided
                                                                                                       processes          intoframe
                                                                                                                     the ST     eMAC   at
(expressMAC)        and  pMAC       (preemptableMAC)             logically.  The    eMAC      processes
 high speed, and the pMAC stores the divided frames in the buffer, merges them into a complete frame,       the  ST   frame    at high
speed, and the pMAC stores the divided frames in the buffer, merges them into a complete frame,
and sends it up to the upper layer. The buffer is located in the receiving MAC merge sublayer, and
the fragmented frames are merged in the buffer and sent to the pMAC. If it is not a fragmented frame,
it is sent directly to the pMAC without buffer storage.

                                 eMAC                                    pMAC
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                                                                                 Buffer
                                                                           1 (Merging
 and sends it up to the upper MAC           Merge
                                   layer. The  buffer is located in the receiving   MAC merge sublayer, and the
 fragmented
  the fragmentedframes frames      Sublayer
                          are merged  in theinbuffer
                               are merged            and sent
                                               the buffer andto  thetopMAC.
                                                               sent          If frames)
                                                                       the pMAC.it isIfnot
                                                                                        it isanot
                                                                                              fragmented  frame,
                                                                                                  a fragmented    it is
                                                                                                               frame,
 sent
  it isdirectly  to thetopMAC
       sent directly             without
                           the pMAC        bufferbuffer
                                       without     storage.
                                                        storage.

                                   eMAC                                        2 fragmented
                                                                            pMAC
                                                            AVB                                AVB
                                                           Frame                              Frame

                                                                                   Buffer
                                 Figure 3. Receiver side MAC merge sublayer structure. 1
                                         MAC Merge
                                                                                               (Merging
                                         Sublayer                                               frames)
     When transmitting a frame to the pMAC, it is necessary to know whether                           the frame is a fragmented
frame, and how many frames are fragmented. This information, together with the frame preemption,
consists of additional formats provided by IEEE 802.1Qbu and IEEE802.1br (see Figure 4). The format
includes the beginning, end, and the sequence information                               2 offragmented
                                                                               identifier          the  fragmented frame (see
                                                             AVB                                    AVB
Table 2). The frame is split according to this format,      Frame     and    the   fragmented      Frame is restored to the
                                                                                                      frame
original frame at the receiving node with reference to the identifier (see Figure 3). As the development
progresses, the frame may Figure Figure
                                 be     3.3.Receiver
                                    divided     moreside
                                             Receiver  sideMAC
                                                       than  MAC   merge
                                                                    mergesublayer
                                                             necessary.           orderstructure.
                                                                              sublayer
                                                                             In            structure.
                                                                                           to control this problem, another
parameter is configured to limit the maximum number of times that one frame can be divided.
      When
       Whentransmitting
                transmittingaaframe
                                 frametotothethepMAC,
                                                 pMAC,ititisisnecessary
                                                                necessarytotoknow  knowwhether
                                                                                            whetherthe   theframe
                                                                                                              frameisisaafragmented
                                                                                                                           fragmented
 frame,  and   how   many    frames
  frame, and how many frames are     are   fragmented.
                                             fragmented.    This
                                                             This information,
                                                                   information,       together
                                                                                       together     with
                                                                                                     with  the
                                                                                                            the frame
                                                                                                                 frame  preemption,
                                                                                                                         preemption,
                                        Table 2. Fragmented frame identifier.
 consists
  consistsofofadditional
               additionalformats
                             formatsprovided
                                      providedby    byIEEE
                                                        IEEE802.1Qbu
                                                               802.1Qbuand    andIEEE802.1br
                                                                                    IEEE802.1br(see    (seeFigure
                                                                                                              Figure4).4).The
                                                                                                                           Theformat
                                                                                                                                format
 includes
  includes the beginning, end, and the sequence information identifier of the fragmented frame(see
           the   beginning,    end,  and
                           Identifiers      the  sequence     information
                                                                  Functions      identifier      of the   fragmented      frame    (see
 Table
  Table2).
         2).The
             Theframe
                    frameisis split
                               splitaccording
                             SMD-Sx  according    totothis
                                                Field  to   format,
                                                           check
                                                        this       firstand
                                                             format,           the
                                                                                thefragmented
                                                                          fragmented
                                                                         and                 frame frame
                                                                                      fragmented         frameisisrestored
                                                                                                                     restoredtotothethe
 original frame    at  the receiving
                             SMD-Cx  node     with
                                            Field   reference
                                                   to  check   ifto the
                                                                  the    identifier
                                                                       fragment       is (see   Figure
                                                                                          continuing
  original frame at the receiving node with reference to the identifier (see Figure 3). As the development3). As  the  development
 progresses,
  progresses,the theframe
                      framemaymaybe
                             SMD-Fxbedivided     more
                                      dividedFieldmoreto than  necessary.
                                                           check
                                                          than                 InInorder
                                                                   last fragmented
                                                                 necessary.                  totocontrol
                                                                                    orderframe    controlthisthisproblem,
                                                                                                                  problem,another
                                                                                                                               another
 parameter    is configuredFragto limit
                                 Count  the    maximum      number
                                                      Fragmented        of
                                                                       frametimes    that
                                                                                 sequence   one
  parameter is configured to limit the maximum number of times that one frame can be divided.      frame    can  be divided.

                Preamble 7                   Fragmented 7frame identifier.
                                          Preamble
                                    Table 2.
                  SFD     1                SMD-Sx 1
                MAC DA 6Identifiers       MAC DA Functions
                                                         6        Preamble 6                                 Preamble         6
                          6
                MAC SA SMD-Sx              MACtoSA
                                         Field     check6first fragmented
                                                                  SMD-Cxframe   1                            SMD-Fx           1
                         SMD-Cx           Ethertype
                                      Field              2 fragment
                                             to check if the      Fr ag Count   1
                                                                        is continuing                         Fr ag Count     1
                  Data   SMD-Fx           Field to check last fragmented frame
                                              Data                   Data                                       Data
                               Frag Count                  Fragmented frame sequence
               FCS     4                 FCS       4            FCS        4       FCS        4
              Preamble 7                Preamble 7
     (a) Normal frame    1
                 SFD format                          1
                                         SMD-Sx(b) Fragmented        frame format
              MAC DA 6                  MAC DA 6               Preamble 6         Preamble 6
              MAC SA 6 Figure          IEEE
                            Figure4.4.IEEE
                                        MAC 802.1Qbu
                                           802.1Qbu  6frameformat.
                                               SA frame     format.
                                                               SMD-Cx 1           SMD-Fx 1
                                        Ethertype    2         Fr ag Count
                             Table 2. Fragmented frame identifier.           1    Fr ag Count   1
4. Simulation    Data
                                IdentifiersData                   Data   Functions   Data
4.1. IVN Model Design      SMD-Sx             Field to check first fragmented frame
                       FCS   4
                          SMD-Cx
                                                 FCS         4             FCS      4
                                          Field to check if the fragment is continuing
                                                                                               FCS        4
     An IVN model was designed
                           SMD-Fx
                                    based on  the  traffic required   for autonomous
                                              Field to check last fragmented frame
                                                                                       driving vehicles (see
Figure (a) Normal
       5). The basicframe  format
                     IVN Frag
                         structure
                              Countand traffic information
                                                           (b)were
                                                  Fragmented
                                                                Fragmented
                                                                     provided
                                                                 frame
                                                                              frame  format
                                                                              by a major
                                                                       sequence          motor company in
Korea, and we redesigned the IVN of each domain based on the traffic information. To illustrate the
                                   Figure 4. IEEE 802.1Qbu frame format.
overall IVN structure, we configured a vehicle to four domains (Infotainment, Body, PT/Chassis, ADAS).
 4. Simulation
  4. Simulation
 4.1. IVN Model Design
  4.1. An
       IVNIVN
           Model Design
               model  was designed based on the traffic required for autonomous driving vehicles
 (see Figure 5). The  basic IVN structure
        An IVN model was designed   based and  traffic
                                          on the       information
                                                 traffic required forwere provideddriving
                                                                      autonomous   by a major  motor
                                                                                          vehicles (see
  Figure 5). The basic IVN structure and traffic information were provided by a major motor company in
  Korea, and we redesigned the IVN of each domain based on the traffic information. To illustrate the
  overall IVN structure, we configured a vehicle to four domains (Infotainment, Body, PT/Chassis, ADAS).
Sensors 2019, 19, 1111                                                                                                    6 of 11

company in Korea, and we redesigned the IVN of each domain based on the traffic information.
Sensors 2019, 19, x FOR PEER REVIEW                                                                                        6 of 11
To illustrate the overall IVN structure, we configured a vehicle to four domains (Infotainment, Body,
PT/Chassis,
Each domain ADAS). had ECUs  Each
                                anddomain
                                     sensors,had andECUs       and (GW)
                                                       a gateway      sensors,
                                                                             for and
                                                                                 eachapart
                                                                                         gateway
                                                                                              of the (GW)    forGWs
                                                                                                      vehicle.    eachare part
                                                                                                                            usedof
the  vehicle.      GWs    are used    to  interconnect       other   domains     as  necessary.
to interconnect other domains as necessary. In addition, the ADAS sensor fusion was designed as an  In  addition,   the    ADAS
sensor
ECU forfusion       was designed
           autonomous       driving. asTheanADAS
                                               ECU sensor
                                                      for autonomous
                                                                fusion ECUdriving.       The
                                                                               collects the      ADAS sensor
                                                                                             information    fromfusion      ECU
                                                                                                                   the sensors,
collects
analyzesthe  theinformation
                  information from
                                 from the    sensors,
                                         adjacent        analyzes
                                                    vehicles     and the
                                                                      the information     from adjacent
                                                                           road environment,                vehicles
                                                                                                   and extracts          and the
                                                                                                                   information
road  environment,       and   extracts   information       necessary   for  driving.   This   information
necessary for driving. This information leads to control commands necessary for autonomous driving.           leads   to  control
commands
The IVN model   necessary    for autonomous
                     was configured                driving.
                                         so that the   sensorsThe     IVN model
                                                                  required            was configured
                                                                             for autonomous       drivingso  thatcontinuously
                                                                                                          were     the sensors
required    for autonomous      driving    were  continuously       generating   data  (see
generating data (see Table 3). The sensors included radio detection and ranging (RADARs) and Table  3). The  sensors    included
                                                                                                                             light
radio
detection and ranging (LIDARs). The RADAR was used to determine the distance, direction, was
        detection    and   ranging   (RADARs)       and    light  detection   and   ranging   (LIDARs).    The   RADAR        and
used   to determine
altitude   of nearby the     distance,
                         vehicles   anddirection,
                                           the LIDAR  andwas altitude
                                                                  usedoftonearby
                                                                            identify vehicles   and the LIDAR
                                                                                       the surrounding       routeswas andused  to
                                                                                                                             road
identify   the  surrounding      routes   and  road   conditions.     The  AVM    (around     view
conditions. The AVM (around view monitoring) is a vehicle camera information system that can see     monitoring)    is a  vehicle
camera    information
360 degrees     outside thesystem   thatincan
                              vehicle       thesee  360 degrees
                                                driver’s    seat. Theoutside   the vehicle
                                                                       DSM (driver     statusinmonitoring)
                                                                                                 the driver’sisseat.
                                                                                                                 alsoThe    DSM
                                                                                                                       a camera
(driver  statussystem
information        monitoring)
                          which iswasalso  a camera
                                        mounted         information
                                                     inside             system
                                                              the vehicle         which was
                                                                            to recognize    themounted
                                                                                                  pupil andinside   thedrowsy
                                                                                                              prevent     vehicle
to recognize     the  pupil  and  prevent    drowsy     driving.   In  addition,  ECUs    for
driving. In addition, ECUs for infotainment of vehicles and ECUs for stream information coming infotainment    of vehicles    and
ECUs    for stream
from outside       the information    comingsafety,
                       vehicle for control,      from outside      thearranged.
                                                          etc., were    vehicle for control, safety, etc., were arranged.

           Infortainment                      Body                      PT/Chassis                      ADAS
              Domain                         Domain                      Domain                         Domain

                                                                                                    RADAR
              AMP                           Cluster                       ESC
                                                                                                      x5

            Integrated                     Head Up                                                 Ultrasonic
                                                                         MDPS
             Antenna                       Display                                                   wave

                                          Mirrorless                                              AVM CAM
             Display
                                           Display                                                  x4

            Rear Seat                                                                            Mirrorless CAM
          Entertainment                                                                                x3

            Rear Left                            ADAS sensor fusion                              Forward CAM
            Monitor

            Rear Right
                                                                                                 Laser scanner
             Monitor

                                                                        Ethernet                   DSM CAM
                GW               ECUs              Sensors                   100Mbps
                                                                             1Gbps               Infrared CAM

                                 Figure 5. IVN model for autonomous driving vehicle.

            Table 3. Background stream for advanced driving assistant system (ADAS) sensor fusion.
            Table 3. Background stream for advanced driving assistant system (ADAS) sensor fusion.
                             Sensor               Type          Stream Size         Number of Stream
                                Sensor            Type       Stream Size Number of Stream
                             RADAR
                               RADAR               AVB
                                                  AVB             10 Mbps
                                                               10 Mbps          5 5
                         Ultrasonic wave           AVB            15 kbps          1
                           Ultrasonic
                            AVM CAM
                                       wave       AVB
                                                   AVB
                                                               15 80
                                                                  kbps
                                                                     Mbps
                                                                                1 4
                              AVM    CAM
                         Mirrorless CAM           AVB
                                                   AVB         80 Mbps
                                                                  80 Mbps       4 3
                           Mirrorless
                         Forward    CAMCAM        AVB
                                                   AVB         80 Mbps
                                                                  80 Mbps       3 1
                          Laser  scanner
                            Forward CAM            AVB
                                                  AVB             10 Mbps
                                                               80 Mbps          1 1
                            DSM CAM                AVB            80 Mbps
                            Laser scanner         AVB          10 Mbps          1 1
                          Infrared CAM             AVB            80 Mbps          1
                              DSM CAM             AVB          80 Mbps          1
                            Infrared CAM          AVB          80 Mbps          1

4.2. Configuring Parameter Value
    Prior to the overall simulation test, it was necessary to measure the change in end-to-end delay
according to the preemption guard band size, one of the variable parameters. As described above,
Sensors 2019, 19, 1111                                                                                               7 of 11

4.2. Configuring Parameter Value
      Prior to the overall simulation test, it was necessary to measure the change in end-to-end delay
according to the preemption guard band size, one of the variable parameters. As described above,
using preemption reduces E2E delay and increases network efficiency. The most significant factor in
preemption is the size of the guard band that forms the time window between the ST and the non-ST.
Depending on the size of the guard band, more non-STs may be sent, so that the segmented traffic
is fully integrated and can reach the destination quickly. Therefore, we conducted experiments to
see how the delay changed according to the setting of the guard band size when transmitting ST
 Sensors
and   AVB2019, 19, x FORfor
            streams       PEER   REVIEW
                            a simulation      time of 5 s. We specified two streams (Stream 1, 2 in Table 5)7 and       of 11

measured the preemption occurrence frequency and delay variation at the point where they intersected
 using
(see     preemption
      Table              reduces E2Eperiod
             4). The transmission         delay and     increases
                                                   of the          network
                                                           ST stream         efficiency.
                                                                       was set to 10 ms,Theandmost     significant factor
                                                                                                 the transmission   period in
 preemption      is  the size   of the  guard    band   that forms   the time  window     between
of the AVB stream was set to 125 µs, which conforms to the transmission requirements of the SR Class  the ST  and  the non-
 ST.The
A.    Depending
          minimum     onguard
                         the size   of the
                                 band       guard
                                         size was band,
                                                     set to more  non-STs
                                                            80 bytes        may be64sent,
                                                                       (minimum        bytesso of
                                                                                               that  the segmented
                                                                                                  frame   processingtraffic
                                                                                                                       plus
 is fully integrated     and   can  reach   the  destination   quickly.  Therefore,
additional header information), and the maximum guard band size was set to 512 bytes. we  conducted     experiments   to see
 how the delay changed according to the setting of the guard band size when transmitting ST and AVB
 streams for a simulationTable    time4.ofE2E
                                            5 s.delay
                                                 We specified    two streams
                                                      variation according      (Stream
                                                                           to guard  band1,size.
                                                                                             2 in Table 4) and measured
 the preemption occurrence frequency and delay variation at the point where they intersected (see Table
 5). The transmission periodPreemption
                                     of the ST stream   X was set to 10 ms, and theO transmission period of the AVB
 stream was set to    Guard
                         125 band    size (byte)
                               μs, which     conforms- to the transmission
                                                                   80        128 requirements
                                                                                        256       of512
                                                                                                      the SR Class A. The
 minimum guardE2E      band    size
                           Delay    was   set
                                          ST  to  80 bytes
                                                       64.5 (minimum
                                                                  64.5   64 bytes
                                                                            64.5   of frame
                                                                                        64.5  processing
                                                                                                    64.5 plus additional
 header information), and the maximum guard band size was set to 512 bytes. 235
                          (µs)           AVB           234        201        198        233

       Experimental results
      Experimental     results show
                               show that   if the
                                     that if  the guard
                                                   guard band
                                                            band becomes
                                                                   becomes too
                                                                             too large
                                                                                  large oror small,
                                                                                              small, the
                                                                                                      thefrequency
                                                                                                          frequency ofof
 preemption    decreases  or increases, resulting   in poor   data transmission    efficiency.  Taken   together,
preemption decreases or increases, resulting in poor data transmission efficiency. Taken together, it can         it can
 be concluded
be   concluded that
                that the
                      the optimal
                          optimal guard
                                   guard band
                                           bandsize
                                                  sizeisis128
                                                           128bytes
                                                               bytes(see
                                                                      (seeFigure
                                                                           Figure6).
                                                                                   6).Based
                                                                                       Basedon onthese
                                                                                                  theseexperimental
                                                                                                          experimental
 results, the overall TSN  performance    test was   conducted   with   the guard  band   size
results, the overall TSN performance test was conducted with the guard band size of 128 bytes. of 128  bytes.

           300

                                                                           233                     235
           250
                          201                      198
           200
                          142                      135
           150
                                                                           103

           100
                                                                                                    45
            50

             0
                           80                      128                     256                     512
                                                       Guard band size (byte)

                                      E2E Delay (μs)            Preemption occurrence numbers

              Figure 6. E2E delay and preemption frequency variation according to guard band size.
              Figure 6. E2E delay and preemption frequency variation according to guard band size.

4.3. Performance Test on TSN Integrated Environment
     For the TSN performance experiment, the stream of each ECU and sensor was allocated after the
design of the IVN model. It was divided into a total of 16 streams, and periodic data transmission
was performed by specifying the source to the destination according to the ST and AVB transmission
formats defined in the TSN standard (see Table 3). Depending on the IVN domain, links exceeding
100 Mbps were replaced by 1 Gbps links. This is because relatively large video and voice data are
mixed in the domain of ADAS and Infotainment. The size of the guard band was set to 128 bytes,
which was derived as the optimal value.
Sensors 2019, 19, 1111                                                                                                                                   8 of 11

                                                             Table 5. TSN streams for autonomous driving.

                                                                                                          Bandwidth       E2E Delay (µs)
                         Stream Info        Type     Source          Destination          Size (Byte)                                         * Diff. (µs)
                                                                                                          Allocation
                                                                                                                       Gen1           Gen2
                                                                                                            (bps)
         1               Navigation/AVM      ST    Infotainment         ADAS                   60           704 k      98.5            64.5       34
                          Navigation
         2                                  AVB    Infotainment         HUD                     2           80 M       334.5           198       136.5
                              data
         3               Navigation/Audio   AVB    Infotainment        Cluster                 2             48 k      217.8           110       107.8
         4                   Audio          AVB    Infotainment         AMP                   11            125 k       200            98.5      101.5
         5               Entertainment      AVB    Infotainment         RSE                  1250           125 k       120           120.9      −0.9
                                                                      Rear Left
                         Entertainment      AVB        RSE                                   1250           80 M       212.9           212        0.9
         6                                                            Monitor
                                                                     Rear Right
                         Entertainment      AVB        RSE                                   1250           80 M       212.9           212        0.9
                                                                      Monitor
                                                    Integrated
         7                 GPS/V2X          AVB                     Infotainment               16            1M        54.4            54.4        0
                                                     Antenna
         8               Control data        ST        Body          PT/Chassis                 4            3k        101             50.9      50.1
                         PT/Chassis                                 ADAS Sensor
         9                                   ST    PT/Chassis                                 230           184 k      100             50.2      49.8
                             info                                      fusion
                         ADAS sensor               ADAS Sensor
        10                                  AVB                        Cluster                  2           125 k      125            123.3       1.7
                           fusion                    fusion
                         ADAS sensor               ADAS Sensor
        11                                  AVB                         HUD                     2           125 k      125            123.3       1.7
                           fusion                    fusion
                          Forward                  ADAS Sensor       Integrated
        12                                  AVB                                               250           80 M       315.4          345.6     −30.2
                           camera                    fusion           Antenna
                                                   ADAS Sensor
        13               Control data        ST                          ESC                  625           500 k      99.3            57.1      42.2
                                                     fusion
                                                   ADAS Sensor
        14               Control data        ST                         MDPS                  625           500 k      99.3            57.1      42.2
                                                     fusion
                                                   ADAS Sensor
        15                AVM image         AVB                        Display               1250           80 M       210.7          209.8       0.9
                                                     fusion
                          Mirrorless               ADAS Sensor       Mirrorless
        16                                  AVB                                              1250           80 M       205.7           199        6.7
                           image                     fusion           Display
                                                                     * Diff. = Difference of E2E delay.
Sensors 2019, 19, 1111                                                                                  9 of 11

4.3. Performance Test on TSN Integrated Environment
      For the TSN performance experiment, the stream of each ECU and sensor was allocated after the
design of the IVN model. It was divided into a total of 16 streams, and periodic data transmission
was performed by specifying the source to the destination according to the ST and AVB transmission
formats defined in the TSN standard (see Table 3). Depending on the IVN domain, links exceeding
100 Mbps were replaced by 1 Gbps links. This is because relatively large video and voice data are
mixed in the domain of ADAS and Infotainment. The size of the guard band was set to 128 bytes,
which was derived as the optimal value.
      Experimental results show that applying the TSN preemption in combination with ST transmission
was more efficient in terms of the E2E delay than using AVB only. It was shown that the delay was
reduced in most cases except for streams 5 and 12. Concerning the difference of E2E delay in Table 5,
the delay was not reduced due to the fact that the preemption occurred more frequently than necessary
under too much traffic by chance. Based on this result, it can be inferred that the proper spacing of the
ST, placement of the IVN link, and setting of the guard band size in the preemption are important for
IVN design for autonomous driving. As a result of comparing the E2E delays between an AVB and
TSNs through experiment, it was confirmed that TSNs satisfy the ST transmission requirements and
the frame preemption required to compensate for the delay time caused by AVB stream transmission
interruptions (see Table 5).
      Through this experiment, it was found that the results can vary greatly depending on how the
traffic is arranged and the parameter values are configured in the environment where the functions of
TSN standards are integrated. In the future, it may be necessary to modify some of the requirements or
recommended parameters of existing standards. This is because the performance of TSNs may not be
as desirable when various standards, such as the queuing policies and the link speed configurations
of IEEE 802.3 with speeds of 10, 100 Mbps, or greater than 1 Gbps, are integrated into newly revised
802.1Q. We will proceed with further implementation and experimentation to address these issues.

5. Conclusions
     In this paper, a simulator was developed by integrating the main TSN functions under
development. Based on the ST for streaming and control data from various sensors provided by a major
motor company in Korea, we constructed a TSN in a vehicle for autonomous driving. When testing
various standard functions in the integrated environment, it was found that the TSN time-division
transmission method was required to satisfy the requirements and that the preemption was required to
compensate for the AVB delay. Also, the optimal size of the guard band was found to be 128 bytes for
autonomous vehicles through analysis. We anticipate that various future standards for TSNs will be
published and that when these standards are applied to an integrated environment, the requirements
presented in the existing standards will need to be reconsidered.
     In the future, we plan to integrate key features of the upcoming standards such as IEEE 802.1Qci,
802.1Qch, 802.3cg, 802.3ch, and so forth into the simulator developed. This next research topic would
include additional performance tests by collecting vehicle traffic data from vehicle original equipment
manufacturers (OEMs).

Author Contributions: Conceptualization, J.L. and S.P.; investigation, J.L.; software, J.L.; supervision, S.P.;
validation, J.L.; and writing, review, and editing, J.L. and S.P.
Funding: This work was funded by the National Research Foundation of Korea (NRF) grant funded by the Korea
government (MOE: Ministry of Education) (No. 2018R1D1A1A02048970).
Acknowledgments: This work was supported by the National Research Foundation of Korea (NRF) grant funded
by the Korea government (MOE: Ministry of Education) (No. 2018R1D1A1A02048970).
Conflicts of Interest: The authors declare no conflict of interest.
Sensors 2019, 19, 1111                                                                                     10 of 11

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                         © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
                         article distributed under the terms and conditions of the Creative Commons Attribution
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