Analysis of Ethernet-Switch Traffic Shapers for In-Vehicle Networking Applications Sivakumar Thangamuthu, Nicola Concer Pieter J.L.Cuijpers and Johan J.Lukkien Central R&D, CTO Office Department of Mathematics and Computer Science NXP Semiconductors Technische Universiteit Eindhoven [email protected] [email protected] and [email protected] Abstract—Switched Ethernet has been proposed as network with minimal configuration complexity, low implementation technology for automotive and industrial applications. IEEE cost but with a guaranteed Quality of Service (QoS). AVB is a collection of standards that specifies (among other elements) a set of network traffic shaping mechanisms (i.e., rules In the entertainment domain the IEEE defined Audio/Video to regulate the traffic flow) to have guaranteed Quality of Service Bridging (AVB), a set of standards that allows switches to for Audio/Video traffic. However, in-vehicle control applications identify different types of traffic patterns, categorize them into like advanced driver-assistance systems require much lower specific traffic classes, and assign a different QoS to each latencies than provided by this standard. Within the context class. An important element of AVB is IEEE 802.1Qav ”For- of IEEE TSN (Time Sensitive Networking), three new traffic warding and Queuing for Time-Sensitive Streams” (FQTSS). shaping mechanisms are considered, named Burst Limiting, Here IEEE defined the Credit-Based Shaper (CBS), the main Time Aware and Peristaltic shaper respectively. In this paper AVB mechanism responsible for selecting the next frame to be we explain and compare these shapers, we examine their worst case end-to-end latencies analytically and we investigate their transmitted from a network interface of switches or end-nodes. behavior through a simulation of a particular setup. We show Through the (scheduling) rules defined by this shaper, specific that the shapers hardly satisfy the requirements for 100Mbps guarantees are given to time-sensitive traffic such as video Ethernet, but can come close under further restrictions. We also and audio streams. Timing properties resulting from AVB show the impact the shapers have on AVB traffic. traffic shaping are not sufficient for automation and control applications. To build upon the success of the AVB standards, Keywords: Ethernet switching, IEEE 802.1AVB, IEEE 802.1TSN, In automotive and industrial OEMs together with software and Vehicle Networks electronic-components suppliers joined their efforts in the AVnu alliance [4], to further extend the capabilities of the AVB standards [5]. The AVnu alliance participated in the I. INTRODUCTION definition of a new set of requirements captured in the revised The bandwidth requirements of modern and future au- version of the IEEE AVB standards, recently renamed as tomotive applications are quickly reaching the limits of the IEEE Time-Sensitive Networking, IEEE 802.1TSN [6]. A key established In-Vehicle Networking (IVN) technologies such new feature of TSN is the definition of new traffic shaping as LIN, CAN and FlexRay. The recent introduction of the mechanisms capable of accommodating hard real-time streams BroadR-Reach technology enabled the use of a 100Mbps with deterministic end-to-end delays. At the time of writing, Ethernet link over an unshielded twisted pair copper wire while TSN is evaluating a set of new traffic shaping mechanisms, limiting the electro-magnetic interference emissions below the respectively called Time-Aware (TAS), Burst-Limiting (BLS) threshold imposed by automotive application requirements [1], and Peristaltic (PS) shaper. [2]. BroadR-Reach, which is now under standardization in the Contribution. In this work we perform the analysis and working group IEEE P802.3br, implements a point to point comparison of these three traffic shapers with respect to delay communication technology. More complex network topologies performance. We evaluate the worst-case behavior of the traffic are defined by using ISO Layer 2 (bridges) or Layer 3 (routers) shapers through analysis and simulation in a scenario where the switches. controllers are synchronized to avoid intra-control interference. This allows us to focus on the traffic shaping rather than on Switches enable complex network topologies while of- the access control mechanism. In particular, we evaluate the fering basic services such as relaying of frames from one impact of AVB traffic on control traffic, and vice-versa. source node to multiple destinations, as well as more complex ones such as channel bandwidth allocation, network partition- Related Work. The capabilities of switched Ethernet to ing via Virtual LANs (VLANs) and traffic prioritization [3]. accommodate real-time data traffic have been investigated Switched Ethernet networks have been implemented in the extensively. Two main approaches include the synchronized automotive market for supporting telemetry (via On-Board time-triggered based medium access approach and the asyn- Diagnostic, OBD2 port) and bandwidth-intensive applications chronous event-triggered approach by over-provisioning and such as vehicle surround-view applications. It accomodates prioritizing. An example of the former technique is TTEthernet recent developments in the entertainment and Advanced Driver (AS6802) [7] and of the latter technique, the IEEE802.1AVB Assistance Systems (ADAS) domains that require very flexible standard with Credit Based traffic shaping (CBS) [3]. Bordoloi networks targeted to support a vast range of traffic patterns et.al. investigate the worst-case response time for standard 978-3-9815370-4-8/DATE15/c 2015 EDAA 55 Traffic Class Frame Interval Max End-to-End Delay Traffic Class Max Frame Size Min Frame Interval Max End-to-End Delay Class A 125μs 2ms over 7 hops Class CDT 128 bytes 500μs 100μs / 5 hops Class B 250μs 50ms over 7 hops Class A 256 bytes 125μs 2ms / 7 hops Class BE n.a. n.a. Class B 256 bytes 250μs 50ms / 7 hops Class BE 256 bytes n.a. n.a. TABLE I. TRAFFIC CLASSES SPECIFICATIONS IN IEEE 802.1AVB. NO RESTRICTION ON FRAME SIZES. TABLE II. TRAFFIC SPECIFICATIONS IN IEEE802.1TSN AVB streams targeting applications with hard real-time con- straints [8]. The paper proposes a precise model to first analyze the CBS mechanism and then propose a set of updates to im- prove the performance of the shaper. Boiger et.al. [9] provide a comparative study of the Burst-Limiting and Peristaltic shapers which are also considered in our work. Different from our approach, the authors consider a traffic-overloaded scenario and do not discuss the end-to-end latencies achieved by the control data traffic, which is the main contribution of our analysis. Gotz¨ et.al. compare the Burst-Limiting and the Time- Aware shapers, also considered in our work, considering a Fig. 1. Operation of a Burst-Limiting shaper. large industrial network [10]. Here the authors investigate the each queue representing one or more priority levels. Each impact of the frame size on the overall network performance. time the underlying physical interface becomes available a In our work we target smaller automotive networks which also transmission-selection mechanism selects the next frame to support AVB streams. Meyer et al. present a network scenario transmit choosing among the queues that are enabled for to analyze the impact of the Time-Aware shaper on AVB Class transmission. A generic queue associated with Class BE traffic A traffic [11]. The authors present a theoretical analysis for the is enabled if at least one frame is stored in the corresponding maximum end-to-end latency of an AVB Class A traffic class queue. A queue supporting AVB traffic classes A or B is and compare it with results from simulation. In our work we enabled for transmission precisely when the following two address such analysis as well but we include the Burst-Limiting conditions hold: i), a frame is stored in the queue and ii), the and Peristaltic shapers. Cummings describes the performance CBS associated with that queue is enabling the transmission. tradeoffs to achieve a certain end-to-end latency in AVB [12]. In our work, we use the papers of Rahmani and Cummings IEEE AVB also defines a set of standards that provide for defining a static schedule for control data traffic in the features specifically designed for audio and video transmission. TAS. Finally the presentations of D.Pannel, C.Boiger and IEEE 802.1AS is a Timing and Synchronization protocol that M.Kießling from various IEEE meetings provide illustrations enables the definition of a common time-reference which is and theoretical methods to compute the worst case end-to-end essential for distributed audio and video playback applications. latency for a control data frame [13], [14], [15]. These works IEEE 802.1Qat ”Stream reservation protocol” is a distributed offer valuable details for identifying the worst case behavior of protocol that allows the sources of audio and video streams, each of the traffic shapers. In our work we used these details called talkers,toadvertise available streams to potential listen- in computing the theoretical maximum values for end-to-end ers. This protocol also enables listeners to register to a stream latencies. by reserving and allocating the necessary bandwidth in the switches located on the path between the talker and itself. IEEE 802.1Qav specifies the mentioned Credit-Based shaper II. IEEE AUDIO VIDEO BRIDGING mechanism that enables the transmission of AVB and non-AVB IEEE802.1AVB defines a collection of standards aimed at legacy Ethernet frames. CBS is not explained in detail in this optimizing the transmission of audio and video streams over work as the focus is to compare the emerging traffic shaping an Ethernet network. AVB Streams are classified according mechanisms. Finally IEEE 802.1BA - Audio Video Bridging to a set of Traffic Specifications composed by two main Systems defines the AVB profile of configurations and features elements: i) Maximum Frame Size: indicating how much data that all AVB-compliant systems should have.