Pre-shaping bursty transmissions under IEEE802.1Q as a simple and efficient QoS mechanism

Paper #:
  • 2018-01-0756

  • 2018-04-03
To meet the diverse automotive communication requirements there is a need for protocols that go beyond what standard Ethernet has to offer in order to provide additional QoS to demanding applications such as ADAS systems. The main protocols currently considered for that purpose are IEEE802.1Q, AVB with the Credit Based Shaper mechanism (IEEE802.1Qav) and TSN with its Time-Aware Shaper (IEEE802.1Qbv) and the upcoming frame preemption extensions (IEEEP803.3br/802.1Qbu). AVB/CBS and TSN/TAS both provide efficient QoS mechanisms and they can be used in a combined manner, which offers many possibilities to the designer. Their use however requires dedicated hardware and software components, and global clock synchronization for TAS. Previous studies have also shown that their efficiency depends much on the application at hand and the value of the configuration parameters. In this work, we explore the use of “pre-shaping” strategies under IEEE802.1Q for bursty traffic such as audio/video streams as a simple and efficient alternative to AVB/CBS and TSN/TAS. Pre-shaping means inserting “well-chosen” minimum distance between the frames of a burst on the sender side only, all the other characteristics of traffic remaining unchanged. On two realistic automotive case-studies, we show how the use of pre-shaping (w/o frame preemption) for audio/video leads to a drastic reduction of the communication latencies for best-effort streams while meeting deadlines of the rest of the traffic. We discuss how to set the pre-shaping parameters on a per-stream basis and the limitations of the technique when the number of hops grows.
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