Support for AVB/CBS, TAS and ATS shapers is now available in RTaW-Pegase, both timing-accurate simulation and worst-case traversal time analysis.
TSN is the new real-time Ethernet: The IEEE 802.1 TSN TG (Time Sensitive Networking Technical Group), started in 2012, develops and standardizes technologies to address QoS requirements pertaining to timing and reliability on top of Ethernet. In particular, the TSN TG has developed several mechanisms that provide a predictable, sometimes deterministic, timing behavior in e.g. amendements IEEE 802.1Qbv (Time-Aware Shaper – TAS), IEEE 802.1Qbu (Frame Preemption) and IEEE 802.1Qcr (Asynchronous Traffic Shaper – ATS). These new set of mechanisms add to the well-known Credit-Based Shaper (CBS), standardized in IEEE 8021.Qav, which pre-dates TSN.
TSN allows for a combination of several QoS mechanisms at a single output port: These QoS protocols can be used in a combined manner in addition to the mere use of priorities. This opens up a large space of possibilities for the designer. However, a mission-critical network must remain predictable from the timing perspective. RTaW-Pegase supports combinations of QoS mechanisms that correspond to a wide range of possible practical use-cases, and offers a network-calculus-based worst-case analysis for each of them.
Thus, at each egress port, it is for instance possible to use a combination of ATS and CBS, or TAS and CBS. The QoS mechanism for a given queue can be chosen independently of the other queues. Importantly, CBS and ATS can be used at any priority level and for an arbitrary number of queues.
In addition, it is possible to have “time-triggered traffic” (aka “scheduled traffic”, defined in 802.1Qbv), with reserved transmission windows, for one of the 8 queues. TSN, with the help of a gate system based on a schedule (the “Time Aware Shaper”) allows certain queues to transmit packets or forbids them from transmitting packets over pre-defined time intervals. The most common configuration strategy at this time is called “exclusive gating”: the highest criticality traffic has an exclusive access to the link during pre-defined time intervals, while outside of those intervals, the other traffic classes have access to the link.
Finally, with Pegase, it also possible to model the use of frame preemption for each of the queues, which offers an alternative to TAS to reduce the interferences of low-priority packets (interested in the different types of interferences on a TSN network? Consult this post).
RTaW-Pegase provides you exclusive features:
- RTaW-Pegase is the only tool that offers both simulation and worst-case analysis in a single environment,
- It also is the only one that can combine CBS, TAS, priorities and ATS at a single output port, considering the timing interactions between schedulers.
Interested in network calculus? You may be interested in our recent works: algorithmic complexity improvements, a new worst-case analyses for AVB/CBS and Network-on-Chips co-authored with our partner Onera. Coming soon: Cyclic Queuing and Forwarding (P802.1Qch) study.