Work-in-Progress: Layering Concerns for the Analysis of Credit-Based Shaping in IEEE 802.1 TSN

Flow control is of particular importance in TimeSensitive Networking (TSN), where timeliness of messages is guaranteed through several types of traffic shaping. This has given rise to a number of papers discussing the worst-case response time analysis of, in particular, the credit-based traffic shaping approach. In this work-in-progress paper, we concern ourselves with the possibility that traffic shaping can be applied in different layers of the protocol stack, e.g., the physical layer and link layer, which may give rise to different credit behaviors. We convey our concern that the analysis performed in literature seems to assume application of traffic shaping in the physical layer, and that the analysis therefore cannot be readily used in a context where shaping is applied in a higher layer. In particular, assuming application of credit-based shaping in the link layer, there are different interpretations possible for credit behavior. Depending on the interpretation, some of the basic properties of credit, that are crucial for the analysis, may no longer be valid after overhead is added by the physical layer. As an ongoing effort, we plan to revisit the eligible interval analysis of [1] with an adaptation for a link layer interpretation of the standard concerning application of traffic shaping.