Routing algorithms for IEEE802.1Qbv networks

Abstract

The recently published IEEE 802.1Qbv standard specifies enhancements for providing real-time communication guarantees for time-triggered flows while also handling best-effort traffic in a converged Ethernet network. The enhancements include a programmable time-based gating mechanism for stipulating which of the queues of an egress port are available for transmission at any given point of time. By appropriately programming (opening and closing) these gates, the traversal of packets through the network can be controlled to precisely follow a precomputed schedule that satisfies the timing constraints of the time-triggered flows. Computing such transmission schedules requires routing of the flows in the first step, followed by the computation of gate schedules for the flows along their respective routes. So far off-the-shelf algorithms like shortest path routing, which optimize the number of hops over which flows are routed, have been used for computing routes for the time-triggered traffic. In this paper, we explore how the routing of time-triggered flows affects their schedulability. Moreover, we identify additional parameters that must be considered while routing time-triggered traffic and propose ILP-based algorithms for the purpose. Our evaluations show that the proposed routing algorithms could improve the slack in the computed schedules by upto 60 % and 30 % compared to shortest path routing and equal cost multi-pathing (ECMP), respectively, and, thus, increase the capacity of the network to accommodate more time-triggered traffic.