Prophet: Real-time Queue Length Inference in Programmable Switches

Programmable switches enable the implementation of many complex network functions directly in the data plane. Protocol Independent Switch Architecture (PISA) is a stateof-the-art architecture for programmable switches [1]. After entering a PISA switch, packets first go through an ingress pipeline, then enter the traffic manager that maintains multiple queues, and are finally processed by an egress pipeline. However, there exists an intrinsic constraint in PISA. The traffic manager generates metadatas of queue lengths which are only accessible in egress, while the ingress has no visibility in the queue status. This prevents PISA switches from supporting many advanced network functions. For instance, DRILL [3] employs per-packet load balancing by deciding which queue a packet should enter based on the lengths of candidate queues. The decision has to happen in ingress before packet queuing, which cannot be supported in PISA.