Congestion-Aware Multipath Tunnel Selection for Transport Services

This document addresses the transport-layer challenges of path selection in environments with multiple available tunneling options and congestion control mechanisms. It identifies congestion control conflicts that arise from nested tunneling protocols and proposes a congestion-aware multipath tunnel selection algorithm that conforms to the guidelines established in [RFC9599] for adding congestion notification to protocols that encapsulate IP. The proposed approach considers Explicit Congestion Notification (ECN) propagation, transport protocol characteristics, and network conditions to optimize path selection while avoiding multilevel congestion control issues. This work aligns with current Transport and Services Working Group efforts on Non-Queue-Building (NQB) behaviors, careful congestion control resume, and multipath transport protocols.