  Bundling multiple access technologies increases capacity, resiliency and
robustness of network connections. Multi-access is currently being standardized
in the ATSSS framework in 3GPP, supporting different access bundling
strategies. Within ATSSS, a multipath scheduler needs to decide which path to
use for each user packet based on path characteristics. The Cheapest Path First
(CPF) scheduler aims to utilize the cheapest path (e.g. WiFi) before sending
packets over other paths (e.g. cellular). In this paper, we demonstrate that
using CPF with an MP-DCCP tunnel may lead to sub-optimal performance. This is
due to adverse interactions between the scheduler and end-to-end and tunnel
congestion control. Hence, we design the Adaptive Cheapest Path First (ACPF)
scheduler that limits queue buildup in the primary bottleneck and moves traffic
to the secondary path earlier. We implement ACPF over both TCP and DCCP
congestion controlled tunnels. Our evaluation shows that ACPF improves the
average throughput over CPF between 24% to 86%.
