From 3388bd9e9b82df6d7fe79fa4eee7c22a3277624e Mon Sep 17 00:00:00 2001 From: Dimitri Staessens Date: Tue, 21 Jul 2026 06:54:55 +0200 Subject: ipcpd: Add flow overshoot protection to mb-ecn The ECN marks were the only source of congestion information, and going into congestion collapse (dropping a lot of ECN packets and causing loss of signal) was unrecoverable. The sender's slow-start ramp clock now tracks a measured RTT to avoid overshooting into congestion collapse on the previously fixed (14ms) doubling on long-delay (e.g. 100ms) links. The flow allocator now carries a periodic heartbeat/ack to keep RTT estimates up-to-date. The heartbeat also serves as a congestion collapse detector: consecutive heartbeat losses will go into loss recovery, halving the window and pausing Additive Increase until the path is clear. The DT component now has a max_rtt config parameter that serves as a hint for the layer RTT to optimize slow-start for low-latency networks. These two mechanisms follow TCP, however only during slow start up to the first ECN signal and to recover from a total collapse until the ECN signal returns. MB-ECN is still fully RTT-independent in the AI/PD region. A shorter RTT path will just reach its equal fair share faster than a longer RTT path. Signed-off-by: Dimitri Staessens Signed-off-by: Sander Vrijders --- src/ipcpd/unicast/main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/ipcpd/unicast/main.c') diff --git a/src/ipcpd/unicast/main.c b/src/ipcpd/unicast/main.c index 1155b88b..86cb1f06 100644 --- a/src/ipcpd/unicast/main.c +++ b/src/ipcpd/unicast/main.c @@ -67,7 +67,7 @@ static int initialize_components(struct ipcp_config * conf) log_info("IPCP got address %" PRIu64 ".", addr_auth_address()); - if (ca_init(conf->unicast.cong_avoid)) { + if (ca_init(conf->unicast.cong_avoid, conf->unicast.dt.max_rtt)) { log_err("Failed to initialize congestion avoidance."); goto fail_ca; } -- cgit v1.2.3