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/lib/pb/ipcp_config.proto | 1 + 1 file changed, 1 insertion(+) (limited to 'src/lib/pb/ipcp_config.proto') diff --git a/src/lib/pb/ipcp_config.proto b/src/lib/pb/ipcp_config.proto index eac4da37..a111b6d8 100644 --- a/src/lib/pb/ipcp_config.proto +++ b/src/lib/pb/ipcp_config.proto @@ -42,6 +42,7 @@ message dt_config_msg { required uint32 eid_size = 2; required uint32 max_ttl = 3; required routing_config_msg routing = 4; + optional uint32 max_rtt = 5; } message dir_dht_config_msg { -- cgit v1.2.3