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/tools/irm/irm_ipcp_bootstrap.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'src/tools') diff --git a/src/tools/irm/irm_ipcp_bootstrap.c b/src/tools/irm/irm_ipcp_bootstrap.c index de73b076..cc8bf8fa 100644 --- a/src/tools/irm/irm_ipcp_bootstrap.c +++ b/src/tools/irm/irm_ipcp_bootstrap.c @@ -105,7 +105,8 @@ static char * usage_str = \ " [Data Transfer Constants]\n" " [addr
(default: %d)]\n" " [eid (default: %d)]\n" - " [ttl , default: %d)]\n\n" + " [ttl , default: %d)]\n" + " [rtt (default: %d)]\n\n" "if DIRECTORY_POLICY == " DHT_DIR "\n" " [dht_alpha (default: %u)]\n" " [dht_k (default: %u)]\n" @@ -152,7 +153,7 @@ static void usage(void) /* unicast */ FLAT_RANDOM, DHT_DIR, SHA3_256, LINK_STATE, MB_ECN_CA, /* dt */ - DT(addr_size), DT(eid_size), DT(max_ttl), + DT(addr_size), DT(eid_size), DT(max_ttl), DT(max_rtt), /* dht */ DHT(alpha), DHT(k), DHT(t_expire), DHT(t_refresh), DHT(t_replicate), @@ -184,6 +185,7 @@ int do_bootstrap_ipcp(int argc, uint8_t addr_size = DT(addr_size); uint8_t eid_size = DT(eid_size); uint8_t max_ttl = DT(max_ttl); + uint16_t max_rtt = DT(max_rtt); struct routing_config routing = default_routing_config; enum pol_addr_auth addr_auth_type = UNI(addr_auth_type); enum pol_cong_avoid cong_avoid = UNI(cong_avoid); @@ -250,6 +252,8 @@ int do_bootstrap_ipcp(int argc, eid_size = atoi(*(argv + 1)); } else if (matches(*argv, "ttl") == 0) { max_ttl = atoi(*(argv + 1)); + } else if (matches(*argv, "rtt") == 0) { + max_rtt = atoi(*(argv + 1)); } else if (matches(*argv, "port") == 0) { port4 = atoi(*(argv + 1)); port6 = port4; @@ -422,6 +426,7 @@ int do_bootstrap_ipcp(int argc, conf.unicast.dt.addr_size = addr_size; conf.unicast.dt.eid_size = eid_size; conf.unicast.dt.max_ttl = max_ttl; + conf.unicast.dt.max_rtt = max_rtt; conf.unicast.dt.routing = routing; conf.unicast.addr_auth_type = addr_auth_type; conf.unicast.cong_avoid = cong_avoid; -- cgit v1.2.3