ipcpd: Add flow overshoot protection to mb-ecntestingbe

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 <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 1 insertions, 0 deletions

diff --git a/irmd.conf.in b/irmd.conf.in
index b9b79782..02cb1da3 100644
--- a/irmd.conf.in
+++ b/irmd.conf.in
@@ -113,6 +113,7 @@ autobind=true           # Defaults to false.
 # addr_size=4           # Defaults to 4 (32-bit addresses).
 # eid_size=8            # Defaults to 8 (64-bit endpoint IDs, only accepted option).
 # max_ttl=60            # Defaults to 60 (max 255).
+# max_rtt=200           # Defaults to 200 (max 65535).
 # addr-auth="flat"      # Defaults to flat (currently only option).
 # routing="lfa"         # Defaults to link-state (options: link-state, lfa, ecmp).
 # ls_t_recalc=4         # Forwarding Function update interval (s) (Default 4).