ipcpd: Rework congestion avoidance

Congestion avoidance is a property of the layer, orthogonal to ARQ
and to flow control: FRCP retransmits and lets the peer pace the
sender, per flow, end-to-end; the IPCP paces path aggregates. Each
signal means one thing: a loss triggers a retransmission, a mark
means congestion, the peer window means a slow receiver. Every flow
is paced by the same rate law whatever its QoS, so a greedy raw
sender shares a bottleneck fairly with a reliable stream.

The unit of control is the (destination address, QoS cube)
aggregate: all flows toward that destination share one controller
and one rate; a start-time fair-queuing pacer divides the rate
across them by deadline instead of blocking the send path, and a
new flow rides the aggregate's estimates at its current rate, with
no probing of its own. Slow start runs once per aggregate.

The congestion signal is a multi-bit magnitude: forwarders mark
packets with their standing queue depth, MAX-combined across hops,
so a packet carries the deepest queue on its path. The receiver
feeds back a time-integral mean over a window that adapts to the
flow's byte rate, measuring a slow flow with the same fidelity as a
fast one. The sender runs AIMD scaled by elapsed wall-clock time,
which makes the steady-state allocation RTT-independent.

The PCI gains one byte: the path capacity as a quarter-log2 code.
Forwarders estimate their egress rate from busy-period drain and
MIN-stamp the byte, the receiver returns the window minimum with
its feedback, and the sender scales its rate floor and additive
slope to the bottleneck (C / 32). A deep cut implies a backlogged
bottleneck and a backlogged bottleneck advertises its capacity, so
the scaled floor is live exactly when recovery needs it: the probe
heals a halving in seconds at any link rate, and the floor bounds
the deepest hole to a factor 32 below the bottleneck.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lib/ssm/rbuff.c b/src/lib/ssm/rbuff.c
index 7886b5c2..04978d82 100644
--- a/src/lib/ssm/rbuff.c
+++ b/src/lib/ssm/rbuff.c
@@ -74,7 +74,7 @@ struct ssm_rbuff {
         ssize_t *         shm_base;     /* start of shared memory   */
         size_t *          head;         /* start of ringbuffer      */
         size_t *          tail;
-        size_t *          flags;          /* out-of-band flags (RB_*) */
+        size_t *          flags;        /* out-of-band flags (RB_*) */
         pthread_mutex_t * mtx;          /* lock for cond vars only  */
         pthread_cond_t *  add;          /* signal when new data     */
         pthread_cond_t *  del;          /* signal when data removed */