congure_reno: initial import of TCP Reno congestion control

sys/Makefile.dep

@@ -41,6 +41,14 @@ ifneq (,$(filter congure_test,$(USEMODULE)))
   USEMODULE += fmt
 endif
 
+ifneq (,$(filter congure_reno,$(USEMODULE)))
+  USEMODULE += congure_reno_methods
+endif
+
+ifneq (,$(filter congure_reno_methods,$(USEMODULE)))
+  USEMODULE += seq
+endif
+
 ifneq (,$(filter eepreg,$(USEMODULE)))
   FEATURES_REQUIRED += periph_eeprom
 endif

sys/congure/Kconfig

@@ -9,6 +9,7 @@ menu "CongURE congestion control abstraction"
     depends on USEMODULE_CONGURE
 
 rsource "mock/Kconfig"
+rsource "reno/Kconfig"
 rsource "test/Kconfig"
 
 endmenu # CongURE congestion control abstraction
@@ -22,6 +23,7 @@ menuconfig MODULE_CONGURE
 if MODULE_CONGURE
 
 rsource "mock/Kconfig"
+rsource "reno/Kconfig"
 rsource "test/Kconfig"
 
 endif   # MODULE_CONGURE

sys/congure/Makefile

@@ -1,6 +1,12 @@
 ifneq (,$(filter congure_mock,$(USEMODULE)))
   DIRS += mock
 endif
+ifneq (,$(filter congure_reno,$(USEMODULE)))
+  DIRS += reno
+endif
+ifneq (,$(filter congure_reno_methods,$(USEMODULE)))
+  DIRS += reno/methods
+endif
 ifneq (,$(filter congure_test,$(USEMODULE)))
   DIRS += test
 endif

sys/congure/reno/Kconfig

@@ -0,0 +1,14 @@
+config MODULE_CONGURE_RENO
+    bool "CongURE implementation of TCP Reno"
+    depends on MODULE_CONGURE
+    select MODULE_CONGURE_RENO_METHODS
+
+config MODULE_CONGURE_RENO_METHODS
+    bool "Send driver methods for the CongURE implementation of TCP Reno"
+    depends on MODULE_SEQ
+    help
+        Many other congestion control mechanisms are just adaptations of TCP
+        Reno, so this makes the methods of @ref sys_congure_reno available to
+        other @ref sys_congure modules. Use module `congure_reno_methods` to
+        only compile in these modules, but not the driver for
+        `congure_reno_snd_t` or @ref congure_reno_snd_setup().

sys/congure/reno/Makefile

@@ -0,0 +1,3 @@
+MODULE := congure_reno
+
+include $(RIOTBASE)/Makefile.base

sys/congure/reno/congure_reno.c

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2021 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ * @author  Martine Lenders <[email protected]>
+ */
+
+#include "congure/reno.h"
+
+static const congure_snd_driver_t _driver = {
+    .init = congure_reno_snd_init,
+    .inter_msg_interval = congure_reno_snd_inter_msg_interval,
+    .report_msg_sent = congure_reno_snd_report_msg_sent,
+    .report_msg_discarded = congure_reno_snd_report_msg_discarded,
+    .report_msgs_timeout = congure_reno_snd_report_msgs_timeout,
+    .report_msgs_lost = congure_reno_snd_report_msgs_lost,
+    .report_msg_acked = congure_reno_snd_report_msg_acked,
+    .report_ecn_ce = congure_reno_snd_report_ecn_ce,
+};
+
+void congure_reno_snd_setup(congure_reno_snd_t *c,
+                            const congure_reno_snd_consts_t *consts)
+{
+    c->super.driver = &_driver;
+    c->consts = consts;
+}
+
+/** @} */

sys/congure/reno/methods/Makefile

@@ -0,0 +1,3 @@
+MODULE := congure_reno_methods
+
+include $(RIOTBASE)/Makefile.base

sys/congure/reno/methods/congure_reno_methods.c

@@ -0,0 +1,248 @@
+/*
+ * Copyright (C) 2021 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ * @author  Martine Lenders <[email protected]>
+ */
+
+#include <assert.h>
+#include <stdint.h>
+
+#include "clist.h"
+#include "seq.h"
+
+#include "congure/reno.h"
+
+static int _snd_in_fast_retransmit(congure_snd_t *cong)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    return (c->dup_acks >= c->consts->frthresh);
+}
+
+static inline congure_wnd_size_t _calc_init_wnd(congure_reno_snd_t *c)
+{
+    /* see https://tools.ietf.org/html/rfc5681#section-3.1 */
+    if (c->mss > c->consts->cwnd_upper) {
+        return 2 * c->mss;
+    }
+    else if (c->mss <= c->consts->cwnd_lower) {
+        return 4 * c->mss;
+    }
+    else {
+        return 3 * c->mss;
+    }
+}
+
+static void _fr_cwnd_dec(congure_reno_snd_t *c)
+{
+    if (c->consts->fr_cwnd_dec) {
+        c->consts->fr_cwnd_dec(c);
+    }
+    else {
+        /* max(c->mss * 2, c->super.cwnd / 2) */
+        c->ssthresh = ((c->mss * 4) > c->super.cwnd)
+                      ? (c->mss * 2) : (c->super.cwnd / 2);
+        c->super.cwnd = c->ssthresh + (3 * c->mss);
+    }
+}
+
+static void _enforce_fast_retransmit(congure_reno_snd_t *c)
+{
+    if (!_snd_in_fast_retransmit(&c->super)) {
+        c->dup_acks = c->consts->frthresh;
+    }
+    _fr_cwnd_dec(c);
+    c->consts->fr(c);
+}
+
+static void _dec_flight_size(congure_reno_snd_t *c, unsigned msg_size)
+{
+    /* check for integer underflow */
+    if ((c->in_flight_size - msg_size) > c->in_flight_size) {
+        c->in_flight_size = 0U;
+    }
+    else {
+        c->in_flight_size -= msg_size;
+    }
+}
+
+void congure_reno_set_mss(congure_reno_snd_t *c, congure_wnd_size_t mss)
+{
+    c->mss = mss;
+    c->super.cwnd = _calc_init_wnd(c);
+}
+
+void congure_reno_snd_init(congure_snd_t *cong, void *ctx)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    c->super.ctx = ctx;
+    c->mss = c->consts->init_mss;
+    c->last_ack = UINT32_MAX;
+    c->super.cwnd = _calc_init_wnd(c);
+    c->ssthresh = c->consts->init_ssthresh;
+    c->dup_acks = 0;
+}
+
+int32_t congure_reno_snd_inter_msg_interval(congure_snd_t *cong,
+                                            unsigned msg_size)
+{
+    (void)cong;
+    (void)msg_size;
+    return -1;
+}
+
+void congure_reno_snd_report_msg_sent(congure_snd_t *cong, unsigned sent_size)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    if ((c->in_flight_size + sent_size) < c->super.cwnd) {
+        c->in_flight_size += sent_size;
+    }
+    else {
+        /* state machine is dependent on flight size being smaller or equal
+         * to cwnd as such cap cwnd here, in case caller reports a message in
+         * flight that was marked as lost, but the caller is using a later
+         * message to send another ACK. */
+        c->in_flight_size = c->super.cwnd;
+    }
+}
+
+void congure_reno_snd_report_msg_discarded(congure_snd_t *cong,
+                                           unsigned msg_size)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    assert(msg_size <= c->in_flight_size);
+
+    _dec_flight_size(c, msg_size);
+}
+
+int _check_resends(clist_node_t *node, void *ctx)
+{
+    congure_snd_msg_t *msg = (congure_snd_msg_t *)node;
+
+    (void)ctx;
+    if (msg->resends == 0) {
+        return 1;
+    }
+    return 0;
+}
+
+int _mark_msg_lost(clist_node_t *node, void *ctx)
+{
+    congure_snd_msg_t *msg = (congure_snd_msg_t *)node;
+    congure_reno_snd_t *c = (void *)ctx;
+
+    _dec_flight_size(c, msg->size);
+    return 0;
+}
+
+void congure_reno_snd_report_msgs_timeout(congure_snd_t *cong,
+                                          congure_snd_msg_t *msgs)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    if (msgs) {
+        if (clist_foreach(&msgs->super, _check_resends, NULL)) {
+            /* see https://tools.ietf.org/html/rfc5681#section-3.1 equation 4 */
+            c->ssthresh = ((c->in_flight_size / 2) > (c->mss * 2))
+                          ? (c->in_flight_size / 2)
+                          : (c->mss * 2);
+        }
+        /* do decrementing of flight size _after_ ssthresh reduction,
+         * since we use the in_flight_size there */
+        clist_foreach(&msgs->super, _mark_msg_lost, c);
+        /* > Furthermore, upon a timeout (as specified in [RFC2988]) cwnd
+         * > MUST be set to no more than the loss window, LW, which equals
+         * > 1 full-sized segment (regardless of the value of IW). */
+        c->super.cwnd = c->mss;
+    }
+}
+
+void congure_reno_snd_report_msgs_lost(congure_snd_t *cong,
+                                       congure_snd_msg_t *msgs)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    clist_foreach(&msgs->super, _mark_msg_lost, c);
+    _enforce_fast_retransmit(c);
+}
+
+void congure_reno_snd_report_msg_acked(congure_snd_t *cong,
+                                       congure_snd_msg_t *msg,
+                                       congure_snd_ack_t *ack)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    if (seq32_compare(ack->id, c->last_ack) <= 0) {
+        /* check for duplicate ACK according to
+         * https://tools.ietf.org/html/rfc5681#section-2
+         * An acknowledgment is considered a "duplicate" [...] when
+         * (a) the receiver of the ACK has outstanding data, */
+        if ((c->in_flight_size > 0) &&
+            /* (b) the incoming acknowledgment carries no data, */
+            (ack->size == 0) &&
+            /* (c) the SYN and FIN bits are both off */
+            (ack->clean) &&
+            /* (d) the acknowledgment number is equal to the greatest
+             *     acknowledgment received on the given connection, and */
+            (ack->id == c->last_ack) &&
+            /* (e) the advertised window in the incoming acknowledgment equals
+             *     the advertised window in the last incoming acknowledgment. */
+            ((ack->wnd == 0) || (c->consts->same_wnd_adv(c, ack)))) {
+            c->dup_acks++;
+            if (_snd_in_fast_retransmit(cong)) {
+                _fr_cwnd_dec(c);
+                c->consts->fr(c);
+            }
+        }
+    }
+    else {
+        c->dup_acks = 0;
+        c->last_ack = ack->id;
+        if (c->super.cwnd < c->ssthresh) {
+            /* slow start */
+            if (c->consts->ss_cwnd_inc) {
+                c->consts->ss_cwnd_inc(c);
+            }
+            else {
+                c->super.cwnd += (c->in_flight_size < c->mss)
+                                 ? c->in_flight_size
+                                 : c->mss;
+            }
+        }
+        else {
+            /* congestion avoidance */
+            if (c->consts->ca_cwnd_inc) {
+                c->consts->ca_cwnd_inc(c);
+            }
+            else {
+                c->super.cwnd += c->mss;
+            }
+        }
+        assert(msg->size <= c->in_flight_size);
+        _dec_flight_size(c, msg->size);
+    }
+}
+
+void congure_reno_snd_report_ecn_ce(congure_snd_t *cong, ztimer_now_t time)
+{
+    congure_reno_snd_t *c = (congure_reno_snd_t *)cong;
+
+    /* see https://tools.ietf.org/html/rfc8311#section-4.1 */
+    (void)time;
+    c->super.cwnd /= 2;
+    c->ssthresh -= c->mss;
+}
+
+/** @} */