[RFC] tcp: Add TCP ROCCET congestion control module.

[Tim Fuechsel <t.fuechsel@gmx.de>]

TCP ROCCET is an extension of TCP CUBIC that improves its overall
performance. By its mode of function, CUBIC causes bufferbloat while
it tries to detect the available throughput of a network path. This is
particularly a problem with large buffers in mobile networks. A more
detailed description and analysis of this problem caused by TCP CUBIC
can be found in [1]. TCP ROCCET addresses this problem by adding two
additional metrics to detect congestion (queueing and bufferbloat)
on a network path. TCP ROCCET achieves better performance than CUBIC
and BBRv3, by maintaining similar throughput while reducing the latency.
In addition, TCP ROCCET does not have fairness issues when sharing a
link with TCP CUBIC and BBRv3. A paper that evaluates the performance
and function of TCP ROCCET has already been peer-reviewed and will be
presented at the WONS 2026 conference. A draft of this paper can be
found here [2].

[1] https://doi.org/10.1109/VTC2023-Fall60731.2023.10333357
[2] https://arxiv.org/abs/2510.25281

Signed-off-by: Lukas Prause <lukas.prause@ikt.uni-hannover.de>
Signed-off-by: Tim Fuechsel <t.fuechsel@gmx.de>
---
 net/ipv4/Kconfig      |  12 +
 net/ipv4/Makefile     |   1 +
 net/ipv4/tcp_roccet.c | 686 ++++++++++++++++++++++++++++++++++++++++++
 net/ipv4/tcp_roccet.h |  52 ++++
 4 files changed, 751 insertions(+)
 create mode 100644 net/ipv4/tcp_roccet.c
 create mode 100644 net/ipv4/tcp_roccet.h

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index b71c22475c51..781a0db37309 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -664,6 +664,18 @@ config TCP_CONG_CDG
 	    delay gradients." In Networking 2011. Preprint:
 	    http://caia.swin.edu.au/cv/dahayes/content/networking2011-cdg-preprint.pdf
 
+config TCP_CONG_ROCCET
+	tristate "ROCCET TCP"
+	default n
+	help
+      TCP ROCCET is a sender-side only modification of the TCP CUBIC
+      protocol stack that optimizes the performance of TCP congestion
+      control. Especially for networks with large buffers (wireless,
+      cellular networks), TCP ROCCET has improved performance by maintaining
+      similar throughput as CUBIC while reducing the latency.
+       For more information, see: https://arxiv.org/abs/2510.25281
+
+
 config TCP_CONG_BBR
 	tristate "BBR TCP"
 	default n
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index ec36d2ec059e..35fa62b6d07f 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
 obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o
 obj-$(CONFIG_INET_RAW_DIAG) += raw_diag.o
 obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o
+obj-$(CONFIG_TCP_CONG_ROCCET) += tcp_roccet.o
 obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o
 obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
diff --git a/net/ipv4/tcp_roccet.c b/net/ipv4/tcp_roccet.c
new file mode 100644
index 000000000000..998a97bcb03e
--- /dev/null
+++ b/net/ipv4/tcp_roccet.c
@@ -0,0 +1,686 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * TCP ROCCET: An RTT-Oriented CUBIC Congestion Control
+ * Extension for 5G and Beyond Networks
+ *
+ * TCP ROCCET is a new TCP congestion control
+ * algorithm suited for current cellular 5G NR beyond networks.
+ * It extends the kernel default congestion control CUBIC
+ * and improves its performance, and additionally solves an
+ * unwanted side effects of CUBIC’s implementation.
+ * ROCCET uses its own Slow Start, called LAUNCH, where loss
+ * is not considered as a congestion event.
+ * The congestion avoidance phase, called ORBITER, uses
+ * CUBIC's window growth function and adds, based on RTT
+ * and ACK rate, congestion events.
+ *
+ * A peer-reviewed paper on TCP ROCCET will be presented at the WONS 2026 conference.
+ * A draft of the paper is available here:
+ *		https://arxiv.org/abs/2510.25281
+ *
+ *
+ * Further information about CUBIC:
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
+ * Home page:
+ *	http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
+ * This is from the implementation of CUBIC TCP in
+ * Sangtae Ha, Injong Rhee and Lisong Xu,
+ *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
+ *  in ACM SIGOPS Operating System Review, July 2008.
+ * Available from:
+ *	http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
+ *
+ * CUBIC integrates a new slow start algorithm, called HyStart.
+ * The details of HyStart are presented in
+ *  Sangtae Ha and Injong Rhee,
+ *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
+ * Available from:
+ *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
+ *
+ * All testing results are available from:
+ * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
+ *
+ * Unless CUBIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include "tcp_roccet.h"
+#include "linux/printk.h"
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+#include <linux/math64.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+/* Scale factor beta calculation (max_cwnd = snd_cwnd * beta) */
+#define BICTCP_BETA_SCALE 1024
+
+#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
+
+/* Alpha value for the sRrTT  multiplied by 100.
+ * Here 20 represents a value of 0.2
+ */
+#define ROCCET_ALPHA_TIMES_100 20
+
+/* The amount of seconds ROCCET stores a minRTT.
+ * Enable "calculate_min_rtt" first.
+ */
+#define ROCCET_RTT_LOOKBACK_S 10
+
+/* Parameters that are specific to the ROCCET-Algorithm */
+static int sr_rtt_upper_bound __read_mostly = 100;
+static int ack_rate_diff_ss __read_mostly = 10;
+static int ack_rate_diff_ca __read_mostly = 200;
+static bool calculate_min_rtt __read_mostly;
+static bool ignore_loss __read_mostly;
+static int roccet_min_rtt_interpolation_factor __read_mostly = 70;
+
+module_param(sr_rtt_upper_bound, int, 0644);
+MODULE_PARM_DESC(sr_rtt_upper_bound, "ROCCET's upper bound for srRTT.");
+module_param(ack_rate_diff_ss, int, 0644);
+MODULE_PARM_DESC(ack_rate_diff_ss,
+		 "ROCCET's threshold to exit slow start if ACK-rate defer by given amount of segments.");
+module_param(ack_rate_diff_ca, int, 0644);
+MODULE_PARM_DESC(ack_rate_diff_ca,
+		 "ROCCET's threshold for ack-rate and cum_cwnd, in percentage of the current cwnd.");
+module_param(calculate_min_rtt, bool, 0644);
+MODULE_PARM_DESC(calculate_min_rtt,
+		 "Calculate min RTT if no lower RTT occurs after 10 sec.");
+module_param(ignore_loss, bool, 0644);
+MODULE_PARM_DESC(ignore_loss, "Ignore loss as a congestion event.");
+module_param(roccet_min_rtt_interpolation_factor, int, 0644);
+MODULE_PARM_DESC(roccet_min_rtt_interpolation_factor,
+		 "ROCCET factor for interpolating the current RTT with the last minRTT (minRTT = (factor * currRTT + (100-factor) * minRTT) / 100)");
+
+static bool fast_convergence __read_mostly = true;
+static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
+static int initial_ssthresh __read_mostly;
+static int bic_scale __read_mostly = 41;
+static bool tcp_friendliness __read_mostly = true;
+
+static u32 cube_rtt_scale __read_mostly;
+static u32 beta_scale __read_mostly;
+static u64 cube_factor __read_mostly;
+
+/* Note parameters that are used for precomputing scale factors are read-only */
+module_param(fast_convergence, bool, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(bic_scale, int, 0444);
+MODULE_PARM_DESC(bic_scale,
+		 "scale (scaled by 1024) value for bic function (bic_scale/1024)");
+module_param(tcp_friendliness, bool, 0644);
+MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
+
+static inline void roccettcp_reset(struct roccettcp *ca)
+{
+	memset(ca, 0, offsetof(struct roccettcp, curr_rtt));
+	ca->bw_limit.sum_cwnd = 1;
+	ca->bw_limit.sum_acked = 1;
+	ca->bw_limit.next_check = 0;
+	ca->curr_min_rtt_timed.rtt = ~0U;
+	ca->curr_min_rtt_timed.time = ~0U;
+	ca->ece_srrtt = 0;
+	ca->ece_cwnd = 2;
+}
+
+static inline void update_min_rtt(struct sock *sk)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+	u32 now = jiffies_to_usecs(tcp_jiffies32);
+
+	if (now - ca->curr_min_rtt_timed.time >
+		    ROCCET_RTT_LOOKBACK_S * USEC_PER_SEC &&
+	    calculate_min_rtt) {
+		u32 new_min_rtt = max(ca->curr_rtt, 1);
+		u32 old_min_rtt = ca->curr_min_rtt_timed.rtt;
+
+		u32 interpolated_min_rtt =
+			(new_min_rtt * roccet_min_rtt_interpolation_factor +
+			 old_min_rtt *
+				 (100 - roccet_min_rtt_interpolation_factor)) /
+			100;
+
+		ca->curr_min_rtt_timed.rtt = interpolated_min_rtt;
+		ca->curr_min_rtt_timed.time = now;
+	}
+
+	/* Check if new lower min RTT was found. If so, set it directly */
+	if (ca->curr_rtt < ca->curr_min_rtt_timed.rtt) {
+		ca->curr_min_rtt_timed.rtt = max(ca->curr_rtt, 1);
+		ca->curr_min_rtt_timed.time = now;
+	}
+}
+
+/* Return difference between last and current ack rate.
+ */
+static inline int get_ack_rate_diff(struct roccettcp *ca)
+{
+	return ca->ack_rate.last_rate - ca->ack_rate.curr_rate;
+}
+
+/* Update ack rate sampled by 100ms.
+ */
+static inline void update_ack_rate(struct sock *sk)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+	u32 now = jiffies_to_usecs(tcp_jiffies32);
+	u32 interval = USEC_PER_MSEC * 100;
+
+	if ((u32)(now - ca->ack_rate.last_rate_time) >= interval) {
+		ca->ack_rate.last_rate_time = now;
+		ca->ack_rate.last_rate = ca->ack_rate.curr_rate;
+		ca->ack_rate.curr_rate = ca->ack_rate.cnt;
+		ca->ack_rate.cnt = 0;
+	} else {
+		ca->ack_rate.cnt += 1;
+	}
+}
+
+/* Compute srRTT.
+ */
+static inline void update_srrtt(struct sock *sk)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	if (ca->curr_min_rtt_timed.rtt == 0)
+		return;
+
+	/* Calculate the new rRTT (Scaled by 100).
+	 * 100 * ((sRTT - sRTT_min) / sRTT_min)
+	 */
+	u32 rrtt = (100 * (ca->curr_rtt - ca->curr_min_rtt_timed.rtt)) /
+		   ca->curr_min_rtt_timed.rtt;
+
+	// (1 - alpha) * srRTT + alpha * rRTT
+	ca->curr_srrtt = ((100 - ROCCET_ALPHA_TIMES_100) * ca->curr_srrtt +
+			  ROCCET_ALPHA_TIMES_100 * rrtt) /
+			 100;
+}
+
+__bpf_kfunc static void roccettcp_init(struct sock *sk)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	roccettcp_reset(ca);
+
+	if (initial_ssthresh)
+		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
+
+	/* Initial roccet parameters */
+	ca->roccet_last_event_time_us = 0;
+	ca->ack_rate.last_rate = 0;
+	ca->ack_rate.last_rate_time = 0;
+	ca->ack_rate.curr_rate = 0;
+	ca->ack_rate.cnt = 0;
+}
+
+__bpf_kfunc static void roccettcp_cwnd_event(struct sock *sk,
+					     enum tcp_ca_event event)
+{
+	if (event == CA_EVENT_TX_START) {
+		struct roccettcp *ca = inet_csk_ca(sk);
+		u32 now = tcp_jiffies32;
+		s32 delta;
+
+		delta = now - tcp_sk(sk)->lsndtime;
+
+		/* We were application limited (idle) for a while.
+		 * Shift epoch_start to keep cwnd growth to cubic curve.
+		 */
+		if (ca->epoch_start && delta > 0) {
+			ca->epoch_start += delta;
+			if (after(ca->epoch_start, now))
+				ca->epoch_start = now;
+		}
+		return;
+	}
+}
+
+/* calculate the cubic root of x using a table lookup followed by one
+ * Newton-Raphson iteration.
+ * Avg err ~= 0.195%
+ */
+static u32 cubic_root(u64 a)
+{
+	u32 x, b, shift;
+	/* cbrt(x) MSB values for x MSB values in [0..63].
+	 * Precomputed then refined by hand - Willy Tarreau
+	 *
+	 * For x in [0..63],
+	 *   v = cbrt(x << 18) - 1
+	 *   cbrt(x) = (v[x] + 10) >> 6
+	 */
+	static const u8 v[] = {
+		/* 0x00 */ 0,	54,  54,  54,  118, 118, 118, 118,
+		/* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
+		/* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
+		/* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
+		/* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
+		/* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
+		/* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
+		/* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
+	};
+
+	b = fls64(a);
+	if (b < 7) {
+		/* a in [0..63] */
+		return ((u32)v[(u32)a] + 35) >> 6;
+	}
+
+	b = ((b * 84) >> 8) - 1;
+	shift = (a >> (b * 3));
+
+	x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
+
+	/* Newton-Raphson iteration
+	 *                         2
+	 * x    = ( 2 * x  +  a / x  ) / 3
+	 *  k+1          k         k
+	 */
+	x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
+	x = ((x * 341) >> 10);
+	return x;
+}
+
+/* Compute congestion window to use.
+ */
+static inline void bictcp_update(struct roccettcp *ca, u32 cwnd, u32 acked)
+{
+	u32 delta, bic_target, max_cnt;
+	u64 offs, t;
+
+	ca->ack_cnt += acked; /* count the number of ACKed packets */
+
+	if (ca->last_cwnd == cwnd &&
+	    (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
+		return;
+
+	/* The CUBIC function can update ca->cnt at most once per jiffy.
+	 * On all cwnd reduction events, ca->epoch_start is set to 0,
+	 * which will force a recalculation of ca->cnt.
+	 */
+	if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
+		goto tcp_friendliness;
+
+	ca->last_cwnd = cwnd;
+	ca->last_time = tcp_jiffies32;
+
+	if (ca->epoch_start == 0) {
+		ca->epoch_start = tcp_jiffies32; /* record beginning */
+		ca->ack_cnt = acked; /* start counting */
+		ca->tcp_cwnd = cwnd; /* syn with cubic */
+
+		if (ca->last_max_cwnd <= cwnd) {
+			ca->bic_K = 0;
+			ca->bic_origin_point = cwnd;
+		} else {
+			/* Compute new K based on
+			 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
+			 */
+			ca->bic_K = cubic_root(cube_factor *
+					       (ca->last_max_cwnd - cwnd));
+			ca->bic_origin_point = ca->last_max_cwnd;
+		}
+	}
+
+	/* cubic function - calc */
+	/* calculate c * time^3 / rtt,
+	 *  while considering overflow in calculation of time^3
+	 * (so time^3 is done by using 64 bit)
+	 * and without the support of division of 64bit numbers
+	 * (so all divisions are done by using 32 bit)
+	 *  also NOTE the unit of those variables
+	 *	  time  = (t - K) / 2^bictcp_HZ
+	 *	  c = bic_scale >> 10
+	 * rtt  = (srtt >> 3) / HZ
+	 * !!! The following code does not have overflow problems,
+	 * if the cwnd < 1 million packets !!!
+	 */
+
+	t = (s32)(tcp_jiffies32 - ca->epoch_start);
+	t += usecs_to_jiffies(ca->delay_min);
+
+	/* change the unit from HZ to bictcp_HZ */
+	t <<= BICTCP_HZ;
+	do_div(t, HZ);
+
+	if (t < ca->bic_K) /* t - K */
+		offs = ca->bic_K - t;
+	else
+		offs = t - ca->bic_K;
+
+	/* c/rtt * (t-K)^3 */
+	delta = (cube_rtt_scale * offs * offs * offs) >> (10 + 3 * BICTCP_HZ);
+	if (t < ca->bic_K) /* below origin*/
+		bic_target = ca->bic_origin_point - delta;
+	else /* above origin*/
+		bic_target = ca->bic_origin_point + delta;
+
+	/* cubic function - calc bictcp_cnt*/
+	if (bic_target > cwnd)
+		ca->cnt = cwnd / (bic_target - cwnd);
+	else
+		ca->cnt = 100 * cwnd; /* very small increment*/
+
+	/* The initial growth of cubic function may be too conservative
+	 * when the available bandwidth is still unknown.
+	 */
+	if (ca->last_max_cwnd == 0 && ca->cnt > 20)
+		ca->cnt = 20; /* increase cwnd 5% per RTT */
+
+tcp_friendliness:
+	/* TCP Friendly */
+	if (tcp_friendliness) {
+		u32 scale = beta_scale;
+
+		delta = (cwnd * scale) >> 3;
+		while (ca->ack_cnt > delta) { /* update tcp cwnd */
+			ca->ack_cnt -= delta;
+			ca->tcp_cwnd++;
+		}
+
+		if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
+			delta = ca->tcp_cwnd - cwnd;
+			max_cnt = cwnd / delta;
+			if (ca->cnt > max_cnt)
+				ca->cnt = max_cnt;
+		}
+	}
+
+	/* The maximum rate of cwnd increase CUBIC allows is 1 packet per
+	 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
+	 */
+	ca->cnt = max(ca->cnt, 2U);
+}
+
+__bpf_kfunc static void roccettcp_cong_avoid(struct sock *sk, u32 ack,
+					     u32 acked)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	u32 now = jiffies_to_usecs(tcp_jiffies32);
+	u32 bw_limit_detect = 0;
+	u32 roccet_xj;
+	u32 jitter;
+
+	if (ca->last_rtt > ca->curr_rtt)
+		jitter = ca->last_rtt - ca->curr_rtt;
+	else
+		jitter = ca->curr_rtt - ca->last_rtt;
+
+	/* Update roccet parameters */
+	update_ack_rate(sk);
+	update_min_rtt(sk);
+	update_srrtt(sk);
+
+	/* Reset ECE handling if we already have more bandwidth
+	 * than we received the last ECE.
+	 */
+	if (ca->ece_srrtt > 0) {
+		if (tcp_snd_cwnd(tp) >= ca->ece_cwnd)
+			ca->ece_srrtt = 0;
+	}
+
+	/* ROCCET drain.
+	 * Do not increase the cwnd for 100ms after a roccet congestion event
+	 */
+	if (now - ca->roccet_last_event_time_us <= 100 * USEC_PER_MSEC)
+		return;
+
+	/* LAUNCH: Detect an exit point for tcp slow start
+	 * in networks with large buffers of multiple BDP
+	 * Like in cellular networks (5G, ...).
+	 * Or exit LAUNCH if cwnd is too large for application layer
+	 * data rate.
+	 */
+
+	if ((tcp_in_slow_start(tp) && ca->curr_srrtt > sr_rtt_upper_bound &&
+	     get_ack_rate_diff(ca) >= ack_rate_diff_ss) ||
+		(!tcp_is_cwnd_limited(sk) && tcp_in_slow_start(tp))) {
+		ca->epoch_start = 0;
+
+		/* Handle initial slow start. Here we observe the most problems */
+		if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
+			tcp_sk(sk)->snd_ssthresh = tcp_snd_cwnd(tp) / 2;
+			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) / 2);
+		} else {
+			tcp_sk(sk)->snd_ssthresh =
+				tcp_snd_cwnd(tp) - (tcp_snd_cwnd(tp) / 3);
+			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) -
+						     (tcp_snd_cwnd(tp) / 3));
+		}
+		ca->roccet_last_event_time_us = now;
+		return;
+	}
+
+	if (tcp_in_slow_start(tp)) {
+		acked = tcp_slow_start(tp, acked);
+		if (!acked)
+			return;
+	}
+
+	if (ca->bw_limit.next_check == 0)
+		ca->bw_limit.next_check = now + 5 * ca->curr_rtt;
+
+	ca->bw_limit.sum_cwnd += tcp_snd_cwnd(tp);
+	ca->bw_limit.sum_acked += acked;
+
+	if (ca->bw_limit.next_check < now) {
+		/* We send more data as we got acked in the last 5 RTTs */
+		if ((ca->bw_limit.sum_cwnd * 100) / ca->bw_limit.sum_acked >=
+		    ack_rate_diff_ca)
+			bw_limit_detect = 1;
+
+		/* reset struct and set next end of period */
+		ca->bw_limit.sum_cwnd = 1;
+
+		/* set to 1 to avoid division by zero */
+		ca->bw_limit.sum_acked = 1;
+		ca->bw_limit.next_check = now + 5 * ca->curr_rtt;
+	}
+
+	/* Respects the jitter of the connection and add it on top of the upper bound
+	 * for the srRTT
+	 */
+	roccet_xj = ((jitter * 100) / ca->curr_min_rtt_timed.rtt) +
+		    sr_rtt_upper_bound;
+	if (roccet_xj < sr_rtt_upper_bound)
+		roccet_xj = sr_rtt_upper_bound;
+
+	/* This is true if we recently received an ECE bit.
+	 * Therefore we should respect the srRTT at this point.
+	 */
+	if (ca->ece_srrtt < roccet_xj && ca->ece_srrtt > 0)
+		roccet_xj = ca->ece_srrtt;
+
+	if (ca->curr_srrtt > roccet_xj && (bw_limit_detect || ca->ece_srrtt > 0)) {
+		ca->epoch_start = 0;
+		ca->roccet_last_event_time_us = now;
+		ca->cnt = 100 * tcp_snd_cwnd(tp);
+
+		/* Set Wmax if cwnd is larger than the old Wmax */
+		if (tcp_snd_cwnd(tp) > ca->last_max_cwnd)
+			ca->last_max_cwnd = tcp_snd_cwnd(tp);
+
+		tcp_snd_cwnd_set(tp, min(tp->snd_cwnd_clamp,
+					 max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U)));
+		tp->snd_ssthresh = tcp_snd_cwnd(tp);
+		return;
+	}
+
+	/* Terminates this function if cwnd is not fully utilized.
+	 * In mobile networks like 5G, this termination causes the cwnd to be frozen at
+	 * an excessively high value. This is because slow start or HyStart massively
+	 * exceed the available bandwidth and leave the cwnd at an excessively high
+	 * value. The cwnd cannot therefore be fully utilized because it is limited by
+	 * the connection capacity.
+	 */
+	if (!tcp_is_cwnd_limited(sk))
+		return;
+
+	bictcp_update(ca, tcp_snd_cwnd(tp), acked);
+	tcp_cong_avoid_ai(tp, max(1, ca->cnt), acked);
+}
+
+__bpf_kfunc static u32 roccettcp_recalc_ssthresh(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	if (ignore_loss)
+		return tcp_snd_cwnd(tp);
+
+	/* Don't exit slow start if loss occurs. */
+	if (tcp_in_slow_start(tp))
+		return tcp_snd_cwnd(tp);
+
+	ca->epoch_start = 0; /* end of epoch */
+
+	/* Wmax and fast convergence */
+	if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
+		ca->last_max_cwnd =
+			(tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta)) /
+			(2 * BICTCP_BETA_SCALE);
+	else
+		ca->last_max_cwnd = tcp_snd_cwnd(tp);
+
+	return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+__bpf_kfunc static void roccettcp_state(struct sock *sk, u8 new_state)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	if (new_state == TCP_CA_Loss)
+		roccettcp_reset(ca);
+}
+
+__bpf_kfunc static void roccettcp_acked(struct sock *sk,
+					const struct ack_sample *sample)
+{
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	/* Some calls are for duplicates without timestamps */
+	if (sample->rtt_us < 0)
+		return;
+
+	/* Discard delay samples right after fast recovery */
+	if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
+		return;
+
+	u32 delay = sample->rtt_us;
+
+	if (delay == 0)
+		delay = 1;
+
+	/* first time call or link delay decreases */
+	if (ca->delay_min == 0 || ca->delay_min > delay)
+		ca->delay_min = delay;
+
+	/* Get valid sample for roccet */
+	if (sample->rtt_us > 0) {
+		ca->last_rtt = ca->curr_rtt;
+		ca->curr_rtt = sample->rtt_us;
+	}
+}
+
+__bpf_kfunc static void roccet_in_ack_event(struct sock *sk, u32 flags)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct roccettcp *ca = inet_csk_ca(sk);
+
+	/* Handle ECE bit.
+	 * Processing of ECE events is done in roccettcp_cong_avoid()
+	 */
+	if (flags & CA_ACK_ECE) {
+		ca->ece_srrtt = ca->curr_srrtt;
+		ca->ece_cwnd = tcp_snd_cwnd(tp);
+	}
+}
+
+static struct tcp_congestion_ops roccet_tcp __read_mostly = {
+	.init = roccettcp_init,
+	.ssthresh = roccettcp_recalc_ssthresh,
+	.cong_avoid = roccettcp_cong_avoid,
+	.set_state = roccettcp_state,
+	.undo_cwnd = tcp_reno_undo_cwnd,
+	.cwnd_event = roccettcp_cwnd_event,
+	.pkts_acked = roccettcp_acked,
+	.in_ack_event   = roccet_in_ack_event,
+	.owner = THIS_MODULE,
+	.name = "roccet",
+};
+
+BTF_KFUNCS_START(tcp_roccet_check_kfunc_ids)
+BTF_ID_FLAGS(func, roccettcp_init)
+BTF_ID_FLAGS(func, roccettcp_recalc_ssthresh)
+BTF_ID_FLAGS(func, roccettcp_cong_avoid)
+BTF_ID_FLAGS(func, roccettcp_state)
+BTF_ID_FLAGS(func, roccettcp_cwnd_event)
+BTF_ID_FLAGS(func, roccettcp_acked)
+BTF_KFUNCS_END(tcp_roccet_check_kfunc_ids)
+
+static const struct btf_kfunc_id_set tcp_roccet_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set = &tcp_roccet_check_kfunc_ids,
+};
+
+static int __init roccettcp_register(void)
+{
+	int ret;
+
+	BUILD_BUG_ON(sizeof(struct roccettcp) > ICSK_CA_PRIV_SIZE);
+
+	/* Precompute a bunch of the scaling factors that are used per-packet
+	 * based on SRTT of 100ms
+	 */
+
+	beta_scale =
+		8 * (BICTCP_BETA_SCALE + beta) / 3 / (BICTCP_BETA_SCALE - beta);
+
+	cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
+
+	/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
+	 *  so K = cubic_root( (wmax-cwnd)*rtt/c )
+	 * the unit of K is bictcp_HZ=2^10, not HZ
+	 *
+	 *  c = bic_scale >> 10
+	 *  rtt = 100ms
+	 *
+	 * the following code has been designed and tested for
+	 * cwnd < 1 million packets
+	 * RTT < 100 seconds
+	 * HZ < 1,000,00  (corresponding to 10 nano-second)
+	 */
+
+	/* 1/c * 2^2*bictcp_HZ * srtt */
+	cube_factor = 1ull << (10 + 3 * BICTCP_HZ); /* 2^40 */
+
+	/* divide by bic_scale and by constant Srtt (100ms) */
+	do_div(cube_factor, bic_scale * 10);
+
+	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					&tcp_roccet_kfunc_set);
+	if (ret < 0)
+		return ret;
+	return tcp_register_congestion_control(&roccet_tcp);
+}
+
+static void __exit roccettcp_unregister(void)
+{
+	tcp_unregister_congestion_control(&roccet_tcp);
+}
+
+module_init(roccettcp_register);
+module_exit(roccettcp_unregister);
+
+MODULE_AUTHOR("Lukas Prause, Tim Fuechsel");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ROCCET TCP");
+MODULE_VERSION("1.0");
diff --git a/net/ipv4/tcp_roccet.h b/net/ipv4/tcp_roccet.h
new file mode 100644
index 000000000000..5168d57efec5
--- /dev/null
+++ b/net/ipv4/tcp_roccet.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * TCP ROCCET congestion control interface
+ */
+#ifndef __TCP_ROCCET_H
+#define __TCP_ROCCET_H 1
+
+#include <linux/math64.h>
+
+struct ack_rate {
+	u16 last_rate;	/* Last ACK-rate */
+	u32 last_rate_time;	/* Timestamp of the last ACK-rate */
+	u16 curr_rate;	/* Current ACK-rate */
+	u16 cnt;	/* Used for counting acks */
+};
+
+struct bandwidth_limit_detected {
+	u32 sum_cwnd;	/* sum of cwnd during time interval */
+	u32 sum_acked;	/* sum of received acks during time interval */
+	u32 next_check;	/* end/upper bound of time interval */
+};
+
+struct timed_rtt {
+	u32 time;	/* Time of recoding */
+	u32 rtt;	/* Measured RTT */
+};
+
+/* Based on the BICTCP struct with additions specific for the ROCCET-Algorithm */
+struct roccettcp {
+	u32 cnt;		/* increase cwnd by 1 after ACKs */
+	u32 last_max_cwnd;	/* last maximum snd_cwnd */
+	u32 last_cwnd;		/* last snd_cwnd */
+	u32 last_time;		/* time when updated last_cwnd */
+	u32 bic_origin_point;	/* origin point of bic function */
+	u32 bic_K;		/* time to origin point from the beginning of the current epoch */
+	u32 delay_min;		/* min delay (usec) */
+	u32 epoch_start;	/* beginning of an epoch */
+	u32 ack_cnt;		/* number of acks */
+	u32 tcp_cwnd;		/* estimated tcp cwnd */
+	u32 curr_rtt;		/* minimum rtt of current round */
+
+	u32 roccet_last_event_time_us;	/* last time ROCCET was triggered */
+	u32 ece_cwnd;		/* cwnd when a ECE bit was received */
+	u32 ece_srrtt;		/* srRTT when the ECE was received */
+	struct timed_rtt curr_min_rtt_timed;	/* observed minRTT with the timestamp */
+	u32 curr_srrtt;		/* srRTT calculated based on the latest ACK */
+	struct ack_rate ack_rate;	/* last and the current ACK rate */
+	struct bandwidth_limit_detected bw_limit;
+	u32 last_rtt;		/* Used for jitter calculation */
+};
+
+#endif /* __TCP_ROCCET_H */
-- 
2.43.0