tcp: Add TCP ROCCET congestion control module.

TCP ROCCET is a new congestion control algorithm based on TCP CUBIC
that improves its overall performance in cellular networks. 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's main method of addressing the bufferbloat problem is by
adding two additional metrics. The first metric is the relative increase
in RTT from its minimum, the srRTT. Here, bufferbloat can be detected
when RTTs increase due to buffer filling. The second metric is the
acknowledgment arrival rate sampled over 100ms intervals and the bytes
sent and received over 5 RTTs. If CUBIC increases the send rate or
congestion window, and the acknowledgment arrival rate stays at the
same level, the connection is limited by the bottleneck link's capacity.
In such cases, ROCCET reduces the send rate to prevent bufferbloat.
ROCCET uses a modified version of slow start rather than HyStart because
HyStart is known to enter the congestion avoidance phase too early when
used in cellular networks [2]. Therefore, ROCCET uses a combination of
srRTT and the acknowledgment arrival rate to determine when to exit slow
start. For the congestion avoidance phase, ROCCET relies on the srRTT and
monitoring the sent and received bytes to detect the filling of the
bottleneck buffer. To keep the minimum RTT updated, ROCCET performs
minimum RTT probing if no new minimum RTT was found in the last 5 seconds.
To this end ROCCET halves the cwnd and probes for 200ms but at least for
one RTT, for a new minimum RTT. After probing, ROCCET refills the pipe
carefully. In addition, ROCCET reacts to packet loss by adapting CUBIC's
behavior. ECNs are handled as ROCCET congestion event, where the cwnd gets
reduced and ROCCET enters a buffer drain state.

In real-world mobile 5G NR measurements, TCP ROCCET achieves better
performance than CUBIC, by maintaining similar throughput while reducing
the latency. More information about TCP ROCCET and measurement evaluations
can be found here [3].
For the version (2026-07-21), we provide additional performance evaluation
regarding throughput, latency, and bandwidth share [4].

[1] https://doi.org/10.1109/VTC2023-Fall60731.2023.10333357
[2] https://doi.org/10.1109/WMNC.2016.7543932
[3] https://doi.org/10.23919/WONS68803.2026.11501781
[4] http://go.lu-h.de/roccet-2026-07-21

Co-developed-by: Lukas Prause <lukas.prause@ikt.uni-hannover.de>
Signed-off-by: Lukas Prause <lukas.prause@ikt.uni-hannover.de>
Signed-off-by: Tim Fuechsel <t.fuechsel@gmx.de>
Link: https://patch.msgid.link/asdfdDIQb7Nhm692@volt-roccet-vm
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/Kconfig

@@ -663,6 +663,18 @@ 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 (RTT oriented CUBIC congestion control exTension) is a
+	  sender-side-only congestion control algorithm based on the TCP CUBIC
+	  protocol stack/TCP CUBIC congestion control algorithm that optimizes
+	  its performance. Especially for networks with large buffers
+	  (wireless, cellular networks), TCP ROCCET has improved performance by
+	  maintaining a similar throughput as CUBIC while reducing latency.
+	  For more information, see: https://arxiv.org/abs/2510.25281
+
 config TCP_CONG_BBR
 	tristate "BBR TCP"
 	default n

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