# TCP ROCCET :rocket: (RTT Oriented CUBIC Congestion control ExTension)

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
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.

NOTE: A paper for TCP ROCCET is currently under review.
Paper draft:
            https://arxiv.org/abs/2510.25281
 
The oldest Linux kernel version we tested with ROCCET is 6.1.

## Setup

* Debian: `sudo apt install linux-headers-generic`
* Fedora: `sudo dnf install kernel-devel`
(`sudo reboot`)

## Build 
`make`


## Loading & Unloading the Module  
**1.** Insert into Kernel: `sudo insmod tcp_roccet.ko`
In case you get the "Invalid module Format" error, it can help reinstalling the kernel-headers.

**2.** Use the Algorithm:
* Either via globally loading it: `sudo sysctl net.ipv4.tcp_congestion_control=roccet`
* Or via using it in specific measurements: `sudo iperf3 -c <Server-IP> -C roccet`

**3.** Unload the Module: `sudo rmmod tcp_roccet`


## Debugging (Using kprobe)
In order to debug the `tcp_roccet` congestion control algorithm, there exists a Kprobe module (`roccet_kprobe.c`). Using this it is possible to inspect events generated by the algorithm. 

In order to use the Kprobe module the following steps are necessary: 

**1. Specify the event to inspect**
For this head into the `tcp_roccet.c` source code and find the function the Kprobe should attach to. 

For Example: 
```
__bpf_kfunc static void roccettcp_cong_avoid(struct sock *sk, u32 ack, u32 acked);
```
Specify this function name in the field `symbol_name` of the `kprobe` struct in `roccet_kprobe.c` 

Obtain the arguments in the kprobe using the `regs` field. 
(See the System V ABI for Linux under https://en.wikipedia.org/wiki/X86_calling_conventions#List_of_x86_calling_conventions)

**2. Build Kprobe module**
Use the provided Makefile to build the `roccet_kprobe.c` module for the local machine. (`make`)

For this the adequate linux-headers are required 
* Debian: `sudo apt install linux-headers-generic`
* Fedora: `sudo dnf install kernel-devel`

Required files for this are: 
* `Makefile` 
* `roccet_kprobe.c`
* `tcp_roccet.h`
* `tcp_roccet.c` (Optional; Need to remove corresponding entry in Makefile if missing)

**3. Load Kprobe module**
To then load the Module use 
`sudo insmod roccet_kprobe.ko` 
If you are seeing the error "Unknown symbol in module" you need to first load the roccet algorithm.  

**4. See the trace output**
To see the trace output use
`sudo cat /sys/kernel/tracing/trace_pipe`

**5. Unload Kprobe module**
To remove the module again use 
`sudo rmmod roccet_kprobe` 

_See more info at_ https://docs.kernel.org/trace/kprobes.html and https://www.kernel.org/doc/Documentation/trace/kprobetrace.rst

## Further Info
* On TCP-CC Ops: 
    * https://www.yonch.com/tech/linux-tcp-congestion-control-internals
    * https://docs.ebpf.io/linux/program-type/BPF_PROG_TYPE_STRUCT_OPS/tcp_congestion_ops/

# Setup Development Environment 
For specific Kernel:  
1. Download linux source (the version you want to develop for)
2. Create Config via `make defconfig`
3. Compile kernel via `make`
4. Generate clangd Config via `python scripts/clang-tools/gen_compile_commands.py`
5. Copy `compile_commands.json` to development directory