# Project 3: reliable transport

## What is what

| File | Role |
| :--- | :--- |
| `gbn.py` | yours: `Sender.send()`; the receiver is given |
| `sr.py` | yours: `Sender.send()` and `Receiver.receive()` |
| `stopwait.py` | given: stop-and-wait, with the timer, cumulative ACKs and the FIN/FINACK close |
| `packet.py` | given: packet format, Internet checksum, MSS 1000 |
| `channel.py` | given: simulated link for the offline checks |
| `selfcheck.py` | given: public checks over that link |
| `transfer.py` | given: file transfer over UDP |
| `experiments.py` | given: loss and window sweeps, writes `results.json` |
| `challenge.py` | given: client for the class challenge server |
| `PROTOCOL.md` | given: the challenge control exchange |

The grader restores every given file from a clean copy, so leave them as they are.

## Run

Python 3, standard library only.

```text
python3 selfcheck.py                 # both protocols
python3 selfcheck.py gbn             # one side
python3 experiments.py               # both sweeps
python3 experiments.py loss          # loss sweep only
python3 experiments.py window        # window sweep only
python3 challenge.py B-gbn --student your_id
```

A side that is still unwritten prints SKIP after about 30 seconds per check, so run one side at a time while you write code.

The experiments need `ip netns` and `tc netem`. In the course container:

```text
docker run --rm --privileged -v "$PWD/..":/work -w /work/starter cs4220-net
python3 experiments.py
```

The challenge client needs the class server: run it on your own machine, or in the container without `--network none`. We host no local peer.

## Tool references

- [Python socket module](https://docs.python.org/3/library/socket.html)
- [ip-netns](https://man7.org/linux/man-pages/man8/ip-netns.8.html)
- [tc-netem](https://man7.org/linux/man-pages/man8/tc-netem.8.html)
- [Course container help](../../../labs/tools/course-container.canvas.html) and [docker run](https://docs.docker.com/reference/cli/docker/container/run/)