Custom Reliable UDP (RUDP) Protocol for P2P Multiplayer Gaming

Group 3: Dhruv · Krishiv · Piyush · Vivek · Kunal

Network Computing Semester Project

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📌 Overview

This project aims to build a decentralized, serverless multiplayer game engine by developing a custom Reliable UDP (RUDP) protocol. Since TCP is too slow for real-time games and standard UDP drops critical state updates, our custom transport layer guarantees the delivery of important game events without needing a central host.

Key Features:

• P2P Game Client: Developed using Raylib and C++, featuring a peer-to-peer ring topology.
• Custom Transport Protocol (RUDP): Developed from scratch over raw UDP, featuring a 16-byte header, sliding windows with Go-Back-N/cumulative ACKs, Jacobson/Karels RTT estimators, and NAT traversal.
• Benchmarking Suite: Tools to benchmark and compare RUDP's latency and reliability against standard TCP and UDP under simulated network packet loss.
• Wireshark Integration: Custom Lua dissector to demonstrate packet formats live in Wireshark.

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🎮 Game Engine (Raylib P2P)

Compilation Command:

g++ game.cpp -o game.out -lraylib -pthread -std=c++17
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib
./game.out

Dependencies:

• raylib
• pthread
• linux-kernel >= 6.1x.xx (For Windows, replace arpa/inet with winsock)

P2P Ring Topology Architecture:

1. Iterative DNS-inspired Discovery:
   • Host is requested.
   • If the host's next pointer is empty, you become its next pointer.
   • If occupied, the request is redirected further down the chain.
   • The chain connects back to the head to form a complete Peer-to-Peer Ring (🍐2🍐).
2. Game Data Exchange:
   • All peers communicate with their .next peer.
   • Scores are broadcasted down the network chain until resolving back to the origin.

User can switch protocols via the Menu:

• TCP -> Standard reliable but high overhead.
• UDP -> Unreliable default.
• Custom (RUDP) -> Our custom protocol utilizing Go-Back-N (Window Size: 10,000).

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🛠 Complete Transport Layer Stack (C)

While the game client integrates custom rudp.hpp, we have also provided a fully decoupled robust implementation in the /rudp and /transport directories.

RUDP Packet Format

 0               1               2               3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Ver  |        Flags          |         Payload Length        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Sequence Number                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Acknowledgment Number                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Checksum           |           Reserved            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Payload ...                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Header = 16 bytes. Flags: SYN ACK FIN RST PING PONG NAT DATA

Detailed Technical Specifications

For full details on the State Machine, RTT Estimation, Flow Control, and Checksum calculations, please refer to PROTOCOL.md.

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📈 Benchmarking and Performance Evaluation

We provide a complete suite of standard C tools to evaluate throughput, latency, and reliability in simulated lossy environments.

# 1. Start packet loss simulation (Using Linux tc netem)
sudo bash tools/tc_netem.sh setup 20   # 20% Packet Loss

# 2. Run Receiver and Sender (Using the Makefile to build fully decoupled tools)
make benchmark
./bench_receiver --proto rudp --port 9001 --count 1000 &
./bench_sender --proto rudp --host 127.0.0.1 --port 9001 --count 1000 --size 512

# 3. Generate Evaluation Report
python3 benchmark/bench_report.py --proto RUDP --size 512

# 4. Remove rules
sudo bash tools/tc_netem.sh teardown

Protocol Comparison Highlights

Feature	Standard UDP	TCP	RUDP
Header size	8 bytes	20 bytes	16 bytes
Reliability	None	ACK + retransmit	ACK + retransmit
Ordering	None	Strict In-Order	Sliding window
RTT estimation	None	Standard	Jacobson/Karels
Congestion Control	None	Window-based Slow Start	Window-based Flow Control
Head-of-line blocking	No	Yes	No

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🔍 Wireshark Live Demo

To easily demonstrate to the evaluator that our Protocol is actively on the wire, check out WIRESHARK.md for custom display filters and the Lua Dissector code.

Quick Wireshark Display Filter:

udp.port == 9000 || udp.port == 9001

Note for maintainers: The Game UI is tightly coupled to the P2P networking state machine. Do not modify component screen transitions without understanding the full peer discovery handshake flow.