RMTP Protocol Implementation

This project implements RMTP (Reliable Messaging Transfer Protocol), a custom protocol designed for reliable message transmission, along with a proxy server for protocol bridging.

Overview

RMTP is a transport layer protocol that ensures reliable delivery of messages with sequence numbering, acknowledgment handling, and round-trip time estimation. The implementation includes a client, server, and proxy for testing and protocol validation.

Designed Protocol: RMTP (Reliable Messaging Transfer Protocol)

Packet Header

The RMTP packet header consists of the following fields:

Field	Size (Bits)	Description
Reserved	7	Reserved for future use, must be set to 0
ACK Flag	1	Flag to indicate if packet is an ACK. 1 = ACK, 0 = data message
Sequence/ACK Number	32	The unique identifying number of that packet
Timestamp	32	Millisecond timestamp for calculating RTT (round trip time)
Payload Length	16	The length of the payload in bytes

Header Layout

The RMTP packet header is organized as follows:

• Byte 0: Reserved (7 bits) + ACK Flag (1 bit)
• Bytes 1-4: Sequence Number (32 bits)
• Bytes 5-8: Timestamp (32 bits)
• Bytes 9-10: Payload Length (16 bits)
• Bytes 11+: Payload Data

Visual Packet Structure

+------------------+---+-------------------------------+---------------------+------------------+---------+
| Reserved (7 bits)| A | Sequence/ACK Number (32 bits) | Timestamp (32 bits) | Payload Len (16) | Payload |
+------------------+---+-------------------------------+---------------------+------------------+---------+

Proxy Implementation

The proxy server (proxy.c) acts as an intermediary in the RMTP communication chain, forwarding messages between client and server while simulating unreliable network conditions. The proxy:

• Receives RMTP packets from clients
• Forwards packets to the server
• Handles ACK messages from the server back to clients
• Can be configured to randomly drop or delay packets in either direction
• Sends diognostic information to the Companion Logging and Control Server

Installation

Client, Server and Proxy

Building

./generate-flags.sh
./generate-cmakelists.sh
./change-compiler.sh -c <compiler>
./build.sh

Or, if running with GCC:

./run-build-gcc.sh

Running

Terminal A - Server:

./build/server --listen-ip 192.168.0.1 \
--listen-port 4000 \
--log-file-path ./logs/server.log \
--log-server-ip 192.168.0.5 \
--log-server-port 6000

Terminal B - Proxy:

./build/proxy --listen-ip 192.168.0.1 \
--listen-port 4000 \
--target-ip 192.168.0.3 \
--target-port 5000 \
--client-drop 10 \
--server-drop 5 \
--client-delay 20 \
--server-delay 15 \
--client-delay-time-min 100 \
--client-delay-time-max 200 \
--server-delay-time-min 150 \
--server-delay-time-max 300 \
--log-file-path ./logs/proxy.log \
--log-server-ip 192.168.0.5 \
--log-server-port 6000

Terminal C - Client:

./build/client --target-ip 192.168.0.3 \
--target-port 5000 \
--timeout 3 \
--max-retries 5 \
--log-file-path ./logs/client.log \
--log-server-ip 192.168.0.5 \
--log-server-port 6000

Companion Logging + Control Server

This UI can be used to more easily modify proxy parameters and view logs in real time via a concurrent TCP connection from the companion server to the RMTP client, server and proxy.

Obtaining

Navigate to the ../source/src-py folder

Building

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Running

python3 server.py