---
title: "RUDP"
---

> Documentation Index
> Fetch the complete documentation index at: https://openarkstudio.github.io/arknet/llms.txt
> Use this file to discover all available pages before exploring further.

# RUDP

RUDP provides reliable, ordered messages over UDP. Its C++20 ARQ core handles
fragmentation, acknowledgements, retransmission and receive ordering. The public
client, server and session use arknet's CRTP and component architecture.

> **v0.1.0**
>
> The `v0.1.0` release includes ARQ-only, fixed FEC and adaptive FEC [policies](/arknet/features/rudp/fec).
> ARQ-only is the default; peers negotiate FEC, while ARQ remains responsible for
> complete delivery. Deployment capacity and endurance still require [production
> acceptance](/arknet/project/production-readiness). ARK integration additionally
> requires its business regression tests.

## Get started

- [Create a server](/arknet/features/rudp/server): receive and echo complete messages.
- [Create a client](/arknet/features/rudp/client): complete the handshake and verify an echo.
- [Configuration](/arknet/features/rudp/configuration): MTU, windows, limits and compatibility.
- [FEC policies](/arknet/features/rudp/fec): coding parameters, adaptive thresholds and statistics.
- [Performance](/arknet/features/rudp/performance): local measurements and reproduction.

| Capability | Behavior |
| --- | --- |
| Endpoints | `rudp_client`, `rudp_server`, `rudp_session` and CRTP variants |
| Addresses and dependency | IPv4/IPv6; Standalone Asio or Boost.Asio |
| Messages | Empty and binary messages; fragmentation and ordered reassembly |
| Reliability | ACKs, timeout and fast retransmission, bounded retries |
| Optional recovery | Fixed or adaptive Reed–Solomon FEC, with ARQ retransmission fallback |
| Flow control | Send/receive windows and congestion control enabled by default |
| Runtime | Handshake timeout, reconnect, timers, owned or external IO contexts |
| Limits | Bounds on ARQ, FEC, socket queues and server session admission |

## Choosing a transport

Use [native UDP](/arknet/features/udp) for independent datagrams whose loss and order
the application already handles. Use RUDP for reliable message delivery over
UDP. Retransmission adds latency; ordered delivery waits for missing fragments.
[TCP](/arknet/features/tcp) remains the standard choice for reliable byte streams.

RUDP uses KCP-compatible **message-mode segments** and a separate SYN/ACK/FIN
connection envelope. This does not make it interchangeable with a bare KCP
endpoint. It does not provide authentication, encryption, NAT traversal, stream
mode or automatic path-MTU discovery. See [compatibility](/arknet/features/rudp/configuration#wire-compatibility).

A send completion confirms admission into the reliable queue, not a peer ACK
or application receipt. Disconnecting does not replay unacknowledged messages
into a new conversation. Applications that require receipt confirmation or
replay must define that behavior in their own protocol.

Source: https://openarkstudio.github.io/arknet/features/rudp/index.mdx