# Diarkis RUDP

## Overview

The Reliable User Datagram Protocol (RUDP) is an implementation of UDP communication that guarantees data delivery. Diarkis client can use RUDP to transmit data either in communication with the server or in P2P communication, ensuring that critical information necessary for game progression is reliably delivered. This page explains the specifications and settings of Diarkis's RUDP.

## Specifications of Diarkis RUDP

The combinations in which Diarkis RUDP can be established include server-client and client-client (P2P communication). Some features are only available in P2P communication.

In Diarkis RUDP, when data is received, an Acknowledgement (ACK) is returned to inform the sender of the data's arrival. If an ACK is not received within a specified timeframe, the Diarkis client will resend the same data. In this document, this timeframe is referred to as **RetryInterval**. Furthermore, if an ACK is not received after resending the data a specified number of times, the Diarkis client will disconnect the communication with the other party due to a timeout. In this document, this number of retries is referred to as **RetryMaxCount**.

Exclusively in P2P communication with RUDP, a **sequence guarantee toggle feature** is provided in addition to data delivery assurance. When sequence guarantee is enabled, it ensures that the data received by the application is in the order sent by the peer user. The Diarkis library will not pass data to the application until packets are received in the correct sequential order. If the sequence guarantee is disabled, the Diarkis library will pass packets to the application in the order they are received, and this order may vary due to network conditions or the presence of retransmitted packets.

In server-client RUDP communication, sequence guarantee is always enabled.

## Settings for Diarkis RUDP

### Setting RetryInterval

RetryInterval can be adjusted using the following function:

{% code title="udp.h" %}

```cpp
void SetSendRetryInterval(uint32_t minMs, uint32_t maxMs)
```

{% endcode %}

RetryInterval begins with the time specified by `minMs` (milliseconds) and doubles each time the client resends until it reaches the time specified by `maxMs`. For example, if minMs=300ms, maxMs=1000ms, and RetryMaxCount is 5, the RetryInterval changes as 300ms, 600ms, 900ms, 1000ms, 1000ms. If the fifth resend times out, the client disconnects the communication.

By making RetryInterval exponential, you can reduce the network processing load on the client. If you want to set a fixed RetryInterval, specify the same values for `minMS` and `maxMS` to keep RetryInterval constant regardless of the number of retries.

### Setting RetryMaxCount

RetryMaxCount can be adjusted using the following function:

{% code title="udp.h" %}

```cpp
void SetSendRetryMaxCount(uint32_t count)
```

{% endcode %}

RetryMaxCount will be the value specified by `count`.

### Setting Sequence Guarantee

a. When using the [Diarkis Module](/en/diarkis-client/diarkis-module.md), control the operation of RUDP with the `type` argument in functions such as `SendBroadcast` defined in `DiarkisP2PBase.h`. Specify a value from the *enumerated type* `RudpType` for the `type` argument.

{% code title="DiarkisP2PBase.h" %}

```cpp
uint16_t SendBroadcast(const uint8_t* payload, size_t payloadSize, RudpType type)
```

{% endcode %}

{% code title="p2p.h" %}

```cpp
enum RudpType : uint8_t
{
    UNRELIABLE_UNORDERED = 0, // No delivery guarantee, no sequence guarantee (UDP)
    RELIABLE_UNORDERED = 1,   // Delivery guarantee, no sequence guarantee
    RELIABLE_ORDERED = 2      // Delivery guarantee, sequence guarantee
};
```

{% endcode %}

b. When using the library directly, execute the data transmission function for P2P communication shown below with the `bFixedOrder` flag set to `true`.

{% code title="p2p.h" %}

```cpp
Diarkis::System::Result RSend(const uint8_t* message, size_t messageSize, bool bFixedOrder)
```

{% endcode %}

## Cautions in Settings

* `SetSendRetryInterval` and `SetSendRetryMaxCount` set configurations for RUDP communication with the server. For P2P communication settings, use `SetSendRetryIntervalP2P` and `SetSendRetryMaxCountP2P`.
* Be cautious that if RetryInterval is extremely small or RetryMaxCount is large, the client will need to send a large number of packets, increasing the network processing load.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://help.diarkis.io/en/diarkis-client/runtime-library/diarkis-rudp.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.