rudp implements nodejs

In the field of network communication, RUDP (Reliable UDP) is a reliable transmission protocol based on the UDP (User Datagram Protocol) protocol. Based on the UDP protocol, it adds features such as reliability, flow control, and congestion control, allowing it to play an important role in some of the most trustworthy scenarios for data transmission. Below we will introduce how to implement the RUDP protocol in Node.js.

1. Overview of RUDP

In Internet communication, the UDP protocol is one of the most commonly used transmission protocols. It is simple and efficient. However, the UDP protocol does not guarantee the reliability of data transmission, and problems such as packet loss may occur during data transmission. In order to solve these problems, the RUDP protocol came into being.

To implement a network communication system based on the RUDP protocol, you need to have the following characteristics:

1. Reliability:

The RUDP protocol can ensure that data packets can be transmitted completely and correctly to the destination to avoid packet loss, retransmission, etc.

2. Flow control:

Flow control can prevent the sender of the data packet from transmitting too much data, causing network congestion.

3. Congestion control:

Congestion control can ensure the stability of the network, avoid network congestion and maintain network fluency.

2. RUDP implementation

In Node.js, you can use the dgram module to implement the RUDP protocol. First, we need to define a RUDP instance and specify the IP address and port number of the sender and receiver:

const dgram = require('dgram');
const RUDP = require('rudp');

const client = dgram.createSocket('udp4');
const server = dgram.createSocket('udp4');

const rudpClient = new RUDP(client, { remoteAddress: '127.0.0.1', remotePort: 5000 });
const rudpServer = new RUDP(server, { localAddress: '127.0.0.1', localPort: 5000 });

In the above code, we use the dgram.createSocket method to create a UDP socket, and then Use the RUDP class to initialize a RUDP instance and specify the sender or receiver information corresponding to the instance.

Next, we need to implement the three characteristics of the RUDP protocol: reliability, flow control and congestion control.

1. Reliability

The reliability of the RUDP protocol ensures the quality of data transmission through the confirmation and retransmission mechanism. In the RUDP implementation, we need to listen for the acknowledgment message sent by the receiver. Once the receiver successfully receives the packet, an acknowledgment message is automatically sent.

rudpServer.on('message', (data, rinfo) => {
  // 处理接收到的数据包
  // 发送确认信息
  rudpServer.sendAck(rinfo, seq);
});

In the sender's own buffer, the sent packet needs to be saved and stored in the send queue. The sender periodically obtains data packets from the send queue and sends them, and waits for confirmation information from the receiver.

// 发送数据包
rudpClient.send(data, (err) => {
  if (err) {
    console.log('Send error:', err.message);
  } else {
    // 数据包放入发送队列
    // 等待确认
  }
});

// 接收确认信息
rudpClient.on('ack', (ack) => {
  // 从发送队列中删除该数据包
});

2. Flow control

Flow control can ensure that the sender of the data packet does not send too much data, causing network congestion. In the RUDP implementation, we need to utilize the communication control algorithm between the sender and the receiver to achieve flow control.

First, we need to define the size of the sending window and receiving window. The sending window and receiving window respectively represent the number of data packets that the sender and receiver can process at any time.

// 发送窗口的大小
const MAX_WINDOW_SIZE = 1024 * 1024; // 1MB

// 数据包大小
const PACKET_SIZE = 1024; // 1KB

// 发送窗口
let sendWindow = { base: 0, nextSeqnum: 0, maxSeqnum: 0, size: MAX_WINDOW_SIZE / PACKET_SIZE };

// 接收窗口
let recvWindow = { base: 0, maxSeqnum: 0, size: MAX_WINDOW_SIZE / PACKET_SIZE };

Before sending a data packet to the receiver, the sender needs to check whether the size of the sending window exceeds the limit. If the send window size exceeds the limit, the packet cannot be sent.

// 发送数据包
rudpClient.send(data, (err) => {
  if (err) {
    console.log('Send error:', err.message);
  } else {
    // 数据包放入发送队列
    if (sendWindow.nextSeqnum < sendWindow.base + sendWindow.size) {
      // 发送窗口大小未超限，可以发送数据包
    } else {
      // 发送窗口大小已超限，等待下一个时钟周期
    }
  }
});

Before receiving the data packet, the receiver needs to check whether the receiving window has enough space to store the data packet. If the receive window does not have enough space to store the packet, the packet cannot be received.

rudpServer.on('message', (data, rinfo) => {
  if (recvWindow.maxSeqnum - recvWindow.base < recvWindow.size) {
    // 接收窗口大小有空间，可以接收数据包
  } else {
    // 接收窗口大小已满，等待下一个时钟周期
  }
});

3. Congestion control

Congestion control can ensure the stability of the network and maintain the smoothness of the network. In a RUDP implementation, congestion control can be implemented using congestion control algorithms.

The congestion control algorithm is roughly divided into the following two phases:

Slow start phase: In the slow start phase, each time the sender successfully sends a data packet, the size of the congestion window is doubled until Reaches the maximum value.

Congestion avoidance phase: During the congestion avoidance phase, the sender slows down the increase in congestion window size to only one packet per round trip cycle.

const cwnd = { ssthresh: MAX_WINDOW_SIZE / PACKET_SIZE, size: PACKET_SIZE };

// 慢启动阶段
while (cwnd.size < cwnd.ssthresh) {
  // 发送数据包并等待确认
  cwnd.size += PACKET_SIZE;
}

// 拥塞避免阶段
while (true) {
  for (let i = 0; i < cwnd.size / PACKET_SIZE; i++) {
    // 发送数据包并等待确认
  }
  cwnd.size += PACKET_SIZE / cwnd.size;
}

After the implementation is completed, we can start the RUDP instance through the following command:

rudpServer.bind(5000, () => {
  console.log('Server started...');
});

rudpClient.connect(() => {
  console.log('Client started...');
});

The above is how to implement the RUDP protocol in Node.js. By learning and understanding the implementation of RUDP, we can more easily master its application in network communications, thereby achieving reliable data transmission.

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