nodejs build sip server

SIP (Session Initiation Protocol) is a protocol commonly used for audio and video transmission. It can realize functions such as voice, video, and multimedia conferencing, and is widely used in fields such as enterprise communications, mobile communications, and WebRTC. To build a SIP server, we can use Node.js to complete it. This article will introduce how to use Node.js to build a SIP server.

1. Understand the SIP protocol

Before starting to use Node.js to build a SIP server, we need to first understand the basic principles of the SIP protocol. The SIP protocol is a text-based control protocol that communicates through requests and responses and uses the Session Description Protocol (SDP) format to describe session information. Usually transmitted using UDP or TCP protocols.

In the SIP protocol, there are three types of messages: request, response and session description. Requests include INVITE, ACK, BYE, CANCEL, REGISTER, REFER and OPTIONS. Responses include 1xx, 2xx, 3xx, 4xx, 5xx, 6xx and ACK. The session description is used to describe information such as the encoding method, transmission address and port of the media stream.

2. Install Node.js

Before starting to build the SIP server, we need to install Node.js first. You can go to the Node.js official website to download the latest version of Node.js and install it, or you can use the Node.js package manager npm to install it.

3. Install the SIP.js library

To use Node.js to build a SIP server, we need to use the SIP.js library. SIP.js is an open source JavaScript library that provides a set of APIs for processing the SIP protocol. The SIP.js library can be installed using npm.

npm install sip.js

4. Write code

After installing the Node.js and SIP.js libraries, we can start writing code. Here we use the Express framework to build an HTTP server, and use the dgram module of Node.js to implement UDP transmission of the SIP protocol. First, we need to introduce the required dependencies.

const express = require('express');
const dgram = require('dgram');
const sip = require('sip.js');

Next, we define the configuration information of the SIP server. Here we use UDP transmission method and the port number is 5060.

const config = {
  transportOptions: {
    udp: {
      address: '0.0.0.0',
      port: 5060
    }
  }
};

Then, we create the Express server and define routes. Here we only create a GET route that returns a simple string.

const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});

Next, we create the SIP server and let it listen on the UDP port. When the client sends a request, the SIP server will handle it accordingly according to the type of request, such as INVITE, ACK, BYE, CANCEL, REGISTER, REFER and OPTIONS, etc. Here we only process the INVITE request. When the INVITE request is received, the SIP server will return a 200 OK response and start the media streaming channel.

const socket = dgram.createSocket('udp4');
const sipServer = new sip.Server(config);
sipServer.socket = socket;

sipServer.on('invite', (session) => {
  console.log('Received INVITE Request:', session);

  session.accept({
    sessionDescriptionHandlerOptions: {
      constraints: {
        audio: true,
        video: false
      },
      peerConnectionOptions: {
        iceServers: []
      }
    }
  });
});

socket.on('message', (msg, rinfo) => {
  sipServer.receive(msg.toString(), rinfo);
});

After the SIP server processes the request, we send the response result back to the client.

sipServer.on('response', (response, session) => {
  console.log('Sent Response:', response);
  const message = Buffer.from(response.toString());
  socket.send(message, session.request.ruri.port, session.request.headers['Via'][0].received || session.request.ruri.host);
});

Finally, we start the HTTP server and SIP server and listen on the port. In this way, our SIP server built with Node.js is completed.

app.listen(3000, () => {
  console.log('Express server is running on http://localhost:3000');

  sipServer.start();
  console.log('SIP server is running on udp://localhost:5060');
})

5. Test

After completing the code writing, we can test the SIP server built by Node.js through the following steps.

1. Open a terminal window, enter the project root directory, and enter the following command to start the server.

node app.js

2. Open another terminal window and enter the following command to use the telnet tool to simulate the SIP client.

telnet localhost 5060

3. Enter the following content to send an INVITE request to the SIP server.

INVITE sip:3000@localhost SIP/2.0
Via: SIP/2.0/UDP 127.0.0.1:1234;rport
Max-Forwards: 70
From: ;tag=abcd1234
To: 
Call-ID: 1234567890@127.0.0.1
CSeq: 1 INVITE
Contact: 
Content-Type: application/sdp
Content-Length: 194

v=0
o=- 81757 81757 IN IP4 127.0.0.1
s=-
c=IN IP4 0.0.0.0
t=0 0
m=audio 6000 RTP/AVP 0
a=rtpmap:0 PCMU/8000

4. If the server returns a 200 OK response, it means that the SIP server has been successfully established.

Through the above steps, we can use Node.js to build a SIP server. Node.js provides many modules and libraries, allowing us to easily implement complex functions. For the construction of SIP servers, the SIP.js library provides a complete set of APIs, which simplifies our development difficulty.

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