Building an Asynchronous UDP SIP Server with Workerman in PHP

Overview

The article demonstrates how to implement an asynchronous SIP server over UDP using Workerman, a high‑performance PHP socket framework suitable for long‑connection and high‑concurrency network applications.

Understanding SIP

SIP (Session Initiation Protocol) is a signaling protocol that initiates, manages, and terminates real‑time sessions such as voice, video, and messaging over IP networks. It follows a request/response model similar to HTTP.

Business Requirements

The author needed a UDP‑based SIP server to complement existing Workerman+Channel micro‑services handling TCP/UDP/HTTP for IoT devices. Requirements include persistent UDP communication, support for GB28181 national standard, and integration with media servers like SRS, ZLMediaKit, or monibuca for camera/DVR access and possible FreeSwitch‑based voice/video calls.

Implementation Details

When only one worker process is used, socket functions handle UDP listening; with multiple processes, stream_socket_server is used to allow shared port binding.

Worker count should match CPU cores for optimal performance.

Heartbeat: a timer sends keep‑alive packets at least every 60 seconds to prevent Linux kernel session timeout.

Code Example

<?php
chdir(dirname($_SERVER['SCRIPT_FILENAME']));
include_once __DIR__ . '/vendor/autoload.php';
use Workerman\Worker;
use Workerman\Lib\Timer;
$worker = new Worker();
$worker->count = 1; // number of processes
$processName = "sip_server_udp5060";
$worker->transport = "udp";
$worker->name = $processName;
$worker->reusePort = true;
// ... (configuration, event loop, timers, socket creation, send/receive functions) ...
Worker::runAll();

The script sets up global timers to clean up unauthorized or idle sessions, sends periodic test data, and logs received SIP messages. It distinguishes between registered (authenticated) connections stored in $worker->connections and unauthenticated ones in $worker->connections_ur, applying retry limits and timeout policies.

Testing and Sample Output

Initial tests show that with stream_socket the server can reliably send data for about five minutes before the kernel drops the session, while using socket allows longer transmission if firewalls/NAT do not expire the session.

Sample console logs display SIP REGISTER requests with timestamps, source IPs, and SIP headers, confirming that the server correctly receives and processes UDP packets.