PubNub facilitates real-time Publish/Subscribe functionality for PHP, supporting both terminal and web server environments like Apache, Nginx, and Lighttpd, through its PHP Push API. This API enables JavaScript browsers to send messages to PHP servers or CLI programs, ensuring immediate data exchange, and is accessible for PHP developers who can find detailed references and function calls in the PHP Push API Reference Tutorial. A robust push system typically comprises a backend push server, a messaging queue, and delivery services, with common implementations using systems like Redis or RabbitMQ for asynchronous message processing. PHP push APIs maintain persistent connections or utilize third-party services like PubNub to interact with client applications, employing technologies such as RESTful APIs and WebSockets. Secure communication in push notifications is achieved through token-based authentication and encryption, while tracking delivery status is facilitated by services like FCM and PubNub. Additionally, optimizing for scalability involves load balancing, queuing, and using Redis Streams for buffering, while best practices include efficient retry mechanisms, token management, and comprehensive logging for analytics and debugging.