PUSH Technologies - An Overview

PUSH technologies allow servers to deliver updates to clients instantly when data changes, without requiring repeated polling. This article compares the major PUSH mechanisms—Server-Sent Events, WebSockets, MQTT, Long‑Polling, and Web Push—explaining how each works, where they fit, and how to choose between them. It also covers the universal PUSH lifecycle, architectural patterns, and practical considerations.

What “PUSH” Means

PUSH reverses the traditional HTTP request/response flow by enabling servers to send updates the moment something meaningful happens. This requires:

• a persistent or semi‑persistent channel
• a subscription mechanism
• a delivery engine
• event triggers

Summary Comparison Table

Technology	Directionality	Ideal Use Cases	Complexity	PHP-Friendly?
SSE	Server→Client	Notifications, dashboards, workflow updates	Low	Medium (with tuning)
WebSockets	Full-duplex	Chat, collaboration, presence	Medium–High	Low
MQTT	Pub/Sub	IoT, sensors, distributed systems	Medium	Excellent
Long-polling	Simulated PUSH	Legacy fallback	Low	Excellent
Web Push	Server→Browser	Notifications outside browser	Medium	Excellent

Major PUSH Technologies

Server-Sent Events (SSE)

Lightweight one-way PUSH over a long-lived HTTP connection.
Strengths: simple, efficient, REST-friendly.
Limitations: one-way only; PHP-FPM tuning required.

WebSockets

Full-duplex real-time communication.
Strengths: low-latency, binary support.
Limitations: needs event-driven runtime.

Long-Polling

Held-open requests until change.
Strengths: universal fallback.
Limitations: inefficient at scale.

MQTT

Pub/sub protocol designed for IoT and telemetry.
Strengths: massive scalability, durable subscriptions.
Limitations: requires broker, not browser-native.

Web Push API

Notification delivery even when browser is closed. Strengths: great for user-centric alerts. Limitations: not for continuous streams.

Universal PUSH Lifecycle

1. Discovery/Intent 2. Channel Establishment 3. Subscription Registration 4. Delivery

Architecture Patterns

PHP handles authentication, subscription negotiation, and event publishing. A dedicated push daemon (Perl/Node.js/etc.) maintains persistent connections and fan-out.

Diagram

``` Client → PHP API → Redis/Queue → PUSH Daemon → Client ```

When to Use What

• Use SSE for simple one-way notifications.
• Use WebSockets for collaborative apps.
• Use MQTT for IoT/distributed messaging.
• Use Long-polling for legacy compat.
• Use Web Push for browser notifications.

References

• Server-Sent Events — WHATWG
• WebSockets — RFC 6455
• MQTT v5 — OASIS
• Push API — W3C
• Web Push Protocol — RFC 8030