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Explain the websocket vs SSE.

ICSM 358 10-Dec-2025

Explain the websocket vs SSE with example.

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Updated on 14-Jan-2026

ICSM

IT-Hardware & Networking

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Anubhav Kumar

13-Jan-2026

WebSocket and Server-Sent Events (SSE) are both technologies for real-time communication between a client and a server, but they are designed for different communication patterns.

Below is a clear, interview-ready, deep comparison.

1. What is WebSocket?

WebSocket provides a full-duplex (two-way) communication channel over a single persistent TCP connection.

Client ↔ Server (bi-directional)
Connection stays open
Very low latency
Uses ws:// or wss://

Typical Use Cases

Chat applications
Online gaming
Collaborative editors (Google Docs)
Live trading platforms

2. What is Server-Sent Events (SSE)?

SSE allows the server to push data to the client, but communication is one-way.

Server → Client only
Built on top of HTTP
Uses text/event-stream
Client listens using EventSource

Typical Use Cases

Notifications
Live dashboards
News feeds
Stock price updates (read-only)

3. Core Differences (Quick Table)

Feature	WebSocket	SSE
Direction	Bi-directional	Server → Client
Protocol	WebSocket	HTTP
Connection	Persistent TCP	Long-lived HTTP
Client API	WebSocket	EventSource
Auto-reconnect	Manual	Built-in
Message format	Binary & Text	Text only
Browser support	Very good	Good (except IE)
Proxy friendly	Medium	High
Scaling	Harder	Easier

4. Communication Flow

WebSocket Flow

HTTP handshake
Upgrade to WebSocket
Full-duplex messaging
Manual reconnect handling

SSE Flow

HTTP request
Server keeps connection open
Server pushes events
Browser auto-reconnects

5. Code Examples

WebSocket (Client)

const socket = new WebSocket("wss://example.com/chat");

socket.onmessage = (event) => {
  console.log(event.data);
};

socket.send("Hello Server");

SSE (Client)

const eventSource = new EventSource("/events");

eventSource.onmessage = (event) => {
  console.log(event.data);
};

6. Performance & Resource Usage

WebSocket

Very efficient for frequent two-way messaging
Lower overhead after connection
Requires careful connection management

SSE

Slightly more overhead (HTTP headers)
Scales better with many clients
Works naturally with HTTP/2

7. Security

Aspect	WebSocket	SSE
HTTPS support	WSS	HTTPS
CORS	Manual handling	Built-in
Auth	Tokens / cookies	Cookies / headers

8. When to Use What?

Choose WebSocket when:

Client needs to send frequent messages
Real-time bi-directional communication
Low latency is critical

Choose SSE when:

Server → client updates only
Simpler implementation
Better reliability & auto-reconnect

9. SSE Limitations (Important)

One-way only
No binary data
Limited concurrent connections per browser

10. Interview One-Line Answer

WebSocket is full-duplex real-time communication, while SSE is a simple, server-to-client push mechanism over HTTP.

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Explain the websocket vs SSE.

ICSM

Can you answer this question?

1 Answers

1. What is WebSocket?

Typical Use Cases

2. What is Server-Sent Events (SSE)?

Typical Use Cases

3. Core Differences (Quick Table)

4. Communication Flow

WebSocket Flow

SSE Flow

5. Code Examples

WebSocket (Client)

SSE (Client)

6. Performance & Resource Usage

WebSocket

SSE

7. Security

8. When to Use What?

Choose WebSocket when:

Choose SSE when:

9. SSE Limitations (Important)

10. Interview One-Line Answer

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