WebSockets for real-time communication in Computer Networks - Step-by-Step Execution

Concept Flow - WebSockets for real-time communication

Client sends HTTP request to server

↓

Server responds with HTTP 101 Switching Protocols

↓

WebSocket connection established

↓

Client and Server exchange messages anytime

↓

Connection stays open until closed by either side

↓

Connection closed

The client starts by requesting to upgrade to WebSocket. The server agrees, and then both keep the connection open to send messages instantly until one closes it.

Execution Sample

Computer Networks

Client: Send HTTP Upgrade request
Server: Respond with 101 Switching Protocols
Client & Server: Exchange messages freely
Client or Server: Close connection

Shows the steps to establish and use a WebSocket connection for real-time message exchange.

Analysis Table

Step	Action	Message Type	Result	Connection State
1	Client sends HTTP Upgrade request	HTTP Request	Request to switch to WebSocket	Connecting
2	Server responds with 101 Switching Protocols	HTTP Response	Agrees to upgrade	Connecting
3	Connection upgraded to WebSocket	Protocol Switch	Connection established	Open
4	Client sends message	WebSocket Frame	Message received by server	Open
5	Server sends message	WebSocket Frame	Message received by client	Open
6	Client or Server sends close frame	WebSocket Close Frame	Connection closing initiated	Closing
7	Connection closed	None	Connection fully closed	Closed

💡 Connection closes when either client or server sends a close frame, ending the session.

State Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	Final
Connection State	Disconnected	Open	Open	Closing	Closed
Messages Sent	0	0	1 (client)	1 (client)	1 (client)
Messages Received	0	0	0	1 (client)	1 (client)

Key Insights - 3 Insights

Why does the connection stay open after the initial HTTP handshake?

Because after the server sends the 101 Switching Protocols response (see execution_table step 2), the protocol changes from HTTP to WebSocket, which keeps the connection open for continuous message exchange.

What happens if the client sends a message before the server agrees to upgrade?

Messages can only be sent after the connection is upgraded (step 3). Sending messages before that would fail because the connection is still HTTP and not ready for WebSocket frames.

How does the connection close properly?

Either side sends a WebSocket Close Frame (step 6), signaling the intent to close. Both sides then close the connection cleanly (step 7).

Visual Quiz - 3 Questions

Look at the execution_table, what is the connection state after the server sends the 101 Switching Protocols response?

A Connecting

B Open

C Closed

D Closing

💡 Hint

Check the 'Connection State' column at step 2 in the execution_table.

At which step does the client first send a WebSocket message?

A Step 3

B Step 2

C Step 4

D Step 6

💡 Hint

Look for the first 'WebSocket Frame' sent by the client in the execution_table.

If the client closes the connection at step 6, what is the connection state immediately after?

A Closed

B Closing

C Open

D Connecting

💡 Hint

Refer to the 'Connection State' column at step 6 in the execution_table.

Concept Snapshot

WebSockets start with an HTTP Upgrade request.
Server responds with 101 Switching Protocols to switch protocols.
Connection stays open for two-way real-time messages.
Messages are sent as WebSocket frames.
Connection closes when either side sends a close frame.

Full Transcript

WebSockets begin when a client sends an HTTP request asking to upgrade the connection. The server replies with a 101 Switching Protocols response to agree. After this, the connection changes from HTTP to WebSocket and stays open. Both client and server can send messages anytime without waiting. This allows real-time communication. The connection remains open until one side sends a close frame, which starts the closing process. Finally, the connection closes fully. This process enables fast, continuous data exchange between client and server.