HTTP/1.1
In HTTP/1.1 (persistent connections or keep alive connections), the client can indicate that it wants to use a persistent connection by including the Connection: keep-alive header in its request. If the server supports persistent connections, it will respond with the same header to indicate that it will keep the connection open.
sequenceDiagram
participant Client
participant Server
Note over Client,Server: Establish Connection
Client->>Server: GET index.html
Server->>Client: 200 OK
Client->>Server: GET main.css
Server->>Client: 200 OK
Client->>Server: GET main.js
Server->>Client: 200 OK
Note over Client,Server: Close Connection
The persistent connection remains open until either the client or server explicitly closes it, or until a timeout occurs. The server can also choose to close the connection after a certain number of requests have been processed, or after a certain amount of time has elapsed, to prevent resource exhaustion.