Tunneling can also allow communication using a protocol that normally wouldn’t be supported on the restricted network.
[1][2] In this mechanism, the client asks an HTTP proxy server to forward the TCP connection to the desired destination.
This mechanism is how a client behind an HTTP proxy can access websites using SSL or TLS (i.e. HTTPS).
In the example below, the client is starting SSH communications, as hinted at by the port number in the initial CONNECT request.
Since all traffic is encapsulated inside normal GET and POST requests and responses, this approach works through most proxies and firewalls.