Questions about Transport Layer Security (TLS) protocol, which allows client-server apps to communicate across a network in a way designed to try and prevent eavesdropping and tampering.

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols that are designed to provide communication security over the Internet.

The TLS protocol allows client-server applications to communicate across a network in a way designed to prevent eavesdropping and tampering.

Since protocols can operate either with or without TLS (or SSL), it is necessary for the client to indicate to the server whether it wants to set up a TLS connection or not. There are two main ways of achieving this; one option is to use a different port number for TLS connections (for example port 443 for HTTPS). The other is to use the regular port number and have the client request that the server switch the connection to TLS using a protocol-specific mechanism (for example STARTTLS for mail and news protocols).

Source: http://en.wikipedia.org/wiki/Transport_Layer_Security