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TLS is a layered protocol, and consists of the record protocol, the handshake protocol and the alert protocol. The record protocol is to serve all other protocols and is above the transport layer. The record protocol offers symmetric encryption, and data authenticity4. The alert protocol offers some signaling to the other protocols. It can help informing the peer for the cause of failures and other error conditions. See The Alert Protocol, for more information. The alert protocol is above the record protocol.
The handshake protocol is responsible for the security parameters’ negotiation, the initial key exchange and authentication. See The Handshake Protocol, for more information about the handshake protocol. The protocol layering in TLS is shown in Figure 3.1.
In early versions of TLS compression was optionally available as well. This is no longer the case in recent versions of the protocol.