It serves encryption to higher layers, which is normally the function of the presentation layer. TLS runs "on top of some reliable transport protocol (e.g., TCP)," which would imply that it is above the transport layer. TLS and SSL do not fit neatly into any single layer of the OSI model or the TCP/IP model. If any one of the above steps fails, then the TLS handshake fails and the connection is not created. This concludes the handshake and begins the secured connection, which is encrypted and decrypted with the session key until the connection closes.
Transport Layer Security ( TLS), the successor of the now-deprecated Secure Sockets Layer ( SSL), is a cryptographic protocol designed to provide communications security over a computer network.