TLS (Transport Layer Security) is a cryptographic protocol providing secure data transfer between nodes in the Internet. TLS uses asymmetric cryptography for traffic key authentication, symmetric encryption for preserving confidentiality and authentication codes for message integrity monitoring.
TLS provies the client/server applications in the network with the communication that makes it impossible to listen for the packets and to gain unauthorised access.
Since most of the communication protocols can be used with or without TLS, it is required to explicitly indicate to the server if the client wishes to install TLS when establishing a connection. It can be done using a unified port number with which the connection is always established using TLS (e.g. port 443 for HTTPS) or utilizing an arbitrary port and a special command to the server from the client to switch the connection to TLS using special protocol procedures.