IPsec
IPsec is an end-to-end security solution and operates at the Internet Layer of the Internet Protocol Suite, comparable to Layer 3 in the OSI model. Other Internet security protocols in widespread use, such as SSL, TLS and SSH, operate in the upper layers of these models. This makes IPsec more flexible, as it can be used for protecting all the higher level protocols, because applications do not need to be designed to use IPsec, whereas the use of TLS/SSL or other higher-layer protocols must be built-in the application.