Interoperability
As mentioned above the client and server negotiate the cryptographic suite. This happens when the session is started, briefly the client sends a list of supported algorithms and the server chooses a suite, or refuses the connection. The standard does not mandate support of any algorithm. An endpoint (either client or server) that needs to be interoperable with any other endpoint may need to implement every algorithm (including some covered by intellectual property rights).
Read more about this topic: Wireless Transport Layer Security