What are the four communication patterns that any MCP transport must handle?

Any MCP transport must handle four communication patterns. Client to server request, where the client initiates a call like listing tools or calling a function. Server to client response, where the server returns the result of that request. Server to client request, where the server initiates communication like asking the client to call Claude through sampling. Client to server response, where the client returns the result of the server's request. The STDIO transport handles all four naturally because either party can write to the pipe at any time without restrictions.