On the left side of this illustration, we see a three-layer protocol stack consisting of (from top to bottom): Application, TCP, and IP. Connecting the Application and TCP layers is a fourth layer shaded dark blue and labeled "TCP socket." This protocol stack is identified as TCP API.

On the right side of this illustration, we see again the three-layer protocol stack. Between the Application and TCP layer is a layer shaded light blue and labeled "SSL sublayer." Connecting the Application and SSL sublayer is a layer shaded dark blue and labeled "SSL socket." These top three layers-Application, SSL socket, and SSL sublayer-are identified as the "Application layer." Between the SSL sublayer and the TCP layer is a layer shaded dark blue and labeled "TCP socket." This protocol stack is identified as TCP enhanced with SSL.