Read why Hector Menendez says that trust begins with layer 1 encryption on Dark Reading :
At which network layer should we handle security of in-flight data? Some argue the application layer is most appropriate because this is where the user’s personal data, semantics and security requirements reside. Others argue that security should start in the network and physical layers, protecting even the protocol information involved in moving data — implementing encryption as deeply as possible, even at Layer 1.
Read his full article here.