Final answer:
The statement regarding the Internet protocol stack is true as transport and application layers are implemented on end systems and not on routers. Refraction plays a crucial role in the functionality of fiber optic cables as it allows light to be guided along the cable with minimal loss.
Step-by-step explanation:
The statement that the transport and application layers of the Internet protocol stack are implemented in the end systems but not in the routers in the network core is true. Routers primarily deal with the network and link layers, where they focus on routing packets to their destination based on the Internet Protocol (IP) addresses. The transport layer (e.g., TCP/UDP) and application layer (e.g., HTTP, FTP) protocols are indeed executed on the end systems, such as computers, where they manage the establishment of host-to-host communications and support application-specific services respectively.
Refraction is indeed useful in fiber optic cables for transmitting signals. This is because refraction allows light, which is the medium for signal in fiber optics, to be confined within the core of the cable enabling the signal to travel great distances with low loss. Refraction occurs when light passes through materials with different refractive indices, which is the basic principle that allows fiber optics to work so effectively.