Final answer:
a.True
The Transport layer indeed creates a segment or datagram and hands it down to the Network layer; this process is core to the functioning of the OSI model for data transmission. Additionally, refraction plays a vital role in the operation of fiber optic cables, making them effective for signal transmission.
Step-by-step explanation:
The statement that the Transport layer creates a segment or datagram and hands it down to the Network layer is true. The Transport layer of the OSI model is responsible for the logical communication between application processes running on different hosts within a layered architecture of protocols and other network components.
When it transmits data, the Transport layer organizes the data into segments for TCP (Transmission Control Protocol) or datagrams for UDP (User Datagram Protocol). Those formatted data packets are then handed down to the Network layer, which is responsible for logical addressing, routing, and packet forwarding.
For questions 12 and 13:
The statement that refraction is useful in fiber optic cables for transmitting signals is true. Refraction is the change in direction of a wave passing from one medium to another caused by its change in speed. This principle is critical in the functioning of fiber optic cables, where light is transmitted through the core of the fiber cable.
The refraction at the core-cladding interface keeps the light confined to the core, allowing it to travel long distances with minimal signal loss.