Final answer:
The Time-To-Live of a network datagram is stored in the header of an IP packet, not in the data-link layer frame.
Step-by-step explanation:
The Time-To-Live (TTL) of a network datagram is found within the header of a packet. The TTL is a mechanism that limits the lifespan of data in a computer or network. Specifically, in the context of Internet Protocol (IP), it is an 8-bit field in the IP header. Each router that processes the packet decrements the TTL value by one before forwarding the packet on. If the TTL value reaches zero, the packet is discarded, preventing it from circulating indefinitely.
It is important to note that network frames at the data-link layer do not carry a TTL field. The TTL resides strictly within the network layer. Therefore, the correct answer to the question is: a) Header, which is part of the IP packet structure, not the data-link layer frame.