What defines addressing methods and structures for datagram encapsulation that allows the delivery of packets from a source to a destination?

The Internet Protocol (IP) is essential for addressing methods and structures related to datagram encapsulation, enabling the correct delivery of packets from a source to a destination over a network. IP operates at the Network Layer of the OSI model and is responsible for routing data packets across networks by assigning unique IP addresses to devices. This ensures that data can be accurately sent and received by devices that are not necessarily on the same local network.

IP encapsulates data into packets called datagrams, each containing both source and destination IP addresses, which are essential for the routing process. When data is transmitted, routers use these addresses to determine the best path for the packet to reach its intended destination. This role of IP in addressing and packet delivery is critical in various network environments, including both local and wide area networks.

While other protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), operate above IP at the Transport Layer and focus on how packets are delivered and manage data integrity and session establishment, they do not define the addressing or encapsulation methods themselves. Instead, they rely on IP for those fundamental tasks, making Internet Protocol the correct and central choice in this context for the question regarding datagram encapsulation and packet delivery.