The correct answer is: D. header compression, fragmentation, and layer 2 forwarding.
The 6LoWPAN Adaptation Layer (6LoWPAN) is a layer 3 protocol that provides a link-layer abstraction for IPv6 over IEEE 802.15.4 networks. It does this by compressing IPv6 headers, fragmenting packets, and forwarding packets to the next hop.
Header compression is necessary because IPv6 headers are much larger than IEEE 802.15.4 frames. Fragmentation is necessary because IEEE 802.15.4 frames have a maximum payload size of 128 bytes, while IPv6 packets can be much larger. Layer 2 forwarding is necessary because IEEE 802.15.4 networks are typically mesh networks, and packets need to be forwarded from one node to another to reach their destination.
Here is a brief explanation of each option:
- Header compression: Header compression is a technique that reduces the size of IPv6 headers. This is necessary because IPv6 headers are much larger than IEEE 802.15.4 frames. Header compression is typically done using a static table of compressed headers.
- Fragmentation: Fragmentation is a technique that divides a large packet into smaller packets that can fit within the maximum payload size of an IEEE 802.15.4 frame. This is necessary because IEEE 802.15.4 frames have a maximum payload size of 128 bytes, while IPv6 packets can be much larger.
- Layer 2 forwarding: Layer 2 forwarding is a technique that forwards packets from one node to another in a mesh network. This is necessary because IEEE 802.15.4 networks are typically mesh networks, and packets need to be forwarded from one node to another to reach their destination.