a) Explain why the Internet has a hierarchical routing architecture. (Hint: Think Inter-AS and Intra-AS structures!)

b) A datagram packet can be split into pieces on the way from computer A to computer B. For these datagram fragments, how does computer B determine that the fragment it received is the first fragment of the original datagram? How does computer B determine that a piece it received is the last piece of the original datagram? Explain.