I need help with R 2 question

Consider the transportation analogy in Section 6.1.1. If the passenger is analogous to a datagram, what is analogous to the link layer frame? If all the links in the Internet were to provide reliable delivery service, would the TCP reliable delivery service be redundant? Why or why not? What are some of the possible services that a link-layer protocol can offer to the network layer? Which of these link-layer services have corresponding services in IP? In TCP? Suppose two nodes start to transmit at the same time a packet of length L over a broadcast channel of rate R. Denote the propagation delay between the two nodes as d_prop. Will there be a collision if d_prop