In Section $7\mathrm{.}3\mathrm{.}4,$ we said that the Transport layer turns the inherently unreliable Network layer into an error$-$free delivery service. However, the Network layer uses the services of the Data Link layer, which is guaranteed to correctly deliver messages on a point$-$to$-$point link. For example, assume we have the following four$-$node network:DetailsIf the Network layer is sending a message from A to D via B$,$ it can be sure that a message sent by the Data Link layer from A to B will always correctly get to B$,$ and a message sent from B to D will always correctly get to D$.$ How then is it possible for the Network layer to be unable to correctly deliver a message from A to D