19. (a) Draw an example internetwork where the BIDIR-PIM route from a source's router to a group member's router is longer than the PIM-SM source-specific route. (b) Draw an example where they are the same.

Explain the role of a router in the OSI model and give an example of a real-world scenario where a router operates at the network layer.

First and foremost, what is a router's purpose?2) What is a data packet? How is it put together? What happens to packets when they are wrapped up?

Are routers employing layer-2 protocols that pose difficulties? What is the reason for the persistence of ICMP packets despite modifications to the subnet of a PPP-encapsulated router's serial interface?