* What are the two most important network-layer functions in a datagram network? What are the three most important network-layer functions in a virtual-circuit network?
--> Three network- layer :: Datagram-based network layer, forwarding, routing. Additional function of VC-based network layer: call setup.
* What is the difference between routing and forwarding?
--> Both of these are used in the network layer for the purpose of data sending on different paths.In the forwarding network layer function, the data or packet is transferred form one incoming link and then reached to the other outgoing link, the main thing is that all these transfer of packets is done within a single router. When any packet reach at the input link of the router, then router must have to transfer the packet to its correct output link.
On the other hand the routing function is used to send the packets form one pc to another pc within two different routers. Its means that routing occur between the two routers of network, their combined communication by means of routing protocols decide the routes or paths, that packets would acquire, on their journey from source to destination. It is the responsibility of the network layer that, it would decide the appropriate path for the packet, for sending it to its desired receiver. For selecting the correct path for sending the data, the network layer use the routing algorithm. The routing algorithm is responsible for choosing the best path out of many paths. Means the path which is more clear, short and with out