Design issues of network layer
1. The services provided should be independent of the underlying technology. Users of the service need not be aware of. the physical implementation of the network.
2. The transport layer should be shielded from the number, type and different topologies of the subnets user uses.
3. Finally, there is a need for some uniform addressing scheme for network addresses:
(i) Connection Oriented Network Services
(ii) Connectionless Network Services.
4. A connection-oriented service is one in which the user is given a “reliable” end to end connection.
5. To communicate, the user requests a connection, then uses the connection to his hearts content, and then closes the connection.
6. In a connectionless service, the user simply bundles his information together. Puts an address on it and sends it off. In the hope that it will reach its destination.
7. There is no guarantee that the bundle will arrive. So a connectionless service is one reminiscent of the postal system.
8. A letter is sent, that is, put in the post box. It is then in the Postal network”.