Connection-oriented and connectionless services
Layer n offers 2 types of services to n+1:
Connection-oriented: Like phone system. Dial, talk, hang up. To use a connection-oriented network service user first establishes connection, uses the connection and finally releases the connection. The connection should be thought of as a water-pipe. Water (bits) is pumped from one end and comes out the other in FIFO order.
Connectionless: Each packet is routed through the system independent of the others. Possible for message 1 to arrive after message 2. In connection oriented services this is impossible.
Quality of service: Reliable services don’t lose data. Unreliable services may. Reliability is obtained by having recipient acknowledge each message. PTO for more details.
Network software/connection+connectionless.