Perspective
Network users: services and performance that their applications need, e.g., guarantee that each message it sends will be delivered without error within a certain amount of time
Network designers: cost-effective design e.g., that network resources are efficiently utilized and fairly allocated to different users
- Users + designer perspectives enough to meet 3 factors of interface/architecture design. But ...
Network providers: system that is easy to administer and manage e.g., that faults can be easily isolated and it is easy to account for usage
- Require management tools and interfaces.
- Often considered to the basic protocol interface design