Networks traditionally provide best effort service. Every packet is treated equally with no delivery guarantees.
Best effort:
- Simple. No state tracking.
- Works when network is underutilized
- Unpredictable during congestion
Guaranteed service:
- Reserved bandwidth for flows
- Bounded latency and jitter
- Predictable performance
- Requires admission control
The tradeoff is complexity versus predictability. Best effort scales easily. Guaranteed services need resource reservation at every hop. Most enterprise networks use differentiated services as a middle ground.