Ensures network performance meets the requirements of different applications.
Parameters:
- Reliability
- Delay
- Jitter
- Bandwidth
Different types of applications have different QoS requirements.
| Application | Delay | Jitter | Bandwidth |
|---|---|---|---|
| Not critical | Not important | Low | |
| Web | < 2 s | Not important | Medium |
| Video streaming | Not critical | Significant | High |
| Telephony | < 0.2 s | Critical | Low |
QoS Techniques
Methods used to achieve QoS:
- Overprovisioning
Increase network capacity to more than the expected traffic load - Buffering
Store packets temporarily to smooth out traffic bursts - Traffic shaping
Control traffic rate
QoS Technologies
Integrated Services
Aka. IntServ. Resources are reserved per individual flow before transmission begins.
Properties:
- Guarantees QoS per individual flow.
- Does not scale in large networks (per-flow state at every router).
Protocol: Resource Reservation Protocol (RSVP).
Used in:
- Real-time video conferencing
- VoIP calls
- Interactive multimedia systems
Differentiated Services
Aka. DiffServ. Divides traffic into classes with different priorities.
Properties:
- Each class receives different bandwidth, delay, and priority treatment.
- Scales well in large networks.
- Does not guarantee QoS for individual flows.
Uses the Differentiated Services (DS) field in the IP header, an 8-bit field:
- DSCP (6 bits)
Indicates the QoS class or priority level of a packet. - ECN (2 bits)
Signals congestion without dropping packets. ECN-capable transports adjust their sending rate in response.