Ensures network performance meets the requirements of different applications.
Parameters:
- Reliability
- Delay
- Jitter
- Bandwidth
Different type 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 reserved per individual flow. Guarantees QoS for each flow. Does not scale in large networks.
Example:
- Resource Reservation Protocol (RSVP)
Used in applications requiring strict performance guarantees:
- Real-time video conferencing
- VoIP calls
- Interactive multimedia systems
Differentiated Services
Aka. DiffServ. Divides traffic into classes with different priorities.
Each class receives different bandwidth, delay, and priority. Scales well in large networks. Does not guarantee QoS for individual flows.
Uses Differentiated Services (DS) field in the IP header. A 8-bit field. Includes:
- Differentiated Services Code Point (DSCP) field
6-bit field. used to indicate the QoS class or priority level of a packet in DiffServ networks. - Explicit Congestion Notification (ECN) field
2-bit field. used to indicate network congestion without dropping packets. ECN-capable transport protocols can use this information to adjust their sending rates and avoid congestion collapse.)