Performance, QoS, and Congestion Management
Measuring Network Performance
Key metrics
Important performance metrics include bandwidth, throughput, latency, jitter, and packet loss. The best design depends on the application's tolerance for delay and loss.
Goodput vs throughput
Throughput measures all delivered bits per second; goodput measures useful application payload excluding protocol overhead and retransmissions.
Congestion
Congestion occurs when traffic demand exceeds available capacity. Symptoms include queueing delays, packet drops, retransmissions, and reduced user experience.
Performance terms
| Term | Meaning |
|---|---|
| Latency | Time for a packet to travel end to end |
| Jitter | Variation in latency over time |
| Bandwidth | Maximum capacity of a link |
| Packet loss | Packets dropped before delivery |
Which metric matters most for real-time voice quality fluctuations?
Real-time media is sensitive to variation in delay, not just average delay.
Correct answer: Jitter
What is the difference between bandwidth and throughput?
Real traffic is affected by overhead, congestion, and errors, so throughput is often lower than theoretical capacity.
Correct answer: Bandwidth is the link capacity, while throughput is the actual rate achieved
QoS and congestion control
Quality of Service
Quality of Service, or , prioritizes traffic classes so important flows such as voice, video, or control traffic get better treatment under congestion.
What is the purpose of QoS prioritization?
QoS is about preferential handling of traffic classes when resources are limited.
Correct answer: Give important traffic better treatment during congestion
Basic congestion response
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Step 1: Detect symptoms using latency and packet loss measurements.
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Step 2: Identify the congested link or queue.
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Step 3: Increase capacity, reduce demand, or prioritize critical traffic.
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Step 4: Re-test under load to confirm improvement.