Core Networking · Study deck

Network Performance Lab: Calculations and Experiments

A protocol header is the control information placed before a message's payload, the sensor data it carries.

Packet Pete is your guide for this deck.

performance
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After studying this chapter

Learning objectives

You will be able to:

  • Explain: The first arrow leads to throughput, the bits actually delivered, and the label on the way tells you what was taken: loss and retries.
  • Explain: The button is the only input; pressing it injects a burst of traffic, which is how you drive utilisation up on demand.
  • Explain: Bandwidth is how much data a link can carry in a given time; latency is the wait for a message to arrive.
  • Explain: Depending on the bottleneck, reduce queue load, improve scheduling, shorten the path, move processing nearer the sensor, or increase constrained-link capacity.
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Major section

Start With the Decision

A protocol header is the control information placed before a message's payload, the sensor data it carries.

  • On a small message, the header can take most of the bytes.
  • Bandwidth is how much data a link can carry in a given time; latency is the wait for a message to arrive.
  • A calculation and simulator run show where the time and bytes go.
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Major section

Try It: Protocol Overhead Calculator

The first arrow leads to throughput, the bits actually delivered, and the label on the way tells you what was taken: loss and retries.

  • The second arrow leads to goodput, the application data that finally arrives, and there the cost is headers.

Key terms

Each step
Each step is a different kind of overhead, charged by a different part of the stack.
Diagram showing the relationship between bandwidth, throughput, and goodput with typical loss factors
Diagram showing the relationship between bandwidth, throughput, and goodput with typical loss factors
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Major section

Circuit Diagram

The button is the only input; pressing it injects a burst of traffic, which is how you drive utilisation up on demand.

  • The three LED groups then report what the burst did.
  • The serial link back to the computer carries the numbers.
Circuit diagram for network performance lab showing ESP32 with LED indicators and button input
Circuit diagram for network performance lab showing ESP32 with LED indicators and button input
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Major section

Bandwidth Alone Does Not Cut Latency

The Mistake: "We upgraded from 100 Mbps to 1 Gbps, so our IoT sensor latency should decrease 10x.".

  • The outcome depends on packet size, load, and the full path.
  • Total latency: ≈1–100 ms from the listed components, so the 7.2 µs saved in serialization is negligible.
  • Depending on the bottleneck, reduce queue load, improve scheduling, shorten the path, move processing nearer the sensor, or increase constrained-link capacity.

Why it matters

Why It's Wrong: A faster link reduces serialization time and may relieve queues, but it does not reduce propagation distance or every processing delay.

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Deck summary

Key takeaways

A protocol header is the control information placed before a message's payload, the sensor data it carries.

  • The first arrow leads to throughput, the bits actually delivered, and the label on the way tells you what was taken: loss and retries.
  • The button is the only input; pressing it injects a burst of traffic, which is how you drive utilisation up on demand.
  • The Mistake: "We upgraded from 100 Mbps to 1 Gbps, so our IoT sensor latency should decrease 10x.".
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Retrieval practice

Recall check 1 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q1A packet has 80 payload bytes and 20 header bytes. The link sends at 1 Mb/s. How long does serialization take, ignoring other delays?

A0.8 ms.
B0.64 ms.
C0.1 ms.
D8 ms.
Show answer

Answer: A Include header and payload, convert bytes to bits, then divide by the link rate.

Q2Place each performance measurement where it lives so you can separate offered load, the tested path, and the quality evidence it produces.

ANetwork Under Test
BControl Network
CManagement Network
DTest Server
Show answer

Answer: A Control the load, name the path, and observe distinct metrics so you can compare network performance without mixing cause and measurement.

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Retrieval practice

Recall check 2 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q3A factory IoT network has a Wi-Fi link with 54 Mbps bandwidth. During peak hours, the actual data rate measured by sensors is only 12 Mbps. An engineer claims the network is broken. What is the correct explanation?

AThe Wi-Fi access point is faulty and operating at reduced speed
BBandwidth is the maximum theoretical capacity while throughput is the actual achieved rate
CThe sensors are misconfigured and only connecting at 12 Mbps instead of 54 Mbps
DThe factory needs to upgrade to 802.11ac to achieve the advertised speeds
Show answer

Answer: B

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Retrieval practice

Recall check 3 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q4An industrial IoT system monitors a robotic arm using sensors that send position data every 10 ms. The network has average latency of 15 ms but jitter varies between 5 ms and 45 ms. Which metric is most critical for this application and why?

ABandwidth, because position data requires high throughput
BLatency, because 15 ms average delay causes the robot to lag behind real-time
CPacket loss, because missing a single position update would crash the robot
DJitter, because timing variation drives instability.
Show answer

Answer: D The 5–45 ms delay range spans 40 ms, so the 15 ms mean hides late updates.

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Print reference

Answers

Answer key.

  1. A · Include header and payload, convert bytes to bits, then divide by the link rate.
  2. A · Control the load, name the path, and observe distinct metrics so you can compare network performance without mixing cause and measurement.
  3. B
  4. D · The 5–45 ms delay range spans 40 ms, so the 15 ms mean hides late updates.
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