Core Networking · Study deck
Wi-Fi Access: Scanning and Deployment
A link budget predicts coverage, but the site has competing networks and changing users.
Packet Pete is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Explain: Keeping one SSID across every AP in a coverage area lets client radios roam to the strongest AP on their own, instead of a person choosing between differently named networks by hand.
- Explain: A temperature sensor, badge reader, camera, and commissioning laptop may all be "low bandwidth" in application terms, but each association, DHCP lease, TLS handshake, multicast burst, and acknowledgment still consumes channel time.
- Explain: Overlapping AP cells by roughly 15-25% avoids both extremes: too little overlap leaves dead zones between APs, and too much wastes channels on redundant coverage.
Major section
Wi-Fi Fit Record
Wi-Fi is not just a range or speed choice.
- Each retransmission spends more airtime before the application receives a single useful payload.
- A temperature sensor, badge reader, camera, and commissioning laptop may all be "low bandwidth" in application terms, but each association, DHCP lease, TLS handshake, multicast burst, and acknowledgment still consumes channel time.
Major section
Wi-Fi Fit Record (continued)
The Wi-Fi decision must include the access point, channel width, band, security method, client power behavior, and backhaul path as one service contract.
- A good fit record separates coverage, capacity, and operations evidence.
- Coverage proves the client can hear and be heard.
- Capacity proves the channel has enough airtime during busy periods.
Major section
Wi-Fi Fit Record (continued)
Operations evidence proves the design can survive firmware updates, credential rotation, AP replacement, and site changes without forcing a truck roll for every sleeping device.
- Address: a device can show acceptable signal strength and still lose service when the channel is busy.
- Receipt: coverage proves the client can be heard -- capacity proves the channel has time to hear it back.
- For wi-fi fit record, retain: Decision, limits, review as evidence for the resulting choice.
Major section
Wi-Fi Capacity Record
It should show what each device sends, how often it wakes, which access point serves it, what minimum signal quality is acceptable, and what happens when the channel is busy.
- Overlapping AP cells by roughly 15-25% avoids both extremes: too little overlap leaves dead zones between APs, and too much wastes channels on redundant coverage.
Major section
Wi-Fi Capacity Record (continued)
Keeping one SSID across every AP in a coverage area lets client radios roam to the strongest AP on their own, instead of a person choosing between differently named networks by hand.
- The record should also document what the design will not support.
- A 2.4 GHz-only sensor may be acceptable for low-rate telemetry, but it competes with legacy clients and neighboring networks.
- A high-resolution camera may need 5 GHz or 6 GHz capacity, but it may lose range faster through walls.
Major section
OFDMA and TWT Schedule Contention
Wi-Fi 6 improves dense IoT service by giving the access point better tools for scheduling.
- OFDMA divides a channel into resource units so multiple clients can send in a coordinated transmission window.
- Target Wake Time lets clients agree on sleep and wake schedules instead of listening constantly.
- Those tools do not remove the shared medium.
Major section
OFDMA and TWT Schedule Contention (continued)
Beacons, probe traffic, acknowledgments, retransmissions, hidden nodes, low modulation rates, and neighboring networks still consume airtime.
- Classic Wi-Fi access is contention-based.
- A station listens before transmitting, waits through interframe spacing, chooses a random backoff when the medium is busy, and expects an acknowledgment for unicast frames.
- Target Wake Time is also a contract.
Major section
OFDMA and TWT Schedule Contention (continued)
If the acknowledgment is missed, the frame is retried at additional airtime cost.
- OFDMA changes the scheduling granularity, not the need for planning.
- That helps dense small-packet workloads, but it depends on compatible clients, firmware behavior, AP scheduler policy, channel conditions, and whether the traffic arrives in patterns the scheduler can combine.
- The AP and client agree when the client can wake for service, so the device spends less energy listening between events.
Deck summary
Key takeaways
Wi-Fi is not just a range or speed choice.
- The Wi-Fi decision must include the access point, channel width, band, security method, client power behavior, and backhaul path as one service contract.
- Operations evidence proves the design can survive firmware updates, credential rotation, AP replacement, and site changes without forcing a truck roll for every sleeping device.
- It should show what each device sends, how often it wakes, which access point serves it, what minimum signal quality is acceptable, and what happens when the channel is busy.
- Wi-Fi 6 improves dense IoT service by giving the access point better tools for scheduling.
Retrieval practice
Recall check 1 of 2
Packet Pete says: answer from memory, then check your reasoning.
Q1A theme park deploys 2,000 wearable wristbands across 1 km². Wristbands need 16-hour battery, location updates every 30s, and <2s payment latency. Which is suitable?
Show answer
Answer: D see answers page
Q2Place each Wi-Fi role where it lives so you can plan shared airtime, power saving, and coverage for unlike IoT clients.
Show answer
Answer: A Interactive clients, the access-point radio, and building sensors impose different airtime and power needs so you can size a Wi-Fi cell instead of treating every device alike.
Retrieval practice
Recall check 2 of 2
Packet Pete says: answer from memory, then check your reasoning.
Q3A warehouse Wi-Fi IoT deployment has strong RSSI at most sensors, but uploads stall when forklifts move through the aisles. What should the capacity record check first?
Show answer
Answer: B Good RSSI alone does not prove usable Wi-Fi capacity.
Print reference
Answers
Answer key.
- D · Wi-Fi 6 is the correct solution: OFDMA handles 2,000 concurrent devices in a dense outdoor environment, <2s payment latency is achieved (~230ms typical), and TWT allows wristbands to sleep between 30-second location updates to achieve 16-hour battery life.
- A · Interactive clients, the access-point radio, and building sensors impose different airtime and power needs so you can size a Wi-Fi cell instead of treating every device alike.
- B · Good RSSI alone does not prove usable Wi-Fi capacity.