Wi‑Fi basics: notes from Mist training

Wi‑Fi Basics / Mist training

Notebook cover page — IEEE, Wi‑Fi Alliance, 2.4 vs 5 GHz

1. IEEE standards & Wi‑Fi Alliance

Standard Notes from class
IEEE 802.15.1 Bluetooth (Bluetooth SIG)
IEEE 802.15.4 Zigbee (wireless light), low‑power communication
IEEE 1394 Old iMac FireWire / iPod era
IEEE 802.3 Ethernet (PoE via amendments)
IEEE 802.11 Standard wireless LAN

Wi‑Fi Alliance

  • Branding + ensures interoperability between vendors
  • Example members noted: Apple, Comcast, Sony, Intel, Qualcomm, T‑Mobile
  • Keywords: WPA / WPA2 / WPA3, WMM, Wi‑Fi 6

2. 2.4 GHz vs 5 GHz bands

2.4 GHz 5 GHz
Frequency Low High
Wavelength (class sketch) Longer (~4.9”) Shorter (~2.5”)
Range Typically more Less range
Crowding More crowded Less crowded
Non‑Wi‑Fi interference More Less
Amendments 802.11 b / g / n / ax 802.11 a / n / ac / ax
  • 2.4 / 5 GHz → unlicensed spectrum
  • 802.11n → either 2.4 or 5
  • 802.11ac → only 5 GHz

3. Major 802.11 amendments

Amendments table and 1/6/11 channel sketch

Amendment Year Band Max signal rate (as written) Modulation / mode Channel width
802.11 (prime) 1997 2.4 2 Mbps DSSS 22 MHz
802.11b 1999 2.4 11 Mbps HR‑DSSS 22 MHz
802.11a 1999 5 54 Mbps OFDM 20 MHz
802.11g 2003 2.4 54 Mbps ERP‑OFDM 20 MHz
802.11n (Wi‑Fi 4) 2009 2.4 & 5 600 Mbps HT 20, 40
802.11ac (Wi‑Fi 5) 2013 5 6933 Mbps VHT 20, 40, 80, 160
802.11ax (Wi‑Fi 6) — 2.4 & 5 9600 Mbps HE 20, 40, 80, 160

Class comparison:

  • 802.11a → ~90 feet but fast
  • 802.11b → ~300 feet but slow
  • 2.4 GHz note: 11 channels / ~60 MHz usable picture in many regions
  • Non‑overlapping channels: 1, 6, 11

4. Co‑channel vs adjacent interference

Half duplex, CCI, ACI, channel reuse sketches

Co‑channel interference

  • Wi‑Fi is half duplex (data then ACK; one useful talker at a time on the channel)
  • Slow devices consume more airtime
  • Data rate is based on signal strength (and SNR)

Adjacent channel interference

  • STAs on overlapping channels corrupt each other’s transmissions
  • Example conflict: channel 6 next to channel 7
  • Mist guidance in notes: stick to 1, 6, 11

Channel reuse

  • A good channel plan minimizes co‑channel interference
  • HR‑DSSS → 802.11b
  • CH 14 — Japan

5. 5 GHz channels, bonding, dB vs dBm

UNII bands, channel bonding, dB/dBm

5 GHz (~25 channels in notes)

  • UNII‑1: 36, 40, 44, 48
  • UNII‑2: 52, 56, 60, 64
  • UNII‑2 Extended: 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144
  • UNII‑3: 149, 153, 157, 161
  • ISM: 165
  • UNII‑2 / Ext → DFS (Doppler weather radar exists in these channels)

Channel bonding

  • Started prominently in 802.11n: two 20 MHz → 40 MHz
  • 802.11ac: 20 / 40 / 80 / 160 MHz
  • Bonding sketch for 36–48: Sec / Primary / Sec / Sec over channels 36, 40, 44, 48

Practical notes:

  • 2.4 GHz → not enough BW for wide enterprise bonding
  • 5 GHz → 40 MHz in low density; 20 MHz in high density
  • 80 MHz → never default in enterprise (per notes)
  • 160 MHz → not practical

Signal strength wording

  • dB → change in signal strength
  • dBm → absolute value

6. Rules of 3s & 10s, dBm targets, IDs, other wireless

Rules of 3s & 10s

  • +3 dB → double the signal strength
  • −3 dB → half the signal strength
  • +10 dB → 10× more
  • −10 dB → 10× less

dBm examples from notes

dBm Note
−60 dBm 0.000001 mW
−70 dBm 0.0000001 mW
−30 dBm Good signal
−65 dBm Voice app / mobile device
−67 dBm Streaming video
−75 dBm Web browsing, email, IM
−80 dBm Generally reliable (as written)
−90 dBm Drowning in the noise floor

Network identifiers

  • BSSID → MAC address of AP’s radio
  • SSID → friendly name of Wi‑Fi network
  • ESSID → multiple APs in the Wi‑Fi network (same SSID / ESS)

Other wireless technologies

  • BLE → 2.4 GHz; location services; blue‑dot indoor navigation
  • Zigbee → 2.4 GHz; low power / throughput; ~250 kbps; mesh
  • CBRS → Citizens Broadband Radio Service; 3.5–3.7 GHz; widths 5 / 10 / 15 / 20 / 40 MHz
    • dedicated and tiered licensing model
    • upcoming / new technology (at time of notes)
    • limited early handset support (Phone 11 / Pixel / Samsung called out)

6 GHz

  • Wi‑Fi in new spectrum
  • Potential for lots of new channels
  • Upcoming / potential new technology (Wi‑Fi 6E era)

7. BLE vs Wi‑Fi channels, Ethernet vs wireless NIC

  • BLE uses advertising channels 37, 38, 39
  • Those sit between Wi‑Fi channels 1, 6, 11 in the class diagram
  • Notes claim BLE is placed to avoid colliding with those Wi‑Fi centers

Ethernet

  • CSMA/CD
  • Only receives frames destined for it
  • Consistent data rate / throughput ≈ line rate

Wireless NIC

  • CSMA/CA — listen or send/receive
  • Demodulates all 802.11 frames it hears
  • Data rate varies with signal strength, SNR, traffic on the channel

8. Throughput, SNR, data rates, management frames

  • Actual throughput is roughly half the data rate
  • Throughput decreases as client count increases

How to make Ethernet / wireless faster

  • Decrease interference (shielding, twist rate on copper side)
  • Better signal strength / better SNR

SNR

  • How much signal is above background noise
  • Example sketch: RSSI ≈ −60 dBm, noise floor ≈ −95 dBm → SNR ≈ 35 dB

Data rates

Management frames (STA associating / disassociating)

  • Beacon
  • Probe request / Probe response
  • Auth request / Auth response
  • Association request / Association response
  • Disassociation

9. Control/data frames, airtime arbitration, roaming, association

Airtime arbitration timeline and association sketch

Control frames — control the RF medium / help delivery

  • ACK, Block‑ACK, RTS/CTS

Data frames — high‑level protocol data

  • DATA, QoS, Null data

Beacon → about 10 times / sec

Airtime arbitration (CSMA/CA sketch)

Timeline ideas from notes: NAV, DIFS (~50 µs in sketch), random backoff (examples 7 and 9), RTS → SIFS → CTS → DATA → ACK, remaining backoff slots, some STAs defer.

Wi‑Fi roaming

  • Client decides when to roam
  • Client decides who to roam to
  • Green diamond (Keith Parsons / WLAN Pros): decision matrix using SNR, signal strength, retry rate — noted as a teaching model (“totally made up”)

Client association process (as sketched)

Probe Req / Probe Resp → then join path including Ass Req / Ass Resp, Auth Req / Auth Resp, and 4‑way handshake (WPA2).
(Standard open‑system order is usually Auth → Assoc → 4‑way; keep that in mind when reading captures.)

10. Wi‑Fi security & design questions

Security

  • Open → no auth and no encryption
  • WEP → hex key; broken
  • WPA → stop‑gap; ~54 Mbps era
    • WPA‑Personal / PSK → 8–63 character pre‑shared key
    • WPA‑Enterprise → credentials via RADIUS
  • WPA2 → new cipher suite; required new hardware
  • WPA3
    • Enhanced Open / OWE for open networks
    • Personal → forward secrecy with SAE
    • Enterprise → stronger encryption

Design

“If you aim at nothing, you’ll hit it every time.” — Zig Ziglar

Network requirements to capture:

  • Where do you need Wi‑Fi?
  • Where do you not need Wi‑Fi?
  • What devices will you use?
  • How many devices / users?
  • What applications (web, voice, video, …)?

11. Design thresholds & carrier sense (Wi‑Fi Basic‑2)

  • Not all clients support all channels
  • APs on unsupported channels are invisible to that client
  • Client capability reference: clients.mikealbano.com

Design requirements from notes

  1. Primary coverage min −67 dBm
  2. Secondary coverage min −75 dBm
  3. Minimum data rate 24 Mbps (raw rate, not throughput)
  4. SNR target 25 dB
  5. Channel overlap: max 1 AP above −85 dBm on a shared channel

Also noted: Ekahau for design work.

Review

  • Wireless is half duplex
  • Physical carrier sense detects whether the channel is busy

Energy detect

  • Listen for any RF on the channel
  • Question: “Do I hear RF on my channel?”
  • Threshold ≈ −62 dBm

Clear Channel Assessment (Wi‑Fi detect)

  • Question: “Do I hear any other Wi‑Fi device on the channel?”
  • Threshold ≈ −82 dBm (backoff)

12. Virtual carrier sense, duty cycle, utilization

NAV, duty cycle, utilization sketches

Virtual carrier sense

  • NAV = Network Allocation Vector
  • Tells other devices how long a device will use the channel
  • Notes: up to ~0.3 sec max; also 1–32000 µs range noted

Duty cycle

  • How often things are talking (L1)
  • % of time transmitting (ON / OFF / ON …)

Utilization

  • L1 measurement of raw RF activity in the spectrum
  • Spectrum analysis view
  • Sketch contrast: g/n rectangular‑ish pulses vs b / DSSS bell curve

Airtime utilization

  • Above L1 → Layer 2 measurement
  • How much time 802.11 devices reserved to talk
  • Measured with packet capture / analysis

13. Things that consume airtime (Wi‑Fi Basic‑3)

  • More devices (co‑channel interference)
  • Poor coverage (device talks slower)
  • Legacy data rates
  • Too many virtual SSIDs

Multi‑Preshared Key

  • Avoid multiple SSIDs when possible
  • One SSID, different policies (printers, etc.)

Site survey note

  • Identify rogue antennas / APs, etc.

SLE → Service Level Expectation (Mist)

Data rate influencers

  • Spatial streams
  • Modulation
  • Channel width
  • SGI (short guard interval) — spacing between symbols / transmits

14. Modulation: ASK / FSK / PSK / BPSK

ASK FSK PSK and BPSK constellation sketches

Bit sequence example: 0 1 0 0 1 0

  • Baseband → square wave of bits
  • ASK → amplitude changes with bits
  • FSK → frequency changes with bits
  • PSK → phase flips with bits

BPSK (binary phase shift keying) — simple modulation

  • 0 → −SIN
  • 1 → +SIN
  • Peaks idea: 0 near 270°, 1 near 90°
  • EVM (Error Vector Magnitude) → how far the symbol lands from the ideal 0/1 target

15. QPSK and 16‑QAM

QPSK and 16‑QAM constellation sketches

QPSK → quadrature phase shift keying → 2 bits at a time
Patterns: 00, 01, 10, 11 on a 4‑point constellation (EVM still matters)

16‑QAM → phase and amplitude → 4 bits

  • Phase → where the wave peaks
  • Amplitude → how far from center
  • Constellation grid with EVM / amplitude / phase vectors

16. Higher QAM, retries, SNR vs rate

  • 64‑QAM → 6 bits
  • 256‑QAM → 8 bits/symbol (802.11ac)
  • 1024‑QAM → 10 bits/symbol (802.11ax)

Relationships from notes:

  • Very close to AP → excellent rate due to dense QAM
  • SNR ↓ → rate‑shift to lower QAM
  • Weaker signal → larger EVM box → less data rate
  • Bad SNR → receiver stops getting usable ACKs
  • Data rate behavior is tightly tied to retries
  • Airtime goes up as SNR goes down

17. OFDM subcarriers & spatial streams

OFDM subcarriers and SISO / diversity sketches

  • 802.11 a/g/n/ac/ax → OFDM family (table / rectangular spectrum sketch)
  • 802.11b → DSSS (curve / bell shape)

Teaching model for 20 MHz OFDM:

  • 64 subcarriers / 20 MHz
  • 56 used → 4 pilot + 52 data (plus nulls)
  • Spacing note: 312.5 kHz
  • Null → no data
  • Pilot → reference (“where to send”)
  • Data → “strings on the guitar”

Each transmit places a symbol on each used subcarrier; the transceiver decodes BPSK / QAM variants.

SISO → 1 radio / 1 antenna

  • Multipath (reflections, out of phase) hurts SISO

SISO with diversity → 1 radio / 2 antennas

  • Any one antenna used (switch / select)

18. MIMO & antenna patterns

MIMO, azimuth/elevation, antenna types

MIMO

  • Size / battery / cost tradeoffs
  • 2×2 smaller clients
  • 3×3
  • 4×4 high‑end APs
  • MRC (Maximum Ratio Combining): receiver aligns out‑of‑phase copies → increases amplitude
  • Spatial multiplexing: different data streams on different antennas / paths → faster rate

Antenna pattern

  • Do not blindly use a generic AP pattern assumption
  • Azimuth = horizontal / top‑down
  • Elevation = side view

Antenna types

  • Omnidirectional (e.g. AP43 with external options)
  • Directional patch → warehouse / car parking
  • High‑density patch → ~30° beam width; notes mention multiple unique antennas in the external assembly

19. AP43E & AP architectures

Reference also noted: badfi.com

AP43E (from notes)

  • 2.4 GHz 4×4
  • 5 GHz 4×4
  • Scanning radio 2×2 (RRM scanning)
  • 6 dual‑band connectors

Architectures

  1. Autonomous

    • No central management
    • No AP coordination
    • Traffic sent directly to DS

  2. Lightweight AP

    • Centrally managed
    • APs coordinated
    • Tunnels traffic to controller
    • Controller puts traffic on DS

  3. Cloud managed (Mist)

    • Cloud managed / coordinated
    • Traffic usually sent directly to DS
    • Optional path via Mist Edge

Mist Edge

  • Functions like a controller for tunnel use cases
  • Tunnel all traffic to Mist Edge like a traditional controller
  • L2TP endpoint note / port 1701 in notes

20. Mist templates, security classes, RRM

Mist positioning

  • Microservices that scale automatically with AI (different from classic controller vendors)

Templates

  • Config template → e.g. high‑density min data rate 18 Mbps, WLAN SSIDs
  • RF template → 2.4 / 5 GHz power
  • Flow: RF template → site configuration → config template

Network security classes

  • Rogue AP → connected to some physical / wired network
  • Honeypot → may not be on your LAN; advertises same SSID as Mist
  • Neighbor AP
  • Approved AP

Mist RRM

  • Network → Radio Management
  • AP density idea in notes: how many APs can hear each other (0.7–0.8) with low coverage gap

Global RRM (AI driven)

  • Uses large dataset over days
  • Uses reinforcement learning
  • Runs daily ~3 am local / site (Scheduled RRM)
  • Can be manually triggered per band (Triggered RRM)
  • Global RRM is like a site RF “reset” button

Local RRM

  • Runs ad‑hoc
  • Reacts to local device events
  • Cloud independent
  • Event types from notes:
    • Auto channel selection
    • Auto triggered ACS
    • Interference AP co‑channel
    • Interference non‑Wi‑Fi
    • Interference co‑channel external
    • Neighbor AP down / recover
    • Radar detected
    • Post‑radar