Overview

This is a collection of important notes and information that I have collected over the years through my studies to act as a quick reference/refresher for myself.

Important WiFi Metrics

  • RSSI
  • SNR
  • MCS
  • Data Rate
  • Security
  • Congestion
  • Responsiveness
  • Scans
  • Selection Decisions
  • Roaming Scans

CAPWAP Ports

  • 5246 โ€“ Control (DTLS)
  • 5247 โ€“ Data

RF Design Guidelines

AP Spacing

  • ~44โ€“70 ft apart (~20% overlap)
  • Avoid straight lines; stagger placement

AP per Area

  • Data only: 1 AP per 5,000 sq ft
  • Voice: 1 AP per 3,000 sq ft
  • High density: 1 AP per 11โ€“120 sq ft
  • Cisco: 1 AP per 2,000 sq ft

Install Height

  • 10โ€“15 ft above ground
  • Avoid HVAC, lights, beams

AP Separation

  • 10 ft between APs
  • 3 ft from obstructions

Design Tips

  • Design at half power
  • Model actual AP characteristics

Signal Strength Targets

Cell Edge (RSSI)

  • -67 dBm for data
  • -65 dBm for voice
  • -75 dBm for location accuracy

Roaming

  • Target -70 dBm as roaming edge
  • Voice latency: โ‰ค100ms

Client Tx Power

  • Avg: 14 dBm (match AP when possible)

SNR

  • Minimum: >20 dB
  • More critical than RSSI

Channel Planning

Unique Channels

  • 2.4 GHz: 3
  • 5 GHz: ~25
  • 6 GHz PSC: 15 primary (every 4th)

Interference Types

  • CCI: Co-Channel Interference (same channel)
  • ACI: Adjacent Channel Interference

Channel Bonding

  • Adds 3 dB noise
  • OBSS = Overlapping bonded channels

Performance Metrics

  • Retries: <5%
  • Packet Loss:
    • <1% for voice
    • <3% for data
  • Latency: <150ms
  • Jitter: <20ms
  • Channel Utilization:
    • Voice: <50%
    • Video: <30%
  • Carrier Sense Threshold: <-82 dBm
  • Energy Detect: ~-62 to -72 dBm

Power & Attenuation

  • Same Channel Separation: >19 dB
    • (e.g., -67 dBm edge, next AP < -86 dBm)
  • Distance Rule: Every 6 dB drop โ‰ˆ 2ร— distance
  • Attenuation Test:
    • Place AP 12โ€“16 ft from wall
    • Measure both sides

Client Handling

  • Clients per AP:
    • Typical: 30โ€“50
    • High-density: 20โ€“30
  • RTLS Requirements:
    • Min 4 APs
    • โ‰ฅ3 APs at -62 dBm

Outdoor Antennas

  • Vertical Separation: 3โ€“12 m (2.4/5 GHz)
  • Horizontal Separation:
    • 5 GHz: 7.5โ€“15 m
    • 2.4 GHz: 1โ€“5 m
  • Max Cable Length: 30 ft (10 m)

Protocol & Behavior

  • CAPWAP Heartbeat: 30s default
  • SSID Limit: 3โ€“4 recommended
  • Management Frames: Lowest basic rate
  • Multicast Frames: Highest basic rate
  • Neighbor Ads: Sent at max AP Tx power

6 GHz Specifics

  • Probing

    • No legacy probes on DFS
    • FILS: every 20 ms
    • PSC: 15 channels (best at 80 MHz)

  • 6 GHz Boost

    • +3 dB SNR
    • +3 dBm EIRP to match 5 GHz

Roaming & Discovery

  • NDP (Neighbor Discovery Protocol): Max 34
  • Probes:
    • 2.4/5 GHz: 10/sec
    • 6 GHz: via FILS (20ms), RNR, PSC

Frame Types

  • Management: Beacon, Probe, Auth, Assoc
  • Control: RTS, CTS, ACK
  • Data: All other frames

Inter-Frame Spaces

  • SIFS: Used by APs (high priority)
  • DIFS: Used by clients (low priority)
  • Max duration: 32,767 ฮผs (~0.03 sec)

Modulation & Timing

Symbol Time

  • 802.11n/ac: 3.2 ฮผs
  • 802.11ax: 12.8 ฮผs

Guard Interval

  • Indoor:
    • Long: 800 ns
    • Short: 400 ns
  • Outdoor:
    • 802.11ax: 1.6 ฮผs or 3.2 ฮผs

Delay Spread

  • Max: 200 ns

Miscellaneous

  • RTLS: >3 APs at -62 dBm
  • RF Distance to Humans: >20 cm
  • Speed Estimate: Throughput โ‰ˆ Advertised Rate รท 2
  • POA vs POP:
    • POA = Current (Foreign)
    • POP = Original (Anchor)
  • Bluetooth/Zigbee: IEEE 802.15