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Integrating Accurate Capacity Planning into WLAN Design
Andrew von Nagy!@revolutionwifi!
CWNE #84 CCIE #28298
Goal of this Presentation:To share my methodology for integrating capacity planning into
WLAN design with the community !
What works for me might work for you!
Agenda:!!
1. Network Performance Concepts!2. WLAN Design Methodology!3. Introduction to the Revolution Wi-Fi
Capacity Planner Tool!4. Real-World Example
Network Performance
Source: Martin Geddes
Link Speeds Reaching Limits
Source: Martin Geddes
WLAN Capacity
Single Client Multiple Client Coordinated APs
All APs
Defining WLAN Capacity
Net WLAN Capacity
(-) (+)Spectral InventorySpectral Efficiency
Medium ContentionRF Interference
Goal: Increase spectral inventory and efficiency, decrease medium contention and RF interference
Medium Contention
DFS Non-DFS
20 MHz 22 9
40 MHz 10 4
80 MHz 5 2
160 MHz 1-2* 0-1*
United States Regulatory Domain!* 80+80 MHz Channels
42
58
106
138
106
58 138
One cell ‘buffer’ before !channel must be re-used
138 58
42
58 138
Co-channel Interference (CCI)!• Typical WLAN (omni antennas, standard overlap for roaming)!
• Need ≥4 non-overlapping channels to effectively minimize co-channel interference at -85dBm
106
Medium ContentionAirtime Demand within a Channel / Frequency
Airtime UtilizationWhere is the breaking point?
Airtime UtilizationAirtime saturation varies by WMM Access Category
3% airtime demand per-client in this example Source: Comsis
Measuring Capacity
Spatial !Streams
Channel!Width
Client Mix
Signal!Quality
Protocol!Version
Frequency!Bands
Application!Throughput
Airtime Demand
Airtime Demand
Y% airtime utilization (each)
Z% airtime utilization (each)
X Qty.
X Qty.
Total airtime utilization based on client mix
Aggregate of individual client demands !
Dependent on application requirements, packet sizing & timing. (Remember that airtime saturation is dependent on WMM AC)
Design Methodology
Iterative ApproachRF!
DesignCapacity!Design
Input AP / Radio Quantities;!Revise RF Design to Provide Required!
Frequency Re-Use (e.g. Antennas, Power)
1. AP / Radio Quantities Required to ! Provide Coverage in All Areas!2. Channel Planning & Frequency Re-Use
Revise Capacity Design if Frequency Re-Use Cannot be Obtained!(e.g. per-device throughput, 5 GHz channel width, !
capacity distribution across bands vs. channel inventory)
1. AP / Radio Quantities Required for Capacity!2. Throughput Required for WAN / Backhaul
Hands-On
Real-World Example• Advertising Firm in Manhattan!
• Apple-centric computing environment!
• MacBook Air/Pro (3yr lifecycle)!
• BYOD (tablets, smartphones)!
• Some Windows (Finance Dept.)!
• Heavy graphics and media content!
• Open / Collaborative floorplan!
• Large Event Space (e.g. TED Events)
Floor Layout
Open Office (~36k sq ft)!350 Seats!20 Conference Rooms!!
Graphic Designers!- 1 Apple Laptop ea.!- 1 BYOD ea.!
!
Existing WLAN:!- 66% concurrent online!- 50% concurrent active
Event Space (~15k sq ft)!300 Seats (inside room)!200 Seats (overflow area)!!
Large Events:!- 500 mobile devices!
!
Internal Meetings:!- 300 laptops!
Inflection!Point
Capacity Plans!One for each unique use-case area (in this example 3)
Iteration between!Capacity and RF Planning
• Initial Capacity Plan!
- Select initial variables using informed idea of what you think can be achieved!
- Channel width, dual-band APs (no radios disabled)!
• RF planning - use capacity results as starting point!
- Can you fit the AP radios into the space without CCI?!
- Determine if adjustments are necessary (directional antennas, different channel widths, disable some 2.4 GHz radios, etc.)!
• Revise capacity plan, perform RF planning again (… iterate!)
2.4 GHz RF Propagation
5 GHz RF Propagation
5 GHz AP Layout
5 GHz CCI
2.4 GHz AP Layout
2.4 GHz CCI
Recap1. Network performance is increasingly reliant on
minimizing contention delay!
2. Wi-Fi medium contention is dependent upon two causes:!
• Co-Channel Interference (CCI)!
• Airtime Demand (within a channel)!
3. Airtime saturation occurs at different points based on WMM Access Category
Recap (cont.)4. WLAN capacity is measured by airtime demand of
clients within a channel!
5. WLAN design should account for BOTH capacity and coverage!
• Don’t guess!!!!
• I recommend an iterative design approach!
6. Revolution Wi-Fi Capacity Planner: http://www.revolutionwifi.net/capacity-planner
