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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