planning for vowifi jai rawat, airtight networks jai.rawat@airtightnetworks.net

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Planning for VoWiFi

Jai Rawat, AirTight Networksjai.rawat@airtightnetworks.net

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Agenda

• Wireless Medium Characteristics• RF Basics• VoWiFi Deployment Challenges• VoWiFi Deployment Best Practices/Solutions• Interactive Workshop• Take Away• Q&A

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Wireless Medium Characteristics

• Access Point (AP) coverage depends on– Building material– Building layout– AP location– Mount type (ceiling, wall, desktop)– Antenna type and orientation– AP transmit power– Transmit protocol (802.11 a/b/g)

• Coverage is not static/predictable– Fluctuates constantly due to multipath and moving objects– Interference due to neighbor APs or other sources of noise– Packet collisions

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RF Basics

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10-3

101

10-6

Power

10W

Source

1 W

d2d1

1mW (= 0 dBm)

10,000 times

40 dB

RF Basics : What is dB?

1,000 times

30 dB

Path loss from source to d2 = 70dB

(= 40 dBm)

(= -30 dBm)

dB: relative measure of signal strength at log scale

dBm: absolute measure with 1mW power defined as 0 dBm

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Antenna Basics

Isotropic Dipole High gain directional

0 dBi 2.2 dBi 14 dBi

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Sample RF Propagation

• Wi-Fi is invisible• RF does not propagate in

circles• Different vendor products

behave differently• Site layout and construction

have a significant impact

Resulting in• Coverage holes• Dead spots

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VoWi-Fi Deployment Challenges

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Voice over Wi-Fi Deployment Challenges

• Planning

• Monitoring

• Security

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VoWiFi Challenges: Planning

What kind of APs and Antennas ?

Where should APs to be placed?

What is an Optimum network design ?

What is my security exposure?

What is the estimated network performance?

Am I getting a minimum connectivity speed everywhere?

Can I quickly run what-if scenarios?

How many Access Points do I need?

What is the optimal AP configuration to minimize interference and maximize coverage?

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VoWiFi Challenges: Planning

1. Capacity Planning

2. AP Placement and Configuration Planning

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Planning: 1. Capacity Planning

• What type of applications will be deployed? Do they require QoS?

– Data, Voice, Video, other services?

• How much network capacity is needed for each of these application types?

– Dedicated capacity for QoS applications

• What is the projected growth for these applications?

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Planning: Example Capacity Planning

• 200 sqft/user

• 8 hour work day

• 150 Mb of avg data traffic/user over WLAN

• Peak usage is 3x (i.e. need to assume 450 Mb data traffic/user)

• 0.15 ERLANG of voice load

• VoIP connection requires 64Kbps in each direction

Call radius 50 ft

Users 39

Active Phone Lines 12

Concentration X:1 3.25

Bandwidth (Mbps)

Voice Uplink 0.77

Voice Downlink 0.77

Data Downlink 3.25

Data Uplink 1.63

Total Throughput 6.41Assumes 100% wireless

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Planning: 2. AP Placement Planning

• Determine coverage requirements– Are you coverage limited or capacity limited?– What is the required signal strength?

• How can you ensure proper coverage?– How many APs?– Location?

• What is the optimal AP configuration?– Power, channel, antennas etc

• How do you minimize interference?

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Planning: AP Placement

Which signal coverage are you going to assume?

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Building Material Matters

Material type Attenuation in 2.4Ghz band

6” Brick wall 4.4 dB

Concrete slab 10 dB

Dry walls 4 dB

Cubicle [Wood/Sheetrock]

2 dB

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Building Material Matters

Concrete construction

Dry wall Construction

(better coveragewith fewer

APs)

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APs placed inside

wiring closet[ Incomplete coverage ]

Better Coverage

with 4APs

AP Placement Matters

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AP TX power matters

AP TX power # AP required (for similar coverage)

100 mW 3

50 mW 5

30 mW 7

20 mW 8

5 mW 9

1 mW 10

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Coverage target matters

Coverage target

[TX Power 100mW]

Number of AP required

-70 mW 7

-75 mW 5

-80 mW 4

-85 mW 3

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Protocol Matters

• 802.11b– 11, 5.5, 2, or 1 Mbps

• 802.11g, 802.11a– 54, 48, 36, 24, 18, 12, 9, 6

Mbps

• 802.11 b/g have a greater range than 802.11a but only have 3 non-overlapping channels

• Observed throughput is 50% or lower than the link speed

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AP Placement Planning Methods

• Ad hoc deployment

• Best Practices

• Site Surveys

• Predictive Planning

• Predictive Planning with site calibration

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Ad hoc deployment

• Unplanned growth - deploy as you need additional coverage or capacity

• Was good 5 yrs ago

• Works for 1-2 AP ‘Home’ networks

Negatives

Not scalable

Bad Performance

Interference

Less Reliability

Suboptimal AP utilization

Low (No) Manageability

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Best Practices

• Rule-of-thumb planning

• Better than no planning (ad-hoc)

• Good for Small deployments 4-5 AP network

Negatives

Site characteristics are not modeled

Low reliability

Underperforming network

Suboptimal AP Utilization

Can be very misleading

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Site Surveys

• On-site visit to take measurements

• Can take site characteristics into account

• Good for medium to large scale business

Negatives

Cost

Repetitive and Time Consuming

May not be scalable

Doesn’t provide a complete picture

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Predictive Planning

• Use of software modeling tools to predict coverage

• Accurate Results

• Ability to play with ‘What If’ scenarios

• Scalable

• Good for all size deployments

Negatives

Accuracy is only as good as the site model created

May not be possible to model certain environments

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Predictive Planning with Site Calibration

• Predictive planning combined with a sample on-site measurement

• Good accuracy

• Accounts for modeling and other human errors

• ‘What If’ scenarios

• Scalable

Negatives

Cost – requires site visit

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Increase in Network Performance

Reduction inPlanning Cost

Reduction in Planning Time

Reduction in Equipment Cost

0%

20%

40%

60%

80%

100%

120%

100%

0%

20%

60%

80%

120%

40%

RF Predict Ad-hoc Deployment Best Practices Site Surveys

35%

50%60%

95%

10%

100%

10%3%

100%

10%5%

1%

54%

69% 71%

100%

Predictive Planning vs. Alternative Methods

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Voice over Wi-Fi Deployment Challenges

• Planning

• Monitoring

• Security

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VoWiFi Challenges: Monitoring

• Link capacity fluctuates over time

• Link quality is not guaranteed

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Signal Strength

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

1 61 121 181 241 301 361 421

Time

RS

SIChannel 3 Channel 4 Channel 5 Channel 10

Signal fluctuates because of multipath fading and people movement.Provision enough link margin ( ~ 10dB) for reliable coverage

Coverage Fluctuates

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Link Capacity Fluctuation

1. Channel is shared & all active devices have equal access to the medium

2. Data/Voice is carried on the same channel and data applications tend to hog all available capacity

• Issue 1 & 2 being addressed by 802.11e

3. Interference from neighbor APs can reduce channel capacity (SIR should be well above 15 dB)

4. Noise from other EM sources can also reduce channel capacity. (SNR ratio should be well above 15 dB)

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Link Quality is not Guaranteed

• Packet loss rate is higher due to• Interference from co-channel

and adjacent channel WLAN devices

• Noise from other sources (Microwaves, bluetooth etc)

• Collisions in the medium

• Frequent connection/reconnection due to

• Hand-offs

• Quality of signal – client may start scanning for better connection

• Dead spots

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Solution: Live Monitoring

Sample Live Monitoring Charts

Required to ensure on-going optimal network performance

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Voice over Wi-Fi Deployment Challenges

• Planning

• Monitoring

• Security

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VoWiFi Challenges: Security

• Wi-Fi is inherently insecure– Signal bleeds through walls and windows– No central point of control

• Easy to break in if proper security standards are not used– Legacy VoWiFi devices don’t support latest security

standards

• Wi-Fi networks can be easily disrupted– DoS attacks are easy to launch– Usual security precautions don’t work against DoS

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Solution: Live Security

Wireless Intrusion Prevention System (WIPS)

• Provides 24 x 7 security coverage

• Three key functions:– Detects and automatically

classifies wireless events & devices – to determine which are threats are which are not

– Robustly prevents (multiple) wireless threats

– Accurately locates wireless threats

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Deployment Best Practice

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Deployment Best Practice

• Plan• Anticipate performance needs of

VoIP application in advance. Deploy/configure WiFi infrastructure to obtain the best possible performance

• Monitor• Monitor for changes that cannot be

anticipated at the planning stage. Adjust network configuration to respond to environment changes

• Secure• Protect against malicious threats that

can disrupt VoIP application• Protect VoWiFi infrastucture

vulnerabilities that can easily be exploited to breach corporate network security

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Deployment Best Practice

Factors affecting WiFi performance

Pre-deployment Planning

Live Monitoring Detect & Prevent Threats

Site layout, construction material

Co-channel interference from deployed AP

Co-channel interference from neighbor APs and clients

Can only be estimated when the network is in operation

Usage, Contention, Traffic

Dynamic and can only be measured when the network is operational

Noise Noise level can change over time

Security (e.g. DoS attacks)

Need to detect & respond in real-time

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Take Away

• Analyze current and future requirements• Use a planning tool to help meet the

requirements• Perform on-site measurements if necessary• Invest in a live monitoring and security system

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Questions?

Plan

Mon

ito

rSecure

VoWiFi