Aruba utilities on mobile devices v30

Mobile Devices and Wi-Fi Peter Thornycroft

June 2014

CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

2 #AirheadsConf

Agenda

The commercial value chain Consumer device reference models Battery life QoS Location 5GHz and DFS channels Authentication & Passpoint Handover behavior Bluetooth Low Energy

3 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

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Commercial models

•  What we see: –  The chain leads to the

cellular operator and consumer

•  What we want to see: –  Some recognition for the

enterprise user

Consumers (your typical Gen-Y) who don’t care too much about Wi-Fi performance at work

Chip vendor incorporates driver, is really responsible for Wi-Fi functionality, selling to …

Phone / device vendor who has cost constraints, won’t waste time on features not of interest to its biggest customers who are…

Cellular Operators, for whom Wi-Fi is a minority interest in the first place and anyway sell to …

Mobile OS vendor does some influencing


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WLANs differ from home APs

Home AP reference model A single AP, not doing much of interest

WLAN reference model Many, APs with same SSID and coordinated, seamless handover (no DHCP, common authentication etc.)

-  No point in looking for other APs because there (usually) aren’t any

-  Established (~correct) behavior is to hang onto the AP until the signal is very weak, then switch to cellular data if available

-  There is always a ‘better’ AP -  But the device needs to scan (or use neighbor

report) to be aware of the ‘better’ AP.

Benefits of good WLAN client behavior… -  Devices get higher rates -  Other devices get more airtime, better network

capacity -  Less time on the air - better battery life -  Less mutual (co-channel) interference

Same effects are seen in public places, hot zones – ‘always best connected’ activity in Hotspot 2.0 ph3 groups.


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Network reference models

•  What we see: –  One dual-band home AP –  “give me battery life, and

keep me connected”

•  What we want to see: –  Option for multiple-AP WLAN

The current model is the single-AP home network. In this framework, the best thing is to hold onto your AP until the signal is too weak to work, then hope you can switch to cellular data. Probe requests are a waste of battery life because there’s only one AP. We want to see either a dual-model or a more flexible architecture. Maybe sense that there are other APs in the same system (spot the neighbor report?) and flip to a multi-AP algorithm. Under a multiple-AP network, there is always a really-good signal (except at the edge). It’s just a question of probing more often to find the better APs. But it’s difficult to move device, OS and chip vendors away from their well-established model. They are wary of breaking what has taken several years to ‘perfect’. We’ll also see that consumer APs still don’t offer the advanced features we incorporated some years ago.


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Power Save Modes

sleeping

time

beacon DTIM

Traffic for you

give sleeping

WMM-PS

beacon DTIM

pkt

Traditional Power-Save

U-APSD (WMM-PS)

pkt

pkt

pkt

pkt

pkt

pkt

pkt

pkt pkt

pkt

buffered

time

DTIM


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Battery life

•  What we see: –  Minimum possible probing

•  What we want to see: –  More probe requests in

WLAN –  Using 11k reports –  U-APSD within a beacon

interval

Mobile devices are usually unaware of better AP signals because they don’t probe enough. They don’t probe enough because of an over-zealous focus on battery life, and a model that has only one AP. Sometimes when a device has an ‘acceptable’ signal it stops probing altogether. Later, when it starts to move, it may not re-enable probing until too late to maintain the connection. In fact, Wi-Fi accounts for less battery consumption than the cellular subsystem, and far less than the display or CPU processing app tasks and GPU. So our focus is on showing device vendors they can ‘go passive’… only using the 802.11 radio in receive mode. ‘WFA Voice-Enterprise light’, or a collection of features that enable the device to be multi-AP-aware without reducing battery life.


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The mystery of missing smartphone QoS

Android

App Code (QoS – unaware coder)

Driver & microcode Multi-level QoS priority API (that’s OK)

Parrots the driver API (that’s not OK)

Can’t spell QoS anyway so it’s inconsequential

Wi-Fi air interface

•  QoS priority (~WMM)is there if app developers want to use it

•  But… it’s not documented And anyway… app developers are not QoS-aware –  Socket.setTrafficClass(int value) IPTos

•  The OS has a hard time figuring out the QoS Pri required by each app…

•  Thus WMM priority is seldom used in mobile device apps

Same observations apply to WMM-PS (U-APSD) for intra-beacon power save.


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QoS

•  What we see: –  WMM functionality exists in

mobile device OS –  But APIs are arcane –  No documentation or

promotion

•  What we want to see: –  Better API support –  Developer guidelines

WMM QoS is enabled through the OS to the chip/driver. But to invoke a high-priority connection, the app developer must add some parameters to the commands that open sockets . App developers are unaware of the need to apply Wi-Fi QoS, and/or are not informed of the required APIs, and/or are not technically capable of understanding that aspect of app programming. This includes developers of voice and video apps including those in vertically-integrated companies.


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Location (distance) enhancements

RTT “Round-Trip-Time” A standard (actually two standards and several proprietary variants) “802.11k” Location Track Notification, Modified (to finer timestamps) in “802.11mc” Fine Timing Measurements

Distance Calculations

Measure with me!

Now here are my times t1, t4

OK, here

t1

t3

t4

t2

Challenges: -  Need to combine/average several

frames to get a good reading. -  Averaging many frames affects

battery life, network capacity

Challenges: - Measuring to nanoseconds (speed of light: 1 ft per nsec) - Setting up circuitry to timestamp the right frame - Calibration for time frame leaves (arrives) at the antenna

Once all four timestamps are in one place, subtraction and /2 gives time-of-flight and multiply-by-speed-of-light gives distance

Got it

Implementation In mobile device Wi-Fi chips late 2014 In access points 2015 (early implementation 2014) No Wi-Fi Alliance certification >> may cause interoperability teething troubles Accuracy should be 1 – 5 metres, depending on the number of frames averaged & underlying hardware Most useful in line-of-sight, but better accuracy at longer distances than RSSI Many variations possible with WLAN topologies

d = ((t4 – t1) – (t3 – t2)) * c / 2


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Location

•  What we see: –  RSSI reports

•  What we want to see: –  RTT support –  Raw data for RTT, RSSI

Location and location-based-services have attracted the attention of many commercial and technical principals across the industry. Current development is focused on time-based distance (mostly Round-Trip-Time) measurements: - 802.11mc Fine Timing Measurement -  Wi-Fi Alliance Wireless Network Management ++ -  In-Location Alliance

Look for RTT announcements and features over the next 12 months. There is a significant danger that this location technology reverts to proprietary, closed islands rather than developing along open, standard APIs. For example: -  Will raw data be available via OS API calls, or mysteriously

processed within the chip/driver or OS itself? -  Will devices built on different chip families interoperate for

RTT location?


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DFS channels – useful at last!

How many radar triggers?

frequency

insallations

0 / year 5 / hour

Usually none, but in some places > comfortable

Devices supporting DFS Apple > 2 years Intel > 2 years Samsung > 1 year Others getting there

Most WLANs

A few

Special concerns

No active client scanning in DFS bands because they don’t passive-scan for radar -  slow AP acquisition -  fixed (eventually) by neighbor

report

5GHz Channel count 13 20MHz channels, no DFS 22 20MHz channels including DFS

Channel strategy

Dot them around?

Use the spectrum!


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5GHz band

•  What we see: –  Beginning to favor 5GHz

over 2.4 –  Spreading DFS support

•  What we want to see: –  Overweight 5GHz bias –  100% DFS support

About 18 months ago Apple supposedly reversed from unconditionally preferring 2.4GHz to favoring 5GHz. Unfortunately the battery-saving imperative (see earlier) means that when a device has an acceptable signal from its AP, it will stop scanning for a better one. Especially scanning in other bands. This can cause difficulties when the WLAN seeks to move a device to a different band: it may refuse to scan the alternate band. DFS support is improving, now available on all Apple devices (since iPhone 4S) and many Android (since early 2013: e.g. Samsung Note, Galaxy S4). We believe this is a good time to start deploying DFS channels.


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Passpoint

Identify a hotspot with Internet reachability and friendly authentication

Pre-association discovery

What have you got?

T-Mobile BT Comcast Orange…

-  Pre-association -  New GAS/ANQP protocol -  Lists service providers -  Acceptable authentication

Authenticate to home SP

T-Mobile BT Orange

Accuris Aicent BSG…

Hub (settlement)

RADIUS

e.g. DIAMETER

WPA2 Options -  EAP-TLS -  EAP-TTLS -  EAP-SIM -  EAP-AKA(‘)

Make a list of available options, decide which to use

Prioritise account options

T-Mobile home (have SIM) BT visiting (have pwd) Orange visiting (have pwd) Comcast visiting (have cert) Home AP (not Passpoint) Local (not Passpoint) hotspot

SPs, phone designers all want a say -  Distinction between ‘home’

and ‘visiting’ hotspot -  May have different tariffs -  Policy for time-of-day,

location…

ANDSF is a cellular protocol that can pass policy to the device to help it make offload decisions. Passpoint phase 2 introduces se mi-automatic online sign-up and policy services.

T-Mobile SIM


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Authentication

•  What we see: –  Beginning to support HS2.0

(Passpoint)

•  What we want to see: –  Passpoint with EAP-SIM

everywhere –  SPs supporting Passpoint

Passpoint (Hotspot 2.0, from 802.11u) was released as a WFA certification in June 2012. For the following 12 months, while SP and enterprise WLAN equipment supported Passpoint, you could not purchase a commercial device that was compliant. That has changed in the last 6 months (iOS7, Samsung Galaxy S4). Now, we realize that no SP has deployed a network with standard HS2.0 support. Why not? -  Actually, NTT has… -  AT&T stayed proprietary -  Cellular operators (see commercial chain above) have no

incentive to allow others (MSOs) to steal their customers -  The enterprise WLAN vendors are waiting for wider

availability

But it’s time! Public facing vendors should take AOS 6.4, contact a hub vendor, fire it up and advertise support.


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Current handover narrative

A

Good signal, this is dandy!

Time / distance

0 sec

Signal Strength


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A


OMG, the signal is getting really low!

Time / distance

0 sec ~30 sec

Signal Strength


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A



SOS, sending 10 probe requests on 3 channels

Time / distance

0 sec ~30 sec 35 sec 38 sec

Signal Strength


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A

B

C D

E




Wowza, responses from 20 APs, how to choose?

Time / distance

0 sec ~30 sec 35 sec 38 sec

Signal Strength


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A

B

C D

E




Wowza, responses from 20 APs, how to choose?

Let’s reauthenticate with this one!

Time / distance

0 sec ~30 sec 35 sec 38 sec 40 sec reauthentication request 40.2 sec reauthenticated

Signal Strength


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‘Good’ handovers captured


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Sticky smartphone


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Typical smartphone


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Aruba Utilities on Nexus 7


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802.11 k, v, r

•  Many features, most important are:

•  Neighbor report from AP to client (802.11k) •  Channel report from AP to client (802.11k) •  Beacon report from client to AP (802.11k) •  BSS Transition Management from AP to client (802.11v) •  Fast Transition by client (802.11r) •  (All rolled up in 802.11-2012, 2014)


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802.11r fast BSS transition

C D

R0 key

C

802.1X authenticator

R0 key

S0 key S1 key PTK

Initial Authentication establishes level 0 key

WLAN distributes level 1 keys

R1 key C D

On reassociation, client presents level

1 key to new AP

R1 key PTK

S0 key S1 key PTK

Mobility domain: A group of APs covered by a level 0 keyholder

Over-the-air reassociation widely adopted, over-the-DS reassociation (via the current AP) not used

Key suite includes: Level 0 key (derived at initial authentication, never exposed OTA) Level 1 key (per-AP keys) used to derive… Pairwise temporal keys (to encrypt communication)

PTK R1 key

Differences between FT and OKC? … Not much

keyscope keyscope


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802.11k, v, r features

B

C D

E

Neighbor report

AP chan secy key beacon scope offset B 6 WPA2 0 45 D 52 WPA2 0 12 E 161 WPA2 0 74

Information about other APs to help with handover candidate discovery

C

Beacon report Client reports how it hears (RSSI) the beacons of other APs

BSSID RSSI AP B -65 AP D -72 AP E -65

C

BSS Transition Management AP instructs client to move to another AP

Move to AP D…

E D B

D

C

Channel report AP informs client of channels used by the WLAN

Channel 6 52

161

Overlaps with neighbor report


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802.11k Neighbor report

•  Advertised by AP in the beacon (for all clients, non-associated) and sent solicited per-client

•  List of ‘neighbor’ APs with same SSID includes: –  BSSID –  Channel –  Beacon time offset –  PHY type –  QoS capability –  ‘Key scope’ for common authenticator

•  802.11 does not require neighbor list to be cropped or ordered or modified per-client (but infrastructure may do so)

•  Eliminates the need for active probe request-response scanning


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The evils of active scanning

•  Takes time –  Need to probe on each selected channel in turn, wait ‘reasonable’ interval for responses –  Need to return to current channel for beacon (DTIM)

•  Inaccurate results –  RSSI of a single probe response varies ~ +/- 6dB from ‘average’ –  Some APs will miss probe requests, or responses are lost –  If the device returns to current channel after ~15msec, sometimes misses responses

•  Consumes power –  Typical pattern is to send 2 probe requests per channel, stay awake ~15–20msec –  Each probe request generates ~6 probe responses in a ‘typical’ WLAN –  Each probe response needs an ack

•  Consumes airtime, affecting others’ performance –  Frames are sent at low rates, probe responses are retried


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Better handover performance with ‘11k’

Current handover sequence:

1. Figure out it’s time to scan 2. Figure out channels to scan 3. Send probe requests, get responses 4. Identify best AP 5. Reauthenticate to new AP

802.11k handover sequence:

1. Periodically request neighbor report 2. Passive scan for neighbor beacons 3. Note if a neighbor AP is ‘better’ 4. Reauthenticate to new AP

Probe requests & responses

Signal strength

Time, distance

Signal strength

Time, distance

Behavior c 1999 Behavior c 2013

Signal strength

Time, distance Neighbor reports & passive scanning

Behavior c 2014 ?


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Signal Strength

Proper ‘11k’ handover narrative

A


Time / distance

0 sec


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B C D

Signal Strength


A

B

C D

E


Check neighbor report every ~10sec

Identify ‘best’ AP and check for beacon (passive scan)

Time / distance

0 sec ~10 sec 20 sec 30 sec B C

C D


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Signal Strength


A

B

C D

E




Signal is low, but I have already identified the best AP

Time / distance

0 sec ~10 sec 20 sec 30 sec B C

B C D

C D


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B C

B C D

C D

D C

Signal Strength


A

B

C D

E




Signal is low, but I have already identified the best AP

Reauthenticate

Time / distance

0 sec ~10 sec 20 sec 30 sec 30 sec reauthentication request 30.2 sec reauthenticated


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Client Match

Client Match forms a virtual Beacon Report:

1.  APs measure RSSI from client

2.  APs receive beacon reports from the client

3.  Estimate the ‘best’ AP

4.  If client is _far_ from ‘best’ AP…

5.  Redirect (force handover) to ‘best’ AP

B

C D

E

A

track

-50 -60 -70 -80

A B E

Signal strength

distance


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Galaxy Nexus with AU app


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Nexus7 with AU app


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Samsung GS4 with AU app


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All together

Galaxy Nexus

Nexus 7

Galaxy S4


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Again…

Galaxy Nexus

Galaxy S4

Nexus 7


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If 11k, why Client Match ?

•  ‘11k’ makes information available to the client –  Neighboring APs, channels, beacon offsets…

•  ‘11k’ cannot confirm that the client receives information or how it prioritises the information –  Neighbor report information may not be used

•  Transmitting (or receiving) ‘11k’ does not guarantee that the client will act on the information –  Handover decisions may not be improved

•  Client Match uses information from the infrastructure and the client (if supports beacon reports)

–  The infra knows more about the client’s situation than the client does

•  Client Match completes the task by forcing a handover


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Handover

•  What we see: –  Not much

•  What we want to see: –  More probe requests when

in WLAN –  Or… use passive 11k

reports –  Reauthenticate with

802.11r or OKC

Most people think inter-AP handovers take ~1second. In fact, inter-AP handovers take 30msec, or 250msec, or 7sec depending on the syndrome. 7sec outages occur when a device (not probing) does not realize until too late that the signal from its serving AP is dropping fast. By the time it starts to probe, it has lost the AP and has to go into cold-start mode. More frequent probes (or using passive measures as above) would eliminate 7 sec outages. Full WPA2 MSCHAPv2 re-authentication takes 200-250msec to exchange ~50 frames (including acks). This is a stable figure in the absence of very weak signals due to poor choice of target AP (mobile devices usually make good AP choices when aware of their environment through probing). This outage will be barely noticeable to the user. But faster re-authentication is possible, through old-school OKC (from 802.11i) or 802.11r (now available on iPad). … The ‘bad’ handover syndrome can be solved if the mobile device is more aware of its surroundings (neighbor report) or responds to BSS transition management frames (directed handover from the AP).


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Aruba Utilities shows behaviour

•  What we see: –  Frequent long outages

around handover events

•  What we want to see: –  More awareness of

environment –  Faster reaction to losing

signal

Aruba Utilities shows very graphically what goes on when a mobile device moves around an enterprise WLAN.


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iBeacon deployment model for navigation

UUID: Aruba Major: 1000 Minor: 501




-66

-68

-76

-82


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Bluetooth Low Energy overview

•  BLE is also known as Bluetooth Smart, Bluetooth 4.0 •  Evolution of the existing Bluetooth standard (2010) •  Focus on ultra-low power consumption (battery powered devices) •  Differences –  Efficient discovery / connection mechanism –  Very short packets –  Asymmetric design for peripherals –  Client server architecture –  Fixed advertising channels designed around WiFi channels –  Not compatible with older Bluetooth

•  Most new devices support both ‘classic’ Bluetooth and BLE (“Bluetooth Smart Ready”) –  iPhone 4S+, current (2013) iPad, Samsung Galaxy S4+, Nexus 7+


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Bluetooth Low Energy & iBeacon

•  Bluetooth –  Very low-power consumption: years of life from a button cell –  Advertises… ‘beacons’ –  Allows scanning for ‘peripherals’ –  Allows ‘central’ devices to discover ‘peripherals’ –  Two-way communication channel to read/write values

•  iBeacon –  A subset of BLE, just the ‘advertising’ function with special

fields –  Allows a background app to be alerted on proximity –  No explicit location information in an iBeacon, just a

reference ID


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Spectrum for iBeacons & BLE

6 11 2412 2437 2462 2422 2402 2427 2447 2452 2472

1

2400 2483.5

Ch 37 (2402 MHz)

Ch 38 (2426MHz)

Ch 39 (2480MHz)

Wi-Fi

Bluetooth Low Energy Advertisement (iBeacon)

2 MHz channels Gaussian Frequency Shift Keying 0.5 modulation index 1 Msymbol/second rate 1 Mbps data rate ~250 kbps application throughput (in connection mode)

Advertisements are one-way transmissions An advertisement can be sent on any/all of the 3 designated channels Advertisements are repeated every 20 – 10000 msec (500msec typ) Tx power ~ 0 dBm ( ~ 2 year battery life typ) Apple specifications for iBeacons are more constrained (but not widely followed)


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BLE Advertisement and iBeacon

Preamble 1

Advertiser 4

PDU 2 - 39

CRC 3

MAC address 6

Header 2

Data 1 - 31

iBeacon Prefix 9

Proximity UUID 16

Major 2

8E89BED6

0201061AFF4C000215

Minor 2

size, type.. e.g. 112233445566

e.g. 4152554e-f99b-86d0-947070693a78 e.g. 4159 e.g. 27341

BLE Advertisement Frame

BLE Advertisement Payload

iBeacon Data Measured Tx Pwr

2

e.g. -59

iBeacon information

RSSI Measured by receiver

MAC From BLE header

Proximity UUID (can be) company reference

Major, Minor Integer values identifying the tag and/or zone

Measured Tx Pwr Calibrated power at 1m from the iBeacon (dBm)


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RSSI vs distance (iBeacon)

-100

-95

-90

-85

-80

-75

-70

-65

-60

-55

-50

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

iBeacon RSSI (dBm) vs distance (m), line of sight

GS4 with iBeacon 100 GS4 with iBeacon 101 Nexus 7 with iBeacon 100 Nexus 7 with iBeacon 101

iBeacon Tx power 0dBm ‘measured power’ -61dBm @ 1 m


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RSSI vs distance (iBeacon)

-90

-85

-80

-75

-70

-65

-60

-55

-50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

iBeacon RSSI (dBm) vs distance (m), line of sight (RSSI averaged over 5 readings)

GS4 with iBeacon 100 GS4 with iBeacon 101 Nexus 7 with iBeacon 100 Nexus 7 with iBeacon 101 grand average


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Why iBeacons matter on iDevices

•  The iOS app lifecycle puts an app on ice when not in foreground. How to wake up on proximity to a particular location? –  iOS maintains BLE in always-listening mode

–  If the app registers for a UUID, iOS will awaken it when that UUID is seen

–  Event is a ‘region entry/exit’ –  iBeacon background detection can take minutes

•  Even in foreground, iOS will only return data on known, specified UUIDs –  ‘Ranging mode’ in foreground gives RSSI every ~ 1 second

•  Android makes for a much more flexible iBeacon hunter

iOS

Mobile App

BLE radio

BLE air interface

Register for < 20 UUIDs

Continuously scanning for

iBeacons

Woken from background when UUID

heard

Database of UUID-Major-Minor to

locations (part of the app server)


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Use cases

Indoor location –  Beacons are placed throughout the building in such a way that

each location is covered by at least 3 beacons –  The mobile apps will look for nearby beacons, get beacon

locations from the cloud and calculate location locally –  Examples – any public venue with navigation apps: airports,

casinos, stadiums

Proximity –  Beacons are placed nearby exhibits or points of interest –  Mobile apps discover beacon context from the cloud and impart

interesting information –  Examples – museums, self-guided tours, door opening, forgot

keys


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iBeacon hunting with Android


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Thank You

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Aruba utilities on mobile devices v30

Technology

Transcript of Aruba utilities on mobile devices v30