BTLE (Bluetooth Low Energy) and Core Bluetooth

This presentation is on Bluetooth low energy and how Apple's Core Bluetooth framework works to expose the higher level application layer to iOS and Mac developers.

Transcript

1. Bluetooth LE,
   CoreBluetooth
   @zachdennis
   @zdennis
   !
   mutuallyhuman.com
   

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2. Bluetooth LE
   

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3. What is BTLE?
   

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4. A short range, ultra-low
   power consuming
   wireless technology.
   

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5. Shares the “Bluetooth”
   name, but has different
   design goals in mind.
   

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6. Power
   Consumption
   Years, not hours or
   days.
   

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7. Short range
   ~ 50m
   

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8. Packet-based
   Short bursts of data.
   

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9. Intervals
   Ad Ad Ad
   Data Data
   

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10. Multiple channels
    Ad Ad Ad
    Data Data
    Ad Ad Ad
    Data Data
    Ad Ad Ad
    Data Data
    #1
    #2
    #3
    

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11. Device A is looking.
    Ad Ad
    Data Data
    Ad Ad
    Data Data
    Scan
    Ad
    Ad
    Scan Data
    Device B is advertising.
    

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12. Frequency hopping
    

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13. Connection-less
    Devices do not need to maintain
    connections.
    

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14. Pairing
    e.g. iOS - happens when Insufficient
    Authentication error code is sent from the
    peripheral.
    

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15. Security
    Devices pair, keys are distributed, and the
    connection is encrypted.
    !
    Encryption is AES-128.
    

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17. Why BTLE?
    

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18. *Borrowed from 2012 WWDC CoreBluetooth Talk
    

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19. 1 billion+ devices
    

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20. *Borrowed from 2013 Apple WWDC talk
    

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21. How BTLE Works
    

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22. The Stack
    

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23. Key Terms
    • Central
    • Peripheral
    • Service
    • Characteristic
    • Descriptor
    

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24. Central Peripheral
    (has data)
    (wants data)
    

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25. Central Peripheral
    advertising
    

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26. Central Peripheral
    advertising
    scan
    

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27. Central Peripheral
    advertising
    advertising
    scan
    

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28. Central Peripheral
    advertising
    scan advertising
    discover services Heart Monitor
    

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29. Central Peripheral
    advertising
    scan advertising
    discover services
    discover characteristics
    Heart Monitor
    BPM
    

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30. Central Peripheral
    advertising
    scan advertising
    discover services
    discover characteristics
    Heart Monitor
    BPM
    read value 95
    

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31. Central Peripheral
    advertising
    scan advertising
    discover services
    discover characteristics
    Heart Monitor
    BPM
    read value 95
    observe value BPM 95
    

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32. Central Peripheral
    advertising
    scan advertising
    discover services
    discover characteristics
    Heart Monitor
    BPM
    read value 95
    observe value BPM 95
    BPM 95
    BPM 98
    value changed
    

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33. Service
    A service is a human-readable specification of a
    set of characteristics and their associated
    behavior.
    

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34. Two kinds of services
    There are primary services and secondary
    services.
    

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35. Nested services
    Services can contain other services.
    

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36. Characteristic
    A characteristic is a bit of data that has a known
    format labeled with a UUID.
    They are intended for computer-readable format
    as opposed to human-readable text.
    

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37. Profiles
    A profile is a specification that describe two or
    more devices, with one or more services on each
    device, how they discover each other, connect,
    and otherwise interact.
    Profiles define roles for devices to play.
    

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38. Heart Rate Profile
    Collector Heart Rate Sensor
    Heart Rate Service
    Device Information Service
    

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39. Heart Rate Profile
    Collector Heart Rate Sensor
    Heart Rate Service
    Device Information Service
    GATT CLIENT GATT SERVER
    

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40. Profiles & Services
    Profiles contain services.
    Services can be contained by multiple profiles.
    

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41. Peripheral
    Characteristic
    Characteristic
    Service
    Characteristic
    Anatomy of a Peripheral
    Descriptor
    Service
    

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42. Apple’s Approach to
    BTLE
    

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43. Simple
    Powerful
    

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44. Technology Stack
    

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45. *Borrowed from 2012 WWDC CoreBluetooth Talk
    

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46. Supported Profiles
    • Generic Attribute Profile Service
    • Generic Access Profile Service
    • Bluetooth Low Energy HID Service
    • Battery Service
    • Time Service
    • Apple Notification Center Service
    

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47. CoreBluetooth
    

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48. Object Model
    

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49. CBCharacteristic
    CBService
    CBCentral
    CBMutableCharacteristic
    CBMutableService
    Main Objects
    Data Objects
    Helper Objects
    CBUUID CBATTRequest
    CBCentralManagerDelegate CBPeripheralManagerDelegate
    CBCentralManager CBPeripheralManager
    CBPeripheralDelegate
    CBPeripheral
    

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50. Being a Central
    

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51. Central Peripheral
    

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52. CBCentralManager
    Scanning!
    – scanForPeripheralsWithServices:options
    !
    Stop scanning!
    – stopScan
    !
    Connecting to peripherals!
    – connectPeripheral:options
    – cancelPeripheralConnection:
    !
    Retrieving known peripherals!
    – retrieveConnectedPeripheralsWithServices:
    – retrievePeripheralsWithIdentifiers:
    

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53. CBCentralManagerDelegate
    Monitoring Connections with Peripherals!
    – centralManager:didConnectPeripheral:
    – centralManager:didDisconnectPeripheral:error:
    – centralManager:didFailToConnectPeripheral:error:
    !
    Discovering and Retrieving Peripherals!
    – centralManager:didDiscoverPeripheral:advertisementData:RSSI:
    – centralManager:didRetrieveConnectedPeripherals:
    – centralManager:didRetrievePeripherals:
    !
    Monitoring Changes to the Central Manager’s State!
    – centralManagerDidUpdateState:
    – centralManager:willRestoreState:
    

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54. CBPeripheralDelegate
    Discovering Services!
    – peripheral:didDiscoverServices:
    – peripheral:didDiscoverIncludedServicesForService:error:
    !
    Discovering Characteristics and Characteristic Descriptors!
    – peripheral:didDiscoverCharacteristicsForService:error:
    – peripheral:didDiscoverDescriptorsForCharacteristic:error:
    !
    Retrieving Characteristic and Characteristic Descriptor Values!
    – peripheral:didUpdateValueForCharacteristic:error:
    – peripheral:didUpdateValueForDescriptor:error:
    !
    Writing Characteristic and Characteristic Descriptor Values!
    – peripheral:didWriteValueForCharacteristic:error:
    – peripheral:didWriteValueForDescriptor:error:
    !
    Managing Notifications for a Characteristic’s Value!
    – peripheral:didUpdateNotificationStateForCharacteristic:error:
    !
    Retrieving a Peripheral’s Received Signal Strength Indicator (RSSI) Data!
    – peripheralDidUpdateRSSI:error:
    !
    Monitoring Changes to a Peripheral’s Name or Services!
    – peripheralDidUpdateName:
    – peripheral:didModifyServices:
    

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55. > code <
    

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56. Being a Peripheral
    

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57. Central Peripheral
    

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58. CBPeripheralManager
    Services!
    – addService:
    – removeService:
    – removeAllServices:
    !
    Advertising!
    – startAdvertising:
    – stopAdvertising
    – isAdvertising
    !
    Notifying observing devices of updates!
    – updateValue:forCharacteristic:onSubscribedCentrals:
    !
    Responding to Read/Write Requests!
    – respondToRequest:withResult
    

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59. CBPeripheralManagerDelegate
    Monitoring Changes to the Peripheral Manager’s State!
    – peripheralManagerDidUpdateState:
    – peripheralManager:willRestoreState:
    !
    Adding Services!
    – peripheralManager:didAddService:error:
    !
    Advertising Peripheral Data!
    – peripheralManagerDidStartAdvertising:error:
    !
    Monitoring Subscriptions to Characteristic Values!
    – peripheralManager:central:didSubscribeToCharacteristic:
    – peripheralManager:central:didUnsubscribeFromCharacteristic:
    – peripheralManagerIsReadyToUpdateSubscribers:
    !
    Receiving Read and Write Requests!
    – peripheralManager:didReceiveReadRequest:
    – peripheralManager:didReceiveWriteRequests:
    

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60. CBMutableService
    Initializing a Mutable Service!
    – initWithType:primary:
    !
    Managing a Mutable Service!
    – UUID
    – isPrimary
    – characteristics
    – includedServices
    Initializing a Mutable Characteristic!
    – initWithType:properties:value:permissions:
    !
    Managing a Mutable Characteristic!
    UUID
    value
    descriptors
    properties
    permissions
    subscribedCentrals
    CBMutableCharacteristic
    

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61. > code <
    

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62. Foreground vs.
    Background
    

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63. Two background
    modes.
    

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64. bluetooth-central
    “Uses Bluetooth LE accessories” in Xcode
    

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65. bluetooth-peripheral
    “Acts as Bluetooth LE accessory” in Xcode
    

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66. Specify background
    modes in Info.plist.
    

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67. Nuances of
    backgrounding
    

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68. Central Scanning
    • Scanning (as a Central) acts differently in the
    background.
    • Scan options are ignored. Multiple discoveries
    of a peripheral are coalesced into one.
    • The scan interval may increase and your app
    may take longer to discover a peripheral.
    

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69. Peripheral Advertising
    • Advertising in the background differs from
    foreground mode:
    • The CBAdvertisementDataLocalNameKey is not
    advertised.
    • The frequency at which your app advertises
    may decrease.
    • Service UUIDs may not be advertised. Apple
    does best effort.
    

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70. Peripheral Events
    • iOS will wake up your app to receive events:
    read, write, and subscribe events.
    

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71. Caching
    • Services, characteristics and characteristic
    descriptors are cached
    • Characteristic value is kind of cached. When
    discovered the last read value will be provided,
    but it’s put to you to use it (static values) or read
    the value (dynamic values) from the peripheral.
    

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72. State Preservation and
    Restoration
    • Optional feature.
    • Why? if your app is background it can be terminated
    the OS
    • iOS will store the state of the application and act on
    behalf of it as a proxy. When it receives an event your
    app is waiting for it will start the app back up in the
    background to allow it to process it
    • Single method for you to implement to restore the
    state of your app.
    

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73. iBeacons
    

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75. A part of CoreLocation
    

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76. Just a data format in the
    advertising packets.
    !
    Apple to release actual
    profile on ___________.
    

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77. Tips
    

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78. CoreBluetooth lives in
    IOBluetooth for Mac
    apps.
    

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79. No more
    simulator
    support
    as of
    iOS7
    

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80. Keep references to
    CBPeripheral and CBCentrals
    if you plan on using them.
    

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81. YOSO!
    YOCO!
    DSWYDNT
    

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82. Done with peripheral,
    disconnect.
    

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83. CBPeripheral and
    CBCentral objects can be
    dictionary keys.
    

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84. If you’re a peripheral
    support characteristic
    notifications.
    

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85. Require paired
    connections to acquire
    sensitive information
    

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86. Finding peripherals the system
    already knows about
    – retrieveConnectedPeripheralsWithServices:
    – retrievePeripheralsWithIdentifiers:
    CentralManager
    

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87. MTU Exchange Requests
    *Borrowed from 2013 Apple WWDC talk
    

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88. • Allows more data to be sent in one go
    • Less packet overhead
    • up to 20% increase in throughput
    • Free.
    MTU Exchange Requests
    

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89. App store recommendations
    from Apple
    • include the device with your submission
    • be explicit about services the device provides
    • provide instructions for how to use the device/
    app
    • or don’t and cross your fingers
    

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90. @zachdennis
    @zdennis
    !
    mutuallyhuman.com
    

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