This document provides an overview of Bluetooth Low Energy (LE) usage on iOS. It discusses key concepts like central and peripheral roles, the use of universally unique identifiers (UUIDs) for discovery and connection, and the steps involved in connecting including discovering services, characteristics, and transferring data. It also shares results of experiments measuring average transfer speeds between iPhone models of around 3.3 MB/s or 26.4 Mbps. Links are provided for additional Bluetooth and CoreBluetooth documentation.

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Bluetooth LE:
User experience with iOS
Serhii Suprun
GlobalLogic Lviv iOS TechTalk
16.11.2016

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Radio transmit technology based on 2.4 to 2.485 GHz
Protocols
Initiated in 1989 (1.1 in 2002 and 5.0 in june 2016)
Dr. Nils Rydbeck CTO at Ericsson Mobile and Dr.
Johan Ullman
Runes
What is Bluetooth ?

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Runes
ᚼand ᛒ
Scandinavian runes

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LE == Low Energy ?
Up to 4-5 years of work on one battery
- 1 Mbit/s (radio)
- 270 Kbit/s (application limit)
- 26 kbit/s (iOS-iOS my tests)

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Central
Client
Peripheral
Server
iOS
?
Who is who?

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Device to CBPeripheral magic
CoreBluetooth

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Red pill

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Identifiers
Everything is uuid
128 bit (289ed316-defc-48de-8a74-2c9e854e5ab3)
16 bit (0xFE8B)

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Discovery
UUID is everything
func scanForPeripherals(withServices serviceUUIDs: [CBUUID]?, options: [String : Any]? = nil)
func stopScan()
optional func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral,
advertisementData: [String : Any], rssi RSSI: NSNumber)
CBCentralManager
CBCentralManagerDelegate

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Connect: 1 connect
CBCentralManager
func connect(_ peripheral: CBPeripheral, options: [String : Any]? = nil)
func cancelPeripheralConnection(_ peripheral: CBPeripheral)
optional func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral)
CBCentralManagerDelegate

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Connect: 2 services
CBPeripheral
func discoverServices(_ serviceUUIDs: [CBUUID]?)
optional func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?)
CBPeripheralDelegate

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Connect: 3 characteristic
CBPeripheral
func discoverCharacteristics(_ characteristicUUIDs: [CBUUID]?, for service: CBService)
optional func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?)
CBPeripheralDelegate

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Connect: 3 characteristic
CBPeripheral
func discoverCharacteristics(_ characteristicUUIDs: [CBUUID]?, for service: CBService)
optional func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?)
CBPeripheralDelegate

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Data transfer
CBPeripheral
func readValue(for characteristic: CBCharacteristic)
func writeValue(_ data: Data, for characteristic: CBCharacteristic, type: CBCharacteristicWriteType)
optional func peripheral(_ peripheral: CBPeripheral,
didUpdateValueFor characteristic: CBCharacteristic,
error: Error?)
CBPeripheralDelegate

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Transfer speed
Packets
Connection Interval Min ≥ 20 ms
Default MTU: 23 bytes
23*50 = 1150 bytes per second
9200 bit per second
Max MTU: 512 bytes
512*50 = 25600 bytes per second
204800 bit per seconds (200 kbit/s)
128 kbit - low quality audio stream

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Under the hood

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iphone 6 to iphone 5s
average
bytes time interval (second) bytes/sec
82939 25.147522 3298.098318
82939 24.842042 3338.654689
82939 24.637974 3366.307636
82939 24.557985 3377.272199
82939 24.590379 3372.823168 bytes/sec kbit/s kbyte/s
82939 25.016174 3315.415059 3344.761845 26.75809476 3.266368989
iphone 5s to iphone 6
87771 27.235893 3222.622442
average
87771 26.602149 3299.395098
87771 26.506242 3311.333232
87771 26.216806 3347.890662
87771 26.595411 3300.231006 bytes/sec kbit/s kbyte/s
87771 26.41587 3322.661718 3300.689026 26.40551221 3.223329127
Experiments

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Time between chunks

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Problemaz
- Pairing
- Rename
- Speed?
New in iOS 10?

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Links
https://en.wikipedia.org/wiki/Bluetooth
https://developer.apple.com/videos/play/wwdc2013/703/
https://developer.apple.com/videos/play/wwdc2012/703/
https://developer.apple.com/videos/play/wwdc2012/705/
https://developer.apple.com/hardwaredrivers/BluetoothDesignGuidelines.pdf
https://www.google.com

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Questions please
Thanks

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Thank you