When an iOS BLE peripheral enters the background state, the advertising packets are not emitted in the regular manner and they are placed in a special “overflow” area which is only detectable by another iOS device explicitly looking for this device.
The bluetooth-peripheral Background Execution Mode
That said, you should be aware that advertising while your app is in the background operates differently than when your app is in the foreground. In particular, when your app is advertising while in the background:
• The CBAdvertisementDataLocalNameKey advertisement key is ignored, and the local name of peripheral is not advertised.
• All service UUIDs contained in the value of the CBAdvertisementDataServiceUUIDsKey advertisement key are placed in a special “overflow” area; they can be discovered only by an iOS device that is explicitly scanning for them.
Is there any way an Android central (scanner) can detect any advertised custom UUID without having to connect to the iOS peripheral?
With "overflow" area I guess they mean Scan Response Data. To get that data, a device must perform an active scan, rather than a passive scan. In an active scan, the scanner sends a scan request packet immediately after it detects an advertisement packet. The advertising device will only broadcast the scan response data if it detected a scan request.
Android devices only perform active scans, so you should be fine.
EDIT: the answer above is not correct. See http://www.davidgyoungtech.com/2020/05/07/hacking-the-overflow-area for correct information.
Related
I work on iOS application which is using BLE for communication with our custom made BLE unit.
We want to send specific commands via BLE to the unit automatically.
When user is near unit and specific criteria are met, the app should connect to the unit, "login" the user, send command via BLE and disconnect right away.
These specific criteria are based on manufacturer data from advertisement (i.e. the unit is in "available to login" state when manufacturer data has last byte 0x01, when it's "NOT available to login", last byte is 0x00).
In foreground, this mechanism works flawlessly.
We want to do this even when app is in background or terminated (swipe up in dashboard on iPhone).
The mechanism we have implemented:
the unit has capability of acting as iBeacon
when unit is NOT available for login, the iBeacon is OFF
when it IS available for login, the iBeacon will turn ON and wakes up application, upon that the BLE scan will start in background mode
background mode setting is bluetooth-central
Problem here is that no matter what I tried, the advertisement:
sometimes it's not discovered at all (looks like it's timing issue?)
when it's discovered, it does NOT contain manufacturer data
Did anyone come across something similar?
Any help is appreciated and have a nice day!
An app simply cannot read raw BLE manufacturer advertisement data when in the background on iOS -- the operating system prohibits it.
Two exceptions to this rule:
iBeacon, which itself is implemented as a specific type of manufacturer advertisement. An app can detect iBeacons in the background on iOS, although only four bytes of readable data (encoded in the major and minor fields) are fully usable. If you can modify your device to send information this way, it will do what you want. However you must use CoreLocation APIs to detect iBeacon, as CoreBluetooth does not allow reading manufacturer data from iBeacon advertisements. If you do use CoreLocation, you cannot use the detections to establish a Bluetooth connection with CoreBluetooth as the two APIs are sandboxed.
Overflow Area advertisements. Backgrounded iOS apps can read these special types of manufacturer advertisements when in the background but only if the screen is turned on. (It is often possible to force the screen on at specific times by sending a local notification.) See my blog post here for more info: http://www.davidgyoungtech.com/2020/05/07/hacking-the-overflow-area
An alternative to detecting manufacturer advertisements is to use BLE Service advertisements with attached data. For this to work, you'd need to define a 16 bit or 128 bit GATT Service UUID and send out an advert with attached data bytes. Eddystone beacon formats work this way, and allow detection in the background on iOS. This is probably the best approach if you can alter the BLE hardware.
I need my app to act as a BLE beacon, even when it is in the background.
I've already made the beacon part - works fine when I'm using the app.
The problem is I've never made anything run in the background before, and not sure what the limitations are - if I will be allowed to let the app act as a beacon in the background.
Was wondering if this is possible or not (both technically, as well according to App Store rules)
Is this technically possible ? Can my app act as a beacon, even when the app is not in the foreground.
Is it within App Store rules ?
Unfortunately, iOS apps cannot emit iBeacon advertisements unless they are in the foreground. If you program your app to advertise iBeacon frames, as soon as the screen turns off or the app is not visible, iOS changes the advertising format to a special generic background advertisement that does not match the iBeacon format.
This proprietary background advertisement is useless for identification of a device. It is designed for connection to BLE GATT services from other iOS devices. Unless you want to advertise a connectable BLE GATT service to other iOS devices this advertisement has little value. EDIT: There is a way to make use of this advertisement. See below.
Apple's documentation describes this limitation here in the section titled "The bluetooth-peripheral Background Execution Mode":
you should be aware that advertising while your app is in the background operates differently than when your app is in the foreground. In particular, when your app is advertising while in the background:
The CBAdvertisementDataLocalNameKey advertisement key is ignored, and the local name of peripheral is not advertised.
All service UUIDs contained in the value of the CBAdvertisementDataServiceUUIDsKey advertisement key are placed in a special “overflow” area; they can be discovered only by an iOS device that is explicitly scanning for them.
If all apps that are advertising are in the background, the frequency at which your peripheral device sends advertising packets may decrease.
It may not be obvious that the above causes iBeacon transmissions to break, but I assure you that is absolutely a consequence.
Read my blog post here for more information on how to put useful beacon data into this background "Overflow Area" advertisement.
I work on iOS application with acts as Bluetooth peripheral. I need to implement a searching for my iOS peripheral from non iOS centrals. I’m faced with a problem while my iOS application advertising in background mode. When it is advertising in foreground, my central can read primary service UUID from advertising data, but when it is advertising in background, I can’t see the name or the UUID of peripheral – there is only Apple manufacturer data in advertising packet.
The essence of the problem lies in the fact that my non iOS central can’t determinate – is it advertising my peripheral in background or any other peripheral in background. I have to connect every iOS device with advertising in background, enumerate its services to look for my service UUID.
The documentation says that during background advertising all service UUIDs go to special “overflow” area and only iOS devices can read it specifying service in CBCentralManager’s scanForPeripherialWithServices method. It looks like Apple have an ability to check background advertising packet data for service UUID.
After searching on SO I found some interesting information about service hashed UUID. Background mode advertising packet always contains Apple manufacturer data (14 FF 4c 00 01) and undocumented 128 bit value, where one of these 128 bits equals 1. I tried to change my service UUID several times and found out than this 128 bit value after Apple manufacturer data changes too.
I’d like to use this value to filter peripherals around and reduce
connections to wrong (not mine) peripherals. Can anyone give any
information how this value depends on service UUID? Is there any
hash function that is used on specified service UUID in
scanForPeripherialWithServices method?
Can I be sure that the background advertising packet will always be the same for the immutable service UUID which will never change?
Is there any other way to send my custom information while
advertising in background mode? Maybe I can add my data into BLE
SCAN RESPONSE packet?
Best Regards,
Dezmond
We need in our project to detect the proximity of an iPhone that is running a custom APP that is using Bluetooth LE.
The detector (Scanner, Central...) will be implemented using a BLE Integrated Circuit (from Texas or Nordic). I mean that the scanner is not another IOS device... running Core Bluetooth as a Central..
For the detector to guess the proximity, the idea is very simple, just advertise a service with an UUID proprietary.
While in foreground all works OK, and the UUID and a Local name are advertised (The UUID in the main advertise packet, and the Local Name in the SCAN Response packet....), and our scanner is able to decide if this iOS device is running our App.
The problem arises when going to background .....
The iOS stops broadcasting UUID and Local Name. (As the documentation of Core Bluetooth Explains... I Know...)
At this moment (Background), IOS begin to broadcast a SPECIAL MANUFACTURER DATA in the main advertise packet, and nothing in the SCAN Response packet)
The data packet we see using a Bluetooth Sniffer is :
0x14 (length of packet not including this byte).
0xFF (Manufacturer specific data AD Type).
And then :
0x4C, 0x00 (this data is the manufacturer identifier, if the packet is compliant with BLE 4.0 specification).
0x01, 0x00,0x00, 0x00, 0x00,0x00,0x80, and ten 0x00 more....
I know Apple says that while in background ONLY ANOTHER IOS DEVICE SEARCHING FOR A SPECIFIC SERVICE CAN DISCOVER IT. (Really I do not know how they can achieve that, unless they connect to the peripheral and retrieve the services, or if the peripheral knows about other IOS device is scanning because of it´s Address in the SCAN REQUEST and then changes the advertisement data in background).
The main questions are :
Is there any documentation or knowledge of what this manufacturer data means....Perhaps it would be possible to the scanner to know based on this info that this is an iOS device advertising in background and then connect to look if the custom service is there. (Not a quick and clean solution...but I do not see any other workaround....)
Does anybody worked with this scenario...and found a clean solution .....
I have heard from people that forces the application not to go to background.
This limitation, will stop a lot of possible projects.
I'm trying to use an iOS BLE device as BLE peripheral which also advertises in background.
I already figured out how to advertise in background and got it detected by another device looking for the specific bluetooth UUDID.
Unfortunately the advertiser-info is not transmitted when the app is in background. Is there a way to send a short string or something else device specific when the app is in background? It would be ok if the app would be woken up for a short period (if this is possible).
The advertised services are removed from the advertisement packages when the app is backgrounded. Only foreground scanning iOS devices will be able to obtain the services.
The advertised services are arbitrary UUIDs. You can easily figure out some encoding to store characters in them. However, this has several caveats, like
the general scheme is usually that the scanner finds your peripheral by the service UUIDS. If the data can be anything, then this is tricky.
the peripheral will not be able to change the advertisement data while backgrounded.
I suggest you not try to trick around with the system. Rather plan for connecting to the peripheral for a short time and sending the data to the central during this interval.