Android BLE Limitation - Max Notification Reached, Registration Failed.

[Abhishek Sharma]

Hi,

I am developing an android ble based application where I register for multiple BLE services and receive notifications. It works fine with concurrent notification received for four BLE characteristics. As soon as I register for notification for the fifth one, I get the following error:

E/bt-btif ( 1193): Max Notification Reached, registration failed.

After digging into the android source code, I have found that it is defined as a constant. They allow only 4 concurrent register notifications.

#define BTA_GATTC_NOTIF_REG_MAX 4 (Source: http://androidxref.com/4.4_r1/xref/external/bluetooth/bluedroid/bta/gatt/bta_gattc_int.h#323)

This is a limitation of Android BLE SDK unlike other platform SDK (ex: iOS). Are there any reasons for such limitation because it is really holding android back as compared to other platforms?

[Niclas Granqvist]

4 sounds low ...

[Abhishek Sharma]

It has been increased to 7 after 4.4 update.

[Friedrich Mäckle]

I am interested in this issue as well as i am having problems with this limitation.

Is there any technical reason to limit these notifications to 7? I am working on a relatively complex device with several sensors (7) and several actors (7).

I created characteristics for each sensor and actor which seemed to be the way to go. But due to this limitation i cant subscribe to all of them. So what can i do?

1.) Stuff multiple characteristics into one, bad since i will transmit unchanged sensor values and create a lot of dummy data.

2.) Use notification only and set the sensor which is transmitted within the payload.

3.) Read manually interval based.

This is annoying since i will have to go with solution 1.) and stuff more data into one characteristic. I think this is crippling the possibilities i have and seriously affecting the design of my solution.

[Niclas Granqvist]

I am sure Google can change this if there is a need.

In the mean time I propose that you solve the problem

by adding a multiplexer protocol on top of GATT.

I guess that one byte is enough and a one byte extra 

load is negligible from current consumption point of view. 

This way you don't need to resend the data.

You could also use the byte to invent new payloads

in the future.....

Niclas Granqvist

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Kind Regards,

Niclas Granqvist
Skype: niclas_granqvist_work
mobile: +41(0)798149161