Long connection delay with Android, iOS superfast

[blungreen]

Hello,

i have the following setup: nrf52 as peripheral, smartphone as central. Peripheral's purpose is to be an interface between appliance and smartphone. It has no pairing/bonding feature and it advertises with 22ms interval and public static address.

While iOS always performs connection in about 200ms, Android is very inconsistent. Sometimes it connects as fast as iOS, but most of the times it takes 4-5 seconds to get connected.

The peripheral has no low power restriction so it is setup to perform at its maximum, with connection interval, slave latency and supervisor timeout configured as low as possible, as defined in iOS Design Guidelines.

I have tried to analyze sniffer trace but there is no suitable information, the delay is seen between the connect action on Android, and the CONNECT_REQ on the sniffer.

I moved to HCI dump on Android side and i could see the delay, which looks like this:

    No.     Time                Prot.   Len  Info
    38272	1511777537.552557	HCI_CMD	 29	 Sent LE Create Connection
    38273	1511777537.556675	HCI_EVT	 7	 Rcvd Command Status (LE Create Connection) 
    38274	1511777537.591402	HCI_EVT	 22	 Rcvd LE Meta (LE Connection Complete) //300ms, GOOD!
    ...
    ...
    74093   1511781742.368168	HCI_CMD	 29	 Sent LE Create Connection
    74094   1511781742.371541	HCI_EVT	 7	 Rcvd Command Status (LE Create Connection)
    74095   1511781746.930870	HCI_EVT	 22	 Rcvd LE Meta (LE Connection Complete)  //4.5s, BAD!

It can be seen that between frame 38273 and 38274 the delay is 0.3 seconds, while between 74093 and 74094 there is a 4.5 seconds time delay.

Android is connecting with autoConnect=false, so no backgound connection is performed.

This is the nordic sniffer trace, on a long connection delay case:

5430	49.623224000	Test_device	        <broadcast>		  54	ADV_IND
5431	49.692073000	Test_device	        <broadcast>		  54	ADV_IND
5432	49.698782000	6a:15:34:0b:f7:e0	dc:2c:8c:aa:c3:f7 60	CONNECT_REQ
5433	49.704162000	Master	            Slave		      26	Empty Data PDU
5434	49.708205000	Slave	            Master		      26	Empty Data PDU
5435	49.712125000	Master	            Slave		      35	LL Control PDU: LL_FEATURE_REQ
5436	49.743382000	Master	            Slave		      35	LL Control PDU: LL_FEATURE_REQ

Between the last ADV packet (5431) and the CONNECT_REQ (5432) there is only a 6ms delay, which should mean that the delay is all at the Android side.

Can anyone explain why is this happening? Is there any margin of improvement?

Thank you

[blungreen]

UPDATE: i might have found a possible cause, Google's NearbyMessageService

I was trying to figure out why not being able to connect with Huawei P8 Lite smartphone to any BLE peripheral, so after searching the net i came across with someone saying that on some smarphones if there is a background service doing BLE scan, connection will always fail with error 133.

Looking at the logcat of the Huawei it showed that there was a fast scan on background always present with Bluetooth enabled.

Killing NearbyMessageService from Google Play Services stopped the background scan and i was able to get the phone to connect to BLE peripherals.

On my LG G6 i don't see any backgound scan, but i tried to stop the service to see if it could help with my long delay issue. And it did, now i can connect as fast as iOS.

Disabling Nearby notification on Google settings doesn't stop the scan on Huawei phone, neither helps on my LG.

I will investigate further to understand how this service works

[blungreen]

Yes i did, without luck. Tried to disable pretty much everything from Google settings. On Samsung S7 there is also a specific setting for Nearby under Connections menu. But haven't tried.

Bluetooth Classic still works, on Huawei P8 Lite it seems that only BLE is compromised. There is also a highly chance that Samsung A5 is affected by same problem (same BT chip maybe?), i have a customer that is experiencing the same problem but didn't have a chance to verify.

I have tried to post issue on Google Play Help forum and they said my best luck is to ask Huawei. Nice answer. Looking at Google Play app review there are really lots of complains about battery drain and i believe that.