Significant difference in connection time with different adv intervals

RE: Significant difference in connection time with different adv intervals

run_ar — Thu, 15 Feb 2018 20:09:07 GMT

The problem is the scanner will block the radio for 300 ms during the scan window. So you need a connection supervision timeout that is long enough to allow that, and accept that you could get that amount of latency on the connection. For reference the scheduling documentation for the SD is available here.

RE: Significant difference in connection time with different adv intervals

nordicdev — Tue, 06 Feb 2018 22:24:14 GMT

Hi run_ar,

thanks for the reply.

I thought that once connection has established, if the connection interval is short and frequent that would have less impact even if the scan interval is long - please correct me if I am wrong (in my case, my min connection interval = 7.5msec and max connection interval = 30msec; adv interval = 200msec; scan window = 300msec and scan interval = 600msec). In other words, do you mind explaining the relation between the connection interval and scan interval in my case and the cons of having the above settings in my set-up once the connection has established? Thanks.

RE: Significant difference in connection time with different adv intervals

run_ar — Mon, 05 Feb 2018 08:00:15 GMT

As long as you only need to interact with one device that would probably be fine. But you risk that it still takes a couple of seconds to establish the connection. If you are interacting with several devices I would recommend that you use a shorter scan interval, i.e. something that matches your connection interval.

RE: Significant difference in connection time with different adv intervals

nordicdev — Fri, 02 Feb 2018 03:45:02 GMT

Hi run_ar, thanks for the reply. What if I have advertisement interval as 200msec and scan window as 1000msec and scan interval as 2000msec? Then, more chances are for not missing all 5 advertisement packets (0 to 1000msec has five 200 msec advertisement packets). Will there be any problems in this set up?Your thoughts, please.

RE: Significant difference in connection time with different adv intervals

run_ar — Wed, 31 Jan 2018 13:35:51 GMT

The scan window cannot be larger that the scan interval. But, yes, if you scan all the time that would increase the chance of establishing the connection faster. Or at least receive the advertisement packet. If you have several scanners performing active scanning it might not be a good idea if all of them scans and sends scan requests that interfere with the connection request.

RE: Significant difference in connection time with different adv intervals

nordicdev — Tue, 30 Jan 2018 23:07:48 GMT

Hi run_ar, This makes sense. Thank you very much for the clear explanation. What if I have the scan interval as 40msec and scan window of 50msec? Then, there would be more chance of hits than misses, right?

RE: Significant difference in connection time with different adv intervals

run_ar — Tue, 30 Jan 2018 09:50:30 GMT

This means that with a scan interval 100ms and a scan window 50, when using an advertisement interval of 50 ms or 200 ms, there is a significatn risk you will have to wait for a long time. Maybe you could try using 190ms as advertisemenet interval instead? I would also assume that if you use 40 instead of 50 ms you should see considerable faster connection esthablishement.

Diclaimer: the advertising random delay is not accounted for in the picture above.

RE: Significant difference in connection time with different adv intervals

nordicdev — Mon, 29 Jan 2018 22:24:57 GMT

Hi run_ar, thanks for the reply. Please find my settings:

Hash define SCAN_INTERVAL 0x00A0 // Determines scan interval in units of 0.625 millisecond.

Hash define SCAN_WINDOW 0x0050 // Determines scan window in units of 0.625 millisecond.

Hash define SCAN_TIMEOUT 0x0000 // Timout when scanning. 0x0000 disables timeout.

Hash define MIN_CONNECTION_INTERVAL MSEC_TO_UNITS(7.5, UNIT_1_25_MS)

Hash define MAX_CONNECTION_INTERVAL MSEC_TO_UNITS(30, UNIT_1_25_MS)

I thought, from a logical point of view, there wouldnt be much of a difference (from a user point of view - seeing how long it takes to connect) when advertisement interval is 50msec Vs200msec. Please correct me if I am wrong.

RE: Significant difference in connection time with different adv intervals

run_ar — Mon, 29 Jan 2018 10:11:19 GMT

Most likely it is expected behavior. But could you also tell us what you scan interval and window is? that could help understanding this. Rememer that the time it takes to establish a connection depends on both the advertiser and the scanner settings.