Heavy scanning activity from Android (and iOS) devices might prevent connecting to BLE GAP Peripheral

Question

Dear Nordic team and community, 
 Have you encountered the problem where standard BT4.0/4.1 GAP Peripheral device would be "blocked" from connection (kind of "denial of service" situation) by too many actively scanning GAP Scanners/Centrals? We are seeing this with certain mobile phones (especially Android) in "observing" role and this is pretty independent on adv. interval we use (typically 20-200ms). All adv. events are "loaded" with SCAN_REQ packets when there are 5 or more "scanning" phones and beside SCAN_REQ collisions (which are typically not critical for BLE solutions) basically all CONNECT_REQ collide with some SCAN_REQ packet and thus Peripheral never follows the connection. 
 Any suggestions (beside trying to lower scanning activity on phones' side which obviously isn't always possible)? 
 Thanks Jan

Hung Bui · Accepted Answer

Hi Jan, 
 I agree on what you are discussing in the comments. It could be an issue if we have an environment where several phones, device keeps scanning and sending scan request or connection request. 
 I just want to add, some solutions if you want to establish a connection in a crowded environment: 
 
 
 Reduce TXpower when advertising, and put the device you want to connect closer to your central. This is to avoid the unwanted scanners to send scan/connect request. 
 
 
 Use Out of Band to send address of the central to your peripheral for example with NFC. After that let the peripheral advertising in directed mode so that other scanner will not send scan/connect request

Heavy scanning activity from Android (and iOS) devices might prevent connecting to BLE GAP Peripheral

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