Gatttool: Limited to 5 Connections

Cannot disconnect BLE connection

I can confirm this problem on Ubuntu 14.04 with BlueZ 5.40 and 5.43.

Workaround 1: Disconnect from the other side.

Workaround 2: Use

sudo hciconfig hciX down
sudo hciconfig hciX up

where hciX is your controller (e.g. hci0). Unfortunately, this will remove all connections.

Maximum no. of BLE Connection using BlueZ

I've come against this issue... it's messy.

A1. The connection limit is based on the hardware. I've used devices that are limited to 3 and others that seem to go past 7.

A2. The devices are supposed to return errors when you try to establish a connection beyond what the hardware is able to support. Different devices report different errors but they're usually something related to running out of resources. HOWEVER, I've used devices that DO NOT report any error and things just stop working properly after a while when exceeding some unknown limit. What I encountered was some of the connections stopped returning notifications. So, it all depends on whether you have a well-designed and well-behaved controller.

A3. Not sure I understand the question... BlueZ et la don't add any sort of limitations themselves.

A4. There's no design limitation in BLE regarding the number of connections. However, most consumers don't need to connect to 100 devices so bluetooth dongles tend to only contain the necessary resources to maintain a much smaller number of connections. So, it's completely dependent on the manufacturer as to how many devices they want to support.

Remember, each connection requires the hardware to retain state information and things like whitelists also require memory to store. Memory requires hardware and hardware costs money. Since most dongles are relatively cheap the manufacturers have to compete by doing as much as needed with the least amount of hardware they can. And testing also takes time and money and connection limits aren't usually something consumers come against.

Cannot connect to BLE device on Raspberry Pi

I had to disable the plugin pnat in /etc/bluetooth/main.conf -> DisablePlugins=pnat. I read that it's unstable, but I don't know much about this plugin.

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