The maximum number. BLE connections using BlueZ

Question

Q1. Is there a connection limitation for the central BLE when connecting to BLE peripherals using BlueZ 5.34?

My question is about general connectivity using BlueZ not white list.

Q2. If not. The connection depends on the controller. Is there any way to find the maximum limit?

Q3. Does / Can the host BlueZ or Bluedroid add a limit to max no. LE connections supported by the controller?

Q4. If there is a connection restriction for LE devices, which means the author says “no inherent limit” as the block cited in the paragraph below.

Information from the Robin Heydon BLE Developer's Reference

It also means that there should be no restrictions inherent in the number of devices that this device can talk to at the same time. If a device wants to talk to another device, then it should just be able to do this, and not worry that there are only seven possible slave devices that can be connected at a time, which is the limit imposed by classic Bluetooth.

Experiments: As can be seen from the links below, I also saw different sizes of the LE white list when using different controllers, 32 for plug-in usb4btle and 24 for the internal Bluetooth adapter. (Using the command: hcitool lewlsz) In my test setup, I was able to connect to 12 BLE devices (I had no more than 12 BLE peripherals). I used BlueZ 5.34 on Ubuntu 15.04 and used the usbbt4le plugin.

• Gatttool: Limited to 5 connections?
• Concurrent BLE Connections

Answer 1

I opposed this problem ... it's random.

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

A2. Devices are expected to return errors when trying to establish a connection that exceeds what the hardware supports. Different devices report different errors, but they are usually associated with a lack of resources. HOWEVER, I used devices that DO NOT report any error, and something stops working fine after a while, when some unknown limit is exceeded. What I came across are some of the connections that stopped returning notifications. Thus, it all depends on whether you have a well-designed and well-managed controller.

A3. Not sure if I understand the question ... BlueZ et la does not add any restrictions.

A4. There are no design restrictions on the number of connections in BLE. However, most consumers do not need to connect to 100 devices, so Bluetooth keys, as a rule, contain only the necessary resources to maintain a much smaller number of connections. Thus, it is completely up to the manufacturer to determine how many devices they want to support.

Remember that each connection requires that the hardware store state information, and things like whitelisting also require memory storage. Memory requires hardware and hardware costs. Since most dongles are relatively cheap, manufacturers must compete, performing as much as necessary, with the least equipment they can. And testing also takes time, and money and connection restrictions are usually not something consumers have.