Different capabilities on BLE peripheral device with multi-link, multi-peripheral and multi-role features

Question

Hello, 
 
 I am using nRF52840, SDK_16.0.0, SoftDevice S140 V7.0.1 and Segger for flashing the image. I am using ‘ble_app_blinky’. 
 
 Initially I was in assumption that once BLE peripheral connected to a master, will stop advertisement and cannot connect to another masters. After going through BLE Core_4.2 standards I read below statements and gone through couple of Nordic examples like Multi-link, Multi-Peripheral and Multi-Role examples. 
 
 “Within a physical channel, a physical link is formed between a master and each slave. Direct physical links between slaves in a piconet are not supported. 
 Slaves are permitted to have physical links to more than one master at a time. A device is permitted to be master and slave at the same time. Role changes between a master and slave device are not supported at this time.” 
 
 My further queries are with respect to Core_4.2 (Page : 173). I need inputs from the BLE experts like you rather than googling and getting different answers and having wrong interpretations. 
 
 1) “Direct physical links between slaves in a piconet are not supported.” 
 This means two Slaves cannot connect and communicate directly. But whether two slaves can connect to same master and exchange data. Similar to ZigBee with Star topology. Where once slave can communicate to other slave within network via Master or Router. 
 
 2) “Slaves are permitted to have physical links to more than one master at a time.” 
 This means same slave can connect to different Masters. Even after connection, still slave can do Advertisement (Ex: ble_app_multiperipheral). In case of nRF52832/40, how may max masters can be connected by single slave. 
 
 3) “A device is permitted to be master and slave at the same time.” 
 As a Master whether it can connect to multiple slave devices and the same device as slave whether it can connect to multiple masters. 
 
 4) “Role changes between a master and slave device are not supported at this time.” 
 Bit confused about this statement and above statement. If same device can act as Master and Slave at same time, then what does Role change is not supported. 
 
 5) In below link I am seeing the statement “least 1 Peripheral + 8 Central + Broadcaster roles in parallel” 
 https://devzone.nordicsemi.com/f/nordic-q-a/24140/can-i-use-ble-connection-and-advertising-at-the-same-time 
 Whether same device will act as 8 Centrals. To my understanding there will be only one Central in same network. Please correct if I am wrong. 
 
 Please let me know your inputs for each point separately, so that it will be clear. 
 
 Thanks & Regards 
 Vishnu Beema

Sigurd · Accepted Answer

Hi, 
 1) Correct. 
 2) Correct. With the S132/S140 SoftDevice on nRF52-series you can have max 20 links, freely configurable roles. A device can have e.g.

20 central links 
 19 central links 1 peripheral 
 10 central links 10 peripheral 
 19 peripheral links and 1 central 
 20 peripheral links 
 15 peripheral links 5 central 
 etc, etc 
 
 You might find this multilink demo relevant: https://www.youtube.com/watch?v=tbl6Dui-_w4 
 3) Correct. 
 4) I think this means that you cannot suddenly change your role while you are in a active connection. 
 5) Two masters cannot communicate with each other directly, one device need to be the slave. But a device can both be a central for one device, and a peripheral for another device at the same time. E.g. in ble_app_hrs_rscs_relay example . The relay is both central and peripheral. 
 
 BR, 
 Sigurd

Sigurd · Answer

Hi, 
 beemavishnu said: a) Whether the same device can act as connectable peripheral + Central + Non-Connectable peripheral. 
 Yes, that is possible. 
 beemavishnu said: What does “least 1 Peripheral + 8 Central + Broadcaster roles in parallel " mean. beemavishnu said: b) What does 8 central mean. 
 This is outdated information for the old versions of the SoftDevice(version 1, 2 and 3). In these old versions the SoftDevice, it could be configured with one connections as a Peripheral and up to eight connections as a Central. Starting from SoftDevice version 4, this was improved, and we now support 20 connections (f reely selectable role (Central/Peripheral) for each link ) 
 BR, 
 Sigurd

Different capabilities on BLE peripheral device with multi-link, multi-peripheral and multi-role features

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