Multi-Role, Multi-Link Optimal Timing Configuration For reliable Connections and Max Throughput

[David]

SDK 15.2

I am wondering if anyone could point me in the right direction for optimal Timing configurations for the following parameters:
1. Advertising Interval
2. Scanning Interval
3. Scanning Window
4. Connection Interval Minimum
5. Connection Interval Maximum
6. Flash Access
7. MTU Size
8. Event Length

Scenario:
Making a connected mesh which allows up to 120 nodes all up and 8 connections per device (each device the same all NRF5832 or NRF5840).
The Device will send out adverts and will also scan for adverts from other Nodes
it can handle Peripheral connections and Central Connections

4 Peripheral
4 Central

I have this working however i am experiencing some issues with throughput with the connected nodes. i have looked through the documentation but i think that i don't quite understand the relationship between some of the timing events.. e.g. Central Role vs Peripheral Role timing issues vs Flash Access vs Scanning / Advertising etc...

Can anyone help me come up with configurations for allowing max throughput but also maintaining reliability between the connected pairs, and also the discovery and connection to new nodes entering the area?

That would be greatly appreciated

Thanks,

David Hutchinson

[Sigurd]

Hi,

Please take a look at the throughput chapter in the SoftDevice Specification, in table 3 we have some expected throughput numbers for 8 connections. You could maybe try the configuration used there, with connection interval at 20ms and event length of 2.5ms. When nodes start to connect, you might want to increase the advertising/scan interval a bit.

The flash memory writing halts the CPU, but the SoftDevice will make sure that flash memory accesses are scheduled to not disturb radio events. See this link

[David]

I have adjusted the event_length and connection_interval based off the configurations in table 3. 
and i am now seeing a lot better performance.. however some of the connections are a lot slower than others and i was wondering if there is a way to get all of the connections having the same good throughput

i have 9 Devboards all connected together
about half of the connections will have a throughput of around 20kbps very good.

but the others are sometimes 2kbps (10 x slower)
These connections as well are the Peripheral Connected nodes that seem to have slower throughput... I dont know whether this is coincidental or whether its a determining factor because i did have 1 Central connection that was taking 10 x longer also

I have a MTU of 103
Event_Length 12.5
Connection_interval of 100
Scan_window 40
Scan_interval 1024
Adv_interval 512

I have a payload of 100 Bytes
and sending 100 packets (so 10,000 bytes transmitted) and it is roughly taking 4 seconds on average (20kbps)
however on some it is taking 40+ seconds (2kbps or less)

Thanks,

David Hutchinson