about Connection Interval

[tommy]

We have tried the following changes,  but couldn't get expecting results.

Sometimes unable to pair two devices / Sometimes fails to link with one device

Could you answer the inquiry 1 & 2?

[SDK ver.]

2.7.0

[Changes]

• Changed the Connection Interval from 100ms to 30ms

[Results]

• Link time: Reduced from 7.0s to 2.5s
• Pairing time: Reduced from 7.0s to 0.7s
• The following issues occurred:
  • Unable to pair two devices / Sometimes fails to link with one device

☆[Inquiry 1]

• Please explain the technical reasons for the reduction in link time and pairing time.

☆[Inquiry 2]

• Please explain the causes of the above issues.
• Are there any other parameters that need to be adjusted accordingly?

[Hung Bui]

Hi Tomokuni, 
Please provide more information about the issue:  Unable to pair two devices / Sometimes fails to link with one device

When you reduce the connection interval, the data exchange can be faster and result in shorter time for service discovery and pairing. 
Please elaborate what you meant by "link time" 

My suggestion is to use the sniffer to capture the connection and pairing. 

[tommy]

"Link time" means the elapsed time to establish the connection between Central and Peripheral.
Here are the log of connection captured by the sniffer.
We have changed the value of BLE_ACL_CONN_INTERVA, and tried 30msec and 100msec.

(BTW,BLE_ACL_CONN_INTERVA surely define the Connection interval as circled in red?)

30ms_CONNECTION_FAIL-SUCCESS.pcapng
 -> once failed, but SUCCESSED afterward

30ms_CONNECTION_SUCCESS.pcapng
 -> connection successed

100ms_CONNECTION_FAIL.pcapng

 -> connection failed

100ms_CONNECTION_SUCCESS.pcapng

 -> connection successed

In our environment, we have found the following result;

 30msec: the elapsed time surely reduced, however sometimes it becomes easier for the connection to be lost and recovered.

 100msec:the connection lost rarely happened. 

Is there some way to optimize this parameter?
or are there any optimized value for each SDK?


2677.log.zip

[Hung Bui]

Hi Tomokuni, 

Unfortunately the sniffer traces you captured don't provide much useful information because it didn't follow the connection. 
We have a tutorial that you can follow here regarding the sniffer: https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-6-bluetooth-le-sniffer/

BLE_ACL_CONN_INTERVAL is the normal connection interval, yes.

You can reduce the time from starting advertising until connection established by advertising with shorter advertising interval.