Connection parameters: nRF Connect & finding them in Wireshark

RE: Connection parameters: nRF Connect & finding them in Wireshark

Hung Bui — Mon, 14 Nov 2016 08:41:26 GMT

@Vala: 2. All the transmissions in one connection event is sent in one channel. The channel is changed on every connection event. This is called channel hopping.

The delta time only tell the distance between a packet and the next one. It's not necessary represent the connection interval. The reason is that there are more than one packet per connection event. At least 2 one from master one from slave, there could be more (typical 6 from each side) if the peer has more data to send. The distance between them can be very short, as you already found. When there is nothing to send, only 2 packets per connection event, and you can see the delta time close to the connection interval.

RE: Connection parameters: nRF Connect & finding them in Wireshark

Hung Bui — Fri, 11 Nov 2016 12:18:53 GMT

Hi Vala,

You can have a look at this blog, it discusses a little bit about the flow control and on how to read the connect request packet.

Regarding the connection parameter set by nRF Connect, it actually doesn't set any parameter. Like any Android (and iOS) applications, it can't control initial connection parameter. The parameters are decided by the operating system. However the application can request a connection parameter update using this API.

As far as I know the nRFConnect hasn't provided a way for user to call this.

In short, the connection parameters are various and user can't change it, for now.

You can use the delta time, start to end (start to start is not reliable) to detect the distance between packet and can find which packets are in same connection event and which are not, and can roughly get the interval by doing calculation. But it's easier to look at the connect request and the connection parameter update packet, if any.

RE: Connection parameters: nRF Connect & finding them in Wireshark

Vala — Fri, 11 Nov 2016 10:53:05 GMT

I checked the Core Specification document to see what the SN and NESN fields mean. That raised a question. In the documents it claims that:

"The transmitSeqNum and nextExpectedSeqNum parameters shall be set to zero upon entering the Connection State.

For each new Data Channel PDU that is sent, the SN bit of the Header shall be set to transmitSeqNum.

When a Data Channel PDU is sent, the NESN bit of the Header shall be set to nextExpectedSeqNum."

I see in Wireshark that there are some packets from Master to Slave with the right value of delta time (comparing to the connection interval value), a change in the channel and a event number change with respect to previous packet, all showing the start of a new connection, but showing '1' for the SN and NESN fields. Could some one tell me what it means when these fields are set to '1' at the start of a connection?

RE: Connection parameters: nRF Connect & finding them in Wireshark

Vala — Fri, 11 Nov 2016 10:51:53 GMT

OK I guess I found the answers to the question No.3. There are some items that can show the start of the a new connection, and therefore 'delta time' showing the connection interval.

1- The event counter is updated for each connection.

2- All the transmissions in one connection is sent in one channel. Therefore, changing the number of the channel shows the termination of a connection.

Thus, the delta time of those packets which show a new connection should be checked for connection interval.