Lora join responses : not received and bizarre RF..

[Brian Wyld]

Hi,

Having problemes getting reliable JOIN responses from my MTCT (AEP version).
It works fine for a while, then enters a phase where the join requests are received by the MTCT (I see ‘joined’ UDP packets) but the endpoint doesn’t receive the join response.

Looking at it on a very basic RF analyser (SDR/DVB-T setup!) show that when its working, there’s a very tight transmission (the little orange/red/black stripes), but when its not, I see a kind of long ‘bloc’ of RF… (the orange/red bloc in the waterfall display)
Screenshot:

Note the gateway card is already an RMA replacement….

Any ideas on what’s happening welcome.

Thanks

Brian

[Brian Wyld]

The ‘long block’ is because the response is encoded as SF12 which has a much lower bit rate than the SF9 (the other responses) and which also explains the ‘spread’.
[and which obviously explains why my endpoint doesn’t see the join response : its waiting for a SF9 encoding!]

So my question for support : why is the MTCT (sometimes) using SF12 for responses in the RX2 window, when in the AEP configuration I have explicitly specified SF9?

Is this a bug in the lora-network-server? Seems like this would explain a few of the problems I see on the forum about not receiving join responses….

thanks

Brian

[Jason Reiss]

The default Rx2Channel datarate per LoRaWAN is DR8 SF12BW500 in US and DR0 SF12BW125 in EU. The network server uses these datarates for the 2nd window on the join accept message. With the join accept message are instructions to change the second window datarate to the one specified in the AEP configuration.

If the server used the configured datarate for the 2nd window on join accept message this information would have to be communicated to the mote ahead of time.

[Brian Wyld]

So.

Finally, it seems like:
– the value for the rx2Datarate configured in the lora network server is ONLY for the RX2 window for responses to uplink packets. It is NOT used for the JOIN response.
– there is no means to configure the channel/SPF used for the RX2 window for the join response (its set to the default in the LoraWAN spec and is not changable.

So, setting my reception of the join response for RX2 to be always SPF12, and that for the rx2 for the data packet reception to be the value returned in the join response, all is OK…. just a bit confusing….

Brian

[Brian Wyld]

Thanks Jason for the confirmation. I hadn’t seen your response before posting my own conclusion!

This is ok for us now…

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