Join Accept transmitted after 4 or 5 seconds, instead of 5 or 6?

Gateways
1

Is there a change in the timing for join-accept? imho the join-accept-time was 5sek/6sek. Today i saw my gateway transmitting the join-accept after 4sek (on the transmit frequency) and after 5sek (on 869.525 MHz).
Or is something wrong with my gateway?

Wolfgang

2

Where are you seeing that? And does it still work?

The gateway needs to transmit an OTAA Join Accept at the exact time of 5 or 6 seconds after receiving the Join Request. So, TTN delegates the details to the gateway a bit earlier, to allow for some network latency and to allow the gateway to prepare itself.

TTN Console shows you when TTN sends off the downlink instruction to the gateway, apparently about 4 or 5 seconds after it received the Join Request. So, for RX1 (for EU868: same frequency as the uplink) for which the gateway should transmit 5 seconds after receiving the Join Request, the 4 seconds nicely allows for about 1 second of total network latency and processing at the gateway. (This latency includes the latency for the Join Request to arrive at TTN: the reported time for the Join Request is the time at which TTN received it, and TTN does not know how long it took for that to travel from gateway to TTN.) Same goes for RX2 (for EU868: 869.525 MHz), which is sent to the gateway after about 5 seconds, to allow for transmitting at 6 seconds.

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3

Hello Arjan,
thank you for your reply. To determine the time, I used the difference between the timestamps of Join Request and Join Accept. You are totally right: I should have measured the time-difference on the RF-path.
I startet thinking about the timing because I recognised that my nodes always seem to miss (or ignore) Join Accept in RX1 window. If the gateway transmits the Join Accept in the RX2 window the nodes join.
I will try to measure the time-difference using my SDR-receiver.
btw: Gateway Dragino LPS8, Nodes: LGT-92, LT-33222-L

Wolfgang

4

I found the reason for the rejection of the Join Accept: it is the “unsupported power” problem and not the timing. When transmitting on RX1 TX-power is set to 11 (not supported by the gateway).
When transmitting on RX2 TX-power is set to 24 (supported), the packet is accepted and the node joins.

1 Like
5

Note that https://github.com/TheThingsNetwork/lorawan-stack/issues/2106 claims that 11 should be accepted by the gateway (while, e.g., 17 and 24 are indeed unexpected). Did you change the standard configuration?

6

Dragino issued a new firmware today for the LPS8-gateway which should solve the packet-reject problem. I will try that tomorrow.
I did not change the standard-configuration.

7

With the new firmware (5.3.1584002217) for the gateway LPS8 the problem seems to be solved:

“powe”:11,"
INFO~ Can’t find specify RF power 11dB, use 14dB
JOIN_ACCEPT:{Message …}

The Gateway now uses 14dB instead of 11dB. I assume that it is dBm.
On the other hand - the LPS8 still does not fullfill the requirements because the output power is 3dB (2 times) higher than requested.

The nodes do now not always connect with SF12.

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