I understand that a gateway can listen to multiple channels simultaneously, but how does an end device know which channel to be listening on for an RX1? Is it based upon the uplink frequency?
Also, given there is only one frequency defined for RX2, is there risk of greater congestion compared to RX1?
Looking at RP002-1.0.4, page 55, section 2.8.7, this defines the RX1 Channel Number:
o RX1 Channel Number = Transmit Channel Number modulo NbChannel, where NbChannel is the number of active receive channels.
So yes, this is fixed and known.
(A bit interesting: there are 8 downlink channels - would there be situations where there is a different number of active channels than 8 being active? I don’t know. )
Yes, which is why for instance on EU868, TTN prefers to use SF9 as that allows a roughly 8x throughput compared to using the default SF12.
Stats tell me that the use of Rx2 is very infrequent, so as well as things like SF9 mitigation which you could apply, it’s not something that comes up often unless you have 1,000’s of devices that regularly need a downlink & a few hundred gateways.
Red and green are the usual eight bands, orange is the Rx2 frequency band. For a week, Rx1 frequencies were fully capped at 1% dutycycle and TTN had to move to Rx2 regularly. Looks like someone was abusing airtime with confirmed downlinks - not me! Don’t need 1000s of devices: it takes an uneducated person with only a few poorly configured devices to fill up Rx1…
