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SubjectRe: [RFC net-next 00/15] net: A socket API for LoRa
Alan Cox <> 於 2018年8月10日 週五 下午11:57寫道:
> > Except saving power, mitigating the wireless signal conflict on the
> > air is one of the reasons.
> If the device level is always receiving when not transmitting it has no
> effect on this. The act of listening does not harm other traffic.

My friend had tested practically:
If he changes the LoRa interface to RX mode after TX completes
immediately, he will receive the signals like reflection echo some
That is interesting!

There is a paper "Exploring LoRa and LoRaWAN A suitable protocol for
IoT weather stations?" by Kristoffer Olsson & Sveinn Finnsson
In chapter 3.2 Chirp Spread Spectrum, it describes the reflection echo
I think that is why LoRaWAN places the RX delay time which avoids
receiving the reflection noise.

> > The sleep/idle/stop mitigate the unconcerned RF signals or messages.
> At the physical level it's irrelevant. If we are receiving then we might
> hear more things we later discard. It's not running on a tiny
> microcontroller so the extra CPU cycles are not going to kill us.

According different power resource, LoRaWAN defines Class A, B and C.
Class A is the basic and both Class B and C devices must also
implement the feature of Class A.
If the end device has sufficient power available, it can also
implement the Class C: Continuously listening end-device.
Here are the descriptions in LoRaWAN spec. for Class C:
- The Class C end-device will listen with RX2 windows parameters as
often as possible.
- The end-device listens on RX2 when it is not either (a) sending or
(b) receiving on RX1, according to Class A definition.
- 1. It will open a short window on RX2 parameters between the end of
the uplink transmission and the beginning of the RX1 reception window.
2. It will switch to RX2 reception parameters as soon as the RX1
reception window is closed; the RX2 reception window will remain open
until the end-device has to send another message.

According to the LoRaWAN Regional Parameters, the DataRate (including
spreading factor and bandwidth) and frequency channel of RX1 and RX2
windows may be different.(*)

So, yes! Class C opens the RX windows almost all the time, except the TX time.
And uses different channel to avoid the reflection noise (*).

However, Class C must also implements Class A and C is more complex than A.
I think starting from the simpler one and adding more features and
complexity in the future will be a better practice.

> > > How do you plan to deal with routing if you've got multiple devices ?
> >
> > For LoRaWAN, it is a star topology.
> No the question was much more how you plan to deal with it in the OS. If
> for example I want to open a LORA connection to something, then there
> needs to be a proper process to figure out where the target is and how to
> get traffic to them.
> I guess it's best phrased as
> - What does a struct sockaddr_lora look like

According to LoRaWAN spec, the Data Message only has the device's
DevAddr (the device's address in 4 bytes) field related to "address".
The device just sends the uplink Data Message through the interface
and does not know the destination. Then, a LoRaWAN gateway receives
the uplink Data Message and forwards to the designated network server.
So, end device does not care about the destination. It only knows
there is a gateway will forward its message to some where.
Therefore, only the DevAddr as the source address will be meaningful
for uplink Data Message.

> - How does the kernel decide which interface it goes out of (if any), and
> if it loops back

There is the MAC Header in the Data Message which is one byte.
Bits 5 to 7 indicate which kind of type the message is.
000: Join Request
001: Join Accept
010: Unconfirmed Data Up
011: Unconfirmed Data Down
100: Confirmed Data Up
101: Confirmed Data Down
110: RFU
111: Proprietary

So, end device only accepts the types of downlink and the matched
DevAddr (the device's address) in downlink Data Message for RX.

> remembering we might only be talking to a hub, or we might even be a
> virtualized LORA interface where we are pretending to be some kind of
> sensor and feeding it back.
> Long term yes I think Alexander is right the inevitable fate of all
> networks is to become a link layer in order to transmit IP frames 8)

Yeah, maybe. It will be easier for life.
But I have not seen the formal standard for that yet or I missed it.
If the standard appears, we can try to implement it.

Jian-Hong Pan

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