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 Post subject: Gateway Implementations
PostPosted: Tue Sep 01, 2015 8:44 pm 

Joined: Tue Sep 01, 2015 8:31 pm
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Location: Paris, France
Hello,
as far as I can see OpenTag can be an end node. What about gateway that will connect these nodes to the Internet cloud?

LoRa has a several of these currently: https://www.loriot.io/gateways.html, based usually on SX1301. Does something like this exist in in DASH7 world, and how to construct these gateways.

I suppose that this gateway should be in the center of a star topology to which all other OpenTags in the radius of 3km are connected. And the gateway can for example be a Linux computer connected to the Internet via WiFi, ETH of LTE. If this is the case, how many nodes can be connected to one gateway?

Best regards,
Drasko


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PostPosted: Wed Sep 02, 2015 1:47 pm 
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OpenTag can be a gateway-type device as well as endpoint. It just depends on how it is configured. This usually occurs at compile-time, but a device able to be a gateway can switch between endpoint and gateway modes during runtime -- if there is a reason to do so.

How many devices can connect? This is a hard question when considering that DASH7 doesn't require persistent connections. If you were to replicate the kind of network used in LoRaWAN, where there is occasional synchronization and uplink traffic only, the number of connections will be similar. On the other hand, there are ways to support higher node density in DASH7 using queries.


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PostPosted: Wed Sep 02, 2015 6:54 pm 

Joined: Tue Sep 01, 2015 8:31 pm
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Location: Paris, France
Quote:
OpenTag can be a gateway-type device as well as endpoint. It just depends on how it is configured.


I am really not an RF expert, but it is quite usual that Base Station baseband chip differs than the one on the Mobile Station.

At least, looking at the Semtech transceivers list: http://www.semtech.com/wireless-rf/rf-transceivers/, it looks that SX1272 should be used at the end point node, and SX1301 is the one for base station. Theoretically, even SX1272 can be used as a basic GW, but it would actually be P2P connection (https://openlora.com/forum/viewtopic.php?f=4&t=73).

Now, if I understand your answer correctly, DASH7 protocol works in this way that there is no difference at all between base station RF and end node RF. This is then fantastic, because simplifies the design a lot!

Can you please add some technical details and pointers about this?

BR,
Drasko


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PostPosted: Tue Nov 17, 2015 7:45 pm 

Joined: Tue Sep 01, 2015 8:31 pm
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Location: Paris, France
Also,
I can read here: http://thethingsnetwork.org/wiki/GettingStarted

Quote:
For Communication there are two options for the chip the SX1272/SX1276 option and the SX1301 + SX1257 option. the SX1272/SX1276 only allows for one (1) connection at a time, the SX1301 + SX1257 chips allows up to eight (8() simultaneous connections (typically supporting 10000 ~ 20000 nodes).

As I stated - I am not RF expert. My guess is that there is some kind of TDMA over these 8 channels.

How DASH7 handles simultaneous connections and how many end-nodes can be connected to a central gateway at the same time? Is there any TDMA employed? If yes, how the timing synchonization between gateway and the node is done?

Also,
In your paper "An Advanced Communication System for Wide-Area Low Power Wireless Applications and Active RFID" I can read:
Quote:
2.1.3 Upper Layers
DASH7 Upper Layers represent OSI layer 7, the application layer. DASH7 applications must interface with
the Lower Layers via M2DEF. A DASH7 system can support up to 256 applications, as this is the limitation
of the 8 bit application identifier in M2DEF. DASH7 applications implemented on a separate machine from
the Intermediate or Lower Layers may communicate with these, as well, by piping compliant M2DEF data
over any suitable inter-machine interface (e.g. I 2 C, USB).


What does these applications represent in real life (can you give some example please) - I would like to understand how this limitation of 256 applications is limited - is it only 256 RTOS tasks that can be run at the same time or does it have something to do with number of simultaneously connected end-nodes?

Best regards,
Drasko


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PostPosted: Tue Nov 17, 2015 7:52 pm 
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A normal IP setup can support 65536 ports. An application has an input port and an output port, so there can be 32768 application protocols for TCP, etc. The way data is framed with NDEF is a bit different, but there are 256 possible application protocols for DASH7+NDEF. It's possible to extend this in the future, if necessary, but I doubt it will be.


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PostPosted: Tue Nov 17, 2015 8:00 pm 

Joined: Tue Sep 01, 2015 8:31 pm
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OK, thanks, it is clear now for the application.

Can you please elaborate more on simultaneous connections, TDMA synchronisation, etc...

BR,
Drasko


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PostPosted: Wed Nov 18, 2015 9:03 am 

Joined: Tue Sep 01, 2015 8:31 pm
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Location: Paris, France
Also,
can you tell me if it sounds realistic to use several base-stations (gateways) to cover city-wide area - like LoRaWAN is doing?

If not - what are the constraints?

Best regards,
Drasko


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PostPosted: Wed Dec 23, 2015 10:25 pm 
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The deployment strategy for traditional DASH7 will actually work better if you install lots of low-cost USB stick gateways into WiFi routers and distribute the load that way. But since DASH7 can run on LoRa, if you want to deploy more traditional fixed infrastructure, LoRa is the best way for that because this is what it is designed for.

To do 2-way communication over LoRa-PHY, the best way is to send broadcast/multicast information from the gateway on a reserved channel, and then have the return path from the endpoints be on other channels. DASH7 has good mechanisms for doing this.


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