Are there gateways that can save data locally on SDCard in case of network outages? (Or, always log to SDCard as a backup)? I see that all gateways have SD card for firmware image storage, but not advertising this as backup storage?
It’s been done, and covered here before, but it’s not really compatible with LoRaWAN.
The reason is the frame counter - a network server will reject any packets where the frame counter value appears to have moved backwards in time. So if anyone else’s gateway gets a packet from your node through during the outage, your entire archive is rejected. And if you don’t replay your archive in chronological order before you start reporting in timely packets, it gets rejected.
Granted, for data historical integrity purposes you can probably get the relevant keys out of the TTN server and decode the packets yourself… but it’s an awkward fit with the design of LoRaWAN.
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Got it, thanks for the explanation.
The very loverly @cslorabox isn’t a fan of that, not a bit and I fully understand why.
But the higher end RAK gateways do this once setup and tested. They do it by holding the unsubmitted messages in order and passing them on once they have connectivity restored. So very useful for GSM/LTE connections. However I believe there are issues with timestamps that I haven’t got a handle on, see: https://forum.rakwireless.com/t/rak7258-lte-automatic-data-recovery/2193/10
However, due to the security design, particularly the frame counters, this can go wrong so should be a nice to have in your design and not a definitely must must work.
RAK’s challenge isn’t so much an implementation one as the classic one of diving into writing code without there being a strategy which solves the actual problem. And then when users unsurprisingly have issues, trying to fix a systemic problem in the code of one component.
Upon reconnection, if they start being a gateway immediately, then the archive gets submitted out of order and a LoRaWAN server enforcing frame counts rejects it
Conversely if they drain the archive in order before they start being a gateway again, now the duration of the outage of real time data (and during which ADR keeps falling back due to loss) is magnified. And should any other gateway get a packet in, it’s all for naught.
I think if you really want to do this, you’re better off taking any gateway where you control the code and writing your own backup scheme which uses the storage media in a way that you feel is safe. Then get your node keys and do your own offline decoding of historical data outside of TTN, and write those packets to your historic log of application data with some “recovered” flag on them.
That still doesn’t mean it is a good solution. It will work for gateways out in the boonies with infrequently transmitting nodes and shorter connection interruptions.
In my opinion this tries to solve a fundamental issue of LoRaWAN, the assumption the gateway is always connected to the backend. Solving this requires a rewrite of (parts) of the specification, not hacking the packet forwarder and hoping to get away with it. (Btw it seems kerlinks cpf buffers packets as well so RAK is in good company)
Users at this level should know better.
Ditto - hence the setup and tested bit.
I fully appreciate that a metropolitan based gateway is going to be hammered if it tries to store & forward - but if it’s in that sort of area, there should be overlapping coverage of gateways.
As you say Jac, it’s for the boonies when the mobile network goes off line because it’s raining hard or it’s foggy (something I’ve actually lived with).
Meh… the real market for RAK (and Dragino) boxes running stock firmware is people who want to just plug something in, click through some gui menus, and have it work.
For a user with reliability concerns, they’re more a demonstration of the fact that an MT76x8 chip (or the competing AR9331 that Dragino uses) can be a decent inexpensive gateway platform potentially robustly booting from NOR flash.
You then have the choice of either putting custom software on the offered boxes (via changes captured in the overlay filesystem, or by rebuilding OpenWrt from source) and/or making a custom hardware platform adding in key things that were left out, such as a USB hub to allow using the sole host port for more than just the LTE modem.
NAND to Tetris has nothing on you! When you need a chip, do you go to the beach for the raw materials? 
I suspect the real problem here is that the memo about the fail-fast product to market philosophy that companies are now using hasn’t reached the users who aren’t aware that features are included that may not work until they (we) have tested it and move it out of beta (if we are lucky, sometimes we move it out of alpha). It’s not unusual for me to include a button I think should be on a device to see if anyone needs it and then wait for them to press it and tell me that it didn’t work. Most of the buttons don’t get pressed.
No, I buy the same parts but shuffle them around until they are connected in the right order… for example putting in the missing USB hub. I didn’t even bother routing the SoC to the DDR, that’s a submodule, as of course are the concentrator and the LTE.
It’s not about doing everything yourself, it’s about re-doing the things that need fixing.
That I can agree with, but iterating by buying successive generations of boxes can be costly. And frequent change in offerings is bad for fleet deployment, too.
Or won’t work at all… often the big problem is software written by people who didn’t start from a clear vision of what it needed to do in the overall system context. That and features invented by a marketing department similarly lacking contextual awareness.
There’s a big difference between room for future expansion where the user/customer/client/licensee has the engineering materials to run with these ideas and turn them into something workable, vs. where they’d have to tear substantial parts up and rebuild them from scratch to move forward.
I think if someone wants packet backup on a gateway, they need to validate how it’s going to fit in architecturally and then write their own software to do it. I personally prefer to have that as an entirely separate subsystem outside the packet forwarder and live backhaul and decoding path.
Given the price of memory / FRAM / Flash / grains of sand, I’d cache data on the device with my own over-arching mechanism to tell it that it’s OK to purge - or more likely as I’d anticipate having weeks worth of data stored, just FIFO it and have a re-send range mechanism so if there is a gap, send a message with the range of data to resend.
@ descartes Hi the time stamp in the RAK store and forward backup, is a time delta in micro secs between last packet sent and current. So you have to do a bit work on on your backend to re-hydrate correct time stamp after an backhall outage.
The issue for many of us who use cellular backhall as default, is to get over the flowing. But brings it’s own issues.
// Corp
IT: Gateway can’t be on corp lan/wan must be hidden (often in a ceiling void)
Cyber security: Gateway can Never be on lan/wan or only after 3 months of sec evaluation
// Medium sized enterprise:
You will have to talk to Dave, he’s real busy always got a lot on…
// Small biz
Ow my niece does the IT after school on Thursdays
However, even why you have a wired backhall I’ve encountered the following issues…
- Gateway stolen
- Power turned off at weekends
- Hairy arsed electricians pulling out power cables to gateways as it was needed for something else
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Had a client that would call to say the server was down around 5pm each day - turned out the cleaner was removing the note about not unplugging it …
So for all those situations where the gateway goes awol for what ever reason, my scheme of keeping data points on the device (subject to power & cost issues), seems like a plan.
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I’d say it’s not worth the trouble of duplicated administration, required for decryption. And above all: LoRaWAN being radio in a license-free spectrum, maybe one should not rely on the data to start with?
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Probably not. I suspect this is a confusion based on the free-running microsecond counter of the gateway concentrator chip, which is what the server uses to time downlink replies. It does not measure the time “since” a previous packet as that would break in the case of backhaul packet loss, it is merely a local counter stamp. And it’s the same thing a gateway normally sends when backhaul is live.
It does indeed take some doing to convert it into an actual time - you have to have a sample of both at at point in the same run of the same packet forwarder program, and enough sense of the time to know how many times it has rolled over. And if the concentrator / packet forwarder have been restarted, that breaks the meaning of the counter unless you have a record of the value right before the restart. Uplink frame counts may make as much sense.
But this is also why someone who really wants a packet backup on the gateway should probably write their own. Including an RTC time is quite simple (and yes, if you’re going to this trouble you want a battery backed RTC and not a situation where you only have time after you can connect to an NTP server).
If you’re really stuck, put an RTC in a node and have it announce the time (doesn’t have to be right, just and monotonic) and use that as a time standard to measure other nodes’ packets by.
Hi yes been using frame counts and appreciate the counter role overs but the free-running counter has been consistent enough in terms of delta T to give approximates which is all I’m after. In my case with the RAK it was part on evaluation they make the claim but don’t provide any details on how you would use the feature in a practical way. So one might say it’s a rather nebulous feature but it does point to GW manfs. considering the issue.
I’ve used Multiech AEP GWs with onboard LNS & App server where we can Store & Forward before posting to say AWS-IoT.
What does this refer to? As in, which post above?
Which part of my post? 
@cslorabox already explained why queueing is going to be a nightmare, and won’t work with the idea that the TTN public network can have multiple gateways that receive the uplinks, today or in the future. I just wanted to add that anyone trying to backup/decrypt on the gateway itself, rather than queueing/forwarding, will find that such is a nightmare too. (And, above all: one should expect missing packets anyway.)
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Hi everyone, I’m completely with @arjanvanb on this one. If higher resilience to outages is required then LoRaWAN needs to deploy using the standard distributed control systems architecture of the last 25 years:
- Full system stack at the edge; for LoRaWAN this would be a small cluster of gateways at the edge combined with dual micro LNS with applications and failover.
- Continuous asynchronous replication of data from the edge to the centre.
- Intelligence in the centre to handle fresh data differently from stale data.
- Intelligence in the centre to replicate identity data out to the edge.
A few lost packets because it’s raining hard is one thing, but having a framework that can store on node and re-send after someone has chopped through a comms cable and taken out a network for 36+ hours isn’t such a bad thing if it doesn’t cost much and is simple to manage.
If you are collecting data for a study, larger gaps in data can be irritating at best and ruin that data set at worst. But it’s not time critical, so this would be a useful example - although in some situations you could just go and get an SD card from the node.
If you are running something system critical, then that’s a totally different set of circumstances where it would be prudent to implement one or more additional channels to compliment LoRaWAN, transports such as GSM/LTE/4G, SigFox, NB-IOT or even Iridium. In that respect I’d have LoRaWAN for the monitoring data as notionally cost free transport but keep command & control to other channels, but still leave room for a downlink if the other channel(s) manage to go off line.