Discussion: Reliable delivery


  • Mod

    @hek agreed. My change hard-codes the next hop to be 0 so in this particular case that's not a problem, but for a generic MySensor solution we need a better way. That's why we have no reliable way to send messages in a MySensors network. And it will likely stay that way for the foreseeable future, unfortunately 😞

    I'll do some reading and see if I can come up with something useful to discuss, to get the community started towards a mechanism for reliable delivery.

    EDIT: The original thread diverged into two discussions: one generic about reliable delivery and one about the specific case I was trying to solve. I have forked the topic and I think I managed to pull all relevant posts to this thread. Sorry for the inconvenience.


  • Mod

    @mfalkvidd I recently did some sniffing on a 1.5 network and experienced some ack-storms from the gateway. E.g. a client would send a single message, and the gateway would send all 15 ack's. The client did not get the ack (for whatever reason), and sends the message again. Gateway responds with 15 acks etc. etc. I experienced delays of many seconds because the node and gateway were chattering all the time. This tends to get funky with many nodes...

    Anyway, I thought it had to do with my setup (resend automatically when a message does not get ack'ed), but it would be interesting to see if others experience the same behavior.

    To get 'reliable' message delivery, we would need to buffer messages. At the nodes, repeaters and the gateway.
    I've been thinking about this for quite some time, because it's been at the top of my wish-list for ages.
    Still have to find the time to implement it...


  • Mod

    @Yveaux thanks for your input. Acks getting lost is something we'll have to handle. Exponential backoff is a method used in many protocols, so that might be a remedy. Some sort of book-keeping to determine which packet was ack'ed might be required as well.

    I don't think we necessarily need to buffer in all places though. It would be possible to only buffer at the sender node (which is what TCP does with a window size of 1 packet). We would then need an ack from the gateway (as opposed to an ack from the next hop), which means we can't use the hardware ack in the nrf radios.

    But as usual there are lots of compromises when selecting a design.

    There are lots of existing implementations of message control protocols. Some have had the benefit of large-scale deployment over a long time (like TCP). Some have been developed by research teams. Some have been designed especially for low-power nodes. I don't think we should invent something ourselves. Adopting an existing protocol (or a slight variant of it) should be possible.

    I would like to discuss the following:

    • Use cases. Real-world use cases are very helpful, both when discussing and explaining the design. I will try to collect use-cases that have already been discussed in the forum, but it would be great if everyone can post their use cases below.
    • Scope
      • What does reliable delivery mean? Does it mean at-most-once or at-least-once delivery?
      • To where is the delivery guaranteed (next hop, the destination node, the gateway, a controller, at least n controllers, etc)?
    • Who decides if reliable or best-effort message delivery is to be used? The internet protocol suite leaves the decision to the application (developer), which in our case might correspond to the sketch (developer).
    • Technical information
      • How much buffer space can we realistically assume will be available? Looking at how much ram the example sketches use might give a good clue to a reasonable default value for buffer size.
    • Do we develop something that is agnostic to the underlying communication protocol or do we utilize (or even require) features in the underlying protocol?
    • Which existing protocols would be useful to implement or adapt? - Anyone who knows of a protocol that be useful, please post below.

    imho, this is best discussed over a glass of beer/wine or two but I guess the forum will have to do 🙂


  • Mod

    @mfalkvidd said:

    It would be possible to only buffer at the sender node

    When communicating between sensor & gateway there are, IMHO, at least two sending nodes, as the messages from the gateway towards the sensor also have to be delivered reliably.

    which means we can't use the hardware ack in the nrf radios.

    No problem. I have the feeling it sometimes introduces more problems than it actually solves. Better have a good, portable (e.g. RFM69) implementation in MySensors, then something half-baked in hardware.

    Adopting an existing protocol (or a slight variant of it) should be possible.

    Totally agree!

    • Use cases

    Simple one in my case: assured delivery of a message from source to destination (whether it be gateway -> sensor or the other way around).

    • What does reliable delivery mean? Does it mean at-most-once or at-least-once delivery?

    I'd say exactly once. At most once is what we got now, at least once can hopefully be turned into exactly once quite easily.

    • To where is the delivery guaranteed (next hop, the destination node, the gateway, a controller, at least n controllers, etc)?

    Tricky one, but I'd say between the MySensors' network (excluding the controller as we don't have grip on it).

    • Who decides if reliable or best-effort message delivery is to be used? The internet protocol suite leaves the decision to the application (developer), which in our case might correspond to the sketch (developer).

    Currently, when sending messages, an ack is optional. This mechanism we can keep, or use e.g. compile-time selection.

    • How much buffer space can we realistically assume will be available? Looking at how much ram the example sketches use might give a good clue to a reasonable default value for buffer size.

    That seems like a good start. The size of the buffer could also be selected at compile time. For a simple sensor the amount of messages buffered can be limited, for a repeater or gateway in a large network the amount should be a lot bigger. This need not be a problem as these nodes can be based one of the supported platforms with more ram.

    • Do we develop something that is agnostic to the underlying communication protocol or do we utilize (or even require) features in the underlying protocol?

    No need to implemeng the complete OSI layering. I think we can implement reliable delivery with only a few fields added to the mysensors protocol.

    Which existing protocols would be useful to implement or adapt? - Anyone who knows of a protocol that be useful, please post below.

    And again, the RadioHead library pops into my mind 😉

    imho, this is best discussed over a glass of beer/wine or two but I guess the forum will have to do 🙂

    You're most welcome to come over -- beer's in the fridge, winecellar is open 👍


  • Mod

    It would be possible to only buffer at the sender node

    When communicating between sensor & gateway there are, IMHO, at least two sending nodes, as the messages from the gateway towards the sensor also have to be delivered reliably.

    Are there really two sending nodes? Or are there two messages, that each need to be delivered reliably, independent of each other? The latter case is tremendously easier to solve. TCP, for example, has independent acks for each direction (even though the acks can be piggybacked for higher efficiency but that's not the same thing).

    which means we can't use the hardware ack in the nrf radios.

    No problem. I have the feeling it sometimes introduces more problems than it actually solves. Better have a good, portable (e.g. RFM69) implementation in MySensors, then something half-baked in hardware.

    I agree. We will need to get this working over several different radio (or even wired) protocols anyway. And nothing would prevent adding protocol-dependent sub-layers later, if someone wants to.

    Simple one in my case: assured delivery of a message from source to destination (whether it be gateway -> sensor or the other way around).

    I would prefer something less generic. Generic is hard to discuss. What is a source? What is a destination? It is a good start though.

    • What does reliable delivery mean? Does it mean at-most-once or at-least-once delivery?

    I'd say exactly once. At most once is what we got now, at least once can hopefully be turned into exactly once quite easily.

    I'd be very happy if that is the case. More that half of the first page of search results on my google profile for the phrase "exactly once delivery" link to articles saying that it is not possible. But it would be awesome if it can be done.

    • To where is the delivery guaranteed (next hop, the destination node, the gateway, a controller, at least n controllers, etc)?

    Tricky one, but I'd say between the MySensors' network (excluding the controller as we don't have grip on it).

    I agree. MySensors takes responsibility up to and including the gateway. No less and no more. That's the way signing is handled (we don't require/support signing by the controller) and I think the same should apply to reliable delivery.

    • Who decides if reliable or best-effort message delivery is to be used? The internet protocol suite leaves the decision to the application (developer), which in our case might correspond to the sketch (developer).

    Currently, when sending messages, an ack is optional. This mechanism we can keep, or use e.g. compile-time selection.

    I agree. That means everyone can decide what they want when they write their sketch. Reliable delivery will have some consequences, and sometimes the sketch developer might prefer best-effort delivery so they don't need to deal with those consequences.

    • How much buffer space can we realistically assume will be available? Looking at how much ram the example sketches use might give a good clue to a reasonable default value for buffer size.

    That seems like a good start. The size of the buffer could also be selected at compile time. For a simple sensor the amount of messages buffered can be limited, for a repeater or gateway in a large network the amount should be a lot bigger. This need not be a problem as these nodes can be based one of the supported platforms with more ram.

    Compile-time (or even run-time?) could be great. I like the idea of recommending hardware with more memory for busy nodes/networks.

    Which existing protocols would be useful to implement or adapt? - Anyone who knows of a protocol that be useful, please post below.

    And again, the RadioHead library pops into my mind 😉

    Great. I'll check that out!

    imho, this is best discussed over a glass of beer/wine or two but I guess the forum will have to do 🙂

    You're most welcome to come over -- beer's in the fridge, winecellar is open 👍

    Very nice! I might take you up on that 🙂


  • Mod

    Alright. I have done some reading 🙂

    First, anyone interested in this discussion should probably read this thread where the protocol specification was discussed. Awesome work by @Yveaux @Zeph @ToSa @Damme and @hek !

    If there are any other references on the design decisions for the protocol, please let me know.

    Note: I use the term originating node in the text below. By that I mean a single MySensor node, a leaf node in the routing tree. (or the gateway if reliable messages are sent from the gateway to a MySensor node)

    After reading up on the radiohead rf library and a blog post about the protocol used for ulpnode, combined with my experience from the "internet" world, I realized one thing: There are two philosophies to reliable delivery, and we need to decide which one suits MySensors best.

    hop-to-hop acknowledgment
    As identified in the protocol thread, Radiohead uses a "hop-to-hop acknowledgment" philosophy. The way I see it (everyone is welcome to offer a different view on this) is that the world we live in when we want the "hop-to-hop acknowledgment" looks like this:

    • End nodes are considered extremely low power. They have little memory and/or need to conserve power
    • End nodes want to get rid of the responsibility of a message as soon as possible. Either because they want to go back to sleep, or because they don't have enough memory to buffer messages.

    This puts very high reliability requirements on all relay nodes. If the originating node has gotten an ack, the node that sent the ack is 100% responsible for making sure the message is delivered. Since the originating node might have gone back to sleep, there is no way to let the originating node know if something bad happens. So all relay nodes MUST be able to buffer a lot of messages, maybe not indefinitely but at least for a reasonable long time. The originating node wanted reliable delivery after all, so the relay node(s) really need to make sure the message is delivered. If the message wasn't important, the originating node would not have chosen the reliable delivery mechanism.

    end-to-end acknowledgment
    The most widely used protocol on Internet, TCP, uses a "end-to-end acknowledgment" philosophy. Routers (Internet's equivalent of MySensors' repeat nodes) can (and do) drop packets at any time. They are not responsible for buffering. In fact, buffering leads to worse performance in the network. The philosophy is that the originating node is the node that is most interested in getting the message delivered, and that node is also best equipped to make decisions on timeouts and re-transmission.

    This philosophy also assumes that originating nodes are likely to be less busy than repeat nodes. My come computer does a lot less packet sending than the central routers on the Internet. The originating node might only be having a single conversation, and keeping a single message in memory is no problem: the node needs to have that message in memory anyway to call the send function.

    .

    Does this make sense? If so, which of the philosophies are more suitable when implementing reliable delivery in MySensors?

    The current implementation is sort of "hop-to-hop acknowledgment". But MySensors does not offer high reliability on repeat nodes. As far as I understand, repeat nodes will not buffer and re-transmit messages, even though they have said "Don't worry little guy, I'll take care of this message and deliver it reliably" to the originating node. If the message fails later, the failure will not be detected.

    I don't mean to complain about the current implementation. There were probably lots of design choices that I am not aware of, and what we have is awesome. I just think that we can do better when it comes to reliable delivery.

    Sorry about the long post.


  • Admin

    Good summary @mfalkvidd.

    There is actually another looong thread that should give you more perspective/history here:
    http://forum.mysensors.org/topic/304/2-0-discussion-units-sensor-types-and-protocol
    It's not been realised.

    Just a note. The bool you're getting from send() was never meant to be used for detecting if a message was delivered to its final destination. It's merely exposes the "hardware" acking result from the NRF-module. So, it's an indication if the node is totally off the grid.


  • Mod

    Thanks @hek! Now I have something to read before I go to sleep tonight 🙂


  • Mod

    I have collected some real-world use cases and read the protocol design discussions in the forum. There is something I don't understand though:

    What is the difference between hardware and software ack, and difference between the ack in present/sendSketchInfo/send/sendBatteryLevel/, mSetRequestAck and isAck() in incoming messages.
    I have read these posts but I'm unable to figure out how the library is designed.
    http://forum.mysensors.org/topic/1163/can-anyone-shed-some-clarity-in-this-ack-business-hek/4
    http://forum.mysensors.org/topic/649/rc-from-send-and-how-to-identify-an-ack-message/7

    From @hek's response in the first thread, it looks like the library is designed to support BOTH end-to-end acknowledgment and hop-to-hop acknowledgment, but how to use that isn't very clear, at least not to me. Could anyone care to explain?


  • Admin

    Low-level: When a node wants end-to-end ack, it sets a bit in the message header "req ack". The node that receives this type of message, sends an ack-message with the "req ack" bit off and "is ack" bit on. Otherwise messages would create a endless loop.

    The "hardware ack" functionality is only used to detect if a node loses connection with it's closest neighbor.. and should start looking for a new parent.


  • Mod

    I think I'm most confused by this statement:

    @hek said

    It will first send the hardware ack and then the end-to-end software ack provided by the MySensors library.

    What is the end-to-end software ack? Was it never implemented?


  • Mod

    ok, let's see if I understand now. How much of this is correct?

    Hardware ack is what I get when using send(msg, true) and some other functions like present, sendSketchInfo and sendBatteryLevel

    • Hardware ack is hop-to-hop acknowledgment
    • Sending is a blocking function which returns true if an ack was received and false if ~70ms passed without receiving an hardware ack.
    • Sending ack is handled automatically by the library(/radio)
    • Receiving an ack is handled automatically by the library
    • Re-send needs to be handled manually in each sketch (a while-loop with a counter counting up to maxRetries and using wait() between each resend seems to be the most common solution)

    Software ack is what I get when setting msg.mSetRequestAck before sending the message (is this true? I'm unable to find any documentation on mSetRequestAck on http://www.mysensors.org/download/sensor_api_15)

    • Software ack is end-to-end acknowledgment
    • Sending is a non-blocking function (from the software ack perspective, using hardware ack together with software ack is allowed and in that case the rules for hardware ack applies to hardware ack but the call is not blocked until the software ack comes through)
    • Sending an ack needs to be handled manually in each sketch (by checking msg.mGetRequestAck in incomingMessage? I'm unable to find any documentation on mSetRequestAck on http://www.mysensors.org/download/sensor_api_15 )
    • Re-send needs to be handled manually in each sketch (setting up a timer might be a good solution)
    • Receiving an ack needs to be handled manually in each sketch (by checking msg.isAck() in incomingMessage and clearing the timer mentioned above)

  • Admin

    Nope,

    Hardware ack is always enabled in the MySensors library (except for broadcast messages).

    End-to-end ack is enabled with the true flag.


  • Mod

    But then end-to-end ack is horribly broken? Since the next hop node will respond with an ack even if it is a repeater?


  • Admin

    No, only the findal destination node will answer with a soft ack message.

    Note, the (soft) ack message has to be picked up by yourself in your incomingMessage function.


  • Admin

    You can look at the RelayWithButton example on how to use it.
    https://github.com/mysensors/Arduino/blob/development/libraries/MySensors/examples/RelayWithButtonActuator/RelayWithButtonActuator.ino

    Here the node sends a message with soft ack enabled when someone presses the button. It doesn't change the local (light) state until ack message is received.


  • Mod

    @hek said:

    No, only the findal destination node will answer with a soft ack message.

    Note, the (soft) ack message has to be picked up by yourself in your incomingMessage function.

    Thanks for explaining. Just checking if my understanding is correct:

    bool send(MyMessage &msg, bool ack);
    

    will return the result of the hardware ack, regardless if the second parameter is true or false?

    So my post above should have been like this:

    Hardware ack is always on

    • Hardware ack is hop-to-hop acknowledgment
    • Sending is a blocking function which returns true if an hardware ack was received, and false if ~70ms passed without receiving an hardware ack.
    • Sending hardware ack (when the message has reached the next-hop node) is handled automatically by the library(/radio)
    • Receiving an hardware ack is handled automatically by the library, by setting the return value from the send call mentioned above
    • Up to 15 tries are made automatically by the library. Further re-send needs to be handled manually in each sketch (a while-loop with a counter counting up to maxRetries and using wait() between each resend seems to be the most common solution)

    Software ack is what I get when using send(msg, true) (and is also supported by some other functions like present(), sendSketchInfo() and sendBatteryLevel()

    • Software ack is end-to-end acknowledgment
    • Sending is a non-blocking function
    • Sending ack (when the message has reached its final destination) is handled automatically by the library
    • Re-send needs to be handled manually in each sketch (setting up a timer when sending the original message might be a good solution)
    • Receiving an ack needs to be handled manually in each sketch (by checking msg.isAck() in incomingMessage and clearing the timer mentioned above)

  • Admin

    Yes! Looks correct!

    If you want to dig even deeper you can tune the hardware ack/message burst handled by the radio here:
    https://github.com/mysensors/Arduino/blob/development/libraries/MySensors/core/MyTransportNRF24.cpp#L59

    The radio sends a burst of maximum 15 messages (with a 5us interval) by itself unless it picks up a respond by the other node.


  • Mod

    Very cool! Thanks a lot @hek! Can't believe I have read several hundred forum posts about the protocol design and ack problems the last two weeks without realizing that what I needed was already included in the library.

    From the discussions I've read it looks like almost no-one else has understood either.

    Some ideas to help people understand how to use the built-in features for reliable delivery:

    1. Add an example that has a complete implementation of end-to-end ack usage. This includes
    • setting up timer(s) for re-sending
    • storing sent messages so they can be re-sent
    • determining which message was acked when an ack message is received (there might be several messages that haven't been acked yet)
    • removing acked message from the sent message store and clearing the timer(s)
    • re-sending when the timers expire
    1. Update the documentation for bool send(MyMessage &msg, bool ack); (and similar functions) to explain that the bool returned is the result of the next-hop ack.
    2. Rename the bool ack parameter to bool end-to-end-ack or something similar to make it clear(er) that there are two types of acks
    3. In the documentation for send() (and similar functions), refer to the example in (1) for information on how to use end-to-end ack.
    4. When the example in (1) is good enough, add some of the required code to the MySensors library so people don't need to copy-paste a lot of code into their sketches. Surround the code with ifdefs to make it optional.

    (2) and (3) should be quite easy to do. Can it be done with a pull request or how are documentation improvements handled?

    I'm willing to do 1 (will post the sketch in the forum for public scrutiny/feedback of course).

    4 can be done when the community think the example is "good enough"

    5 can wait until the example has been thoroughly vetted.


  • Admin

    Sounds like a plan.

    The code documentation could be solved with a PR as you say. But the main site isn't available on github (a messy thing) so I have to update that part when PR arrives/has been merged.


  • Mod

    ok. I can create the PR. From where can I clone the repo?


  • Mod

    After a quick chat with hek I now know that I should add code comments to the relevant functions in the code and he'll manually update the API documentation. I'll post a link to the PR when I'm done.



  • Seems like it is impossible now to distinguish for which message we have received acknowledgement. For example, when you just sent two identical messages. Message should contain message ID field (also called packet id or sequence id, unique for sending side) either in protocol headers (need to change protocol and break compatibility) or in user-defined message body (also breaks compatibility).


  • Mod

    @robosensor Yes it is impossible to distinguish between acks for two identical messages. But in which use case is that a problem?



  • @mfalkvidd for example, to know last actuator state.

    Imagine that you are sending three commands:

    1. ON
    2. OFF
    3. ON

    Then you receive two confirmations: ON and OFF. For which one ON ack is received? Is current actuator state after receiving two confirmations ON or OFF? How to determine which message (first or third) is lost and what you need to resend?


  • Mod

    @robosensor good example. As you said before, there is no way to solve that with the current protocol. However, the example can be made even simpler, it is enough to just send OFF then ON. In-order delivery is not guaranteed so you don't know which message was received last.



  • @mfalkvidd yes, I understand that this feature will break everything.

    Also, message id field can help to filter out duplicate messages on receiving side (due to message acknowledgement is not received by sending side) and can help to re-order incoming messages in right way using increasing message ids.

    Even more, sending acknowledgement with only numeric id instead of full message data can help to remove load from MCU (need to parse full message), from RAM (need to store full message), and from 'network' (both wired and wireless, data channel will be busy less time).


  • Mod

    @robosensor yes, I agree.


  • Mod

    I got ready to do a PR for this:

    1. Update the documentation for bool send(MyMessage &msg, bool ack); (and similar functions) to explain that the bool returned is the result of the next-hop ack.

    But the code for 1.5.4 already contains this:

    @return true Returns true if message reached the first stop on its way to destination.
    

    so the problem seems to be the that @return statements didn't make it to http://www.mysensors.org/download/sensor_api_15
    @hek: It seems like a PR won't help in this case?


  • Mod

    @mfalkvidd @return is doxygen formatting info, while the link points to documentation manually written. For 2.0 doxygen is on the agenda, and maybe the manual docs will be replaced by doxygen generated docs. Probably @hek has better insight on the subject.


  • Mod

    @Yveaux yes he has. As mentioned above hek said he would manually update the documentation after I had created a PR but it seems like a PR is not needed.


  • Admin

    It's already building, but only @Anticimex has been a good boy adding the correct doxygen comments to his code .
    http://ci.mysensors.org/job/MySensorsArduino/branch/development/Doxygen_HTML/



  • Has there been any progress on this guys?


  • Mod

    @Mark-Swift thanks for asking. Number 3 and 4 in this post were actually already in place in the code and documentation before this thread was started, but it seems like updating the site to reflect that is quite hard. I don't know how updating the site works unfortunately. The only advice I can give is "Don't look at the online documentation, dig through the source code instead".

    number 1 is blocked by me getting enough motivation to do the work required to get the development channel working without screwing up my existing projects. There are so many changes to folder locations and similar that I am unable to compile anything if I switch to the development version and I'm not looking forward to figuring out how to handle that.


  • Contest Winner

    @mfalkvidd said:

    Add an example that has a complete implementation of end-to-end ack usage. This includes
    setting up timer(s) for re-sending
    storing sent messages so they can be re-sent
    determining which message was acked when an ack message is received (there might be several messages that haven't been acked yet)
    removing acked message from the sent message store and clearing the timer(s)
    re-sending when the timers expire

    Are you referring to this number 1 post?

    Does this functionality need to be part of the bool send(MyMessage &msg, bool ack); function or become a layer over the send() function?

    Maybe i can have a look one of these days...


  • Mod

    @BartE I'm referring to the post that starts with "Very cool! Thanks a lot @hek!"



  • I'd love to see some examples of how we can implement a reliable delivery method into critical nodes, especially now 2.0.0 is out in the wild.



  • Any news on this, guys? Do we have some good examples?



  • @mfalkvidd I just came across this post and I am very supprised by the fact that this information is not written anywhere in the documentation ... I believe this is one of the most important stuff everyone should know to actually use MySensors in a real world application - not just diy/hobby project 😕 till now I was sure that return value of send funtion (which is NOT explained in the documentation !) is the end-to-end confirmation ...


  • Mod

    @rozpruwacz Yes. Unfortunately I can't do much more than agree with you 😞



  • I have to chime in and share my agreement. This seems like a fundamental piece of information, I mean, we all want reliable delivery right? For now I've copied a resend function I found on the forums (with some tweaks), but in my opinion, such code should at least me in the core - with the appropriate explanation.


  • Mod

    The new and still experimental, but quite extensive Doxygen documentation contains the documentation stuff that's available in the source code. For the return value of the send function, see https://ci.mysensors.org/job/Verifiers/job/MySensors/branch/development/Doxygen_HTML/group__MySensorsCoregrp.html#gadbea3e429757e7fbc66a54776590a2e8



  • @mfalkvidd said in Discussion: Reliable delivery:

    the return value of

    that is cool 🙂


  • Mod

    Keep us posted with your progress



  • Returns true if message reached the first stop on its way to destination

    What will be returned in the case of NRF24L01 as gateway's receiver at destination and internal nrf24 buffer is already contains 3 unread messages?


  • Mod

    @robosensor if the gateway is the first stop and the gateway does not acknowledge the message, false is returned.



  • Hi Guyz,

    I have been watching this wonderful forum for a while silently now and just started looking at few implementations myself. I am really surprised to know that so much work has been put in MySensors and this area is not given more attention and I second few opinions here that reliable delivery is one of the most important thing especially for actuators. I will try to do an example of end to end (node to gateway) reliable delivery as gateway to controller is pretty much reliable anyways. Meanwhile if anyone has any example already created, please do share over here.



  • Hi Guyz,
    Not sure if anyone is interested in this but I would like to share my thinking here.

    1. For reliable delivery, Only source and destination should be taking part, transport can do its best but as its can change we cannot expect it to behave precisely.
    2. For the sake of simplicity I am assuming all message to be Idempotent. (i.e if this is executed multiple times result will be same. say turn on a switch). I know about OFF ON OFF scenario but for most of our requirements and times involved, I would say that we can assume that when we are delivering one message other will not come. However if any actuator changes so frequently we should think about it.
    3. For Controller to to Actuator delivery, I am implementing a solution where actuator send its state back to controller on every change. When controller sends a command out to actuator it will wait for a second or two to see if the state is updated. If not it retries and it retries for a max number of times everyday which is getting logged to keep track of reliability in transport. This way if my max retry is not reached I can be sure that every message has reached actuator.
    4. For actuator to controller delivery I am planning to do similar where it sends until it returns true with a acknowledge requested and keep sending it until either ack has come or max retry has been reached. Also keeping track of attempts it had to make and send those as well reliably to controller for analysis. I know this will not ensure gateway to controller delivery but I will see how this one works and if needed will add that later. But not doing it now to avoid dependency of controller on my individual node.


  • @gahlawathome said in Discussion: Reliable delivery:

    When controller sends a

    Hi,

    ad. 1. Do You reffer to source and destination as a piece of code that uses MySensors lib ? If yes then I agree.
    ad. 2. I think that OFF ON OFF scenario is more related to user interfece that to actual message passing. I think that Your assumption is the basics of reliable delivery.
    ad. 3. I would divide this to: Controller -> GW than GW -> Acturator. Basically because communication GW -> Controller is much much more reliable and it simplifies a lot the implementation of the Controller. I would like to know how current implementation of mysesnors mqtt gateway handles this. For now I'm assuming that it does not request ack or if it does then it is not something very fancy (like try couple of times). So in my setyp (OH2) I do not update switches or slider automaticaly but i'm waiting for update from Actuator, if update arrives it changes state of the button, if not the button will not change and i know that (probably) the light didn't turned on. But this is no good for automatic rules, so I would like to be sure that this will be handled by the GW.
    ad. 4. Again I would divide this to Acturator -> GW and GW -> Controller.



  • @rozpruwacz Thanks for your response.

    1. No I meant source as system trying to send message (i.e. Controller for point 3) and destination (Actuator for point3). Transport means mqtt, ethernet gateway, repeater, radio, wires, cloud, ir or anything else in between to reach my destination.
    2. Thanks agreed.
    3. I get your point but home automation system being a small size (finite and few hundred meters) system we do not need to intelligent hops.The moment we introduce GW in picture, a. Gateway becomes intelligent and needs to store information, b. It will not know what to do if it cannot pass the information ultimately. For example lets say that my controller wants to turn actuator ON. It makes sure message reaches GW but the actuator is down at that time. After some time when GW has done everything to reach it needs to take corrective action (even more intelligent GW) and send a message back to controller telling about this but by this time controller might have already initiated some logic (still not fulfilled the purpose ) based on actuator turning on. Hence if we follow just Controller -> Actuator, GW can be dumb as a brick, our controller will only trigger further logic once it is sure that actuator is turned on. I completely agree with you if its a huge network (like internet) or turnaround time is very high.
      Now to answer your question Yes Controller to Gateway is very reliable and although I do not think it has any acknowledgement, I have never seen a failed message here in my setup.
      For Manual action as you mentioned I would know by switch but for automatic I am implementing a retry in rules which will try a finite number of times and keep a track of numbers as well for analysis. Once the tries are exhaused I can take corrective action right there.. e.g if it couldn't turn the boiler ON announce and alert people accordingly.
    4. I think lets first just discuss 3 and then we can come to 4.

 

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