[IOT] Feedback on pubsub for IoT

Peter Waher Peter.Waher at clayster.com
Wed Apr 29 14:44:00 UTC 2015


Hello Eelco.

Thanks for your responses. Some comments:

>> 2. There is currently no best practises in using pubsub or PEP for IoT.
>
>Perhaps it’s time to retake the XEP-writing effort and write down some guidelines for IoT on XMPP using pubsub…
>
>Perhaps it is. I would not mind participating.

Great! I have to retake this effort, as I mentioned. I’ll make sure to include you.

>> 4. I proposed an alternative pubsub like service, that I called ‘dealer’, which acts as a IoT concentrator towards the subscribers and that would subscribe to all Things the clients would want to receive events from.
>
>Ok, not sure I understand. Please tell me more. Would it be an entity that subscribes to data from multiple nodes, and then makes it accessible using XEP-326 to other interested parties?
>
>Something like that except I would use IoT events (https://xmpp.org/extensions/inbox/iot-events.html) and let the ‘dealer’ optimise the subscriptions towards the ‘Things’.
>
>In the dealer pattern the client applications, that want to subscribe to sensor data from the Things, instead subscribe to the dealer service. Once subscribed the clients receive the measurements from all the Things via the dealer.
>The dealer is responsible to subscribe to all the individual Things and when it receives new measurements it will instantly publish these measurement to clients that subscribed to the dealer.
Sounds interesting! This immediately creates several follow-up ideas. Since you base it on iot-events, it provides a unqie way of providing tailored information to subscribers, based on different security considerations.

The first idea is a slight modification of the approach: Instead of having the dealer subscribe to all nodes. This might require a lot of administrative communication, and also a lot of monitoring/supervision for make sure it recovers from different error states. An alternative is to make a component connection (XEP-0114) and publish the dealer as a pubsub server component on the xmpp server, replacing perhaps the “normal” pubsub server. In this way, the dealer would not need to maintain all subscriptions, instead, it would be the owner of the nodes itself. Perhaps the added effort here, is comparable or less than the effort needed to subscribe to all events from a pubsub server, that as you say, anyway might be lacking in some regards. The dealer could still use the iot-event subscription architecture, and so, there would not be a need to implement that part, since it doesn’t provide subscribers to request tailored sets of data.

The second idea, is a continuation of the above, but providing a “normal” pubsub subscription interface: Today, the pubsub pattern has a great weakness: It’s not possible to adapt contents based on rights for individual subscriptions. You need to publish different sets of content on different nodes, which quickly grows to infinity if you allow fine-grained control, as is the case for IoT. This not only becomes complicated, it also quickly removes any gains provided by pubsub, as the basic idea is to reduce the number of packets required for the publisher, to efficiently publish information to a larger set of subscribers. So, while one is creating a component for a new type of pubsub service above, you might build in a connection to a provisioning server (XEP-0324), or build in the same functionality in the same component, and use <canRead> to check what type of information is allowed for different subscribers implicitly, removing the need for a tailored subscription request, as well as a tailored publication, still tailoring output to each subscriber. That would lift the burden from the device, and provide a completely new type of service: Context sensitive, or individually tailored, publish/subscribe.

I have thought about implementing the second idea above, myself. I think such a component might have a very important role for the publish/subscribe pattern in XMPP, and solves many of the security issues in other pubsub solutions. Would you be interested in investigating this further?

A third idea, based on the second idea above is the following: Something that is missing from the XMPP pubsub model, but is available in MQTT, is multi-layered publish/subscribe. While implementing a new context-sensitive pubsub service, this might be something to add. In MQTT you can listen to a “parent node”, or wildcards, and receive events from all its (grand*)child nodes for example. Example: Consider you publish a temperature on node building/floor/apartment/room/temp1. How would you do to listen to all sensors in that room? Or all sensors in that apartment, floor or building? Or all temperature sensors in that building (leaving out other kinds of sensors)? Using a wildcard character (*) you could do this by subscribing to “building/floor/apartment/room/*”, “building/floor/apartment/*”, “building/floor/*”, “building/*” and “building/*/*/*/temp*” respectively in one go. That would provide a great way to subscribe to larger sets of contents, without having to maintain huge amounts of smaller individual subscriptions.

Best regards,
Peter Waher


Från: Cramer, E.R. (Eelco) [mailto:Eelco.Cramer at tno.nl]
Skickat: den 29 april 2015 11:10
Till: XMPP in the Internet of Things
Ämne: Re: [IOT] Feedback on pubsub for IoT

Hi Peter,

Thanks a lot for your comprehensive answer!

I agree with your view on MQTT but from discussion I’m having not a lot of organisations see federation as something that adds value and go for a short term win. You provide me with some good arguments against that :-)

> 2. There is currently no best practises in using pubsub or PEP for IoT.

Perhaps it’s time to retake the XEP-writing effort and write down some guidelines for IoT on XMPP using pubsub…

Perhaps it is. I would not mind participating.


> 3. Management of pubsub nodes (manage subscribers and publishers) is cumbersome and not all functions (authorization schemes) are supported by all XMPP servers.

Some kind of minimum supported server pubsub functionality might be necessary, together with a validation procedure. I know similar work is being done by UPnP to make sure XMPP servers support a minimum set of functionality required. Much of the administration might be taken care of if the server supports model “authorize” which allows node owners to approve or deny subscriptions. The owner can tie this into provisioning (XEP-0324) (canRead), for automated decisionmaking and a single interface for both momentary readouts and publish/subscribe.

That is sort of the approach I wanted to take for pubsub but did not link it to XEP-0324 yet. Thanks.


> 4. I proposed an alternative pubsub like service, that I called ‘dealer’, which acts as a IoT concentrator towards the subscribers and that would subscribe to all Things the clients would want to receive events from.

Ok, not sure I understand. Please tell me more. Would it be an entity that subscribes to data from multiple nodes, and then makes it accessible using XEP-326 to other interested parties?

Something like that except I would use IoT events (https://xmpp.org/extensions/inbox/iot-events.html) and let the ‘dealer’ optimise the subscriptions towards the ‘Things’.

In the dealer pattern the client applications, that want to subscribe to sensor data from the Things, instead subscribe to the dealer service. Once subscribed the clients receive the measurements from all the Things via the dealer.
The dealer is responsible to subscribe to all the individual Things and when it receives new measurements it will instantly publish these measurement to clients that subscribed to the dealer.
Best regards,
Eelco
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