Re: [IOT] An implementer's review of the IoT XEPs
Hello Florian Thanks for the mail, and thanks for sharing your experiences. I’ll try to answer your comments and questions, one at a time.
Now, one key issue that the XEPs try to solve is that a thing ? think of the light-bulb next to you ? can not decide on its own if another thing is his friend or not. So, if the thing receives a friendship request, it basically proxies the request to its provisioning server (PS), which will wait for an decision from the thing's owner. This process is described in the Provisioning XEP and is basically a proxy mechanism for XMPP subscription requests.
It’s called ”delegation of trust”: I.e. if the thing cannot make the decision it self, it can delegate the responsibility to one or more third parties (provisioning servers). How these reach a conclusion is not specified more than through example: To ask the owner. A learning mechanism is also mentioned, but not specified.
The concept of friendship is a fundamental building block of the IoT XEPs, yet it is nowhere formal specified what friendship actually is in terms of XMPP. The XEPs appear map friendship between things to subscription states between XMPP entities, but they do not specify if friendship is a symmetric relation or an asymmetric one. XMPP subscription states are asymmetric: Just because I'm subscribed to your presence, it doesn't mean that your are subscribed to mine. I believe that the IoT XEPs assume that an thing is a friend if both are subscribed to each others presence. But do we really want that?
The provisioning server keeps track of friendship relationsships. This is symmetric in the sense, that both can subscribe to the presence of the other, if they want to. They don’t need to. I’ve added a note to add a description, or definition of the friendship relationship, and how it relates to presence subscriptions.
While implementing we also discovered that the XEPs do not discuss an important protocol flow. One of the test scenarios I implemented in Smack consists of a provisioning server (PS), a thing, a owner and an XMPP entity trying to become a friend of the thing (the 'requestor'). The requestor sends a subscription request to the thing, in order to befriend the thing. Now the thing asks the PS whether or not the requestor is a friend and the PS will immediately return that the requestor is not a friend, because there was no decision from the owner yet. Here ends the story in the XEPs. In our scenario, the owner will eventually accept or reject the friendship request in the PS's web interface. But how does the requestor get notified about the owners decision? Possible XEP-0324 ? 3.2.4 ? but do we want the requestor to act on recommendations send from arbitrary JIDs? We also need to discuss this.
If no rules are defined, rejection is returned by default to the device, since immediate feedback is always assumed. It is also assumed the owner is notified of the action. But since the owner might respond to the action at a much later stage, that response is seen as a separate event. If the owner accepts the request, this event is informed asynchronously, as described in §3.2.4, as you mentioned.
My general impression is that the current IoT XEPs are to large and to complex. It reminds me of the XEP-0136 Messaging Archiving situation, where this big and complex XEP got not much traction because it is so heavyweight and hard to implement. And now we have XEP-0313 Message Archive Management, which is simple, covers most uses cases and is easy to extend, thus allowing the missing use cases to be added on top. We should think big, but write simple and modular XEPs.
And yet much smaller than pubsub, which to many seems to be one of the cornerstones of XMPP. They are modular, that’s why they’ve been separated into 322, 323, 324, 325, 326, 347.
The XEPs are written in style which possible assumes that examples are normative: Some sections consist mostly of figures and examples. The IoT XEPs need more normative texts.
More normative text, and less examples? Many claim the XEPs are too long. But as you say, most of the text consists of examples.
XEP-0323 - Data ===============
The data read scheme out should follow the scheme we re-introduced in XEP-0313: Message Archive Management: IQ-request ? data1 ? ? ? dataN ? IQ-result. This would allow to remove the 'done' attribute and this scheme is a little bit easier to implement. I going to repeat myself, because I said this in MAM thread years ago: I believe we always should use this very scheme when requesting data which we expect to be delivered by multiple stanzas.
Are you suggesting that using data-forms would be “easier” for transporting sensor data? And that constant polling to extract asynchronously retrieved data would be simpler? I cannot see that that would be easier using any objective standard. It also presupposes knowledge about the amount of data to be retrieved, something that might now be known at the onset of the readout.
Timestamp is not using XEP-0082: XMPP Date and Time Profiles.
Time zones are described in §6.1.
Why does it not re-use XSD data types? (SenML [2] also seems like a potential candidate. Haven had time to look into it though.)
What XSD data types are you referring to? The field types available are based on the XSD data types. Regarding SenML: I responded to that comment in a previous mail. As it presupposes knowledge about the data being transmitted, it is not a suitable candidate for interoperable interfaces. It works for simple transport of data, if you control all end-points, or if end-points can be adapted to specific hardware. I meant to present the design principles behind XEP-0323 using the following presentation, at the last IoT SIG meeting: https://www.slideshare.net/peterwaher/xmpp-iot-sensor-data-xep0323
The 32/64-bit integer types: Are they signed or unsigned? I shouldn't be required to look in ? 10. XML Schema to find that out.
Noted. Will update that.
Example 7 shows an IQ send to a bare JID. This is likely meant to be an IQ addressed to a full JID.
I’ve put in the TODO list to update JIDs in examples.
It's unclear if things without a node are allowed.
How do you mean? You mean in the request, response or data format? I’ve made a note do add some clarifying text regarding this, for devices that do not embed nodes.
XEP-0324 - Provisioning ====================
? 3.1.1 "?if the provisioning server is not available in the roster of the device?" This falsely mixes the existence of an roster entry with presence subscription. But the XMPP Roster and Presence Subscription are two (mostly) orthogonal concepts. You can have a presence subscription established without a related roster item, and you can have a roster item without being subscribed.
I agree on the second, but not the first statement. RFC 6121 §2.5.2. clearly states that removing a roster item automatically unsubscribes to any presence. Still, added a note, since I believe the text can be updated to avoid confusion.
? 3.2.2 "Any resource information in the JID must be ignored by the provisioning server." Some XEPs of the IoT XEPs go with a different approach of explicitly disallowing the JID value to be a JID with resourcepart. I suggest consistency and I would favor the approach of explicitly forbidding the JID to contain a resourcepart instead of ignoring the resourcepart.
First, it seems to be Note 2, §3.2.1. But, it seems to be a misunderstanding. What is meant is that rules, in the provisioning server, must be based on the bare JID, not the full JID, of the device. The resource part is assumed to be a random value that can change over time.
? 3.2.4 "isFriend(jid) optional, for security" There is no gain in security if the Device asks the provisioning server if it really should add the JID as friend. If an attacker is able to spoof messages with a 'from' JID of the provisioning server, then he is very likely also able to spoof IQ replies too.
Very likely is not the same as guaranteed.
? 3.5.1 Example 20 uses a bare JID for IQ. Also why isn't the response just an empty IQ result?
I’ve made a note to update JIDs in examples. I’ve also made a note to update the clear cache result, as you suggest.
XEP-0325 - Control =================
Why should we us this instead of XEP-0050: Ad-Hoc Commands? I've seen people controlling their 2015 home automation system (Homematic) with an very old Psi version using XEP-0050. Ad-Hoc Commands and Data Forms are a key strength of XMPP.
There are several reasons. While having access to ad-hoc commands and data forms might be a strength, if you use a full-stack XMPP implementation, it’s not, if you have a light weight implementation, something which is expected, especially within IoT. So, the simplest use cases do not use data forms at all. It’s also possible to map control parameters and sensor data. Another reason is the possibility to execute commands on multiple nodes at the same time, as well as executing multiple control commands in the same request, as well as the added semantics available for interoperability.
? 3.2.2/3: The 32/64-bit integer types: Are they signed or unsigned? I shouldn't be required to look in ? 10. XML Schema to find that out.
Noted.
? 3.1.2: Can we have an empty result IQ instead of an empty <setResponse/> result?
Yes. I’ll write that on the TODO-list for XEP-0325.
? 3.1.2 and ? 6.2: Why put 'xml:lang' in <set/> instead of simply in <iq/>?
If it’s better that it be placed on the iq element, then we can move it there. By setting it on the set element, I just wanted to make sure the attributed was passed on to the specific handler, regardless of underlying implementation.
XEP-0347 - Discovery ====================
? 3.9: Claiming a thing: Why are 5 values required to claim a thing, when a tuple of ID and Key would be sufficient and provide the same security guarantees? Do we really want the user to enter 5 strings, every one adding another error source, in order to claim a thing? Or is it up to the registry/thing/whatever to decide what is sufficient to claim a thing? Claiming should be as simple as possible. I've claimed over a hundert devices in the past months and was always annoyed that I had to enter 5 values.
It’s up to the manufacturer to decide, what is required. And you should not have to enter anything. Instead, another transport method of the conceptual information from device/manufacturer to owner is suggested. The XEP mentions the use of QR-codes, for instance. The point here, is that the number of parameters used in the claim is variable, and defined by the manufacturer. All the XEP does, is require the owner to specify the same set of parameters, in the claim. Note: While from a device perspective, it might be sufficient with the KEY to perform the claim, human users are not good at identifying devices using such information. If a human is claiming multiple devices, one way to inform the user what device is actually being claimed, is by presenting humanly understandable information at the same time, together with the machine understandable information. Depending on situation, it is therefore very possible, that the manufacturer wants to add such conceptual information to the claim, to make sure the owner understands what device is being claimed.
Example 13 is missing 'cacheId'.
You mean cacheType? nodeId, sourceId and cacheType, are all optional, and provide 3 additional axes of identification of nodes behind a concentrator. More about these in XEP-0326.
<claimed/> has two semantic: success response to <mine/> *and* claimed notification to thing. I suggest using two different elements.
Ok. I’ll write this on the TODO list.
Example 46 and 47: When to use a full JID and when to use a bare JID as value of 'jid' in <disown/>?
Example 47 contains an error. Full JIDs are only used in the stanzas, for addressing. Rules and logic are based on bare JIDs. So, the jid attribute in Example 47 should be a bare JID.
? 5.2 Meta Tags: Why is 'V' (Version Number) of type 'numeric'? Is it supposed to be an integer, or a version string like "1.2.3-beta4"?
It’s numeric, to allow for numeric comparison. You might want to do a search for specific devices reporting a version larger than 8 for instance. You would want such a search to contain devices of version 10. Having it as a number, allows for only one decimal separator (major.minor). If (release.build) is also desired, or other information, such as beta, etc., you can always report those using other tag names. No such tag names have been specified however. Best regards, Peter
On 14.11.2016 10:03, Peter Waher wrote:
The concept of friendship is a fundamental building block of the IoT XEPs, yet it is nowhere formal specified what friendship actually is in terms of XMPP. The XEPs appear map friendship between things to subscription states between XMPP entities, but they do not specify if friendship is a symmetric relation or an asymmetric one. XMPP subscription states are asymmetric: Just because I'm subscribed to your presence, it doesn't mean that your are subscribed to mine. I believe that the IoT XEPs assume that an thing is a friend if both are subscribed to each others presence. But do we really want that?
The provisioning server keeps track of friendship relationsships. This is symmetric in the sense, that both can subscribe to the presence of the other, if they want to. They don’t need to.
I’ve added a note to add a description, or definition of the friendship relationship, and how it relates to presence subscriptions.
The question still remains: Do the XEPs envision friendship to be defined as a full presence subscription between the two involved entities. Which I think would very problematic because unsolicited presence stanzas should be avoided (and have caused a lot of trouble in XMPP's past). Usually a thing is not interested in the presence status of its friends, Therefore I suggest to define friendship as follows: "E is a friend of T, iff E is subscribed to T's presence" (where E is an entity, and T is a thing). Note that this does not disallow T to subscribe to E's presence. It is just not required for E to be a friend of T.
While implementing we also discovered that the XEPs do not discuss an important protocol flow. One of the test scenarios I implemented in Smack consists of a provisioning server (PS), a thing, a owner and an XMPP entity trying to become a friend of the thing (the 'requestor'). The requestor sends a subscription request to the thing, in order to befriend the thing. Now the thing asks the PS whether or not the requestor is a friend and the PS will immediately return that the requestor is not a friend, because there was no decision from the owner yet. Here ends the story in the XEPs. In our scenario, the owner will eventually accept or reject the friendship request in the PS's web interface. But how does the requestor get notified about the owners decision? Possible XEP-0324 ? 3.2.4 ? but do we want the requestor to act on recommendations send from arbitrary JIDs? We also need to discuss this.
If no rules are defined, rejection is returned by default to the device, since immediate feedback is always assumed. It is also assumed the owner is notified of the action. But since the owner might respond to the action at a much later stage, that response is seen as a separate event. If the owner accepts the request, this event is informed asynchronously, as described in §3.2.4, as you mentioned.
The XEPs should explicit mention that friendship recommendations are used by the provisioning server (PS) to deliver the owners decision to the thing. And how do you envision the requestor (R) to be notified? I've implemented it in Smack so that the thing forwards the friendship recommendation to R. Because I don't want R to act on friendship recommendations send from the PS, as it's not clear for R which PS is authoritative. But even with this unspecified mechanism, I need nine stanzas to complete friendship and a cache of the last pending friendship requests in R. My suggestion would be to have PS sending a friendship-decision-pending response to T, on which T simply does nothing. This reduces the required stanzas to complete friendship to six and removes the client from the burden to keep track of pending friendship requests. Please note that this and the previous point (definition of friendship) are two of my main concerns about the current XEPs that I'd like to address first. I'd like to use the upcoming Summit (and SIG meetings) to discuss them.
My general impression is that the current IoT XEPs are to large and to complex. It reminds me of the XEP-0136 Messaging Archiving situation, where this big and complex XEP got not much traction because it is so heavyweight and hard to implement. And now we have XEP-0313 Message Archive Management, which is simple, covers most uses cases and is easy to extend, thus allowing the missing use cases to be added on top. We should think big, but write simple and modular XEPs.
And yet much smaller than pubsub, which to many seems to be one of the cornerstones of XMPP.
True, but there are efforts to split PubSub into smaller XEPs.
The XEPs are written in style which possible assumes that examples are normative: Some sections consist mostly of figures and examples. The IoT XEPs need more normative texts.
More normative text, and less examples? Many claim the XEPs are too long. But as you say, most of the text consists of examples.
The XEPs are very long, which makes it very hard to digest. I think from the ones I've looked at (Discovery, Provisioning, Data, Control), half of what is written in there could be moved into an add-on XEP containing the advanced features. The other half would then be a minimal baseline profile which would make it easy to get started with, solve probably 80% of the use cases and gave implementers a quicker "success" experience.
The data read scheme out should follow the scheme we re-introduced i XEP-0313: Message Archive Management: IQ-request ? data1 ? ? ? dataN ? IQ-result. This would allow to remove the 'done' attribute and this scheme is a little bit easier to implement. I going to repeat myself, because I said this in MAM thread years ago: I believe we always should use this very scheme when requesting data which we expect to be delivered by multiple stanzas.
Are you suggesting that using data-forms would be “easier” for transporting sensor data?
No.
And that constant polling to extract asynchronously retrieved data would be simpler?
No. I was trying to describe the ideal pattern/scheme in XMPP used to retrieve N data, where every datum is packed in a single stanza: The requester sends the IQ-request, on which the sender starts sending data1 to dataN in message stanzas, and after sending dataN, the IQ-result is send. This pattern is also used in MAM. Currently the data xep does: IQ-request → IQ-result → data1 → … → dataN-withFin
It also presupposes knowledge about the amount of data to be retrieved,
No it does not.
Timestamp is not using XEP-0082: XMPP Date and Time Profiles.
Time zones are described in §6.1.
Ok, but why not simply re-use XEP-0082 as existing building block? Now I have to implement yet another data/time parser for XEP-0323 just because it varies slightly from a widely established XEP.
Why does it not re-use XSD data types? (SenML [2] also seems like a potential candidate. Haven had time to look into it though.)
What XSD data types are you referring to?
https://www.w3.org/2001/XMLSchema-datatypes Have a look at XEP-0122's 'datatype' attribute. Ideally the IoT Data XEP would re-use the same attribute and its definition.
XEP-0324 - Provisioning ====================
3.1.1 "if the provisioning server is not available in the roster of the device?" This falsely mixes the existence of an roster entry with presence subscription. But the XMPP Roster and Presence Subscription are two (mostly) orthogonal concepts. You can have a presence subscription established without a related roster item, and you can have a roster item without being subscribed.
I agree on the second, but not the first statement. RFC 6121 §2.5.2. clearly states that removing a roster item automatically unsubscribes to any presence.
But unsubscribing does not remove the roster entry. But yes, there are some points where roster and presence interact. Never the less the sentence should be "if the device is not subscribed to the provisioning server, then the device should send a subscription request"
3.2.2 "Any resource information in the JID must be ignored by the provisioning server." Some XEPs of the IoT XEPs go with a different approach of explicitly disallowing the JID value to be a JID with resourcepart. I suggest consistency and I would favor the approach of explicitly forbidding the JID to contain a resourcepart instead of ignoring the resourcepart.
First, it seems to be Note 2, §3.2.1. But, it seems to be a misunderstanding. What is meant is that rules, in the provisioning server, must be based on the bare JID, not the full JID, of the device.
Ahh, ok.
The resource part is assumed to be a random value that can change over time.
That's a good design approach I support! I suggest to make it clear that a thing is defined by it's bare JID, and never by its full JID, or in other words, there can never be two or more things with the same bare JID.
3.2.4 "isFriend(jid) optional, for security" There is no gain in security if the Device asks the provisioning server if it really should add the JID as friend. If an attacker is able to spoof messages with a 'from' JID of the provisioning server, then he is very likely also able to spoof IQ replies too.
Very likely is not the same as guaranteed.
Possible, but everything breaks down if you assume the possibility of spoofed XMPP addresses. It sure is possible if something is not configured correctly, especially considering a federation between multiple independent parties. But if you need absolute confidentially, then use crypto.
XEP-0325 - Control =================
Why should we us this instead of XEP-0050: Ad-Hoc Commands? I've seen people controlling their 2015 home automation system (Homematic) with an very old Psi version using XEP-0050. Ad-Hoc Commands and Data Forms are a key strength of XMPP.
There are several reasons. While having access to ad-hoc commands and data forms might be a strength, if you use a full-stack XMPP implementation, it’s not, if you have a light weight implementation, something which is expected, especially within IoT.
I wouldn't call XEP-0325 lightweight.
So, the simplest use cases do not use data forms at all.
Not sure about that. Smack has pretty good support for data forms. IoT control would have been easier to implement if I would have based it on data forms and not had to implement everything from scratch.
It’s also possible to map control parameters and sensor data.
And that's not possible with data forms? Especially if both data and control would be based on them?
Another reason is the possibility to execute commands on multiple nodes at the same time, as well as executing multiple control commands in the same request,
Ahh, now it gets interesting. First, please consider putting that rationale for not using data forms in XEP-0325. Otherwise be prepared to get asked that very same question over and over again. And secondly: Was it ever evaluated if data forms could be extended by that functionality (executing commands on multiple nodes, or multiple commands in the same request)? I could imagine that such a data forms add-on feature could be beneficial in other areas too.
as well as the added semantics available for interoperability.
Care to elaborate?
XEP-0347 - Discovery ====================
? 3.9: Claiming a thing: Why are 5 values required to claim a thing, when a tuple of ID and Key would be sufficient and provide the same security guarantees? Do we really want the user to enter 5 strings, every one adding another error source, in order to claim a thing? Or is it up to the registry/thing/whatever to decide what is sufficient to claim a thing? Claiming should be as simple as possible. I've claimed over a hundert devices in the past months and was always annoyed that I had to enter 5 values.
It’s up to the manufacturer to decide, what is required. And you should not have to enter anything. Instead, another transport method of the conceptual information from device/manufacturer to owner is suggested. The XEP mentions the use of QR-codes, for instance. The point here, is that the number of parameters used in the claim is variable, and defined by the manufacturer. All the XEP does, is require the owner to specify the same set of parameters, in the claim.
Then please make it clear in the XEP that the PS will require the potential-soon-to-be-owner to enter the exact same values used by the thing to register itself with the PS. But what if the thing wants to provide more metadata values (there a dozens different types already defined), but only have the owner enter one or two? I think the default on-boarding procedure could be much simplified by keeping the same security: Simply let the thing generate a secure token and have the owner present that token as proof of ownership. How the bytes of the token are transported and retrieved from the thing (QR code, via an app, …) can be decided by the manufacturer. (This reminds me a bit of the easy-onboarding efforts in XMPP: https://wiki.xmpp.org/web/Easy_Onboarding ) - Florian
Very interesting to read this thread. Perhaps cut it in separate threads? My effort on http://xmpp-iot.org was to create the easy low threshold examples of using the xeps. with the simple examples from 323 and 325. (should get a pubsub example up soon) Very few read the specs when they start up with a new technology they pull out some examples and starts to test. It's only when they have done the first level testing and starts to get advanced they go into the XEP's Written by Joachim Lindborg on a device running on solar energy from watt-s.com CTO, systems architect Sustainable Innovation SUST.se ,Tel +46 706-442270, linkedin <http://www.linkedin.com/in/joachimlindborg> Barnhusgatan 3 111 23 Stockholm 2017-01-08 20:07 GMT+01:00 Florian Schmaus <flo@geekplace.eu>:
On 14.11.2016 10:03, Peter Waher wrote:
The concept of friendship is a fundamental building block of the IoT XEPs, yet it is nowhere formal specified what friendship actually is in terms of XMPP. The XEPs appear map friendship between things to subscription states between XMPP entities, but they do not specify if friendship is a symmetric relation or an asymmetric one. XMPP subscription states are asymmetric: Just because I'm subscribed to your presence, it doesn't mean that your are subscribed to mine. I believe that the IoT XEPs assume that an thing is a friend if both are subscribed to each others presence. But do we really want that?
The provisioning server keeps track of friendship relationsships. This is symmetric in the sense, that both can subscribe to the presence of the other, if they want to. They don’t need to.
I’ve added a note to add a description, or definition of the friendship relationship, and how it relates to presence subscriptions.
The question still remains: Do the XEPs envision friendship to be defined as a full presence subscription between the two involved entities. Which I think would very problematic because unsolicited presence stanzas should be avoided (and have caused a lot of trouble in XMPP's past). Usually a thing is not interested in the presence status of its friends, Therefore I suggest to define friendship as follows:
"E is a friend of T, iff E is subscribed to T's presence" (where E is an entity, and T is a thing).
Note that this does not disallow T to subscribe to E's presence. It is just not required for E to be a friend of T.
While implementing we also discovered that the XEPs do not discuss an important protocol flow. One of the test scenarios I implemented in Smack consists of a provisioning server (PS), a thing, a owner and an XMPP entity trying to become a friend of the thing (the 'requestor'). The requestor sends a subscription request to the thing, in order to befriend the thing. Now the thing asks the PS whether or not the requestor is a friend and the PS will immediately return that the requestor is not a friend, because there was no decision from the owner yet. Here ends the story in the XEPs. In our scenario, the owner will eventually accept or reject the friendship request in the PS's web interface. But how does the requestor get notified about the owners decision? Possible XEP-0324 ? 3.2.4 ? but do we want the requestor to act on recommendations send from arbitrary JIDs? We also need to discuss this.
If no rules are defined, rejection is returned by default to the device, since immediate feedback is always assumed. It is also assumed the owner is notified of the action. But since the owner might respond to the action at a much later stage, that response is seen as a separate event. If the owner accepts the request, this event is informed asynchronously, as described in §3.2.4, as you mentioned.
The XEPs should explicit mention that friendship recommendations are used by the provisioning server (PS) to deliver the owners decision to the thing. And how do you envision the requestor (R) to be notified? I've implemented it in Smack so that the thing forwards the friendship recommendation to R. Because I don't want R to act on friendship recommendations send from the PS, as it's not clear for R which PS is authoritative.
But even with this unspecified mechanism, I need nine stanzas to complete friendship and a cache of the last pending friendship requests in R.
My suggestion would be to have PS sending a friendship-decision-pending response to T, on which T simply does nothing. This reduces the required stanzas to complete friendship to six and removes the client from the burden to keep track of pending friendship requests.
Please note that this and the previous point (definition of friendship) are two of my main concerns about the current XEPs that I'd like to address first. I'd like to use the upcoming Summit (and SIG meetings) to discuss them.
My general impression is that the current IoT XEPs are to large and to complex. It reminds me of the XEP-0136 Messaging Archiving situation, where this big and complex XEP got not much traction because it is so heavyweight and hard to implement. And now we have XEP-0313 Message Archive Management, which is simple, covers most uses cases and is easy to extend, thus allowing the missing use cases to be added on top. We should think big, but write simple and modular XEPs.
And yet much smaller than pubsub, which to many seems to be one of the cornerstones of XMPP.
True, but there are efforts to split PubSub into smaller XEPs.
The XEPs are written in style which possible assumes that examples are normative: Some sections consist mostly of figures and examples. The IoT XEPs need more normative texts.
More normative text, and less examples? Many claim the XEPs are too long. But as you say, most of the text consists of examples.
The XEPs are very long, which makes it very hard to digest. I think from the ones I've looked at (Discovery, Provisioning, Data, Control), half of what is written in there could be moved into an add-on XEP containing the advanced features. The other half would then be a minimal baseline profile which would make it easy to get started with, solve probably 80% of the use cases and gave implementers a quicker "success" experience.
The data read scheme out should follow the scheme we re-introduced i XEP-0313: Message Archive Management: IQ-request ? data1 ? ? ? dataN ? IQ-result. This would allow to remove the 'done' attribute and this scheme is a little bit easier to implement. I going to repeat myself, because I said this in MAM thread years ago: I believe we always should use this very scheme when requesting data which we expect to be delivered by multiple stanzas.
Are you suggesting that using data-forms would be “easier” for transporting sensor data?
No.
And that constant polling to extract asynchronously retrieved data would be simpler?
No.
I was trying to describe the ideal pattern/scheme in XMPP used to retrieve N data, where every datum is packed in a single stanza: The requester sends the IQ-request, on which the sender starts sending data1 to dataN in message stanzas, and after sending dataN, the IQ-result is send. This pattern is also used in MAM.
Currently the data xep does: IQ-request → IQ-result → data1 → … → dataN-withFin
It also presupposes knowledge about the amount of data to be retrieved,
No it does not.
Timestamp is not using XEP-0082: XMPP Date and Time Profiles.
Time zones are described in §6.1.
Ok, but why not simply re-use XEP-0082 as existing building block?
Now I have to implement yet another data/time parser for XEP-0323 just because it varies slightly from a widely established XEP.
Why does it not re-use XSD data types? (SenML [2] also seems like a potential candidate. Haven had time to look into it though.)
What XSD data types are you referring to?
https://www.w3.org/2001/XMLSchema-datatypes
Have a look at XEP-0122's 'datatype' attribute. Ideally the IoT Data XEP would re-use the same attribute and its definition.
XEP-0324 - Provisioning ====================
3.1.1 "if the provisioning server is not available in the roster of the device?" This falsely mixes the existence of an roster entry with presence subscription. But the XMPP Roster and Presence Subscription are two (mostly) orthogonal concepts. You can have a presence subscription established without a related roster item, and you can have a roster item without being subscribed.
I agree on the second, but not the first statement. RFC 6121 §2.5.2. clearly states that removing a roster item automatically unsubscribes to any presence.
But unsubscribing does not remove the roster entry. But yes, there are some points where roster and presence interact. Never the less the sentence should be
"if the device is not subscribed to the provisioning server, then the device should send a subscription request"
3.2.2 "Any resource information in the JID must be ignored by the provisioning server." Some XEPs of the IoT XEPs go with a different approach of explicitly disallowing the JID value to be a JID with resourcepart. I suggest consistency and I would favor the approach of explicitly forbidding the JID to contain a resourcepart instead of ignoring the resourcepart.
First, it seems to be Note 2, §3.2.1. But, it seems to be a misunderstanding. What is meant is that rules, in the provisioning server, must be based on the bare JID, not the full JID, of the device.
Ahh, ok.
The resource part is assumed to be a random value that can change over time.
That's a good design approach I support! I suggest to make it clear that a thing is defined by it's bare JID, and never by its full JID, or in other words, there can never be two or more things with the same bare JID.
3.2.4 "isFriend(jid) optional, for security" There is no gain in security if the Device asks the provisioning server if it really should add the JID as friend. If an attacker is able to spoof messages with a 'from' JID of the provisioning server, then he is very likely also able to spoof IQ replies too.
Very likely is not the same as guaranteed.
Possible, but everything breaks down if you assume the possibility of spoofed XMPP addresses.
It sure is possible if something is not configured correctly, especially considering a federation between multiple independent parties. But if you need absolute confidentially, then use crypto.
XEP-0325 - Control =================
Why should we us this instead of XEP-0050: Ad-Hoc Commands? I've seen people controlling their 2015 home automation system (Homematic) with an very old Psi version using XEP-0050. Ad-Hoc Commands and Data Forms are a key strength of XMPP.
There are several reasons. While having access to ad-hoc commands and data forms might be a strength, if you use a full-stack XMPP implementation, it’s not, if you have a light weight implementation, something which is expected, especially within IoT.
I wouldn't call XEP-0325 lightweight.
So, the simplest use cases do not use data forms at all.
Not sure about that. Smack has pretty good support for data forms. IoT control would have been easier to implement if I would have based it on data forms and not had to implement everything from scratch.
It’s also possible to map control parameters and sensor data.
And that's not possible with data forms? Especially if both data and control would be based on them?
Another reason is the possibility to execute commands on multiple nodes at the same time, as well as executing multiple control commands in the same request,
Ahh, now it gets interesting. First, please consider putting that rationale for not using data forms in XEP-0325. Otherwise be prepared to get asked that very same question over and over again.
And secondly: Was it ever evaluated if data forms could be extended by that functionality (executing commands on multiple nodes, or multiple commands in the same request)? I could imagine that such a data forms add-on feature could be beneficial in other areas too.
as well as the added semantics available for interoperability.
Care to elaborate?
XEP-0347 - Discovery ====================
? 3.9: Claiming a thing: Why are 5 values required to claim a thing, when a tuple of ID and Key would be sufficient and provide the same security guarantees? Do we really want the user to enter 5 strings, every one adding another error source, in order to claim a thing? Or is it up to the registry/thing/whatever to decide what is sufficient to claim a thing? Claiming should be as simple as possible. I've claimed over a hundert devices in the past months and was always annoyed that I had to enter 5 values.
It’s up to the manufacturer to decide, what is required. And you should not have to enter anything. Instead, another transport method of the conceptual information from device/manufacturer to owner is suggested. The XEP mentions the use of QR-codes, for instance. The point here, is that the number of parameters used in the claim is variable, and defined by the manufacturer. All the XEP does, is require the owner to specify the same set of parameters, in the claim.
Then please make it clear in the XEP that the PS will require the potential-soon-to-be-owner to enter the exact same values used by the thing to register itself with the PS. But what if the thing wants to provide more metadata values (there a dozens different types already defined), but only have the owner enter one or two?
I think the default on-boarding procedure could be much simplified by keeping the same security: Simply let the thing generate a secure token and have the owner present that token as proof of ownership. How the bytes of the token are transported and retrieved from the thing (QR code, via an app, …) can be decided by the manufacturer.
(This reminds me a bit of the easy-onboarding efforts in XMPP: https://wiki.xmpp.org/web/Easy_Onboarding )
- Florian
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Florian Schmaus -
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Peter Waher