You may (I’m not completely sure as of now) get a notification if a server your client has previously subscribedPresence for leaves and then comes back online upon the server’s StartPresence(). However, you will not receive a notification from a server you have never issues SubscribePresence() for. It’s a race condition.
Thanks, Joey Morrow From: David Brody <[email protected]<mailto:[email protected]>> Date: Tuesday, December 12, 2017 at 3:20 PM To: Joseph L Morrow <[email protected]<mailto:[email protected]>> Cc: Gregg Reynolds <[email protected]<mailto:[email protected]>>, iotivity-dev <[email protected]<mailto:[email protected]>> Subject: Re: [dev] Multiple presence server/client on same network Ah, yes, " You will not get notified when a new server comes online.". But that would be true for each server that calls startPresence()? On Tue, Dec 12, 2017 at 3:16 PM, Morrow, Joseph L <[email protected]<mailto:[email protected]>> wrote: Hi David, Presence does not align with “Advertisement.” You will not get notified when a new server comes online. A way to achieve this is to implement a Resource Directory in your set-up. Assume every client observes the Resource Directory. As per my understand, Then every Server in your set-up should Post to the Resource Directory that it has come online. Then I believe every Client should be notified of the new Server posting itself into the resource directory. I have not worked with the Resource Directory directly before. This is how I understand it to work, however. Thanks, Joey Morrow From: David Brody <[email protected]<mailto:[email protected]>> Date: Tuesday, December 12, 2017 at 3:09 PM To: Joseph L Morrow <[email protected]<mailto:[email protected]>> Cc: Gregg Reynolds <[email protected]<mailto:[email protected]>>, iotivity-dev <[email protected]<mailto:[email protected]>> Subject: Re: [dev] Multiple presence server/client on same network Hey guys, thanks. I was able to fix my issue by setting it all to CT_IP_USE_V4. Joseph - thanks for the clarity on this. it does seem that presence is a bit more generic than resources since IoTivity only provides the hostAddress of the presence. Nothing about which resource, etc initiated it. You also note that: * IoTivity offers Discovery to check who’s all out there * IoTivity offers Presence to see when someone has left * IoTivity does NOT offer what I would term “Advertisement” to see when someone new has come. (You may be able to attain this functionality with a Resource Directory, however.) Does subscribing to Presence not align with "Advertisement"? It seems that subscribing to Presence will get notified whenever another device (a unique hostAddress) comes online. Is this not the right way of thinking about it? On Tue, Dec 12, 2017 at 2:38 PM, Morrow, Joseph L <[email protected]<mailto:[email protected]>> wrote: The OIC Spec referred to IoTivity’s Presence feature as “Advertisement.” Please do not mix up OIC’s use of the word “Advertisement” with my use of it at the bottom of my email response below. Thanks, Joey Morrow From: Joseph L Morrow <[email protected]<mailto:[email protected]>> Date: Tuesday, December 12, 2017 at 2:37 PM To: Gregg Reynolds <[email protected]<mailto:[email protected]>>, David Brody <[email protected]<mailto:[email protected]>> Cc: iotivity-dev <[email protected]<mailto:[email protected]>> Subject: Re: [dev] Multiple presence server/client on same network Hi Gregg, The OIC spec used to have “Advertisement” specified. But in push to move OCF and get a spec out, advertisement was removed. At the time, I recall someone stated the intention was to bring it back immediately after OCF 1.0. As you can see it never did. I can give you some hints of what presence did at the time of implementation: * Presence functionality is re-using Observe functionality (code re-use). Except, it’s effectively an Observe-Get response to the “oic/ad” virtual resource. (This is specified in draft versions of OIC. Try checking 0.9 or prior.) * A Presence Notification goes out at Presence start, stop, some TTL, and every time an Observe Notification occurs. (Every time you invoke Notify(), the IoTivity stack also invokes something akin to “PresenceNotifyAll().”) * Notifications for Presence do not contain any useful information about what has changed. The presence payload should contain a ResourceType if the Presence Notification was caused by an ObserveNotification. * Presence also implements a TTL feature. If not set by server application when invoking “StartPresence(int secs = 60)”, then at 50% (and maybe 70%, 80%, 95%, 100%) of 60 seconds, a new Presence Notification will go out unicast to each presence observers. Note “Presence Observers” are called “subscribers.” The client side API offers “SubscribePresence().” If I may add, IoTivity offers Discovery to check who’s all out there. IoTivity offers Presence to see when someone has left. IoTivity does NOT offer what I would term “Advertisement” to see when someone new has come. (You may be able to attain this functionality with a Resource Directory, however.) Thanks, Joey Morrow From: <[email protected]<mailto:[email protected]>> on behalf of Gregg Reynolds <[email protected]<mailto:[email protected]>> Date: Tuesday, December 12, 2017 at 2:19 PM To: David Brody <[email protected]<mailto:[email protected]>> Cc: iotivity-dev <[email protected]<mailto:[email protected]>> Subject: Re: [dev] Multiple presence server/client on same network On Dec 12, 2017 10:03 AM, "David Brody" <[email protected]<mailto:[email protected]>> wrote: .. Any help or clarity would be GREATLY appreciated. The documentation on this is very limited and I've dug into the code a bit too far with no luck. Sorry I cannot help, but if you don't mind I'll piggyback here and ask if somebody can explain "presence". It is not in the OCF specs. What is in the specs is advertising discovery, but the text is indecipherable, to me at least. "Resource to enable discovery" gets my vote as the most impenetrable (and inane) phrase ever written in a tech spec. Have read the spec 123 times, still have no idea what it means. -g
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