The most basic concept of using XMPP is the notion of friends. To exchange data between two endpoints they need to be friends. The friendship is in reality to peers subscribing to one and eachothers precense1 updates.
The friending process starts with one end point asking another for a “precense subscription” Pidgin example The two enpoints can be in any domains email@example.com/resource_id makes a request to firstname.lastname@example.org/
The enpoint confirms the request so now we have a single sided subscription my-thing will recieve precense updates from your-thing. your-thing now sends a “precense subscription” back to my-thing which inturn confirms the request.
The two enpoints now have a dual subscription in talking to each other so they can now send read and write. The information is stored on the servers in the peer’s rosters2
new session the first thing you recieve is your roster, containing the state of al your friend relations.
##Having a Parent, Adding security
The usage of friendship is very good if you are a human that can take your own descisions. But if we are a temp sensor we must talk to a trusted friend to ask for permissions.
Every device can have a “best friend” or “parent” which is the trusted party that takes the descisions regarding the device possibilities to respond to friendship requests and access to specific fields.
Using this way of endpoint security creates endless possibilities with changing the ownership of devcices during first commissioning[^commission] It can even support the usecase of thirdparty delivering unnamed Things that you can buy in any store and then transfer them to be your own property
[^commission] The process when a Thing recieves it first configuration.
JID (jabber id): Every account in the XMPP network have an identity that looks like an email adress it is a uniqe identifier in the domain this is called the Jabber ID or JID.
Resource: For every login to a server a client will recive a Resource this id is used to distinguish between the different session. For example you being logged in to the same account from your ipad, phone, computer etc.
When working with Things it is seldom a Thing has several logins and resources but you should be aware of the possibility.