IMS Presence Resource List Subscription and Notification Flow
IP Multimedia Subsystem (IMS) provides a framework and building blocks for building advanced telecom services. One such service is network wide publication and subscription of presence information. Users can subscribe to presence information for their contacts. If the contact accepts their request, the subscriber will be registered for presence notification. Whenever the friend publishes presence information, the IMS presence framework will notify the subscribed users.
IMS presence information communication can put a lot of load on the network. One way to reduce this load is to predefine the list of friends and family. When you subscribe to the "friends and family" list, a Resource List Server (RLS) in the IMS subscribes to the individual subscribers (presentities) on your behalf. Once the RLS completes the registrations, it collates the individual presence status into a single NOTIFY message.