Apparatus and method for presence service on inter-domain

Disclosed is an apparatus and method for presence service on inter-domain. The apparatus comprises an enhanced inter-domain presence (EIP) module and an enhanced inter-domain presentity/document module. When at least a watcher requests a presence subscription to a foreign domain, the EIP module dynamically collects the foreign-domain presentities for all local watchers having the subscription request, and produces a foreign domain document (FDD). The EIP module also acts as a presence client having the subscription to foreign-domain, and dispatches presence information. The enhanced inter-domain presentity/document module resolves the FDD contents, identifies the subscribed foreign-domain presentities, then obtains a corresponding presence authorization document and sends it to the presence server on the watcher domain.