hnical specifications and technical reports including evolved radio access technologies (e.g., General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)). Notification: The ISC interface shall be able support subscription to event notifications between the application server and S-CSCF to allow the appli- cation server to be notified of the implicit registered public user identities, registration state and user end capabilities and characteristics in terms of SIP user agent capabilities and characteristics. The SIP-event notification mechanism allows a SIP entity to request noti- fication from remote nodes indicating that certain standardized events have occurred. Examples of such of events are changes in presence states, changes in registration states, changes in subscription authorization policies (see [6]) and other events that are caused by information changes in application servers or S-CSCF. It shall be possible to either fetch relevant information once or monitor changes over a defined time. It shall be possible for a user to subscribe to events related to his/her own subscription (e.g., when the user subscribes to his own registration state) or to events related to other users' subscrip- tions (an example is when a watcher subscribes to presence information of a presentity, see [6]). Group Services and Presence Service in 3GPP: [6] The presence service provides the ability for the home network to manage presence information of a user's device, service or service media even whilst roaming. A user's presence information may be obtained through input from C 2009 by Taylor & Francis Group, LLC SIP Event Notification and Presence Information Presence suppliers Watcher applications Presence external agent Presence (presence information provided list server by elements outside the provider's network) Watcher presence proxy Presence user agent (presence information provided by the user) Presentity presence proxy Presence network agent (presence (HLR) information proveded by the network)