T) [6] defined methods SUBSCRIBE, NOTIFY, and UNSUBSCRIBE, which have a similar semantic to SIP. A server can distinguish a PINT SUBSCRIBE request from a SIP SUBSCRIBE by the absence of an Event header field in the PINT request. A server should indicate which event packages it supports by listing them in an Allow-Events header field. If a SUBSCRIBE refresh is sent within a dialog but receives a 481 Dia- log Does Not Exist response, this means that the server has already ter- minated the subscription. The client should consider the dialog and subscription terminated and send a SUBSCRIBE to establish a new dialog and subscription. An event template package is a special type of package that can be applied to any other package including statistical, access policy, and subscrip- tion lists. The application of a template package to a package is shown by SIP Request Messages separating the package and template package names with a "." as in pres - ence. winfo, which is the application of the watcher info template package to the presence package. Table 4.8 lists the current set of SIP event and template packages. Table 4.9 lists the manatory header fields in a SUBSCRIBE request. Pack- ages are standardized in the SIPPING or SIMPLE WG based on the require- ments in [5]. 4.1.9 NOTIFY The NOTIFY method [5] is used by a user agent to convey information about the occurrence of a particular event. A NOTIFY is always sent within a dialog Table 4.8 Event Packages and Template Packages conference Conference information including participant lists, policy information, and SO forth [7] dialog Dialog state and identification information [8] message-summary Messages notification, used for message waiting indicator (mwi) with voicemail [9] presence Presence information [10] refer Refer state implicit subscription created by REFER [2] User registration state [11] winfo Watcher information template package [12] Table 4.9 Mandatory Header Fields for a SUBSCRIBE Call- ID Max-Forwards Contact Event Allow-Events SIP: Understanding the Sessi