 service will define map- pings of those presence information elements onto the PIDF format. 5.6.2 Current Research and Standard of Presence Features That Have Been Developed for SIP PIDF is a very extensible format, and being based on XML allows the trivial addition of namespaces to the basic structure. The most important presence features of SIMPLE are provided by extensions to PIDF. Several of those are outlined below [12]: (1) CIPID [5]: CIPID, Contact Information in Presence Information Data Format is an extension to PIDF. CIPID adds multiple new optional elements for presenting contact information more diversely, such as <card> <display- name>, <homepage>, <icon>, <map> and <sound> CIPID's elements can be easily combined into a buddy list and it does not extend the formal way of presenting the list of tuples, or devices a presentity may have listed. (2) User Agent Capability [13]: User agent capability defines a mechanism for SIP user agents to transport their technical capabilities and characteristics to other user agents. User Agent Capabilities Extension (henceforth UACE) to PIDF introduces an extension that can convey SIP specific media feature tags. These tags contain information on what types of media in what way can a tuple handle. (3) RPID [14]: The rich presence information data format defines a large body of properties that can be included in a presence information entry. They define logical properties such as user mood and activity, as well as physical properties such as location and environment. This information is designed with mobile devices in mind, and provides very specific information about both the device and the user. (4) Partial Presence (PIDF-diff) [15]: Presence Information Data Format (PIDF) Extension for Partial Presence, or PIDF-diff, is an extension to PIDF. The problem with PIDF is that it demands full presence information with every single change or update in presence of an entity. This can cause conges- tion problems with mobile and other low-bandwidth and high latency devices.