 Presence server (home network) BGPPAAA MSC server HSS/HLR S-CSCF server Interfaces Ph, Pi, Pc, Pg Pk and Pl are based on exisiting release 5 procedures e.g CAMEL, MAP, CAP, RADIUS, ISC, Cx, Sh The Pr, Pp interfaces are based on existing release 6 procedures of the 3GPP-WLAN interworking architecture. FIGURE 5.4 Reference architecture to support a presence service. the user, information supplied by network entities, or information supplied by elements external to the home network. Consumers of presence information (watchers) may be internal or external to the home network. It uses [1, 2], and [3] see Figure 5.4 below. The presence server shall be able to receive and manage presence infor- mation that is published by the presence user/network/external agents, and shall be responsible for composing the presence-related information for a cer- tain presentity from the information it receives from multiple sources into a single presence document. The presence list server stores grouped lists of watched presentities and ena- bles a watcher application to subscribe to the presence of multiple presentities using a single SUBSCRIBE transaction. The presence list server also stores and enables the management of filters associated to presentities in the presence list. The presence list server shall attach an associated filter to each individual SUBSCRIBE transaction. It is based on [7] For detail, please see the standard: [6] 5.6.1.2 OMA Presence Service OMA was formed in June 2002 by nearly 200 companies, including the world's leading mobile operators, device and network suppliers, information technology companies, and content and service providers. The fact that the whole value C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security chain represented in OMA marks a change in the way specifications for mobile services are done. Rather than keeping the traditional approach of organizing activities around "technology silos," with different standards and specifica- tions bodies representing di