While the Presence Server is a special SIP application server used
to manage service- and user-related presence information (e.g.
availability, status, situation), in the IPTV context our presence
server also holds valuable context information like the program currently
watched by a user or information about devices that are currently
available. This presence data builds the basis for stream transfer
between devices (video follows) and personalization services.

The Presence Server implementation follows the Open Mobile Alliance Presence Enabler specification and the SIP SIMPLE standards. It supports SIP based subscription and notification mechanisms for presence events, allows publishing presence information and interacts with the XDM Enabler to manage the data persistently.

The Resource List Server (RLS) functionality allows single presence subscriptions on a group of entities that results in an aggregated notification with the requested data. We have integrated this function because it helps saving bandwith which is especially useful in mobile scenarios.

As the presence data has to be protected to ensure privacy issues, the presence server supports an authentication mechanism based on the watcher information event package that allows a user grant presence information access permission to a watcher.

The XML Document Management (XDM) Enabler as specified by the Open
Mobile Alliance (OMA) is a key service enabler for Next Generation
Networks (NGN). It represents a NGN element that stores and manages
user and service related data using standardized interfaces (XCAP,
SIP) which provide an easy and flexible way to access and manipulate
stored data. The used data model is based on extensible XML schema
definitions that constitute the structure of managed XML documents.

In the context of the IPTV infrastructure the XDM Enabler developed
at the DAI-Labor represents a data management component for TV
program data, personalization profiles, and recording information.
To this end, the XDM Enabler was extended by IPTV specific
application usages providing IPTV service and user related data to
several entities like application servers and end devices.

For access and manipulation of managed XML documents the XCAP interface is used. XCAP is an HTTP based protocol that defines conventions “for mapping XML documents and document components into HTTP URIs, rules for how the modification of one resource affects another, data validation constraints, and authorization policies associated with access to those resources.“ [RFC 4825]. By these conventions the XCAP protocol provides CRUD (create, read, update, delete) functionalities on XML documents using the HTTP methods GET, PUT and DELETE with special XCAP URIs (Uniform Resource Identifier).