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"Directory Services Middleware for Multimedia Conferencing" provides its audience with a good understanding of the theory and use of middleware for videoconferencing and voice over IP (VoIP). The focus is understanding the new ITU-T standard, ``H.350 : Directory Services Architecture for Multimedia Conferencing'' that describes a directory services architecture for multimedia conferencing using LDAP. This cookbook explains how a standardized LDAP schema called "commObject" (communications Object class) can be used to represent endpoints on the network and how to associate those endpoints with users. Design and implementation considerations for the interrelation of video and voice-specific directories, enterprise directories, call servers and endpoints are also discussed.
Directory services can provide searchable white pages, automated configuration of endpoints, association of persons with endpoints, user selection from multiple configuration choices, and user authentication based on authoritative data sources. These functions can result in reliable accounting and centralized endpoint management while improving the users' ability to locate and correctly dial other multimedia users. This cookbook also discusses design and implementation considerations for interrelating video-and-voice-specific directories, enterprise directories, call servers and endpoints.
A primary functional object class, called commObject, is used to represent attributes common to any video or voice protocol. The cookbook describes the formal LDAP object class definition and configuration files for commObject and its related protocol-specific auxiliary object classes h323Identity, sipIdentity, h320Identity, and genericIdentity. These classes can be used to represent h.323 endpoints, SIP user agents, h.320 endpoints, and users reachable via non-standard videoconferencing systems such as Access Grid and Virtual Rooms Videoconferencing System, respectively, in a directory.
The commObject class is an abstraction of a video or voice over IP device. The commObject class permits an endpoint (H.323 endpoint or SIP user agent or other protocol endpoint) and all their aliases to be represented by a single entry in a directory. Auxiliary classes can be used alongside commObject to represent specific protocols, such as h.323, h.235, or h.320. These additional classes are fully described in the ITU-T H.350.X series of Recommendations. Multiple H.350.X classes can be combined to represent endpoints that support more than one protocol. For example, endpoints that support H.323, H.235 and H.320 would include H.350, H.350.1, H.350.2, and H.350.3 in their LDAP representations.
Two basic attributes, commOwner (from the commObject class) and commURI (from the commURIObject class), are used to relate a person directory entry to protocol specific information about their video or voice over IP device and to also relate a device to its owner. The commURIObject class is a class whose only purpose is to link a person or resource to a commObject. By placing a commURI 'pointer' in a person's directory entry, that person becomes associated with the particular targeted commObject.
Similarly, commObject contains a pointer called commOwner that points to the person or resource owning or associated with the commObject. In this way, people or resources can be associated with endpoints and endpoints can be associated with the people who use them.
Many organizations and enterprises already have an authoritative directory listing people associated with the enterprise. To support H.350, the only change required in the enterprise directory is the addition of the simple object class commURIObject (a labeled URI). commObject data may be instantiated in the same or in entirely separate directories, thus allowing implementers flexibility in deploying the architecture.