Multimedia conferencing services support real-time communications among users at multiple (usually more than three) locations. The communications use a combination of various types of media such as voice, video, text, graphics, and still pictures. Following is a list of common forms of multimedia conferencing services:
§ Audio-graphic conference. Adds nonvideo data exchange to a normal audio conference. Participants of the conference can, for example, view the same presentation slide as the presenter during his or her presentation.
§ Video conference. Uses video and voice for communications for a virtual face-to-face meeting.
§ Data collaboration. Allows the participants not only to share, but also to edit documents (like word processor files or spreadsheets) jointly.
Multimedia conferencing services can be provided over various types of networks. Figure 1 depicts a scenario where audio conferencing takes place over the PSTN while data conferencing takes place over the Internet. Naturally, the conference participants need both voice access to the PSTN (via a telephone terminal) and data access to the Internet (via a PC). This access could be achieved in several ways:
§ With two POTS lines
§ With a modem that splits a POTS line into voice and data channels
§ With an ISDN line
§ With an xDSL line
§ With a cable or power line, or wireless or enterprise LAN connection for the Internet access
Figure 2 depicts another scenario where audio conferencing takes place over the PSTN as well as an IP network, while data and video conferencing take place over just the IP network.
Figure 2: Another multimedia conferencing scenario.
Regardless of network configuration, conference control and management (or operation) of the conference resources (like media and bandwidth) are important aspects of the multimedia conferencing services. Conference control provides the means for a conference to proceed in a certain order, as determined by a designated conference chairman. The chairman of the conference can give the floor to a conference participant to speak, or grant permission to a participant to transmit supporting media. A participant making a presentation naturally should be given the right to speak as well as transmit and control the visual information. The chairman may also mute a speaker, normally for quick intervention with an important message. The chairman may also organize a private subconference (or side conversation) meant to proceed undetected by the excluded participants.
In addition to the conference chairman, conference control also recognizes the role of the conference controller (both roles are often given to the same person, associated with one terminal). The conference controller can perform the following functions:
§ Add or drop a party (terminal)
§ Split the conference or merge a split conference
§ Extend or terminate the conference
For a video conference, the controller may also be able to change the composition of the video screen displaying images from various locations during the conference.
Conference functions are limited by the capabilities of the terminal equipment. Unlike the telephone sets, which have more or less standard capabilities, multimedia terminals are quite dissimilar. For example, one terminal may handle just audio; another terminal audio, video, and fax; and yet another may handle audio and video capabilities, but with inferior quality. The resource management aspect of multimedia conferencing services must accommodate the varying capabilities of different terminals. There are mechanisms for terminals to negotiate capabilities when joining the conference. These capabilities can be renegotiated while the conference is in progress. Following are three common ways to handle differences in terminal capabilities:
1. All terminals operate in the mode supported by the least capable terminal.
2. Each terminal operates in its own mode, rejecting or ignoring input beyond its capabilities.
3. Specialized conference equipment mediates communications so that each terminal receives and transmits only what it can handle. (This mediation may involve transcoding if the media formats supported by the terminals are incompatible.)
In addition to capability mediation, the conference equipment manages resources by performing the following three actions:
1. Establishing, modifying, and releasing connections to the terminals.
2. Monitoring the activities over each connection and tracking the status of each terminal.
3. Handling media streams received and sent through each connection; switching, distributing, multiplexing, and mixing them as necessary.
Note that conferencing service requirements have been studied by the industry for several years and have been standardized by ITU-T. For more details on the generic multimedia conferencing service and features, consult ITU-T Recommendations F.700 and F.702. Collaborative conferencing is an application that can be further subdivided into broad categories in which the same features are used for different ends. Categories include executive meetings (the model for the introduction and discussion of the major conferencing features), distance learning, and telemedicine.
With distance learning, university classrooms can be brought to corporate locations and even homes. It is less important for the professor to see his or her students than the other way around, so video broadcasting is a viable option for distance learning. As the student works, the professor can access and evaluate the assignment and provide feedback in real time. As a result, the student may actually receive more personal attention than a typical classroom student. Organizations that encourage employees to take distance learning classes save both tuition and commuting time.
Telemedicine also includes meetings of doctors and continuing education (required of physicians by law in many countries), but its more ingenious and often life-saving use is in remote diagnosis, consultation, and patient prescreening. With distance diagnosis, the services of the best physicians can be rendered to patients in the remote geographic areas where treatment is not readily available. The transmission of both static (still) images (e.g., X-rays, electrocardiograms, and biopsy images) and dynamic ones (e.g., ultrasound images or patients’ movements) is possible. In special cases where several variously located specialists must all examine a patient virtually, all features of collaborative conferences can be used. Special features include the ability for doctors to make comments unheard by the patient. The savings due to elimination of travel for both doctors and patients is obvious, but the chief advantage of telemedicine is that it can bring health care services of the highest quality to areas where they were previously unavailable.
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