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U. Glaeser

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Geographical area covered by wireless communication networks is partitioned into a set of cells. A<br />

routing path may be inefficient while a mobile host hands off to another cell coverage area. The connection<br />

paths need to be reestablished each time to continue communication. As a result, the network call processor<br />

can become involved many times during the lifetime of mobile connection. When wireless communications<br />

networks move toward smaller size cells to accommodate more mobile hosts or to provide higher<br />

capacity, the handoff becomes a more frequent part of communications. Conventional routing procedures<br />

for connecting mobile hosts fail due to frequent handoff when the network call processor becomes a<br />

bottleneck. Hence, routing efficiency in wireless communications networks depends critically on the<br />

propagation of location information into the network; however, excessive information propagation can<br />

waste network resources, while insufficient location information leads to inefficient routing.<br />

Wireless communications networks can provide different personal communications services, which<br />

have different transmission time delay requirements. For cellular telephone communication, the shortest<br />

time delay or strict time delay to transmit voice message is required. In portable computer communications<br />

or other data communications, the requirements of transmitted time delay are not very strict.<br />

Transmitted data can be stored in buffers and be transmitted later when channels are available; however,<br />

in order to provide a high QoS, transmission time delay is an important factor in wireless communications<br />

networks. Routing procedure in wireless communications networks should depend on different requirements<br />

of transmission time delay, and on how to balance transmission load and find minimum cost<br />

transmission paths.<br />

30.4 Applications Support<br />

Multimedia<br />

Multimedia communications is the field referring to the representation, storage, retrieval, and dissemination<br />

of machine-processable information expressed in multimedia, such as voice, image, text, graphics,<br />

and video. With high-capacity storage devices, powerful and yet economical computer workstations, and<br />

high-speed integrated services digital networks, providing a variety of multimedia communication services<br />

is becoming not only technically but also economically feasible. Multimedia conference systems can<br />

help people to interact with each other from their homes or offices while they work as teams by exchanging<br />

information in several media, such as voice, text, graphics, and video. Multimedia conference system<br />

allows a group of users to conduct a meeting in real time. The participants can jointly view and edit<br />

relevant multimedia information, including text, graphics, and still images distributed throughout the<br />

LAN. Participants can also communicate simultaneously by voice to discuss the information they are<br />

sharing. This multimedia conference system can be used in a wide variety of cooperative work environment,<br />

such as distributed software development, joint authoring, and group decision support.<br />

Multimedia is the integration of information that may be represented by several media types, such as<br />

audio, video, text, and still images. The diversity of media involved in a multimedia communication<br />

system impose strong requirements on the communication system. The media used in the multimedia<br />

communications can be classified into two categories: discrete media and continuous media.<br />

Discrete media are those media that have time-independent values, such as text, graphics, or numerical<br />

data, bit mapped images, geometric drawings, or any other non-time-dependent data format. Capture,<br />

storage, transmission, and display of non-real-time media data does not require that it happen at some<br />

predictable and fixed time or within some fixed time period.<br />

Continuous media data may include sound clips, video segments, animation, or timed events. Realtime<br />

data requires that any system that is recording or displaying be able to process the appropriate data<br />

within a predictable and specified time period. In addition, the display of real-time data may need to be<br />

synchronized with other data or some external (real-world ) event.<br />

Multimedia data can be accessed by the user either locally or remotely during multimedia communication.<br />

Locally stored data typically resides in conventional mass storage systems such as hard disk, CD-ROMs,<br />

optical disk, or high-density magnetic tape. It can also be stored to and recalled from analog devices that<br />

© 2002 by CRC Press LLC

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