15.01.2013 Views

U. Glaeser

U. Glaeser

U. Glaeser

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

are under the control of the system, video tape disks, videodisk players, CD-audio disks, image scanners,<br />

and printers. In addition, media data can be synthesized locally by the systems or its peripherals. Multimedia<br />

data is typically recorded and edited on local systems for distribution on some physical media and<br />

is later played back using local devices.<br />

Remotely stored multimedia data is accessed via a network connection to a remote system. The data<br />

is stored on that remote server and recalled over the network for viewing, editing, or storage on the user’s<br />

system.<br />

Multimedia communications cover a large set of domains including office, electronic publishing,<br />

medicine, and industry. Multimedia communication can be classified into real-time applications and<br />

non-real-time applications.<br />

Multimedia conferencing represents a typical real-time multimedia communication. In general, high<br />

conductivity is needed for real-time multimedia communications. A guaranteed bandwidth is required<br />

to ensure real-time consistency, and to offer the throughput required by the different media. This<br />

bandwidth varies depending on the media involved in the application. There is also a need for synchronization<br />

between different users, and between different flows of data at a user workstation.<br />

Non-real-time multimedia communications, such as multimedia mail are less demanding than real-time<br />

applications in terms of throughput and delay, but edition tools, exchange formats, and exchange protocols<br />

are essential. Multicast service and synchronization at presentation time has to be offered.<br />

Local non-real-time multimedia characterizes most typical personal computer applications, such as<br />

word processing, and still image editing. Typical text-based telecommunications can be described as<br />

remote non-real-time. Database of text and still image may be interactively viewed and searched, and<br />

audio or video data (perhaps included in mail messages) can be downloaded for display locally.<br />

Multimedia workstations are generally characterized by local real-time applications. Data from video<br />

and audio editing and annotations, interactive animated presentations, and music recording are stored<br />

on local devices and are distributed on physical media for use locally.<br />

Networks that can provide real-time multimedia communication via a high-speed network connection<br />

enable the new generation of multimedia applications. Real-time remote workstation-based multimedia<br />

conferencing, video and audio remote database browsing, and viewing of movies or other video resources<br />

on demand are typical for these systems.<br />

Mobile and Wireless<br />

The support for bandwidth intensive (multimedia) services in mobile cellular networks increases the<br />

network congestion and requires the use of micro/picocellular architectures in order to provide higher<br />

capacity in regard to radio spectrum. Micro/pico cellular architectures introduce the problem of frequent<br />

hand-offs and make resource allocation difficult. As a result, availability of wireless network resources<br />

at the connection setup time does not necessarily guarantee that wireless resources are available throughout<br />

the lifetime of a connection. Multimedia traffic imposes the need to guarantee a predefined QoS to<br />

all calls serviced by the network.<br />

In microcellular networks supporting multimedia traffic, the resource allocation schemes have to be<br />

designed such that a call can be assured a certain QoS once it is accepted into the network. The resource<br />

allocation for multimedia traffic becomes quite complex for different classes of traffic comprising multimedia<br />

traffic. These classes of traffic have different delay and error rate requirements. Resource allocation<br />

schemes must be sensitive to traffic characteristics and adapt to rapidly changing load conditions. From<br />

a service point of view, multimedia traffic can be categorized into two main categories: real-time traffic<br />

with stringent time delays and relaxed error rates, and non-real-time traffic with relaxed time delays and<br />

stringent error rates.<br />

It is important to note that provisioning of QoS to different classes of traffic necessitates a highly<br />

reliable radio link between the mobile terminal and its access point. This requires efficient communication<br />

techniques to mitigate the problems of delay sensitivity, multipath fading, shadow fading, and cochannel<br />

interference. Some methods such as array antennas and optimal combining can be used to combat these<br />

problems.<br />

© 2002 by CRC Press LLC

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!