Survey On Mutilmedia Communication

  2004-10-28 IEEE上的一篇论文:)


一.多媒体(Multimedia)的定义
多媒体本身说明了它包含一种整合操作,包括对以连续数据表示的信息(如音频和视频)和以离散数据表示(如文本和图画)的信息.
这种操作通常是指:capturing(捕获/或者说采集),processsing处理,communicating(通信),presenting(呈现)或者storing(存储).
我们认为连续的数据是一种时间依赖的信息,通信双方必须通过协商达成契约,以一定的时间间隔来处理良好定义的数据.
因此"多媒体通信"研究在数字网络上的离散和连续媒体的传输,协议,服务等机制.
“multimedia communications” deal with the transfer, protocols, services, and mechanisms of/for
discrete and continuous media in/over digital networks.

二.QoS的定义
QoS is defined as the set
of parameters that defines the properties of media streams.
In accordance with [31], we distinguish four layers of
QoS: user QoS, application QoS, system QoS, and network
QoS. The user QoS parameters describe requirements for
the perception of multimedia data at the user interface.
The application QoS parameters describe requirements for
the application services possibly specified in terms of
media quality (like end-to-end delay) and media relations
(like inter/intrastream synchronization). The system QoS
parameters describe requirements on the communications
services resulting from the application QoS. These may
be specified in terms of both quantitative (like bits per
second or task processing time) and qualitative (like multicast,
interstream synchronization, error recovery, or ordered
delivery of data) criteria. The network QoS parameters
describe requirements on network services (like network
load or network performance).
to or an enhancement of resource-management-based QoS;
their concepts are discussed in Section VII. Methods for
“reservation in advance” are needed for several scenarios
to create distributed multimedia applications that resemble
today’s systems; they are described in Section VIII. Before
we conclude this paper, in Section IX, we discuss the
ability of current systems to support distributed multimedia
applications and consider which issues are still missing.

三.分布式多媒体应用的需要
随应用场景的不同而不同,但可以分为两类:对传输的要求和对功能的要求
功能上:多播,多个流的协调
传输上:带宽,延迟,抖动

四.QoS的详细描述
对于需要将AV数据呈现给用户的应用,Overall QoS是必须的(end-to-end QoS),这需要所有参与组件(software,hardware,netword,etc.)的参与.
对端系统上的软件,硬件:
对网络:资源管理(resource-managerment functionality)

Overall, several resource-management components interact
to provide QoS assurance: applications, QoS translators,
admission control, and resource scheduler. Additionally,
further components are needed; for example, a resource
reservation protocol to communicate QoS specifications
among participating systems and a resource monitor, which
measures the availability of resources and whether indeed
the promised QoS is provided.

The notion of QoS is very different at the various
system layers. At the application layer, for instance, QoS
parameters are based on media quality descriptions, and
requirements—e.g., for the workload parameters such as
frame size (e.g., height, width, color specification) and
frame rate—may be used. The end-to-end delay relates to
the final presentation of data to the user, and loss might
be specified in terms of “visibility” to the user. In the
network, the workload description consists of packet size
and rate; loss may be described using measures for bit-error
or packet-error rate. Each of these layers needs the QoS
specified in its own terms, which means that a mapping
between them is necessary. While this mapping is an
important issue for all networked multimedia applications,
no overall solution has been found yet, but only partial
approaches for simple conversions, e.g., between transport
and network layer, have been devised.
In addition to this layer dependence, the notion of QoS is
qualitative and quantitative. For example, delay, throughput,
rate, and buffer specifications are quantitative parameters
on different architectural layers, whereas interstream
synchronization, ordered delivery, and error recovery are
qualitative parameters on different levels of abstractions.
Some of the qualitative parameters, such as lip synchronization,
can be mapped to quantitative parameters if user
characteristics are taken into account.

QoS的重要参数:
带宽,延迟,稳定性(loss and corruption of data),抖动

五.QUALITY OF SERVICE IN COMMUNICATIONS SYSTEMS
六.对网络的适应
1.Scaling
可伸缩性:要求一种feedback control loop机制,并且要能动态的调整自己