Information Technology Reference
In-Depth Information
4.3.5 Impact of Delay
The delay is important when a high interactivity is required, e.g., video confer-
ence, whereas in scenarios like video streaming where a buffer space is created
and as long as the data can be downloaded as fast as it is used up in playback, the
influence of this parameter will practically disappear. Therefore, we have not fur-
ther considered this factor.
4.3.6 Model Proposed
The quality perceived by the user will be obtained mainly from the values of the
bit rate and of the packet loss within the network, this maximum value will be in-
fluenced by the frame rate of the video proportionally. Therefore, the final formula
used to obtain the perceived quality of a video streaming is shown in Equation (6).
MOS l
,
br
,
fps
(
)
=
f
L
l
,
br
(
)
f
R
(
fps
)
l
0,10
[
]
%
(6)
br
150 ,1500
[
]
kbs
fps
5,30
[
]
4.3.7 Adding MPEG-21 Support Enabling Interoperable Cross-Layer
Interactions
In order to provide interoperability when well established layers are broken up,
we propose to utilize MPEG-21 DIA tools for describing functional dependen-
cies between the layers. In particular, QoS mappings as described in Section 3.1
- possibly ranging across well-defined network layers - are instantiated with the
MPEG-21 DIA tools introduced in Section 2.2. In this section we will show how
the proposed QoS model as defined in Equation ( 6 ) can be instantiated using
interoperable description formats according to the three-step approach described
in [7].
The functional dependencies of the MOS function are described using MPEG-
21 DIA AdaptationQoS' stack functions, i.e., XML-based reverse polish notation
(RPN), given a range of possible content frame rate and bit-rate combinations (ex-
pressed via a so-called look-up table) with the objective to maximize the MOS.
The context in which the multimedia content is consumed is characterized through
the packet loss measured at the receiving terminal and communicated towards the
multimedia content providing entity using an MPEG-21 DIA UED. In addition to
the UED, the constraints of the probe - as indicated by Equation ( 6 ) - are ex-
pressed by an MPEG-21 DIA UCD utilizing limitation constraints which are at-
tached to the UED.
Excerpts of the aforementioned interoperable descriptions are shown in
Listing 1. Note that the complete descriptions can be found elsewhere [30].
