ON THE DESIGN OF A SCALABLE MULTIMEDIA STREAMING
SYSTEM BASED ON RECEIVER-DRIVEN FLOW AND
CONGESTION AWARENESS
I
˜
nigo Urteaga, Iraide Unanue, Javier Del Ser
TECNALIA-TELECOM, Parque Tecnologico, Ed. 202, 48170 Zamudio, Spain
Pedro Sanchez, Aitor Rodriguez
Intelligent Transport Systems and Security, IKUSI-Angel Iglesias, S.A., Paseo Miramon 170, 20009 San Sebastian, Spain
Keywords:
Streaming, Scalable multimedia content, Congestion control, Flow control.
Abstract:
In this position paper we present the design of an end-to-end scalable content streaming system that optimizes
the quality of experience of the end-user by allowing each client to retrieve a customized multimedia stream,
based on both network and client states. By taking advantage of multimedia scalability, our proposed receiver-
driven architecture performs a multilayered streaming, where each client is responsible for controlling the
number of multimedia layers it demands from the server. Furthermore, the streaming system proposed herein
implements both congestion and flow control mechanisms, which are also delegated to the receiver. In order
to properly address both network and client states and restrictions, a set of specific metrics (Buffer State,
Interarrival Jitter and Loss Event Rate) are utilized, which have been specifically designed to match the
miscellaneous characteristics of heterogeneous networks and end devices. Built upon such metrics, we present
a decision algorithm that jointly performs congestion and flow control, while maximizing inter-session fairness
and end-user quality of experience. The proposed architecture combines different standard protocols while
guaranteeing independence between components of the streaming system.
1 INTRODUCTION
Multimedia streaming has lately gained momentum
within both industry and academia in light of the
forthcoming redefinition of Internet, mainly moti-
vated by a wide variety of Internet-based applications
envisioned to become vastly demanded in the follow-
ing years. As to mention, in multi-point video confer-
encing each of a number of endpoints require person-
alized versions of a given content, whereas in video-
on-demand the features of the multimedia content de-
livered to each client are established based on service
quality and fees, usable bandwidth, etc.
In this context, as opposed to conventional broad-
cast technologies such as terrestrial or cable televi-
sion, IP (Internet Protocol) networks are inherently
heterogeneous in their underlying communication
This work was supported by the Spanish Centro para
el Desarrollo Tecnologico e Industrial (CDTI) through the
TELMAX project (ref. CEN20071036).
means (i.e. usually composed of combinations of
wired and wireless links with distinct associated com-
munication protocols). This heterogeneity gets even
more involved if one notices that the state, traffic
and characteristics of IP networks usually change
dynamically in time. Besides, the rapidly growing
portable device market has introduced a huge variety
of streaming receivers. Based on this threefold ratio-
nale, scalable multimedia content is called to attain
wide acceptance in the near future, as it provides high
adaptability to all the above scenarios. As research on
scalable content advances with the pioneering Scal-
able (H.264/SVC) and the Multiview (H.264/MVC)
Video Codecs, scalable content based streaming ap-
plications will become broadly adopted.
Research on scalable multimedia streaming has so
far gravitated on the use of MANE (Media Aware
Network Element) entities which fundamentally are
additional intermediate nodes used for manipulating
and customizing streaming sessions, in clear contrast
39
Urteaga I., Unanue I., Del Ser J., Sanchez P. and Rodriguez A. (2010).
ON THE DESIGN OF A SCALABLE MULTIMEDIA STREAMING SYSTEM BASED ON RECEIVER-DRIVEN FLOW AND CONGESTION AWARENESS.
In Proceedings of the International Conference on Signal Processing and Multimedia Applications, pages 39-45
DOI: 10.5220/0002987400390045
Copyright
c
SciTePress
to client-server based end-to-end services. This ap-
proach has been thoroughly analyzed and studied in
the literature. For instance, in (ASTRALS, 2010;
Schierl et al., 2007; Renzi et al., 2008) N RTP (Real
Time Protocol) sessions transmitted by the server are
fused by the MANE into a single RTP flow for each
client according to network conditions. Still, other
contributions (Liebl et al., 2006; Tizon and Pesquet-
Popescu, 2008) propose to use MANEs to perform
an optimized packet scheduling and radio resource
sharing over the last wireless hop of a network by
mapping scalable content layer dependencies to flow
priorities. Unfortunately, the aforementioned use of
MANEs presents several disadvantages: 1) the inser-
tion of an intermediate media-aware device into the
streaming scenario, and 2) the need for modifying
both RTP and RTCP (Real Time Control Protocol)
packets to adapt them to the customized content. De-
ploying MANEs into the streaming system requires to
know beforehand where the final clients are located.
Since the success of streaming services is only
achievable if respecting the self-regulatory nature of
transmissions within the Internet, it is mandatory to
avoid either overloading or under-utilizing network
resources. This justifies the need for providing con-
gestion control techniques. Several congestion con-
trol mechanisms have been presented for streaming
applications in the literature, e.g. see (Feamster et al.,
2001; Ma and Ooi, 2007; Mujica-V. et al., 2004;
Papadimitriou and Tsaoussidis, 2007) and references
therein. However, most of them are source-based
(i.e. the transmitting node is in charge for implement-
ing congestion-aware techniques), which requires ac-
tive probing, information piggybacking or acknowl-
edgement mechanisms. Several drawbacks can be in-
ferred from the application of source-based conges-
tion protocols to heterogeneous IP networks. On one
hand, demanding feedback from the client implies
an overhead in terms of both processing complexity
at the client and bandwidth over-utilization. On the
other hand, in networks where both wired and wire-
less technologies coexist links with highly asymmet-
ric characteristics are likely to appear. Therefore, tak-
ing the two-way path into account is not desirable
in heterogeneous networks, since asymmetric charac-
teristics of paths cannot be reliably estimated at the
server side. Thus, worst conditions prevail in two-
way path congestion control, as it is not possible to
distinguish whether the problem arises in the uplink
or the downlink. The heterogeneous nature of future
networks implies the need for new receiver-driven
congestion control mechanisms. We here propose to
discard considering two-way paths and, in-contrast, to
only account for the down-link state in our receiver-
driven network congestion.
This position paper outlines the key design prin-
ciples of a receiver-driven streaming system based on
scalable multimedia content. Both the management
of the multimedia content and the congestion and flow
control logic are placed on the client, hence minimiz-
ing the computational complexity of the server. In
our approach, not only streaming standards are kept
unmodified, but we also profit from the information
already embedded by such protocols. Furthermore,
each constituent component of our proposed architec-
ture is independent from each other. Another novel
contribution of our work hinges on the metrics uti-
lized for the congestion and flow control mechanisms,
for which we introduce a novel LER (Loss Event
Rate) metric which is proven to offer enhanced stabil-
ity to bursty losses with respect to conventional packet
loss rate metrics.
The remainder of this manuscript is organized
as follows: first Section 2 introduces the reader to
the fundamentals of scalable multimedia streaming
1
,
whereas Section 3 presents our novel receiver-driven
end-to-end streaming system proposal for distributing
scalable media content. Finally, concluding remarks
and future research lines are drawn in Section 4.
2 SCALABLE STREAMING
Due to the heterogeneity of the actual networks and
the proliferation of a wide range of final devices, it
is essential to adapt the streaming content for each
specific context. Early approaches have been based
on storing a number of replicas of the same origi-
nal content or, alternately, on transcoding the original
content in a case-by-case basis. Recently, research
efforts have been conducted towards the generation
of inherently scalable multimedia content as a means
to provide different versions of the same multime-
dia content, without resorting to multiple successive
transcoding tasks. Consequently, processing redun-
dancy and storage occupancy of the encoded multi-
media content are minimized.
This growing interest in scalable codification has
led to several research lines: the SVC (H.264/SVC,
2009) and MVC (H.264/MVC, 2009) extensions of
the so-called Advanced Video Codec (H.264/AVC).
The H.264/SVC standard attains high compression
rates while simultaneously combining three scalabil-
ity levels into a single encoded bitstream, namely spa-
tial (resolution), temporal (frame rate) and signal-to-
noise ratio (SNR) scalability (fidelity). H.264/SVC
1
The authors recommend the reader to skip Section 2 if
familiar with the concepts tackled therein.
SIGMAP 2010 - International Conference on Signal Processing and Multimedia Applications
40
encodes a given video content to a layered structure
consisting of a base layer (comprising the lower lev-
els of each of the mentioned scalabilities) and a num-
ber of enhancement layers. The goal of the enhance-
ment layers is to progressively refine (in terms of each
aforementioned scalabilities) the base layer so as to
obtain better end-user Quality of Experience (QoE)
degrees. The H.264/MVC video codec (currently un-
der development) is also based on a layered bitstream
structure. However, it additionally provides multiple
views of the same scene which allows rendering 3D
perspectives. Thanks to the scalability of this codec,
it is possible to choose a specific viewpoint of a scene,
while keeping high encoding efficiency through inter-
view predictions.
Additionally, the Internet Streaming Media Al-
liance (ISMA, 2010) promotes the use of certain stan-
dard protocols for streaming applications: Real Time
Streaming Protocol (RTSP), Session Description Pro-
tocol (SDP), Real Time Protocol (RTP) and Real Time
Control Protocol (RTCP). RTSP is responsible for es-
tablishing and controlling the streaming sessions in
real time. SDP describes the whole streaming ses-
sion, as it characterizes the content and the stream-
ing session itself. RTP delivers the multimedia con-
tent to destination in combination with RTCP, which
communicates statistics and control information for
each RTP session. Finally, it is important to recall
that standardization organisms periodically evaluate
and update the set of recommended standards to meet
the requirements and constraints of newly designed
multimedia codecs.
3 SYSTEM DESIGN
A block diagram of the proposed end-to-end stream-
ing system design is depicted in Figure 1. As shown,
the first processing steps of the streaming system con-
sist basically of multimedia content encoding and
encapsulation. Without loss of generality we have
hereby adopted the H.264/SVC codec for ensuring
scalability at the encoding process. The only require-
ment imposed by our design is that real-time layer
switching must be supported during the decoding pro-
cess. As for the encapsulation, the MP4 file for-
mat has been selected due to 1) the H.264/SVC spe-
cific extension (AVC, 2008) included in such stan-
dard, and 2) the so-called hint tracks. Hint tracks en-
able a media-unaware streaming server by indicating
how to perform the streaming disregarding the con-
tent itself, thus alleviating the server from the compu-
tational burden derived from analyzing the streaming
peculiarities of each specific content.
Our system performs a multilayered streaming
where the M layers conforming the scalable content
are mapped to N RTP sessions {RT P
i
s
}
N1
i=0
. Observe
that even if the end-user appreciates a single multi-
media stream at reproduction, the content is received
in n N parallel RTP sessions, where n denotes the
actual number of demanded RT P
i
s
by a given client.
As defined in (RTP, 2010), the mapping between SVC
layers and RT P
i
s
can be done by following distinct cri-
teria. In our system the mapping rule is provided to
the server through hint tracks in the encapsulation.
Figure 1: Block diagram of the proposed end-to-end scal-
able content streaming system.
Thanks to multilayered streaming, the character-
istics of received multimedia content are dependent
on the actual number of transmitted RT P
i
s
and there-
fore, diverse end-user requirements can be easily met.
Our system design allows each client to select the
subset of RT P
i
s
that better fulfills its needs, as de-
scribed in Subsection 3.1. Furthermore, the client
performs a receiver-driven congestion and flow con-
trol by adapting n, based on both network and client
conditions (Subsection 3.2). The justification for
this receiver-driven approach is to avoid complex and
highly-loaded servers by balancing the computational
load between clients. Besides, piggybacking other-
wise necessary client information and network state
parameters to the server is circumvented. Finally,
it should be clear that sharp and frequent transitions
among video layers are extremely displeasing for the
QoE. In such situation a smoother video of reduced
bit rate is then preferred rather than an inconsistent
and jerky high quality video. In Subsection 3.2.2 we
outline several criteria to achieve smooth multimedia
reproduction aimed at maintaining a satisfactory QoE.
3.1 Content Streaming Procedure
In our proposal the client is the unique responsible
for (throughout the whole streaming session) dynam-
ically controlling n, i.e. the number of scalable multi-
media layers to be received. We remark that our sys-
tem follows IETF’s specifications concerning scalable
content over streaming protocols (RTP, 2010). The
presented streaming process begins with the client de-
manding information to the server about some spe-
cific multimedia content by sending a RTSP DE-
SCRIBE request. The server responds to the client
ON THE DESIGN OF A SCALABLE MULTIMEDIA STREAMING SYSTEM BASED ON RECEIVER-DRIVEN
FLOW AND CONGESTION AWARENESS
41
with the SDP description of the required content over
RTSP. This SDP description contains all the infor-
mation regarding that particular multimedia stream-
ing session: number and characteristics of each RT P
i
s
that conform the streaming session, dependencies be-
tween different RT P
i
s
, and so on. At this point
the client is capable of selecting a subset of RT P
i
s
,
depending on its processing and memory capabili-
ties. Once this is set, the client triggers the stream-
ing process by sending the RTSP SETUP and RTSP
PLAY commands to the server. Throughout the whole
streaming session, the client is able to cancel or de-
mand (using RTSP commands) each RT P
i
s
described
in the SDP, as long as dependencies among scalable
content layers are met. Once the content is received in
the client, the RTP packets corresponding to different
RT P
i
s
are merged and ordered in a single bitstream,
which is next depacketized and decoded. Finally, the
multimedia content is displayed.
The determination of the optimal number of scal-
able layers and their mapping to RTP
i
s
sessions is both
application and content dependent, however our sys-
tem is generically designed (independent from spe-
cific mappings). Hence, we assume that RT P
i
s
ses-
sions (and, consequently, scalable layers) are cor-
rectly ordered beforehand in the encapsulation pro-
cess, so the user simply needs to comply with the in-
formation provided by the SDP. In order to maximize
the QoE, we propose a soft and stable layer switching
mechanism further detailed in Subsection 3.2.2.
3.2 Flow and Congestion Control
In IP networks, several traffic types and flows com-
pete for the available scarce resources, which re-
quires avoiding either traffic overload or the under-
utilization of the network resources. Congestion can
be induced by both attempting to oversubscribe the
processing capabilities of intermediate nodes or by
over-demanding network link capabilities. This ra-
tionale, along with the diverse memory and process-
ing characteristics presented by end clients, motivates
the need for appropriate congestion and flow control
mechanisms in streaming systems. However, multi-
layered streaming imposes several considerations to
be taken into account. First, both congestion and flow
control must be based not only on a single flow, but on
several parallel RT P
i
s
. Second, each RT P
i
s
has a fixed
transmission bit rate enforced by the scalable content
requirements. Thus, RT P
i
s
by themselves cannot ex-
pand nor reduce their bandwidth usage.
Consequently, congestion and flow control for
multilayered streaming can only be accomplished
based on discrete bitrate intervals. This certainly
poses several design challenges gravitating on the
tradeoff between reactivity to network and client dy-
namic characteristics (which justifies relatively short
control periods) and the QoE degradation due to layer
switching. We intend to balance this tradeoff by ben-
efiting from the specific features of scalable content
streaming, which gives rise to a novel receiver-driven
congestion and flow control mechanism.
3.2.1 Metrics
The proposed metrics are restricted to the information
available at the client side. Therefore, procedures
such as message piggybacking or probing (e.g. for
bandwidth estimation) are discarded. Network state is
inferred by extracting information from the received
RT P
i
s
packets, while reception buffers are monitored
for estimating the client state. The following metrics
will be sampled and computed for each received
RT P
i
s
(i {0,..., n 1}) every T
s
seconds which, at
the early stage of this research, is believed to be a
multiple of the GOP (Group of Pictures) size:
A) Buffer state, B
i
t
: it quantifies the load at the re-
ceiver for each received RTP
i
s
. Let b
i
t
[0, 1] denote
the buffer state of session RT P
i
s
at time t. At this
early stage of our research we define B
i
t
.
= Γ(b
i
t
,b
i
t
)
[1,1], where b
i
t
.
= b
i
t
b
i
tT
s
. Γ(·) is a monotoni-
cally increasing function with its two parameters. No-
tice that this generic definition of B
i
t
not only accounts
for the current state of the buffer, but also accommo-
dates sharp changes on it.
B) Interarrival jitter, J
i
t
: the interarrival jitter is de-
fined as the mean deviation of the difference (D) in
packet spacing at the receiver compared to the sender
for a pair of packets. In our case, computation is done
based solely on the timestamp values of received RTP
packets. Let S
p
and R
p
denote the timestamps for the
p-th RTP packet at transmission and reception, re-
spectively. The packet spacing difference at session
RT P
i
s
for packets p and q will be given by
D
i
(p,q)
.
= (R
i
q
-R
i
p
)-(S
i
q
-S
i
p
) = (R
i
q
-S
i
q
)-(R
i
p
-S
i
p
). (1)
The interarrival jitter for the received packet p within
session RT P
i
s
, denoted as j
i
p
, is given by
j
i
p
= j
i
p1
+ (|D
i
p1,p
| j
i
p1
)/16, (2)
and the continuous interarrival jitter at time t for
RT P
i
s
, denoted as j
i
t
, will be set equal to the interar-
rival jitter j
i
p
of the last received packet for each RT P
i
s
.
It should be noted that j
i
t
is continuously updated
upon reception of each RTP packet. Then, every T
s
seconds the overall Interarrival jitter J
i
t
is computed
as J
i
t
.
= Ψ( j
i
t
, j
i
t
) [1,1], where j
i
t
.
= j
i
t
j
i
tT
s
SIGMAP 2010 - International Conference on Signal Processing and Multimedia Applications
42
and j
i
t
[0, j
MAX
], with j
MAX
denoting the maximum
permissible delay for packet decoding. Similar to
Γ(·), Ψ(·) is a monotonically increasing function with
its two parameters.
C) Loss Event Rate, LER
i
t
: it defines the rate at which
packet loss events occur. Although the fraction be-
tween sent and received packets is typically used as
a congestion indicator, it does present several draw-
backs. When bursty losses occur, the value of such
fraction metric decreases sharply from which serious
network congestion is deduced. However, successive
losses do not necessarily involve severe congestion,
specially in wireless communications subject to inter-
ference and collisions. To overcome this issue, the
novel packet Loss Event Rate LER
i
t
metric proposed
here comprises both isolated and bursty losses within
a predetermined evaluation interval T
eval
le
. In other
words, LER
i
t
is the frequency of packet loss events
(either single or multiple) during a T
eval
le
period for
each RT P
i
s
measured at time t = kT
eval
le
.
To compute this metric, every T
eval
le
seconds the
client detects any packet loss based exclusively on
checking the sequence number information provided
by incoming RTP packets. Two variables are pro-
gressively updated after the loss detection process:
I
last
le
and I
new
le
. The first refers to the index of the
last evaluation period with either bursty or isolated
packet losses, whereas the second is updated to the
current evaluating interval index if any packet loss is
detected. Based on these two variables, the instan-
taneous loss event rate ILER
i
k
for the k-th evaluation
interval is computed as
ILER
i
k
.
=
(
0 if no packet loss detected,
1
I
new
le
-I
last
le
otherwise,
(3)
from which a global weighted Loss Event Rate LER
i
t
is recursively computed every T
eval
le
seconds as
LER
i
t
.
= δ · ILER
i
bt/T
eval
le
c
+ (1 δ) · LER
i
tT
eval
le
. (4)
In the above definition, δ (0,1] is an arbitrary
parameter that trades exhaustive traceability of the
packet losses (δ = 1) for the smooth estimation of
the packet loss trend (δ 0). It is also assumed that
LER
i
t
[0,1]: if no losses occur, LER
i
t
= 0 and, oth-
erwise, if every T
eval
le
any packet is lost, LER
i
t
= 1.
3.2.2 Decision Criteria
The congestion and flow control mechanism builds
upon the above defined B
i
t
(flow), J
i
t
and LER
i
t
(con-
gestion) metrics. In fact, J
i
t
is a significant indicator
for initial network congestion. When the network is
unable to correctly process traffic data, the packet de-
lay increases even in absence of packet losses. When
network congestion increases further, packet losses
occur as the LER
i
t
metric would reflect.
As multilayered streaming is considered in our
system design, the whole set of {RT P
i
s
}
n1
i=0
must be
considered at the receiver. However, note that each
session does not have the same relevance due to the
dependencies between scalable content layers (e.g. as
RT P
0
s
contains the base layer, such session must be
given full processing priority). Thereby, every t = kT
s
seconds a set of accumulated metrics (B
n
t
,J
n
t
,LER
n
t
)
for the n RT P
i
s
sessions is obtained by applying dif-
ferent weights α
i
, namely
B
n
t
=
n1
i=0
α
i
· B
i
t
(Accumulated Buffer State), (5)
J
n
t
=
n1
i=0
α
i
· J
i
t
(Accumulated Jitter), (6)
LER
n
t
=
n1
i=0
α
i
· LER
i
t
(Accumulated LER). (7)
It should be clear that since session RT P
0
s
contains the
base layer, max{α
i
}
n1
i=0
= α
0
. Also observe that the
values of the weights for the three metrics within a
given session index are set equal. Nevertheless, bal-
ancing the importance between B
n
t
, J
n
t
and LER
n
t
is
accomplished by utilizing different coefficients in the
metric fusion stage, which merges the above accumu-
lated metrics into an overall flow-congestion indicator
ζ
t
as
ζ
t
=(
B
n
t
,J
n
t
,LER
n
t
)=γ
B
·B
n
t
+γ
J
·J
n
t
+γ
L
·LER
n
t
, (8)
where it should be remarked that (·) can be set to
any other (not necessarily linear) combination of the
accumulated metrics. Finally, a decision rule is taken
every T
s
based on ζ
t
. The decision logic determines
whether a new RT P
i
s
can be demanded from the server
(i.e. n is increased to n +1) without degrading the per-
formance of both client and network, or if it is instead
mandatory to reduce the number of sessions received
(n = n 1), i.e.
n =
n + 1 if ζ
t
< ζ
a
(n),
n 1 if ζ
t
> ζ
r
(n).
(9)
Note that decision limits ζ
a
(n) (add) and ζ
r
(n) (re-
move) are not static values but depend on the num-
ber of RT P
i
s
sessions received by the client(n). By
following this approach inter-session fairness is guar-
anteed, since we facilitate the demand of new RT P
i
s
for low-quality streams, while restraining high quality
streams from demanding more RT P
i
s
sessions. There-
fore, ζ
a
(n) is a monotonically increasing function
ON THE DESIGN OF A SCALABLE MULTIMEDIA STREAMING SYSTEM BASED ON RECEIVER-DRIVEN
FLOW AND CONGESTION AWARENESS
43
with n, bounded in the range [0 + ε
1
,1 ε
2
], while
ζ
r
(n) is a monotonically decreasing function with n
with support [0 + ε
3
,1 ε
4
], where all εs are design
parameters. Unfortunately, our decision logic still
poses the hazard of entering an unstable state when
iterating between adjacent RT P
i
s
. Since frequent layer
switching degrades the QoE at content reproduction,
we propose a safeguard mechanism: only if the sta-
bility of the system (based on proposed both network
and client metrics) is guaranteed during a predeter-
mined interval T
st
, the scalable layers contained in the
newly received RT P
i
s
are served to the decoder and fi-
nally, delivered to the end-user.
The definition of the (·), Ψ(·) and Γ(·) func-
tions, as well as the obtention of optimum values for
the decision limits ζ
a
(n),ζ
r
(n) and the intervals T
s
and T
st
are not straightforward. In order to perform a
satisfactory receiver-driven flow and congestion con-
trol, the following guidelines should be met:
The receiver-driven control procedure should be
responsive to sudden changes on any of the above
metrics, and allow RT P
i
s
session dropping as the
value of any of such metrics becomes critical, i.e.
B
t
1, J
t
1 or LER
t
1.
The decision rule must be specially sensitive to
the buffer state, as it dominates client’s perfor-
mance even in absence of network congestion.
Iterating between adjacent RT P
i
s
should be cir-
cumvented to avoid continuous layer switching
which in turn degrades QoE.
Inter-session fairness should be achieved. It is
preferable to have equal-quality multimedia flows
than streaming sessions with strongly asymmetric
quality levels.
4 FUTURE RESEARCH
In this paper we have presented a novel end-to-end
scalable content based streaming system aimed at
maximizing the end-user’s QoE. Our system prof-
its from the virtues of the scalable content to per-
form a multilayered streaming, where each client is
able to retrieve a personalized content. Being scal-
able encoding the only limitation imposed to our sys-
tem, we determine to keep intact the involved stream-
ing standards and maximize system component inde-
pendence. Furthermore, due to our receiver-driven
congestion and flow control algorithm, the streaming
session is adapted to both dynamic changes in net-
work’s state and to client’s limitations. Our presented
control metrics (Buffer State, Interarrival Jitter and
Loss Event Rate) are restricted to information already
available in streaming clients. Besides, recall that the
Loss Event Rate has been specifically designed to im-
prove congestion control performance over heteroge-
neous networks.
Further investigation will be conducted towards
the definition of the weights α
i
, the (·), Ψ(·) and
Γ(·) functions, and the decision limits ζ
a
(n) and
ζ
r
(n). To this end, a threefold criteria will be adopted:
1) to be responsive to both sudden changes and crit-
ical values of network’s and client’s state metrics; 2)
to emphasize on client’s buffer state during the con-
trol procedure; and 3) to ensure inter-session fairness
among the streaming clients.
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ON THE DESIGN OF A SCALABLE MULTIMEDIA STREAMING SYSTEM BASED ON RECEIVER-DRIVEN
FLOW AND CONGESTION AWARENESS
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