Admission Control for Distributed VoD System with Scalable
Videos
Jucai Tang , Baoqun Yin, Xiaonong Lu
Department of Automation, University of Science and Technology of China, Hefei 230027, PRC
E-mail: cabbage@mail.ustc.edu.cn,bqyin@ustc.edu.cn,lxn520@mail.ustc.edu.cn
Abstract: Scalable video coding (SVC) is considered as a promising video coding scheme under the new network environment.
However, providing scalable videos in a distributed video on demand (VoD) system brings many additional problems, such as
the adjustment of QoS according to varying terminal capabilities or network conditions, the ensurance of providing acceptable
video quality while avoiding network congestion etc. This paper proposes a novel admission control model for distributed VoD
system with scalable videos. The admission control process of the service system is modeled as a partially observable Markov
decision process (POMDP). The admission control policy of the system is a randomized policy which can be solved by policy
gradient method. Through a numerical experiment, the proposed approach is shown to be well performed.
Key Words: Admission Control, Scalable Video Coding, POMDP, Distributed Video on Demand System, Randomized Policy
1 Introduction
In recent years, distributed VoD system has been wide-
ly used to meet the requirements of the growing number of
users. However, the maximum number of concurrent stream-
s that a distributed VoD system can support is limited be-
cause of the constrained bandwidth. In such a case, exten-
sive researches have been presented to solve the optimal ad-
mission control policy on distributed VoD systems. Some
threshold based policies were presented
[1,2]
. M. Alam mod-
eled the admission control problem as a multiple-choice k-
napsack problem and solve it through a heuristic algorith-
m
[3]
. However, these researches mainly focus on system-
s which provide single encoded bitrate videos. In the last
decade, different video terminals have been developed rapid-
ly, such as mobile phone, computer, TV, flat panel computer
etc. However, different devices varied in screen resolution,
computing power and data transmission speed. Therefore,
single bitrate videos can not meet request from different ter-
minals ranging from mobile phone with a small screen and
restricted decoding capacity to TVs with high definition dis-
plays. Scalable video coding is considered a highly attractive
solution to this problem since it can remove part of the video
bitstreams to adapt it to the various requests from terminals
with different capabilities and network conditions. Howev-
er, the admission control schemes mentioned above cannot
apply to service systems providing SVC videos directly.
Some researches related to scalable video system have
been presented. J. Zou et al. studied scalable video multi-
cast networks
[4]
. P. Chaparro et al. applied scalable video in
MANETs
[5]
. P. Baccichet et al. reduced transmission delay
in P2P video systems by using SVC technology
[6]
. However,
there are few works focus on distributed VoD systems pro-
viding scalable videos. Finding an optimal admission con-
trol policy for such a VoD system remains a complex prob-
lem.
This work is supported in part by National Natural Science Founda-
tion (NNSF) of China under Grant No.61174124 and No.60935001, in part
by the National High Technology Research and Development Program of
China (863 Program) under Grant No.2011AA01A102 and in part by the
”Strategic Priority Research Program” of the Chinese Academy of Sciences
under Grant No.XDA06030900.
Recently, the model-based approach which use Markov
decision process (MDP) to model the admission control pro-
cess of the system have been presented and get a quite good
performance
[7,8]
. However, in the distributed networks, the
state space is usually very large. As a result, the optimal pol-
icy is hard to solve due to the curse of dimensionality. Based
on MDP, POMDP introduces the concept of observation, ac-
cording to which the system makes decisions. Common-
ly the observation space is much smaller than state space.
Thus, the computational complexity is greatly reduced. In
our previous works, the distributed VoD system is modeled
as a POMDP
[9,10]
, but in these works, systems only need to
decide whether to accept a request or not, while in the sys-
tem with SVC, QoS will be taken into consideration by ad-
justing the number of enhancement layers transmitted. Be-
sides, in traditional admission control schemes, node selec-
tion strategies are required to decide the service node, such
as benchmark strategy. In our POMDP model, we combine
the server selection into action space. Through optimiza-
tion, service load will be balanced between different servers,
thus the resource utilization will be better. In addition, when
users exit, the system takes no action in the previous work-
s. However, due to the scalable QoS of the ongoing service,
the system with SVC need to decide the assignment of re-
sources released from the exit user to the ongoing services
whose QoS is lower than their expected.
In this paper, we will study the admission control prob-
lem of distributed VoD systems supporting scalable videos.
The rest of this paper is organized as follows: In Section
2, we briefly introduce distributed VoD system with scal-
able videos and describe our admission control scheme. A
POMDP model is constructed for the service system in Sec-
tion 3. And detailed optimization algorithm is presented in
Section 4. Then in Section 5, we give a numerical example
to show the applicability of our method. Finally, we draw
conclusions in Section 6.
2 System Structure
2.1 Scalable Video Coding
SVC divides a video bitstream into two or more subset
bitstreams called layers. Among them, there is one base lay-
Proceedings of the 34th Chinese Control Conference
Jul
28-30, 2015, Han
zhou, China
6646