A scalable method for DCLC problem using hierarchical MDP model
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Yue Han
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, Mingwu Yao, Zengji Liu
ISN State Key Lab. of Xidian University, Xi’an 710071, China
article info
Article history:
Received 21 November 2012
Received in revised form 1 May 2013
Accepted 7 May 2013
Available online 18 May 2013
Keywords:
DCLC
MDP
Scalability
abstract
It is well known that the delay-constrained least-cost (DCLC) routing problem is NP-comp lete, hence var-
ious heuristic methods have been proposed for this problem. However, these heuristic methods have
poor scalability as the network scale increases. In this paper we propose a new method based on the
Markov Decision Process (MDP) theory and the hierarchical routing scheme to address the scalability
issue of the DCLC routing problem. We construct a new two-level hierarchy MDP model and apply an infi-
nite-horizon discounted cost model to the upper level for the end-to-end inter-domain link selection.
Since the infinite-horizon discounted cost model is independent of network scale, the scalability problem
is resolved. With the proposed model, we further give the algorithm of solving the optimal policy to
obtain the DCLC routing. Simulation results show that the proposed method improves the scalability
significantly.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
The continuous growth in network applications with various
QoS requirements is calling for better transmission qualities than
the best effort service. These emerging applications (video, audio,
interactive multimedia, teleconferencing, etc.) have stringent QoS
requirements and pose a particular difficulty for the QoS routing.
For example, the delay-sensitive applications such as real-time
voice and video require the data stream to be received at the des-
tination within a certain time. Generally, the QoS requirements are
represented by constraints imposed upon the corresponding per-
formance metrics such as delay, jitter, cost, etc. The end-to-end
delay constraint is the most prominent factor of these constraints
for QoS support. In addition, the traffics generally utilize a signifi-
cant amount of resources usually measured by the cost metric.
Hence the need for QoS routing is the ability to satisfy the QoS
requirements of the traffics and to better optimize resource utiliza-
tion. In this paper, we focus on the most typical delay-sensitive
routing problem which has been extensively studied in the past
decade, the delay-constrained least cost (DCLC) routing prob-
lem[1], i.e., to find a path that has the minimal cost subject to a de-
lay constraint.
The DCLC routing plays a very important role in the field of QoS
routing. Much work has been done to solve the DCLC problem.
However, the existing DCLC routing algorithms still have one or
more distinct drawbacks, such as high computational complexity,
high communication complexity and low success ratio to obtain
the optimal path, that seriously hinder the application of DCLC
routing to the practical network environment. Moreover, DCLC
routing has to consider not only the application to a specified net-
work size, but also the application to a larger network scale for the
scalability requirement. Therefore, we see the DCLC problem from
a completely different angle to find a suitable solution that can
achieve 100% success ratio to obtain the optimal path with low
computational complexity, low communication complexity and
better scalability.
With the continuing growth of the network size, the existing
heuristic algorithms for DCLC routing will not work well, leading
to what is called the scalability problem. So far, the scalability
problem of DCLC routing has seldom been addressed. Therefore
our focus is to propose a feasible solution for resolving the scalabil-
ity problem of DCLC routing. We notice that the frequent advertise-
ment of routing information is the critical factor for the scalability
problem of DCLC routing. So our purpose is centered on the
decrease of the advertisement. Under the steady network and link
independence assumptions, MDP theory is appropriately employed
to compute an optimal path for the DCLC problem by means of link
by link way, which is not necessary to frequent advertise the rout-
ing information. To achieve this purpose, we rebuild a two-level
MDP model for DCLC routing, which is an effective structure of
offering better scalability. For the lower level, we adopt the finite
horizon cost MDP to determine the links of a path within a domain.
For the upper level, we adopt the infinite-horizon discounted cost
MDP to determine the inter-domain links. Thus, the end-to-end
DCLC routing is determined regardless of the network size and
then the scalability problem is resolved.
0140-3664/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.comcom.2013.05.003
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Project supported by the National Natural Science Foundation of China (Nos.
61001129, 61179002), the State Key Laboratory Foundation (No.
9140c5302010802).
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Corresponding author. Tel.: +86 029 88201008.
E-mail address: yueh2000_8@163.com (Y. Han).
Computer Communications 36 (2013) 1310–1316
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Computer Communications
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