Dynamic Resource Management in a Railway Station W-LAN
Paolo Conforto and Alessia Miglietta
Alenia Spazio Spa
Via Marcellina 11, 00131 – Rome, Italy
Phone: +390641513125, Fax: +390641514302
E-mail: p.conforto@roma.alespazio.it, alessiamiglietta@libero.it
Abstract - In this paper we present an innovative
solution for a dynamic management of the Wireless
LAN (W-LAN) resources. The proposed solution aims
at overcoming the IEEE 802.11b lack of mechanisms
for the differential handling of classes of traffic
presenting different Quality of Service (QoS)
requirements, at the same time being completely
compatible with the standard. This is realised by
introducing an Inter-Working (IW) layer between the
802.11b Medium Access Control (MAC) and 802.2
Logical Link Control (LLC) layers both in the Access
Point and in the Stations of the W-LAN.
The core of the proposed model is represented by a
Capacity Assignment Module (CAM) which
dynamically assigns W-LAN transmission capacities to
the different classes of traffic so as to follow their real
bandwidth requirements and to support different
service priority levels. The optimal capacity
assignment problem is analytically addressed in the
paper by deriving, in particular, the structure of the
optimal solution. Numerical results are reported which
validate the proposed model.
Keywords: Wireless-LAN, Quality of Service,
Macroflow, Optimal Capacity Assignment, Numerical
Results.
I. INTRODUCTION
The last decade has witnessed a remarkable convergence
and integration process of different typologies of
telecommunication networks (fixed, mobile terrestrial,
satellite) along with content distribution providers [1].
One of the major results of this process is the possibility
to extend the provision of multimedia services from the
traditional fixed environment to the completely new
mobile scenarios. This is the case of the Fast Internet for
Fast Train Hosts (FIFTH) project1 whose objective is to
design and validate a satellite-based infrastructure able to
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1 The FIFTH project (n. IST-2001-39097) is supported by
the European Union in the context of the 5th Framework
Programme – Information Society Technology.
provide multimedia services to passengers of high-speed
trains. Two major typologies of service are considered:
Internet and broadcast digital TV. Moreover, the FIFTH
communication infrastructure may also be usefully
exploited by railway operators for fleet management
purposes.
As long as the train is moving in open air or, generally, in
areas where the satellite is in visibility, the multimedia
services are provided to the passengers by means of a geostationary
satellite system. Unfortunately, the satellite link
is not available within railway station due to the fading
effects caused by the buildings. In order to overcome this
problem, so as to guarantee a seamless provision of
multimedia services, the satellite connectivity is bridged
in the station by means of a IEEE 802.11 Wireless LAN
(W-LAN) [2] (see Fig. 1). The concatenation of the
satellite and W-LAN systems is referred to as extended
segment.
In this scenario a key system element is represented by the
terminal mounted on-board the trains. This terminal is
developed in a multi-mode configuration (see Fig. 2)
where the satellite terminal (ST), to be used when the
satellite’s line-of-sight is available, is complemented by a
W-LAN station (STA) to be activated when the train enters
Fig. 1: Railway Station Access Network
the station. Intelligent contents’ distribution procedures
are adopted which are based on a Content Delivery
Network (CDN) [3] approach. By means of these
GTW
Internet
Train Station Router
Origin Server
W-LAN
AP
On the same
W-LAN channel
Train Station
End Users Traffic
Proxy Server Refilling
Traffic
.....