Issue Seven - Conversations on Technology, Business and Society

Simulation of the differentiated services
QoS scheme under IP Multimedia Systems
David K Osei-Aboagye1 and Peter S Excell2
1802 Global Ltd., Aldermaston, United Kingdom
2Centre for Applied Internet Research, Glyndŵr University, Wrexham, United Kingdom
Corresponding email: david.osei@802global.com
Previously published at Osei-Aboagye, D. & Excell, P. (2009) “Simulation of the Differentiated Services QoS Scheme under IMS”, Proceedings of the 3rd
International Conference on Internet Technologies and Applications (ITA 09), Glyndwr University, Wrexham, Wales, UK, 8-11 September 2009.
ABSTRACT
The evolving standards of mobile
communications, the wide variety of
services they offer and the rapid growth
of the Internet have made a merger of the
two network technologies inevitable. One
of the most prominent platforms that has
been developed to facilitate this and take
mobile communication networks to the next
generation (4G) is IP Multimedia Subsystems
(IMS). Even though the standards for 4G
have not yet been defined, many proposed
standards integrate IMS as the main core
network architecture and Quality of Service
(QoS) is the main concern for customer
satisfaction. A significant approach to this
is the ‘Differentiated Services’ scheme,
and a simulation study of this is presented.
The study covered an IMS core network
architecture modelled with Network Simulator
2 (NS-2), with a Differentiated Services QoS
scheme run over it. Implications for core
network architectures are discussed.
ABBREVIATIONS
CBS Committed Burst Size
CIR Committed Information Rate
EBS Excess Burst Size
FTP File Transfer Protocol
IMS IP Multimedia Subsystem
MN Mobile Node
NAM Network Animator
NS-2 Network Simulator-2
PBS Peak Burst Size
PIR Peak Information Rate
QoS Quality of Service
SIP Session Initiation Protocol
TCP Transmission Control Protocol
UDP User Datagram Protocol
1.0 INTRODUCTION
The next generation of mobile
communications is gradually evolving
towards an IP (Internet Protocol) core
network. This has led to much research into
IP Multimedia Subsystem (IMS), which is an
IP-based network that allows integration of
voice and multimedia as well as permitting
new environments with new purposes [1].
Quoting [1]: “IMS carries signalling and
bearer traffic over the IP layer, functioning
as an intelligent ‘routing engine’ that
matches a user profile with an appropriate
call handling server and switches the call
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control over to the designated handler.”
Most of these applications expected under
IMS have different Quality of Service (QoS)
requirements: to handle these with the same
QoS preferences as all other packet data
routed through the Internet would result in
unsatisfactory performance and customer
dissatisfaction.
Most of the services offered by IMS are
already being offered by existing circuit
and packet-switched mobile networks, but
IMS aims at providing these services with
a guaranteed QoS as well as guaranteed
bandwidth efficiency. Thus certain services
like real-time multimedia applications are
given preference in terms of bandwidth since
they require more bandwidth than non-realtime
services. Circuit and packet-switched
multimedia services give no preference to
real-time or non-real-time sessions.
As a tool to investigate IMS performance
under QoS constraints, a simulation of the
IMS core network architecture was developed
using Network Simulator 2 (NS-2) software,
the network architecture being designed
to carry both session signalling traffic as
well as bearer traffic. The model was then
used to implement a Differentiated Services
QoS scheme on top of the designed IMS
architecture and a performance evaluation
was made for different bearer traffic scenarios.
2.0 SOFTWARE CONFIGURATION FOR
SIMULATION
The IMS core network is managed
mainly by SIP signalling for session setup
and tear down. Due to this, the first
objective is to create a SIP signalling
architecture for the network topology. The
next objective after creating the signalling
architecture would be to create IP traffic
to run over the Signalling architecture to
help facilitate the implementation of the
Differentiated Services (DiffServ) Quality of
Service scheme.
Network Simulator allinone version 2.27
(NS allinone-2.27) is the only NS-2 version
that has a SIP functionality built into its
modules but does not support multi-interface
architecture. NS allinone-2.31, the latest
version of NS-2, has an extension for multiinterface
layers called NSmiracle which can be
integrated into its modules. However it has no
SIP support.
The first objective is to patch the NS
miracle multi-interface layer’s patch onto NS
allinone-2.31 and then patch NS allinone-
2.27’s SIP signalling module functionality onto
NS allinone-2.31. It was observed after the
SIP module patch installation that, due to the
fact that the SIP signalling module was built
on NS allinone-2.27, version issues as well as
backward compatibility issues inherent in NS-2
arose. This led to a failure of the patching
procedure.
There are two possible ways to resolve
the problem. Since the first objective of the
project is to develop an IP Multimedia System
architecture which involves the need for a
multi-interface layer, NS miracle is essential.
The NS allinone-2.27 SIP signalling module’s
patch was manually altered in order to make it
function in NS allinone-2.31.
3.0 NETWORK DESIGN & SIMULATION
The network topology to be simulated
for the IMS core network’s SIP signalling
consists of five routers, two proxies and four
Mobile Nodes (MN). The traffic over the air
interface to the Mobile Node is ignored,
hence its propagation delays are not taken
into account.
P 1
MN 3
R 1
R 3
MN 1
R 0
MN 2
Figure 1 shows the network architecture
to be simulated. P1 represents proxy server
1 which is the proxy for David.com and
P2 represents proxy server 2 which is the
proxy for Demola.com. R0 represents the
SEPTEMEBER - OCTOBER 2010 | PC TECH
R 2
R 4
MN 4
Fig. 1. Diagram of the network architecture to be simulated.
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