Enhanced Wireless Mesh Networking for ns-2 simulator
Vivek Mhatre
Thomson
46 Quai Alphonse Le Gallo
Boulogne-Billancourt, 92100, France.
mhatre@gmail.com
This article is an editorial note submitted to CCR. It has NOT been peer reviewed. Authors take full
responsibility for this article’s technical content. Comments can be posted through CCR Online.
ABSTRACT
The ns-2 simulator has limited sup port for simulating 802.11-
based wireless mesh networks. We have added the following
new features at the MAC and PHY layer of ns-2: (i) cumu-
lative interference in SINR (Signal to Interference and Noise
Ratio) computation, (ii) an accurate and combined shadow-
fading module, (iii) multi-SINR and multi-rate link support,
(iv) auto rate fallback (ARF) for rate adaptation, and (v)
a framework for link probing and link quality estimation as
required by most mesh routing p rotocols. We have made
these modules publicly available. In this p aper, we present
an overview of these new features.
Categories and Subject Descriptors
C.2.1 [Network Architecture and Design]: Wireless
communication; C.2.5 [Computer-Communication Net-
works]: Local and Wide-Area Networks; I.6 [Computing
Methodologies]: Simulation and Modeling
General Terms
Design
Keywords
Wireless network, Wi-Fi, 802.11, mesh network, network
simulation
1. INTRODUCTION
Researchers working in the area of wireless communica-
tions heavily rely on simulations to evaluate the performance
of proposed algorithms. This is primarily because setting
up large scale wireless testbeds, and ensuring repeatability
across multiple testbeds is a difficult task. The ns-2 simu-
lator [3] is one of the most widely used network level simu-
lator for wireless research, since it is publicly available, and
is open source. Users can add new modules to ns-2 with
relative ease, and there is a large user community and ac-
tive mailing lists for both users and developers. Other open
source simulators such as, SWAN [14], JIST [2], Glomosim
[1], and commercial simulators such as, Qualnet [5], and
Opnet [4] are also popular among researchers.
The focus of this paper is the simulation of 802.11-based
wireless mesh networks in ns-2. As pointed out in [17, 14, 6],
the current implementation of MAC and PHY-layer wireless
models in ns-2 does not abide by the following principles of
wireless communication.
1. The computation of SINR (Signal to Interference and
Noise Ratio) should take into account the sum of the
strengths of all the interfering signals instead of just
the strongest interfering signal [17].
2. The channel gain model should be comprehensive in
that it should include distance based path loss, lo-
cation dependent shadowing, and velocity dependent
fading [16, 17, 14, 6].
3. The channel gains could be different in either direction
due to shadow-fading, and the simulator should model
such asymmetric link conditions [14].
4. The simulator should also model fluctuations in the
capacity of a link due to time variations resulting from
fading [14].
Furthermore, ns-2 only allows for a common and fixed
data rate for all the links in a mesh network. In real 802.11
hardware, depending on the channel conditions, a rate adap-
tation algorithm such as Auto Rate Fallback (ARF) [10]
chooses the highest possible data rate among the eight can-
didate data rates (6, 9, 12, 18, 24, 36, 48 and 54 Mbps) to
suit the current channel conditions. Each of these data rates
have a different SI NR requirement; the higher th e SINR,
the higher th e sustainable data rate. A wireless link simula-
tor should have support for such multi-rate and multi-SINR
link model with link rate adaptation. Support for multi-
rate links with ARF was contributed in [19], however this
code relies on comparing th e received signal strength to fixed
thresholds for determining successful reception. Received
power based decision is inaccurate since in real systems, the
SINR determines the success/failure of a transmission.
To overcome the above mentioned limitations, we have
added the following new features to ns-2 (version 2.30):
1. Cumulative interference along with noise power for an
accurate SINR-based reception model,
2. Combined shadow-fading with an accurate shadowing
model (current shadowing model of ns-2 is inaccurate,
and furthermore, it cannot be used in combination
with the fading module),
3. Multi-SINR and multi-rate 802.11 a/g links,
4. Auto-rate fallback (ARF) algorithm for rate adapta-
tion (currently, ns-2 only supports links with fixed
rate), and
ACM SIGCOMM Computer Communication Review 69 Volume 37, Number 3, July 2007