8 research outputs found
Concept and design of the hybrid distributed embedded systems testbed
Wireless mesh networks are an emerging and versatile communication technology.
The most common application of these networks is to provide access of any
number of users to the world wide Internet. They can be set up by Internet
service providers or even individuals joined in communities. Due to the
wireless medium that is shared by all participants, effects like short-time
fading, or the multi-hop property of the network topology many issues are
still in the focus of research. Testbeds are a powerful tool to study wireless
mesh networks as close as possible to real world application scenarios. In
this technical report we describe the design, architecture, and implementation
of our work-in-progress wireless testbed at Freie Universität Berlin
consisting of 100 mesh routers that span multiple buildings. The testbed is
hybrid as it combines wireless mesh network routers with a wireless sensor
network
Practical issues of implementing a hybrid multi-NIC wireless mesh-network
Testbeds are a powerful tool to study wireless mesh and sensor networks as
close as possible to real world application scenarios. In contrast to
simulation or analytical approaches these installations face various kinds of
environment parameters. Challenges related to the shared physical medium,
operating system, and used hardware components do arise. In this technical
report about the work-in-progress Distributed Embedded Systems testbed of 100
routers deployed at the Freie Universität Berlin we focis on the software
architecture and give and introduction to the network protocol stack of the
Linux kernel. Furthermore, we discuss our first experiences with a pilot
network setup, the encountered problems and the achieved solutions. This
writing continues our first publication and builds upon the discussed overall
testbed architecture, our experiment methodology, and aspired research
objectives
Properties and topology of the DES-Testbed
The Distributed Embedded Systems Testbed (DES-Testbed) is a hybrid wireless
mesh and wireless sensor network that has been deployed at Freie Universität
Berlin and was successively extended from November 2007 to December 2010. This
technical report gives an overview of the current topology and the properties
of the IEEE 802.11 wireless mesh network that is part of the DES-Testbed. The
information that was gathered from an experimental study shall enable
researchers to optimize their experiment scenarios, to support the evaluation
of experiments, and to derive improved models of real world deployments. The
differences of testbeds compared with simulation models and how to evaluate
and filter the raw data are addressed. The focus of our study is an up-to-date
description of the testbed state and to highlight particular issues. We show
that the node degree, link ranges, and packet delivery ratios are not normal
distributed and that simple means are not sufficient to describe the
properties of a real world wireless network. Significant differences of the
results from three channels are discussed. As last, the technical report shows
that the DES-Testbed is an overall well connected network that is suited for
studies of wireless mesh network and wireless mobile ad-hoc network problems.09.03.201
State-of-the-art of distributed channel assignment
Channel assignment for Wireless Mesh Networks (WMNs) attempts to increase the
network performance by decreasing the interference of simultaneous
transmissions. The reduction of interference is achieved by exploiting the
availability of fully or partially non-overlapping channels. Although it is
still a young research area, many different approaches have already been
developed. These approaches can be distinguished into centralized and
distributed. Centralized algorithms rely on a central entity, usually called
Channel Assignment Server (CAS), which calculates the channel assignment and
sends the result to the mesh routers. In distributed approaches, each mesh
router calculates its channel assignment decision based on local information.
Distributed approaches can react faster to topology changes due to node
failures or mobility and usually introduce less protocol overhead since
communication with the CAS is not necessary. As a result, distributed
approaches are more suitable once the network is operational and running.
Distributed approaches can further be classified into static and dynamic, in
regard to the modus of channel switching. In dynamic approaches, channels can
be switched on a per-packet basis, whereas in static approaches radios stay on
a specific channel for a longer period of time. Static assignments have been
more in focus, since the channel switching time for current Institute of
Electrical and Electronics Engineers (IEEE) 802.11 hardware is in the order of
milliseconds which is two orders higher than the packet transmission time.
Recently, surveys of channel assignment algorithms have been presented which
cover certain aspects of the research field. The survey in [1] introduces the
problem and presents a couple of distributed algorithms and [2] gives a broad
introduction to centralized and distributed approaches. The survey herein is
focused on distributed approaches for peer- to-peer network architectures.
This report describes the problem formulation for channel assignment in WMNs
and the fundamental concepts and challenges of this research area. We present
different distributed channel assignment algorithms and characterize them
according to a set of classification keys. Since channel assignment algorithms
may change the connectivity and therefore the network topology, they may have
a high impact on routing. Therefore, we present routing metrics that consider
channel diversity and adapt better to the multi- radio multi-channel scenario
than traditional routing metrics designed for single channel networks. The
presented algorithms are discussed and compared focusing on practical
evaluations in testbed and network environments. The implementation for real
networks is a hard and labor-intensive task because the researcher has to deal
with the complexity of the hardware, operating system, and wireless network
interface drivers. As a result, frameworks emerged in order to simplify the
implementation process. We describe these frameworks and the mechanisms used
to help researchers implementing their algorithms and show their limitations
and restrictions
Gossip routing, percolation, and restart in wireless multi-hop networks
Route and service discovery in wireless multi-hop networks applies flooding or
gossip routing to disseminate and gather information. Since packets may get
lost, retransmissions of lost packets are required. In many protocols the
retransmission timeout is fixed in the protocol specification. In this
technical report we demonstrate that optimization of the timeout is required
in order to ensure proper functioning of flooding schemes. Based on an
experimental study, we apply percolation theory and derive analytical models
for computing the optimal restart timeout. To the best of our knowledge, this
is the first comprehensive study of gossip routing, percolation, and restart
in this context
(2nd extended revision)
aktualisierte Version von TR-B-11-0
A survey of flooding, gossip routing, and related schemes for wireless multi- hop networks
Flooding is an essential and critical service in computer networks that is
used by many routing protocols to send packets from a source to all nodes in
the network. As the packets are forwarded once by each receiving node, many
copies of the same packet traverse the network which leads to high redundancy
and unnecessary usage of the sparse capacity of the transmission medium.
Gossip routing is a well-known approach to improve the flooding in wireless
multi-hop networks. Each node has a forwarding probability p that is either
statically per-configured or determined by information that is available at
runtime, e.g, the node degree. When a packet is received, the node selects a
random number r. If the number r is below p, the packet is forwarded and
otherwise, in the most simple gossip routing protocol, dropped. With this
approach the redundancy can be reduced while at the same time the reachability
is preserved if the value of the parameter p (and others) is chosen with
consideration of the network topology. This technical report gives an overview
of the relevant publications in the research domain of gossip routing and
gives an insight in the improvements that can be achieved. We discuss the
simulation setups and results of gossip routing protocols as well as further
improved flooding schemes. The three most important metrics in this
application domain are elaborated: reachability, redundancy, and management
overhead. The published studies used simulation environments for their
research and thus the assumptions, models, and parameters of the simulations
are discussed and the feasibility of an application for real world wireless
networks are highlighted. Wireless mesh networks based on IEEE 802.11 are the
focus of this survey but publications about other network types and
technologies are also included. As percolation theory, epidemiological models,
and delay tolerant networks are often referred as foundation, inspiration, or
application of gossip routing in wireless networks, a brief introduction to
each research domain is included and the applicability of the particular
models for the gossip routing is discussed
The ScatterWeb MSB-A2 platform for wireless sensor networks
Wireless sensor networks (WSN) are in a transition from research to real world
applications. Robust and efficient hardware platforms are needed. These have
to offer sufficient processing power and memory while retaining energy
efficiency. In this technical report we present the newest ScatterWeb hardware
platform that fits the needs to research and prototyping applications of the
near future