Download View File - UET Taxila

Mobile and Pervasive Computing –
10
Wireless Mesh Networks
Presented by: Dr. Adeel Akram
University of Engineering and Technology,
Taxila, Pakistan
http://web.uettaxila.edu.pk/CMS/AUT2016/teMPCms
Introduction
WMNs offer multiple redundant communications paths
throughout the network. Whenever a link fails, the
network automatically routes messages through
alternate paths.
Even in adverse conditions devices in WMNs cooperate with each other in transmitting packets through
the network.
WMNs are believed to be self-configuring and selfhealing networks.
Introduction
Dramatic increase in link quality just by shortening the
distance between the nodes.
Reduction in the distance by a factor of two can result at
least four times more powerful signals at the receiver;
suggests that the links are more reliable without even
having to increase the power of the transmitter in
individual nodes.
The integration of WMNs with other networks such as
Internet, IEEE 802.11, 802.15, 802.16, sensor networks
etc can be accomplished.
Types of nodes in WMNs
Wireless Mesh Router:
contains additional routing functions to support mesh networking.
usually equipped with multiple wireless interfaces built on either the
same or different wireless access technologies
improves the flexibility of mesh networking.
Mesh Clients:
can also work as routers since they also have necessary functions
for mesh networking.
gateway and bridge functions do not exist in these nodes.
usually have only one wireless interface as in Laptop/desktop PC,
pocket PC, PDA, IP phone, RFID reader, etc.
WMN Architecture
Based on the functionality of the nodes the architecture
of WMNs can be classified into:
- Infrastructure mesh Architecture,
- Client mesh Architecture and
- Hybrid mesh architecture
Infrastructure Mesh
In infrastructure mesh architecture, the mesh routers
collectively provide a wireless backbone infrastructure.
Client node is passive in mesh infrastructure.
Infrastructure Mesh
Via Ethernet links conventional clients with
Ethernet interfaces can be connected to mesh
routers.
If the conventional clients have the same radio
technologies as the mesh routers then they can
communicate directly with the mesh routers
If different radio technologies are used then the
clients communicate with their base station that
have Ethernet connections to mesh routers
Client Mesh
Client meshing provides peer-to-peer networks
among client devices. Here no such mesh router is
required. Client will act like a mesh router by
relaying the packets.
Hybrid Mesh
Mesh router provide the backbone of such network.
With the help of network functionalities such as routing and
forwarding of data packets, clients can actively participate
in the creation of the mesh.
Characteristics





Dynamic self-configuration and selforganization
Adaptation
Fault tolerance and robustness
Low-Cost
Integration and interoperability
Applications




Various companies have realized the potential of
WMNs and have started offering mesh networking
products for a range of application scenarios.
Though most of the products are based on
commodity IEEE 802.11 hardware, the majority of
the commercial systems implement their own
mesh protocols for routing and network
configuration.
This makes integration of mesh routers from
different vendors into a single WMN very difficult.
Use of IP as a common network protocol can
resolve the difficulty.
Applications






Broadband home networking
Community and neighborhood networking
Enterprise networking
Metropolitan area networks
Transportation systems
Building automation
Standard
IEEE 802.11s is the most relevant emerging
standards for WMN technology
Efforts are underway in several IEEE working
groups, like 802.11, 802.15, 802.16, and 802.20,
to define mesh standards.
Protocol Layers
Some of the factors that affect the capacity and
performance of WMNs
- network architecture,
- network topology,
- traffic pattern,
- network node density,
- number of channels used for each node,
- transmission power level, and
- node mobility.
In order to develop the protocols we need to clearly
understand the relationship between the above factors
and the capacity of WMNs.
Physical Layer
The wireless radios of WMNs can support multiple
transmission rates by a combination of different
modulation and coding rates.
Adaptive error resilience can be provided through link
adaptation.
Orthogonal Frequency Division Multiple access (OFDM)
and Ultra-Wide Band (UWB) techniques are the schemes
that are being used to support high-speed transmissions.
If we desire to increase the capacity and mitigate the
impairment by fading, co-channel interference, multiantenna, systems such as antenna diversity and smart
antenna have been proposed for wireless communications.
It is more difficult to develop such techniques for WMNs
although these physical-layer techniques are also desired
by other wireless networks.
Physical Layer
Frequency-agile or cognitive radios are being developed
to dynamically capture the unoccupied spectrum to
achieve better spectrum utilization and viable frequency
planning for WMNs.
Since all the components of a radio, such as RF bands,
channel access modes, and channel modulations, are
programmable implementing cognitive radios on a
software radio platform is one of the most powerful
solutions.
Although physical test-beds are currently available, the
software radio platform is not a mature technology yet.
But as it can enable the programmability of all advanced
physical layer techniques, in the future it seems to be a
key technology for wireless communications
MAC Layer
There are differences between the MAC in WMNs and
other wireless networks:
MAC for WMNs is concerned with more than one-hop
communication.
MAC is distributed, needs to be collaborative, and works for
multipoint-to-multipoint communication.
Network self-organization is needed for better collaboration
between neighboring nodes and nodes in multi-hop distances.
Mobility is low but still affects the performance of MAC
For WMNs, a MAC protocol can be designed to work on a single
channel or multiple channels simultaneously.
Routing Layer
The design of the routing protocols for WMNs is still an
area of research although there are many routing
protocols that are available for ad-hoc networks.
However, an optimal routing protocol for WMNs must
possess features like:
- multiple performance metrics
- scalability
- robustness and
- efficient routing with mesh infrastructure.
The routing protocols for ad-hoc networks is equipped
with some of these features, but non of them possesses
all of the above.
Routing Protocols
Multi Radio Routing
In a multi-radio link quality source routing (MR-LQSR) a new
performance metric, weighted cumulative expected transmission time
(WCETT) , is incorporated.
Both link quality metric and the minimum hop count are accounted
for in WCETT which provides a good trade-off between delay and
throughput.
Routing Protocols
Multi-Path Routing:
Better load balancing and providing high fault tolerance are the two
main objectives of using multi-path routing.
Multiple paths are selected between source and the destination
This provides better fault tolerance as when a link is broken another
path can be chosen.
This enhances efficiency since without waiting to set up a new
routing path, the end-to-end delay, throughput, and fault tolerance
can be improved.
Complexity is the major hurdle of multi-path routing.
Also, the availability of node disjoint routes between source and
destination determines the improvement, given an performance
metric.
Routing Protocols
Hierarchical Routing:
The hierarchical routing protocols tend to achieve better
performance when the node density is high.
This is because of less overhead, shorter average routing path, and
quicker set-up procedure of routing path etc.
Maintaining hierarchy definitely adds to the complexity and this
may compromise the performance of the routing protocol.
Routing Protocols
Geographical routing:
This kind of routing scheme forwards packets only by using the
position information of the nodes in the vicinity and in the
destination node unlike the topology based schemes.
This suggests that there is less impact on the geographic routing
due to a topology change than the other routing protocols.
The algorithm used in geographical routing (single-path greedy
routings) suffers from that a delivery is not guaranteed even if a
path exists between a source and the destination as the packet
forwarding decision is made based on the location information
of the current forwarding node, its neighbors, and the
destination node.
Planar-graph based geographic routing algorithms have been
proposed which guarantees the delivery. Theses algorithms
suffer form a major drawback: a higher communication
overhead.
Transport Layer
A large number of transport protocols are
available for ad-hoc networks and WMNs
depend on those transport layer protocols
Till date, there is no transport protocol that has
been proposed specifically for WMNs.
We know that ad-hoc network is also not mature.
It also has various unresolved issues. This
suggests further research in this area.
Application Layer
There are numerous applications that are
supported by WMNs and they are categorized into
various classes.
- Internet access
- Distributed Information Storage and Sharing
- Information Exchange across multiple wireless networks
The areas of research in application areas include
these classes.
Improving existing application layer protocols,
proposing new application-layer protocols for
distributed information sharing, and developing
innovative applications for WMNs are the areas of
more research.
Issues
Issues in Network performance:
Radio techniques, mesh connectivity,
compatibility and inter-operability etc. are the
factors that influence the performance of WMNs.
Security Issues:
Security schemes for WMNs are still not ready.
Due to the distributed nature of WMN, there is no
centralized authority that can be fully trusted and
can distribute a public key.
Other Issues:
Capacity, scalability, and QoS are considered as
the major weakness of current WMN technology.
Conclusion
The nodes in a WMN automatically detect neighbor
nodes and establish and maintain network
connectivity in an ad hoc fashion.
The self-configuring nature facilitates the easy and
rapid deployments of WMNs.
They dynamically adapt to the changing environments
and can self heal in case of link or node failure.
Being inherently redundant they have a high level of
fault tolerance and are hence robust.
The low cost of the hardware based on IEEE 802.11
standards is one of the prominent reasons in the
increasing interests in both research and product
development.
Conclusion
Integration and inter-operation with other networks,
and bridges to legacy networks can be easily
accommodated due to the fact that most WMNs are
based on Internet Protocol standards.
Based on existing technologies, some companies
already have products for sale, while other
companies are still not convinced to the point of
production while others have started to deploy
WMNs in various application scenarios.
Whatever the case be, it we look at the research and
case studies, what we can find is that the
performance of WMNs is still far below what is
expected. There are various open issues that need to
be resolved.
Reference
- E.M. Royer, a. T. (April 1999). A Review of Current
Routing Protocols for Ad hoc Mobile Wireless
Networks'. IEEE Personal Communications Magazine
.
- Perkins, C. (2001). Ad-Hoc Networking. MA:
Addison Wesley Professional, Reading.
- Wang, Xudong, Kiyon, INC (n.d.). A Survey on
Wireless Mesh Networks. Georgia Institute of
Technology
- Yan Zhang, J. L. (2007). Wireless Mesh Networking,
Architectures, Protocols, and Standards. FL: Auerbach
Publications
Questions
- Wireless Mesh Network is a radical network form
of the ever evolving wireless network. The Ad-hoc
network is also a form of the wireless network.
Compare and contrast the wireless mesh network and
the Ad-hoc network that are the categories in the
multi-hop wireless network.
- Explain the characteristics of wireless mesh
network and some of the factors of the mesh
networks influencing the performance. Are these
wireless network reliable and scalable?
- Can you explain some of the management functions
needed to maintain the operations of wireless mesh
networks?
Ad-hoc vs WMNs
There are various factors which can differentiate
wireless mesh network from Ad-hoc Network. The
major differences between these two types of network
are the network topology and mobility of node

Network topology: Ad-hoc network are called as
the infrastructure less network with a highly
dynamic topology where as WMN have a
relatively static network topology

Mobility of relay nodes: In Ad-hoc network the
relay nodes have a higher degree of mobility i.e.
relay nodes aren't fixed whereas in WMN's the
degree of mobility of relay node is much lower
than in Ad-hoc networks.
Ad-hoc vs WMNs



Deployment: Some planning is required to
deploy the WMNs whereas Ad- hoc network is
easy to deploy.
Infrastructure requirement: Ad-hoc network is
infrastructure less whereas WMN has partial or
fully fixed infrastructure.
Energy constraints: In Ad-hoc network energy
constraints is high whereas it is low in the
WMNs.
Characteristics of WMNs
Dynamic self-configuration and self-organization:
The nodes in a WMN automatically detect neighbor nodes and
establish and maintain network connectivity in an ad hoc
fashion.
Typically implemented at the network layer with the use of ad
hoc routing protocols
This self-configuring nature facilitates the easy and rapid
deployments of WMNs.
Adaptation:
WMNs dynamically adapt to the changing environments and can
self heal in case of link or node failure.
Fault tolerance and robustness:
Mesh networks are inherently redundant and hence have a high
level of fault tolerance and robustness.
Characteristics of WMNs
Low-Cost:
The low cost of the hardware based on IEEE 802.11 standards is
one of the prominent reasons in the increasing interests in both
research and product development.
Integration and interoperability:
Integration and inter-operation with other networks, and bridges
to legacy networks can be easily accommodated due to the fact
that most WMNs are based on Internet Protocol standards.
Factors Influencing performance
Radio techniques:
There are various approaches that have been proposed in order
to increase the capacity and flexibility of the wireless systems.
• e.g. Directional antennas and smart antennas, MIMO systems, and
multi-radio/multi-channel systems.
Reconfigurable radios, frequency agile/cognitive radios, and
even software are some of the more advanced technologies that
further improve the performance of a wireless radio.
All these advanced radio technologies are not mature and require
better design in higher layer protocols such as MAC and routing
protocols.
Factors Influencing performance
Scalability:
Without the support of scalability, which is the critical
requirement of WMNs, the network performance degrades as the
network size increases.
If that is the case, effects such as routing protocols may not be
able to find a reliable routing path, transport protocols may loose
connections, and MAC protocols may experience significant
throughput reduction may be prominent.
All the protocols (MAC layer to application layer) needs to be
scalable in order to ensure scalability in WMNs
Factors Influencing performance
Security:
There are many different security solutions proposed for wireless
LANs but the security schemes for WMNs are still not ready.
Due to the distributed nature of WMN, there is no centralized
authority that can be fully trusted and can distribute a public key.
Still, the security schemes that are proposed for ad hoc wireless
networks can be adopted for WMNs.
The architecture for ad hoc network is different, causing
differences in security mechanisms.
If ad hoc networks and WMNs were the same, still since, ad hoc
networks are still in its developmental stage, the security solution
it has is also not mature enough.
This suggests us to keep on looking for more secure and complete
mechanisms
Factors Influencing performance
Broadband and QoS
Most applications of WMNs are broadband services with
heterogeneous QoS requirements.
This is the reason why communication protocols must consider
various performance metrics.
Such performance metrics are: delay jitter, aggregate and pernode throughput, packet loss ratios along with end-to-end
transmission delay, and fairness.
Factors Influencing performance
Ease of Use:
The network management tools that efficiently maintain the
operation, monitor the performance, and configure the different
parameters of WMNs needs to be developed.
For the better performance of the network, routing protocol should
be designed in such a way that it is independent of the power
management, self organization behavior, and robustness in the link
failure and in providing the fast user authentication services.
The above mentioned management tools along with the
autonomous mechanisms in networking protocols helps in the rapid
deployment of WMNs.
Factors Influencing performance
Compatibility and Inter-operability
There are two types of clients: conventional clients and mesh
clients.
WMNs need to be backward compatible with conventional client
nodes i.e. it is a requirement to support both these clients.
This asks for more from the mesh routers. Mesh routers must be
capable of the integration of heterogeneous wireless networks.
Reliability and Scalability?
Reliability from self configuration and self organization
characteristics of the network. WMN automatically detect
neighbor nodes and establish and maintain network
connectivity in an ad hoc fashion, typically implemented at
the network layer through the use of ad hoc routing
protocols.
High level of fault tolerance makes it more reliable, since it
has multiple path for the delivery of data.
This network is scalable for a small network but may be
problematic while setting routing path for larger networks
as it may take longer time to set up the routing path and also
the end to end delay become larger.
Research is still going on to have the better routing protocol
that gives better scalability to the network.
Management Functions
Mobility Management:
Location management handles the location and call delivery.
Thus distributed mobility management is needed for WMN's.
Location information can enhance the performance of MAC and
routing protocols , and it can help to develop better location
related applications.
Proposing accurate or efficient algorithms for location service is
still an open research topic.
Mobility management is closely related to multiple layers of
network protocols, so developing multi-layer mobility
management schemes is another areas of research.
Management Functions
Power Management
Power management controls connectivity, interference,
spectrum-spatial reuse, and topology.
Mesh routers do not have a constraint on power consumption.
Mesh clients desire protocols to be power-efficient.
Network Monitoring
The statistics in the MIB of mesh routers need to be reported to
one or several servers in order to continuously monitor network
performance.
Based on the statistical information collected from the MIB,
data processing algorithms can accomplish many other
functions such as network topology monitoring.
Some Mesh Projects
Open-Source Projects
- OpenWRT http://openwrt.org
- Open-Mesh http://open-mesh.org
- Village Telco http://villagetelco.org
- Quick Mesh Project http://qmp.cat
- Weimarnetz https://weimarnetz.de
- Libre-Mesh http://libre-mesh.org
- Mesh Central https://meshcentral.com (Mesh App)
Comercial Projects
- Open-Mesh http://open-mesh.com
- HyMesh http://www.inovatian.com/hymesh
The Digital Mesh
Trend No. 1: The Device Mesh
Trend No. 2: Ambient User Experience
Trend No. 3: 3D-Printing Materials
Smart Machines
Trend No. 4: Information of Everything
Trend No. 5: Advanced Machine Learning
Trend No. 6: Autonomous Agents and Things
The New IT Reality
Trend No. 7: Adaptive Security Architecture
Trend No. 8: Advanced System Architecture
Trend No. 9: Mesh App and Service Architecture
Trend No. 10: Internet of Things Architecture and Platforms
http://www.gartner.com/smarterwithgartner/topten-technology-trends-signal-the-digital-mesh/
Questions???
Assignment#9

Prepare for Final Exam!