Wireless Mesh Network

1
Wireless Mesh Network

• Members
• Suman Raj Adhikari
• Saroj Raj Regmi

2
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
  co-operate with each other in transmitting
  packets through the network.
• WMNs are believed to be self-configuring and
  self-healing networks.
• Dramatic increase in link quality just by
  shortening the distance between the nodes

3
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.

4
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.

5
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

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Infrastructure Mesh

• In infrastructure mesh architecture, the mesh
  routers collectively provide a wireless backbone
  infrastructure. Client node is passive in mesh
  infrastructure.

7
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

8
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.

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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.

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Characteristics

• Dynamic self-configuration and self-organization
• Adaptation
• Fault tolerance and robustness
• Low-Cost
• Integration and interoperability

11
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.

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Applications

• Broadband home networking
• Community and neighborhood networking
• Enterprise networking
• Metropolitan area networks
• Transportation systems
• Building automation

13
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.

14
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.

15
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 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, delay-spread,
  co-channel interference, fading, multi-antenna,
  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.

16
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

17
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.

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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.

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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 tradeoff between delay and throughput.

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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.

21
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.

22
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.

23
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.

24
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.

25
Issues

• Issue 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 Issue
• Capacity, scalability, and QoS are considered
  as the major weakness of current WMN technology

26
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.

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Conclusion

• Integration and interoperation 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 researchs
  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.

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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

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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?

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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 netowrks.

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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.

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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.

33
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 interoperation 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.

34
Factors Influencing performance

• Radio techniques
• There are various approaches that have been
  proposed inorder 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.

35
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

36
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

37
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 per-node throughput, packet loss
  ratios along with end-to-end transmission delay,
  and fairness.

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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.

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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.

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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.

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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.

42
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.