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Wireless Mesh Network

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Wireless Mesh Network Members Suman Raj Adhikari ... Can you explain some of the management functions needed to maintain the operations of wireless mesh networks? – PowerPoint PPT presentation

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Title: 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

6
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.

9
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.

10
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.

12
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.

18
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.

19
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.

20
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.

27
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.

28
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

29
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?

30
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.

31
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.

32
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.

38
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.

39
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.

40
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.

41
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.
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