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Wireless Mesh Networks


Wireless Mesh Networks By Cunqing Hua The notes of this talk are excerpted from the lecture notes by Prof. Akyildiz at Georgia Institute of Technology – PowerPoint PPT presentation

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Title: Wireless Mesh Networks

Wireless Mesh Networks
By Cunqing Hua
  • The notes of this talk are excerpted from the
    lecture notes by Prof. Akyildiz at Georgia
    Institute of Technology

  • Faccin, S.M. Wijting, C. Kenckt, J. Damle, A.,
    Mesh WLAN networks concept and system design,
    IEEE Wireless Communication, Vol 13, No. 2, 2006.
  • Lee, M.J. Jianliang Zheng Young-Bae Ko
    Shrestha, D.M., Emerging standards for wireless
    mesh technology, IEEE Wireless Communication, Vol
    13, No. 2, 2006
  • Akyildiz, I.F., Wang, X. and Wang, W., Wireless
    Mesh Networks A Survey, Computer Networks
    Journal (Elsevier), March 2005.

  • Application Scenarios
  • Network Architecture
  • Characteristics
  • Protocols Design
  • Standardization Activities

Wireless Mesh Networks
  • Wireless Mesh Networks (WMN) are the networks in
    which each node can communicate directly with one
    or more peer nodes.
  • Different from traditional wireless networks
    (e.g. 802.11 WLANs) requiring centralized access
    points to mediate the wireless connection.
  • Each node operates not only as a host but also as
    a router, forwarding packets on behalf of other
    nodes that may not be within direct wireless
    transmission range of their destinations.
  • It is dynamically self-organized and
    self-configured, nodes can automatically
    establishing and maintaining mesh connectivity
    among nodes

Application Scenarios
  • Broadband Home Networking
  • Community and Neighborhood Networking
  • Enterprising Networking
  • Metropolitan Area Networking
  • Transportation Systems
  • Building Automation
  • Health and Medical Systems
  • Security and Surveillance Systems

Broadband Home Networking
  • Current home network realized through IEEE 802.11
  • Problem ? location of the access points.
  • Homes have many dead zones without service
  • Site survey are expensive and not practical
  • Installation of multiple access points is also
    expensive and not convenient.
  • Communications between nodes under two different
    access points have to go through the access hub,
    not an efficient solution.

WMNs can resolve all these issues in home
Community and Neighborhood Networking
  • Community networks based on cable, DSL and
    last-hop wireless
  • All traffic must flow through Internet, this
    significantly reduces network resource
  • Large percentage of areas in between houses is
    not covered by wireless services.
  • Gateways may not be shared and wireless services
    must be set up individually, network service
    costs may increase.
  • Each home has single path to access Internet

WMNs can mitigate these disadvantages and provide
many applications such as distributed file
storage, distributed file access, and video
Enterprise Networking
  • IEEE 802.11 WLANs
  • Isolated islands, connections among them are
    achieved through wired Ethernet
  • Adding more backhaul access modems only increases
    capacity locally, but does not improve robustness
    to link failures, network congestion and other
    problems of the entire enterprise network.
  • WMNs Solutions
  • Multiple backhaul access modems can be shared by
    all nodes in the entire network
  • Scalable

Metropolitan Area Networks
  • WMNs provide higher transmission rate than
    cellular networks,
  • The communication between nodes does not rely on
    a wired backbone.
  • An economic alternative to broadband networking
  • Covers larger area than home, enterprise,
    building, or community networks.
  • Higher scalability

Transportation Systems
  • WMNs can extend access from stations and stops
    into buses, ferries, and trains.
  • Convenient passenger information services, remote
    monitoring of in-vehicle security video, and
    driver communications.
  • Two key techniques are needed
  • High-speed mobile backhaul from a vehicle to the
  • Mobile mesh networks within the vehicle.

Building Automation
  • Various electrical devices need to be controlled
    and monitored.
  • Standard wired networks is very expensive
  • Wi-Fi networks can reduce the cost of such
    networks. However, the deployment of Wi-Fis for
    this application is still expensive.
  • Low deployment cost of BACnet (Building
    Automation and Control Networks) with WMNs

Health and Medical Systems
  • Monitoring and diagnosis data need to be
    processed and transmitted across rooms for
    various purposes.
  • Large data volume by high resolution medical
    images, various periodical monitoring information
  • Wi-Fi based networks must rely on the existence
    of Ethernet connections, cause high system cost,
    complexity and dead spots.
  • However, these issues do not exist in WMNs.

Security and Surveillance Systems
  • Security surveillance systems is necessity for
    enterprise buildings, shopping malls, grocery
    stores, etc.
  • Still images and videos are the major traffic
    flowing in the network, this application demands
    much higher network capacity than other
  • WMNs are a much more viable solution than wired
    networks to connect all devices.

Network Architecture
  • WMNs consist of two types of nodes Mesh Routers
    and Mesh Clients
  • Mesh router
  • Additional routing functions to support mesh
  • Multiple wireless interfaces with same or
    different wireless access technologies.
  • The gateway/bridge functionalities enable the
    integration of WMNs with existing wireless
    networks(cellular, sensornet, Wi-Fi, WiMAX).
  • Mesh Clients
  • Conventional nodes (e.g., desktops, laptops,
    PDAs, PocketPCs, phones, etc.) equipped with
    wireless network interface cards (NICs), and can
    connect directly to wireless mesh routers.
  • Customers without wireless NICs can access WMNs
    by connecting to wireless mesh routers through,
    e.g., Ethernet.

WMN Routers
Examples of mesh routers based on different
embedded systems (a) PowerPC and (b)
Advanced Risc Machines (ARM)
WMN Clients
Examples of mesh clients (a) Laptop, (b) PDA,
(c) Wi-Fi IP Phone and (d) Wi-Fi RFID Reader.
WMN Architecture Classifications
  • Infrastructure Meshing
  • Client Mesh Networking
  • Hybrid Mesh Networking

Infrastructure Meshing
  • Mesh routers form an mesh infrastructure among
  • Provides backbone for clients and enables
    integration of WMNs with existing wireless
    networks and Internet through gateway/bridge
  • Clients connect to mesh router with wireless link
    or Ethernet

Client WMNs
  • Client nodes constitute peer-to-peer network, and
    perform routing and configuration
    functionalities as well as provide end-user
    applications to customers, mesh routers are not
  • Multi-hop routing.
  • Client nodes have to perform additional functions
    such as routing and self-configuration.

Hybrid WMNs
  • A combination of infrastructure and client
  • Infrastructure provides connectivity to other
    networks such as the Internet, Wi-Fi, WiMAX,
    cellular, and sensor networks
  • Mesh clients can access the network through mesh
    routers as well as directly meshing with other
    mesh clients.
  • The routing capabilities of clients provide
    better connectivity and coverage

WMNs Characteristics
  • Multi-hop wireless networks
  • Support for Ad Hoc networking, and capability
    of self-forming, self-healing, and
  • Mobility dependence on the type of mesh nodes
  • Multiple types of network access
  • Dependence of power-consumption constraints on
    the type of mesh nodes
  • Compatibility and interoperability with existing
    wireless networks

Protocol Design
  • Physical Layer
  • Mac Layer
  • Network Layer
  • Transport Layer
  • Application Layer
  • Network Management
  • Security

Physical Layer Technologies
  • Orthogonal frequency multiple access (OFDM) has
    significantly increased the speed of IEEE 802.11
    from 11 mbps to 54 mbps.
  • Ultra-wide band (UWB) can achieve much higher
    rate for short-distance applications.
  • MIMO can increase system capacity by three times
    or even more.
  • Frequency agile or cognitive radios can achieve
    much better spectrum utilization.

Physical Layer Research Issues
  • Improve the transmission rate and the performance
    of physical layer techniques
  • Multiple-antenna systems
  • Frequency agile
  • Design higher layer protocols to utilize the
    advanced features provided by physical layers
  • MAC protocols for directional and smart antennas
  • MAC protocols for MIMO systems
  • Communication protocols for cognitive radios

MAC Layer
  • Differences between WMNs MACs and Wireless
    Networks MACs
  • MACs for WMNs are concerned with more than one
    hop communication
  • MAC must be distributed and collaborative, and
  • work for multipoint-to-multipoint
  • Network self-organization is needed for better
    collaboration between neighboring nodes and nodes
    in multi-hop distances.
  • Mobility affects the performance of MAC.

Single Channel MACs
  • Improving Existing MAC Protocols
  • Adjust parameters of CSMA/CA
  • Only achieve a low end-to-end throughput.
  • Cross-layer design with advanced physical layer
  • MAC based on directional antenna can eliminate
    exposed nodes, but may introduce more hidden
  • MAC with power control can reduce exposed nodes,
    improve spatial-reuse, but hidden nodes still
  • Proposing Innovative MAC Protocols
  • Revisiting MAC protocols based on TDMA or CDMA
  • Design complexity and cost.
  • Compatibility with existing MAC protocols
  • Not scalable, available bandwidth (1/2)n

Multi-Channel MACs
  • Multi-Channel Single-Transceiver MAC
  • Only one channel is active in each node,
    different nodes can use different channels.
  • Need to coordinate transmissions between nodes
  • Multi-Channel Multi-Transceiver MACs
  • Multiple parallel RF front-end chips and baseband
  • One MAC layer module to coordinate multiple
  • Multi-Radio MACs
  • Multiple radios, each with its own MAC and
    physical layers.
  • Communications in these radios are totally
  • A virtual MAC protocol to coordinate
    communications in all channels.

MAC Layer Research Issues
  • Scalable Single-Channel MACs
  • Distributed and collaborative schemes to ensure
  • Scalable Multi-Channel MACs
  • Overall performance improvement in multiple
  • Network Integration in the MAC Layer
  • Advanced bridging functions in the MAC layer so
    that different wireless radios can seamlessly
    work together.
  • Reconfigurable/software radios may be the
    ultimate solution to these bridging functions.
  • MAC Protocol Implementation
  • Modifying functions in the firmware or hardware
    is much more complicated and costly.
  • New architecture such that MAC functions can be
    completely implemented in the software.

Routing Layer
  • Features of routing protocol for WMNs
  • Multiple Performance Metrics
  • Hop-count is not an effective routing metric.
  • Other performance metrics, e.g., link quality and
    round trip time (RTT), must be considered.
  • Scalability
  • Routing setup in large network is time consuming.
  • Node states on the path may change.
  • Scalability of routing protocol is critical in

Routing Layer
  • Robustness
  • WMNs must be robust to link failures or
  • Routing protocols need to be fault tolerant with
    link failures and can achieve load balancing.
  • Adaptive Support of Both Mesh Routers and Mesh
  • Mesh routers minimal mobility, no constraint of
    power consumption, routing is simpler
  • Mesh clients mobility, power efficiency,
    routing is complicated
  • Need to design a routing protocol that can
    adaptively support both mesh routers and mesh

Destination-Sequenced Distance-Vector (DSDV)
  • Proactive Protocols
  • Each node maintains a routing table which stores
  • next hop towards each destination
  • a cost metric for the path to each destination
  • a destination sequence number that is created by
    the destination itself
  • Sequence numbers used to avoid formation of loops
  • Each node periodically forwards the routing table
    to its neighbors
  • Each node increments and appends its sequence
    number when sending its local routing table
  • This sequence number will be attached to route
    entries created for this node
  • DSDV in WMNs
  • Supporting multidimensional cost metrics (QoS,
    power efficiency, security, etc)

DSDV Protocol
  • Assume that node X receives routing information
    from Y about a route to node Z
  • Let S(X) and S(Y) denote the destination sequence
    number for node Z as stored at node X, and as
    sent by node Y with its routing table to node X,

DSDV Protocol
  • Node X takes the following steps
  • If S(X) gt S(Y), then X ignores the routing
    information received from Y
  • If S(X) S(Y), and cost of going through Y is
    smaller than the route known to X, then X sets Y
    as the next hop to Z
  • If S(X) lt S(Y), then X sets Y as the next hop to
    Z, and S(X) is updated to equal S(Y)

Routing Layer- Research Issues
  • Scalability
  • Hierarchical routing protocols can only partially
    solve this problem
  • Geographic routing relies positioning
  • New scalable routing protocols need to be
  • Better Performance Metrics
  • New performance metrics need to be developed.
  • Need to integrate multiple performance metrics
    into a routing protocol

Routing Layer - Research Issues
  • Routing/MAC Cross-Layer Design
  • Needs to interact with the MAC layer, e.g.
    adopting multiple performance metrics from MAC
  • Merely exchanging parameters between them is not
    enough, merging certain functions of MAC and
    routing protocols is a promising approach.
  • For multi-radio or multi-channel routing, the
    channel/radio selection in the MAC layer can help
    the path selection in the routing layer.
  • Hybrid Routing
  • Mesh routers and mesh clients have different
    constraints in power efficiency and mobility.
  • Need to adaptively support mesh routers and mesh

Transport Layer Research Issues
  • Cross-layer Solution to Network Asymmetry
  • Routing protocol can select an optimal path for
    both data and ACK packets.
  • MAC layer and error control may need to treat TCP
    data and ACK packets differently.
  • Adaptive TCP
  • WMNs will be integrated with the Internet and
    various wireless networks such as IEEE 802.11,
    802.16, 802.15, etc.
  • Same TCP is not effective for all networks.
  • Applying different TCPs in different networks is
    a complicated and costly approach, and cannot
    achieve satisfactory performance.

Application Layer
  • Applications supported by WMNs
  • Internet Access
  • Advantages of WMNs low cost, higher speed, and
    easy installation.
  • Distributed Information Storage and Sharing
  • Data sharing between nodes within WMNs
  • Query/retrieve information located in distributed
    database servers.
  • Information Exchange across Multiple Wireless
  • Cellular phone talks Wi-Fi phone through WMNs,
  • Wi-Fi user monitors the status of wireless sensor

Application Layer Research Issues
  • Improve Existing Application Layer Protocols.
  • Lower layers protocols cannot provide perfect
    support for the application layer.
  • E.g., packet loss and packet delay with a large
    jitter may fail many Internet applications
  • Existing application layer protocols need to be
  • New Application Layer Protocols for Distributed
    Information Sharing.
  • P2P protocols on the Internet may not perform
    well in WMNs,
  • New application layer protocols need to be
  • Develop Innovative Applications for WMNs
  • Applications cannot achieve best performance
    without WMNs.
  • Enable WMNs to be a unique networking solution
    instead of just another option of wireless

Network Management Protocols
  • Mobility Management
  • Distributed scheme for WMNs can be simpler
    because the existence of backbone nodes
  • Take advantages of the network backbone to design
    a light-weight distributed mobility management
    scheme for WMNs.
  • Location service is a desired feature by WMNs.
  • Power Management
  • For mesh routers, power management aims to
    control connectivity, interference, spectrum
    spatial-reuse, and topology.
  • For mesh clients, protocols should be power

Network Management Protocols
  • Network Monitoring
  • Report statistics in the MIB to one or several
  • Data processing algorithms analyze these
    statistical data and determine potential
  • To reduce overhead, schemes for efficient
    transmission of network monitoring information
    are expected.
  • To accurately detect abnormal operation and
    quickly derive network topology of WMNs,
    effective data processing algorithms need to be

  • WMNs lack efficient and scalable security
  • Distributed network architecture
  • Vulnerability of channels and nodes in the shared
    wireless medium
  • Dynamic change of network topology.
  • Two strategies
  • Embedding security mechanism into network
  • Developing security monitoring response systems
  • How to design and implement a practical security
    system, including cross-layer secure network
    protocols and various intrusion detection
    algorithms, is a challenging research topic.

WMNs Standards
  • WPAN Bluetooth, Zigbee
  • WiFi 802.11a, b, g, n
  • WiMAX 802.16

Data Rate
WMNs Standards
  • IEEE 802.16a WMAN Mesh
  • mesh mode in addition to the point-to-multipoint
    (PMP) mode defined in IEEE 802.16.
  • Operating in the licensed and unlicensed lower
    frequencies of 211 GHz, allowing
    non-line-of-sight (NLO) communications, spanning
    up to a 50 km range.
  • Supporting multihop communications.

WMNs Standards
  • 802.11s WLAN Mesh
  • Multi-hop capability added to 802.11g/a/b
  • Auto configure on power up
  • Multi-channel multi-radio operation
  • Topology discovery
  • MAC Path selection protocol
  • Modified forwarding for QOS and mesh control

WMNs Standards
  • 802.11s MCF Sublayer
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