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Wireless Mesh Networks

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Title: Wireless Mesh Networks


1
Wireless Mesh Networks
2
Introduction
  • Wireless mesh network architecture
  • Why Wireless mesh network?
  • When Wireless mesh networks?
  • Routing background
  • Problems in existing routing protocols
  • Problems in frequency allocation

3
Existing wireless networking technologies
4
Wireless Mesh Networks
  • A wireless mesh network (WMN) is a communications
    network made up of radio nodes organized in
    a mesh topology.
  • Wireless mesh networks often consist of
  • mesh clients
  • mesh routers
  • Mesh routers contain additional routing
    functionality due to the presence of wireless
    interface card in them
  • Nodes have two functions
  • Generate/terminate traffic
  • Route traffic for other nodes

5
Characteristics of Wireless mesh networks
  • Multihop Wireless network.
  • Support for adhoc networking and capability of
    self forming, self healing and self organization.
  • Mobility dependence on the type of mesh node.
  • Multiple types of network access.
  • Dependence of power consumption constraints on
    the type of mesh nodes

6
Why WMN?
  • Multi-hop wireless network
  • Support for ad-hoc networking, and capability of
    self-forming, self healing and self organization.
  • Multiple types of network access
  • Mobility dependence on the type of mesh nodes
  • Compatibility and interpretability with existing
    wireless technologies

7
  • Compatibility and inter operatability with
    existing wireless networks
  • Dedicated routing and configuration
  • Mobility

8
Types of WMN
  • Infrastructure/ Backbone WMN
  • Client WMN
  • Hybrid WMN

9
Infrastructure/Backbone WMN
  • Mesh routers form an mesh infrastructure among
    themselves.
  • Provides backbone for clients and enables
    integration of WMNs with existing wireless
    networks and Internet through gateway/bridge
    functionalities.
  • Clients connect to mesh router with wireless link
    or Ethernet

10
Infrastructure/Backbone WMN
11
Client WMN
  • 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
    required
  • Multi-hop routing.
  • Client nodes have to perform additional functions
    such as routing and self-configuration.

12
Client WMN
13
Hybrid WMN
  • A combination of infrastructure and client
    meshing.
  • 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

14
Hybrid WMN
15
Protocol Design
  • Physical Layer
  • Mac Layer
  • Network Layer
  • Transport Layer
  • Application Layer

16
Physical Layer
  • 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.

17
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
    must
  • work for multipoint-to-multipoint
    communication.
  • Network self-organization is needed for better
    collaboration between neighboring nodes and nodes
    in multi-hop distances.
  • Mobility affects the performance of MAC.

18
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
    WMNs.

19
Routing Layer
  • Robustness
  • WMNs must be robust to link failures or
    congestion.
  • Routing protocols need to be fault tolerant with
    link failures and can achieve load balancing.
  • Adaptive Support of Both Mesh Routers and Mesh
    Clients
  • 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
    clients.

20
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.

21
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
    Networks.
  • Cellular phone talks Wi-Fi phone through WMNs,
  • Wi-Fi user monitors the status of wireless sensor
    networks.

22
WMN Standards
  • WPAN Bluetooth, Zigbee
  • WiFi 802.11a, b, g, n
  • WiMAX 802.16

23
WMN 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.

24
WMN 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

25
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
    WMNs.

26
When WMN?
  • Broadband home networking
  • Community and neighborhood networking
  • Enterprise networking
  • Wireless mesh networks
  • Transportation systems
  • Building automation
  • Health and medical systems
  • Security surveillance systems

27
Mesh vs. Ad-Hoc Networks
Ad-Hoc Networks
Wireless Mesh Networks
  • Multihop
  • Nodes are wireless, some mobile, some fixed
  • It relies on infrastructure
  • Most traffic is user-to-gateway
  • Multihop
  • Nodes are wireless, possibly mobile
  • May rely on infrastructure
  • Most traffic is user-to-user

28
Mesh vs. Sensor Networks
Wireless Mesh Networks
Wireless Sensor Networks
  • Bandwidth is generous (gt1Mbps)
  • Some nodes mobile, some fixed
  • Normally not energy limited
  • Resources are not an issue
  • Most traffic is user-to-gateway
  • Bandwidth is limited (tens of kbps)
  • In most applications, fixed nodes
  • Energy efficiency is an issue
  • Resource constrained
  • Most traffic is user-to-gateway

29
Ad Hoc Networks
  • An ad-hoc network is a wireless local area
    network (LAN) that is built spontaneously as
    devices connect.
  • Instead of relying on a base station to
    coordinate the flow of messages to each node in
    the network, the individual network nodes forward
    packets to and from each other.

30
Contd
  • Formed by wireless hosts which may be mobile.
  • Dont need a pre-existing infrastructure/backbone.
  • Routes between nodes pottentially contain
    multiple hopes.

31
Why MANET??
  • Ease, speed of deployment
  • Decreased dependence on infrastructure.
  • Can be used in many scenerios where deployment of
    wired network is impossble
  • Lots of military applications

32
History of Ad Hoc networks
  • In situations where networks are constructed and
    destructed in ad-hoc manner, mobile ad-hoc
    networking is an excellent choice.
  • The idea of mobile ad-hoc or packet radio
    networks has been under development since 1970s.
    Since the mid-90s, when the definition of
    standards such as IEEE802.11 (what we think of as
    WiFi or just 802.11) helped cause commercial
    wireless technology to emerge, mobile ad-hoc
    networking has been identified as a challenging
    evolution in wireless technology.

33
Characteristics of Ad Hoc networks
  • Every node is responsible for forwarding packets
    to other nodes
  • Nodes themselves implement security function
    among themselves
  • Topology changes continuously as nodes are highly
    mobile.
  • Purpose Specific
  • Dynamic
  • No master-slave relationship (Every node is a
    router)

34
Types of MANETs
  • Fully symmetric environment
  • Asymmetric characteristics
  • Asymmetric responsibilities

35
Fully symmetric environment
  • All nodes have identical capabilities and
    respoonsibilities

36
Asymmetric capabilities
  • Transmission range and radios may differ
  • Battery life at different nodes may differ
  • Processing capacity may be different at different
    nodes
  • Speed of movement different

37
Asymmetric responsibilities
  • Only some nodes may route packets
  • Some nodes may act as leader for nearby nodes
    e.g. cluster haed

38
Other variants
  • Traffic characteristics may differ
    (bandwidth,realibility, unicast/multicast/broadcas
    t )
  • Mobility patterns may be different (Little/
    Highly mobile)
  • Mobility characteristics may differ (speed,
    direction of movement, pattern of movement)

39
Challenges
  • Limited wireless transmission range
  • Broadcast nature of wireless medium
  • Packet losses due to transmission errors
  • Environmental issues
  • Mobility induced route changes
  • Mobility induced packet losses
  • Battery constraints

40
Characteristics of Ad Hoc networks
  • Connectivity among the hosts changes with time
  • Nodes are low power devices, low CPU process
    capability, and low memory.
  • Due to above reasons the existing routing
    protocols are highly unstable.

41
Routing protocols
  • Proactive
  • Determine route independent of traffic pattern
  • Used in traditional wired network
  • Reactive
  • Discover/ maintain routes only if needed.

42
Tradeoff of proactive vs reactive
  • Proactive has low while reactive has high latency
  • Reactive have low overhead while proactive have
    high overhead

43
Metrics for Ad Hoc routing
  • Number of hops
  • Distance
  • Latency
  • Load balancing for congested loads
  • cost

44
Wireless Standards for Mobile Ad Hoc networks
  • 802.11b
  • 802.11a
  • 802.11g
  • 802.11n

45
8002.11b
  • Developed in July 1999
  • Maximum bandwidth11 Mbps
  • Uses 2.4 GHZ Frequency range
  • Low cost

46
802.11a
  • Developed in 2001
  • Maximum bandwidth 54 Mbps
  • Uses 5 GHZ frequency band
  • Much faster than 802.11b

47
802.11g
  • Developed in 2003
  • Modified version of 802.11b
  • Maximum bandwidth 54Mbps
  • Uses frequency range2.4 GHZ

48
802.11n
  • Used for faster and long distance communication
  • Not formally published and approved yet.

49
Applications
  • Personal area network
  • Civilian environment
  • Emergency operations
  • Sensor networks
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