Wireless Mesh Networks

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Wireless Mesh Networks
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Introduction

• Wireless mesh network architecture
• Why Wireless mesh network?
• When Wireless mesh networks?
• Routing background
• Problems in existing routing protocols
• Problems in frequency allocation

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Existing wireless networking technologies
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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

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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

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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

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

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Types of WMN

• Infrastructure/ Backbone WMN
• Client WMN
• Hybrid WMN

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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

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Infrastructure/Backbone WMN
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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.

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Client WMN
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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

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Hybrid WMN
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Protocol Design

• Physical Layer
• Mac Layer
• Network Layer
• Transport Layer
• Application Layer

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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.

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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.

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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.

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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.

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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.

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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.

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WMN Standards

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

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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.

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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

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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.

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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

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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

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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

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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.

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Contd

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

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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

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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.

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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)

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Types of MANETs

• Fully symmetric environment
• Asymmetric characteristics
• Asymmetric responsibilities

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Fully symmetric environment

• All nodes have identical capabilities and
  respoonsibilities

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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

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Asymmetric responsibilities

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

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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)

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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

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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.

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Routing protocols

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

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Tradeoff of proactive vs reactive

• Proactive has low while reactive has high latency
• Reactive have low overhead while proactive have
  high overhead

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Metrics for Ad Hoc routing

• Number of hops
• Distance
• Latency
• Load balancing for congested loads
• cost

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Wireless Standards for Mobile Ad Hoc networks

• 802.11b
• 802.11a
• 802.11g
• 802.11n

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8002.11b

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

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802.11a

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

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802.11g

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

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802.11n

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

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Applications

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