Transcript Wireless Mesh Networks

Wireless Mesh Networks
Introduction
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Wireless mesh network architecture
Why Wireless mesh network?
When Wireless mesh networks?
Routing background
Problems in existing routing protocols
Problems in frequency allocation
Existing wireless networking
technologies
Wireless Mesh Networks
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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
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mesh clients
mesh routers
Mesh routers contain additional routing functionality due to the
presence of wireless interface card in them
Nodes have two functions:
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Generate/terminate traffic
Route traffic for other nodes
Characteristics of Wireless mesh
networks
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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
Why WMN?
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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
Types of WMN
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Infrastructure/ Backbone WMN
Client WMN
Hybrid WMN
Infrastructure/Backbone WMN
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Mesh routers form an mesh infrastructure among
themselves.
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Provides backbone for clients and enables
integration of WMNs with existing wireless networks
and Internet through gateway/bridge functionalities.
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Clients connect to mesh router with wireless link or
Ethernet
Infrastructure/Backbone WMN
Client WMN
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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”
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Multi-hop routing.
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Client nodes have to perform additional functions
such as routing and self-configuration.
Client WMN
Hybrid WMN
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A combination of infrastructure and client meshing.
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Infrastructure provides connectivity to other networks such as
the Internet, Wi-Fi, WiMAX, cellular, and sensor networks;
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Mesh clients can access the network through mesh routers as
well as directly meshing with other mesh clients.
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The routing capabilities of clients provide better connectivity
and coverage
Hybrid WMN
Protocol Design
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Physical Layer
Mac Layer
Network Layer
Transport Layer
Application Layer
Physical Layer
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Orthogonal frequency multiple access (OFDM) has significantly
increased the speed of IEEE 802.11 from 11 mbps to 54 mbps.
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Ultra-wide band (UWB) can achieve much higher rate for shortdistance applications.
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MIMO can increase system capacity by three times or even
more.
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Frequency agile or cognitive radios can achieve much better
spectrum utilization.
MAC Layer
Differences between WMNs MACs and Wireless Networks MACs
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MACs for WMNs are concerned with more than one hop
communication
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MAC must be distributed and collaborative, and must
work for multipoint-to-multipoint communication.
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Network self-organization is needed for better collaboration between
neighboring nodes and nodes in multi-hop distances.
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Mobility affects the performance of MAC.
Routing Layer
Features of routing protocol for WMNs:
 Multiple Performance Metrics
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Hop-count is not an effective routing metric.
Other performance metrics, e.g., link quality and round trip
time (RTT), must be considered.
Scalability
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Routing setup in large network is time consuming.
Node states on the path may change.
Scalability of routing protocol is critical in WMNs.
Routing Layer
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Robustness
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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
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Mesh routers : minimal mobility, no constraint of power consumption,
routing is simpler
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Mesh clients : mobility, power efficiency, routing is complicated
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Need to design a routing protocol that can adaptively support both
mesh routers and mesh clients.
Transport layer: research issues
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Cross-layer Solution to Network Asymmetry
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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
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WMNs will be integrated with the Internet and various wireless networks
such as IEEE 802.11, 802.16, 802.15, etc.
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Same TCP is not effective for all networks.
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Applying different TCPs in different networks is a complicated and costly
approach, and cannot achieve satisfactory performance.
Application layer
Applications supported by WMNs:
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Internet Access
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Distributed Information Storage and Sharing
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Advantages of WMNs: low cost, higher speed, and easy installation.
Data sharing between nodes within WMNs
Query/retrieve information located in distributed database servers.
Information Exchange across Multiple Wireless Networks.
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Cellular phone talks Wi-Fi phone through WMNs,
Wi-Fi user monitors the status of wireless sensor networks.
WMN Standards
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WPAN: Bluetooth, Zigbee
WiFi: 802.11a, b, g, n
WiMAX: 802.16
WMN Standards
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IEEE 802.16a WMAN Mesh
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“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 2–11 GHz, allowing non-line-of-sight (NLO)
communications, spanning up to a 50 km range.
Supporting multihop communications.
WMN Standards
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802.11s WLAN Mesh
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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
Routing Layer
Features of routing protocol for WMNs:
 Multiple Performance Metrics
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Hop-count is not an effective routing metric.
Other performance metrics, e.g., link quality and round trip
time (RTT), must be considered.
Scalability
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Routing setup in large network is time consuming.
Node states on the path may change.
Scalability of routing protocol is critical in WMNs.
When WMN?
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Broadband home networking
Community and neighborhood networking
Enterprise networking
Wireless mesh networks
Transportation systems
Building automation
Health and medical systems
Security surveillance systems
Mesh vs. Ad-Hoc Networks
Ad-Hoc Networks
 Multihop
 Nodes are wireless,
possibly mobile
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May rely on
infrastructure
Most traffic is userto-user
Wireless Mesh Networks
 Multihop
 Nodes are wireless,
some mobile, some
fixed
 It relies on
infrastructure
 Most traffic is user-togateway
Mesh vs. Sensor Networks
Wireless Mesh Networks
Wireless Sensor Networks
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Bandwidth is limited (tens of
kbps)
In most applications, fixed
nodes
Energy efficiency is an issue
Resource constrained
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Most traffic is user-to-gateway
Bandwidth is generous
(>1Mbps)
Some nodes mobile, some
fixed
Normally not energy limited
Resources are not an issue
Most traffic is user-to-gateway
Ad Hoc Networks
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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.
Contd…
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Formed by wireless hosts which may be
mobile.
Don’t need a pre-existing
infrastructure/backbone.
Routes between nodes pottentially contain
multiple hopes.
Why MANET??
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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
History of Ad Hoc networks
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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.
Characteristics of Ad Hoc networks
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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)
Types of MANET’s
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Fully symmetric environment
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Asymmetric characteristics
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Asymmetric responsibilities
Fully symmetric environment
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All nodes have identical capabilities and
respoonsibilities
Asymmetric capabilities
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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
Asymmetric responsibilities
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Only some nodes may route packets
Some nodes may act as leader for nearby
nodes e.g. cluster haed
Other variants
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Traffic characteristics may differ
(bandwidth,realibility,
unicast/multicast/broadcast )
Mobility patterns may be different (Little/
Highly mobile)
Mobility characteristics may differ (speed,
direction of movement, pattern of movement)
Challenges
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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
Characteristics of Ad Hoc networks
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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.
Routing protocols
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Proactive:
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Determine route independent of traffic pattern
Used in traditional wired network
Reactive:
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Discover/ maintain routes only if needed.
Tradeoff of proactive vs reactive
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Proactive has low while reactive has high
latency
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Reactive have low overhead while proactive
have high overhead
Metrics for Ad Hoc routing
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Number of hops
Distance
Latency
Load balancing for congested loads
cost
Wireless Standards for Mobile Ad Hoc
networks
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802.11b
802.11a
802.11g
802.11n
8002.11b
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Developed in July 1999
Maximum bandwidth=11 Mbps
Uses 2.4 GHZ Frequency range
Low cost
802.11a
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Developed in 2001
Maximum bandwidth= 54 Mbps
Uses 5 GHZ frequency band
Much faster than 802.11b
802.11g
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Developed in 2003
Modified version of 802.11b
Maximum bandwidth =54Mbps
Uses frequency range=2.4 GHZ
802.11n
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Used for faster and long distance
communication
Not formally published and approved yet.
Applications
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Personal area network
Civilian environment
Emergency operations
Sensor networks