A Survey on Wireless Mesh Networks (WMN)

A Survey on Wireless Mesh Networks
By: Mr. Eyob Sisay (RM0231/10),
School of Electrical and Computer Engineering,
Jimma Institute of Technology,
Jimma University,
Ethiopia
W e l c o m e !

Discussion Points:
 Introduction to WMNs
 The network architectures of WMNs
 Critical factors influencing protocol design
 Open Areas for Research on WMNs
 Result and Analysis
 Conclusions
8/16/2018Eyob S.

I n t r o d u c t i o n
 Wireless mesh networks (WMNs) are comprised of
mesh routers and mesh clients.
 A mesh router contains additional support for mesh networking
with lower transmission power.
 WMNs.. but diversify the capabilities of ad-hoc networks.
Application scenarios:
 broadband home networking, community networking, building
automation, high speed MANs, and enterprise networking.
 IEEE 802.11, IEEE 802.15, IEEE 802.16, are specifications.
18/16/2018Eyob S.

A r c h i t e c t u r e
The architecture of WMNs classified into three types:
1 - Infrastructure/Backbone WMNs.
 enables integration of WMNs with existing wireless networks, via
gateway/bridge functionalities in mesh routers.
2 - Client WMNs.
 Provides peer-to-peer networks among clients.
 No mesh router, same as a conventional ad hoc network.
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Cont..
3 - Hybrid WMNs.
 Combination of both Client and infrastructure meshing.
 clients access through mesh routers or other mesh clients
directly.
 While the infrastructure provides connectivity to other
networks such as Internet, Wi-Fi, WiMAX, Cellular and Sensor
networks, the routing capabilities of clients provide improved
connectivity and coverage inside WMNs.
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Design Factors
 Radio Techniques.
 directional and smart antennas, MIMO and Multi-radio/multi-channel
systems.
 Scalability. - all layers
 Mesh Connectivity.
 Broadband and QoS.
 Most applications are broadband services
 Need more performance metrics
 besides delay, fairness
 delay jitter, aggregate and per-node throughput, packet loss ratio.
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Cont..
8/16/2018Eyob S.
 Security.
 Many schemes of wireless LANs or ad hoc are not fully applicable for
WMNs.
 Ease of Use.
 Autonomous network
 Network management tools.
 Compatibility and Inter-operability.
 Backward compatibility with conventional client nodes
 Integrating heterogeneous wireless networks
7

Advances and Research
Challenges
Despite recent advances in the R. and D. in WMNs, many
challenging problems still remain: the theoretical network
capacity is still unknown, protocols in various layers need
to be improved, new schemes are required for network
management, and the network still lacks security.
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Network Capacity
8/16/2018Eyob S.
 WMNs still have very limited capabilities of integrating
heterogeneous wireless networks.
 The difficulty in building multiple wireless interfaces and the
corresponding gateway/bridge functions in the same mesh router.
 Important guideline to improve capacity of ad hoc networks:
a node should only communicate with nearby nodes.
 Throughput capacity can be increased by deploying relaying nodes.
 Nodes need to be grouped into clusters.
9
Cont..

Cont..
8/16/2018Eyob S.
 Physical Layer
 Mac Layer
 Network Layer
 Transport Layer
 Application Layer
 Network Management
 Security
10
Communication Protocols

Cont..
8/16/2018Eyob S.
 adaptive error resilience through link adaptation – modulation,
coding rates
 For high-speed transmission
 Orthogonal frequency multiple access (OFDM)
 Ultra-wide band (UWB)
 For capacity increase, impairment mitigation
 Antenna diversity, Smart antenna, MIMO
 For better spectrum utilization and viable frequency planning
 Frequency-agile radios, Cognitive radios
11
Physical layer

Cont..
8/16/2018Eyob S.
 A software radio platform is promising technique for physical
layer. Implementing cognitive radios on this software makes:
 all components of a radio, such as RF bands, channel access modes,
and channel modulations, are programmable.
 Open research issues
 Further improve the tx rate
 Interactive working with higher level protocols
 Cross-layer design, low-cost software radio
12
Physical layer

Cont..
8/16/2018Eyob S.
 Single channel MAC approaches
 Modifying existing MAC protocols
 ex) Adjust parameters of CSMA/CA, but low throughput
 Cross-layer design
 Directional antenna-based MACs
 MACs with power control
 Innovative MAC protocols
 TDMA or CDMA MAC protocols
 But, complexity, cost, compatibility with existing MACs
13
MAC layer

Cont..
8/16/2018Eyob S.
 Multi-channel MAC approaches
 Multi-channel single-transceiver MAC
 For cost, compatibility
 Multi-channel multi-transceiver MAC
 Only one MAC
 Multi-Radio MAC
 Each radio has its own MAC, PHY
 Multi-radio unification protocol(MUP) – coordinate communications in
all channels
14
MAC layer

Cont..
8/16/2018Eyob S.
 Open research issues
 Scalable MAC - Need new distributed & collaborative schemes
 MAC/Physical cross-layer design
 Novel MAC protocols for advanced PHY techniques – MIMO, CRs
 Network integration in the MAC layer
 Advanced bridging functions for different wireless radios to work
seamlessly
15
MAC layer

Cont..
8/16/2018Eyob S.
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.
16
Routing layer

Cont..
8/16/2018Eyob S.
 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.
17
Routing layer

Cont..
8/16/2018Eyob S.
 Routing protocols with various metrics – link quality source routing(LQSR)
 selects a routing path according to 4 metrics:
 ETX, per-hop RTT, per-hop packet pair, hop count
 ETX : best for stationary nodes & Hop count : best for mobile nodes
 Multi-radio routing
 A multi-radio LQSR(MR-LQSR)
 Weighted cumulative expected transmission time (WCETT) – Consider link quality metric &
the minimum hop count
 Multi-path routing
 Select multiple paths b/w source and destination
 Use another path when broken
 better load balancing & high fault tolerance
 But, depends on the availability of node-disjoint routes
 complexity
18
Routing layer

Cont..
8/16/2018Eyob S.
 Hierarchical routing
 Form clusters. Select cluster head which communicate with other
clusters
 Better performance in high node density
 complexity of maintaining the hierarchy
 Geographical routing
 Use the position of nodes in the vicinity & the destination
 Unlike early single-path greedy routing, planar-graph based
 An algorithm guarantee delivery, but higher communication overhead
19
Routing layer

Cont..
8/16/2018Eyob S.
 Scalability
 Hierarchical routing protocols can only partially solve this problem
 Geographic routing relies positioning technologies.
 New scalable routing protocols need to be developed.
 Better Performance Metrics
 New performance metrics need to be developed.
 Need to integrate multiple performance metrics into a routing
protocol
20
Routing Layer- Research Issues

Cont..
8/16/2018Eyob S.
 Routing/MAC Cross-Layer Design
 Needs to interact with the MAC layer, e.g. adopting multiple performance
metrics from MAC layer.
 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 clients.
21
Routing Layer- Research Issues

Cont..
8/16/2018Eyob S.
 TCP variants - Tackle these problems
 Non-congestion packet loss
 Unknown link failure
 Network asymmetry
 Different BW, loss rate, latency between forward & backward paths
 Impact ACKs
 Large RTT variations
 The change of routing path may be frequent
 The normal operation of TCP relies on a smooth measurement of RTT
22
Transport Layer:

Cont..
8/16/2018Eyob S.
 New transport protocols
 ATP(ad hoc transport protocol)
 Rate-based transmission, Quick-start for initial rate estimation
 Delay-based congestion detection, No retransmission timeout
 Better performance than TCP variants
 Not compatible with TCP
Real-time delivery:
 A Rate control protocol(RCP) is needed to work with UDP
 An adaptive detection rate control(ADTFRC) scheme
 Multi-metric joint detection approach for TCP-friendly rate control schemes
23
Transport Layer:

Cont..
8/16/2018Eyob S.
 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.
24
Transport Layer: Research Issues

Cont..
8/16/2018Eyob S.
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.
25
Application Layer

Cont..
8/16/2018Eyob S.
 Improve Existing Application Layer Protocols.
 Lower layers protocols cannot provide perfect support for the application layer.
 Ex) packet loss and packet delay with a large jitter may fail many Internet
applications
 Existing application layer protocols need to be improved.
 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 developed.
 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 networking.
26
Application Layer: Research Issues

Cont..
8/16/2018Eyob S.
 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 efficient.
27
Network Management Protocols

Cont..
8/16/2018Eyob S.
 Network Monitoring
 Report statistics in the MIB to one or several servers.
 Data processing algorithms analyze these statistical data and determine
potential abnormality.
 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
developed.
28
Network Management Protocols

Cont..
8/16/2018Eyob S.
 WMNs lack efficient and scalable security solutions
 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 protocols
 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.
29
Security

Result and Analysis
 WMNs is a technology that comes from optical networking
world, and has adapted to the Ethernet market.
 Mesh is very smart way to provides resilient networks.
 Mesh architecture creates the opportunity to change data paths
within a second when problem occur.
 When compared to the older solutions for network resilience,
WMNs really was a big step forward.
308/16/2018Eyob S.

Cont..
8/16/2018Eyob S.
 WPAN: Bluetooth, Zigbee
 WiFi: 802.11a, b, g, n
 WiMAX: 802.16
31
WMNs Standards
Data Rate
WPAN
WiMAX
Wi-Fi
10Mb 100Mb100kb1Mb
50Km
100m

C o n c l u s i o n
 As explained throughout this article, there still remain many
research problems. Among them, the most important and
urgent ones are the scalability and the security.
 Scalability.
 using multiple channels/radios per node or developing wireless radios
with higher transmission speed..
 Security.
 WMNs are vulnerable to security attacks in various protocol layers.
328/16/2018Eyob S.

S o u r c e:
8/16/2018Eyob S.
 IEEE Radio Communications

A Survey on Wireless Mesh Networks (WMN)

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