Wireless Mesh Networks

Wireless Mesh Networks

Myungchul Kim

[email protected]

- IEEE Communications Magazine, pp. 523-530, Sept 2005

• Introduction – Mesh routers and mesh clients

– Multi-hop communications with much lower transmission power

– Mesh router with multiple wireless interfaces

– Mesh client with a single wireless interface

– Customers without wireless NICs can access WMN through for example, Ethernet

– Advantages: low up-front cost, easy network maintenance, robustness, reliable service coverage, etc.

– The available MAC and routing protocols are not scalable; throughput drops significantly as the number of nodes or hops in WMNs increases.

A Survey on WMNs

• Network architecture - Infrastructure/backbone WMNs

- Fig 1.

Network architecture and critical design factors

- Client WMNs

- Actually the same as a conventional ad hoc network

- Routing and self-configuration

- Hybrid WMNs

- Fig 2


- The characteristics of WMN

- Supports ad hoc networking: self-forming, self-healing and self-organization

- Multi-hop wireless networks

- Minimal mobility and dedicated routing and configuration

- Mobility of end nodes

- Mesh routers integrate heterogeneous networks, wireless and wired

- Power-consumption constraints are different

- Compatible and interoperable with other wireless networks


• Critical design factors

- Radio techniques- Directional and smart antennas, multiple input and multiple output

(MIMO) systems, and multi-radio/multi-channel systems

- Refconfigurable radios, frequency agile/cognitive radios, software radios

- Scalability

- Mesh connectivity: network self-organization and topology control algorithms are needed

- Broadband and QoS

- Security: no centralized trusted authority to distribute a public key in a WMN

- Ease of use

- Compatibility and interoperability


• Network capacity

- The guideline to improve the capacity of ad hoc networks: a node should only communicate with nearby nodes [1].

- Througput capacity can be increased by deploying realying nodes. -> utilizing the node mobility -> transmission delay and buffer

- Nodes need to be grouped into clusters.

• Layered communication protocol

– Physical layer• Advanced physical-layer technques: congnitive radios dynamicaly

capturing the unoccupied spectrum

• Enable the programmability of all advanced physical layer techniques

• Open research issues: improve the trasmission rate and the performance of physical-layer techniques and utilize the cross layer design between MAC and the physical layer

Advances and research challenges

– MAC layer in WMN• More than one-hop communcations

• Distributed for multipoint-to-multipoint communication

• Network self-organization

• Mobility is low

• Single-channel MAC and Multi-channel MAC

– Single-channel MAC• Modifying existing MAC protocols

• Cross-layer design: directional antenna-based MACs and MACs with power control -> hidden terminal problem

• Proposing innovative MAC protocols: how to design a distributed TDMA MAC protocols overlaying CSMA.CA?


– Multi-channel MAC• Multi-channel single-transceiver MAC

• Multi-channel multi-transceiver MAC

• Multi-radio MAC

• Open research issues: scalable MAC, MAC/physical cross-layer design, network integration in the MAC layer

– Routing layer• Optimal routing protocol features

– Multiple performance metrics: how about hop-count?

– Scalability

– Robustness: link failures or congestion, load balancing

– Efficient routing with mesh infra


– Routing layer (con’t)• Routing protocols with various performance metrics

– Link quality source routing (LQSR)

– Link quality metrics

– Expected transmission count (ETX)

• Multi-radio routing– Weighted cumulative expected transmission time (WCETT)

– Link quality metric and the minimum hop-count

• Multi-path routing– Better load balancing and high fault tolerance

• Hierarchical routing– Clusters


– Routing layer (con’t)• Geographic routing

– Position information of nodes in the vicinity and the destination node

– Delivery is not guaranteed even if a path exists between source and destination

• Open research issues– Scalability

– Better performance metrics

– Routing/MAC cross-layer design

– Efficient mesh routing


– Transport layer• Reliable data transport

– Non-congestion packet loss

– Unknown link failure due to wireless channels and mobility in mesh clients

– Network asymmetry: TCP is critically dependent on ACK

– Large RTT variations

• Ad hoc transport protocol (ATP)– Rate-based and quick-start

– Congestion detection is a delay-based approach -> congestion cause

– No retransmission timeout

– Congestion control and reliability are decoupled

• Real-time delivery– A rate control protocol (RCP) is needed to work with UDP


– Transport layer (con’t)• Open research issues

– Cross-layer solution to network asymmetry

– Adaptive TCP on various wireless networks

– Application layer• Internet access

• Distributed information storage and sharing

• Information exchange across multiple wireless networks– Improve existing applications layer protocols

– Propose new application-layer protocols for distributed information sharing

– Develop innovative applications for WMNs


– Network management• Mobility management

– Distributed mobility management

• Power management

• Network monitoring

– Security• Factors such as distributed network architecture, vulnerability of

channels and nodes in the shared wireless medium, and the dynamic change of network topology

• An AAA centralized server?

• No central authroity for managing security keys

• An open issue: A distributed authentication and authorization sheme with secure key management


– Cross-layer design• One approach is to improve the performance of a protocol layer

by taking into account parameters in other protocol layers.

• Another approach is to merge several protocols into one component.


Wireless Mesh Networks

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