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Wireless Mesh Networks. Myungchul Kim mckim@icu.ac.kr. - 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

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wireless mesh networks

Wireless Mesh Networks

Myungchul Kim

mckim@icu.ac.kr

a survey on wmns

- 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 and critical design factors4

Client WMNs

Actually the same as a conventional ad hoc network

Routing and self-configuration

Hybrid WMNs

Fig 2

Network architecture and critical design factors
network architecture and critical design factors5

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

Network architecture and critical design factors
network architecture and critical design factors6

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 architecture and critical design factors
advances and research challenges

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
advances and research challenges8

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?

Advances and research challenges
advances and research challenges9

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

Advances and research challenges
advances and research challenges10

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

Advances and research challenges
advances and research challenges11

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

Advances and research challenges
advances and research challenges12

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

Advances and research challenges
advances and research challenges13

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

Advances and research challenges
advances and research challenges14

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

Advances and research challenges
advances and research challenges15

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.

Advances and research challenges