Xiuzhen ChengXiuzhen Cheng cheng@gwu.edu

CsciCsci332332 MAS Networks – Challenges MAS Networks – Challenges and State-of-the-Art Research and State-of-the-Art Research

– Wireless Mesh Networks – Wireless Mesh Networks

Introduction

In conventional wireless networks each host sends it packets to a central router.

In WMN Nodes Mesh Routers and Clients

Each node operates as a host. In addition each node also forwards packets on behalf of other nodes. These nodes may not be in the direct transmission range of their destination. Mesh architecture.

Gateway/Bridge functionalities in Mesh Routers Easy integration with other type of networks.

Mesh Routers

Routing functionsBasic gateway/repeater functions

Supports mesh networking

Also performs bridge functionalities

Equipped with multiple wireless interfaces

Multiple wireless interfaces built on either the same or different wireless technologies

Compared to a conventional wireless routerBuilt on a similar hardware platform or on different embedded systems (PowerPC or ARM)

A wireless router can achieve the same coverage with much lower transmission power through multihop communications

Enhanced MAC protocol for better scalability

Mesh Clients

Have necessary functions for mesh netorkingCan work as routers without gateway/bridge functions

Have only one wireless interface

Compared to mesh routersSimpler hardware platform and software

Simpler construction

Have higher variety of devices: laptops PDAs, IP phone, etc.

WMN Architectures

Infrastructure/Backbone WMNsMesh routers form an infrastructure for clients that connect to them.Most commonly usedCommunity and neighborhood networks

Client WMNsClient nodes form the actual network and perform routing functionalities.Peer-to-peer networks among client devicesNo mesh routers is neededOne types of radios for all clientsIncreased requirements such as routing and self-configuration are placed

Hybrid WMNsThe combination of infrastructure and client meshingMost applicable

Infrastructure/Backbone WMNs (1/3)

Client WMNs

Hybrid WMNs

Characteristics

Multihop wireless networkExtend coverage, non-LOS connectivity

Support for ad hoc networking, and capability of self-forming, self-healing, and self-organization

Mobility dependence on the type of mesh nodesMesh clients can be mobile

Multiple type of network access

Dependence of power-consumption constraints on the type of mesh nodes

Mesh clients may need power efficient protocols

Compatibility and interoperability with existing wireless networks

Compared to Ad Hoc Netoworks

Wireless infrastructure/backboneMore reliable, higher coverage

IntegrationFor both wireless and wired clients

Dedicated routing and configurationLoad on end-users are decreased

Multiple radiosBetter performance

MobilityMesh routers usually do not move

Applications

Broadband home networking

Community ad neighborhood networking

Enterprise networking

Metropolitan area networks

Transportation systems

Building automation

Health and medical systems

Security surveillance systems

A superset of Ad Hoc Networks

broadband homenetworking

Compared to WiFi

Better coverage

Flexible

Direct communication

Community Networking

Enterprise Networking

Factors Influencing Network Performance

Radio techniques

Scalability

Mesh connectivity

Broadband and QoS

Compatibility and inter-operability

Security

Ease of use

Factors influencing network performance (contd.)

Link level factors/issues:Links have intermediate loss rates

Node distance is not strongly correlated with loss rate

Links have non-bursty loss patterns

High signal strength Low loss rate

Optimum 802.11 bit-rate significant loss rate

Most significant factor Multi-path fading

Issues at each layer

Physical layerNew wideband transmission schemes required to achieve higher transmission rate in a larger area.

Multiple-antenna systems are complex and costly.

To utilize the advanced features provided by physical layer, higher layer protocols (esp. MAC layer) need to be carefully designed.

Issues at each layer

MAC layerScalability issues in multi-hop ad hoc networks

MAC protocol for ad hoc network cannot be used in WMN because of several differences

Advance bridging functions required

Multi-channel MAC protocols for multiple transceiver based radio cannot be used as they are costly

Development of MAC protocol with multiple QoS metrics like delay, packet loss, jitter

Issues at each layer

Network layerNew scalable routing protocols required

Integrating multiple performance metrics into a routing protocol

Routing protocol for multicast applications

Cross-layer design between MAC and routing protocol

Routing protocol that treats mesh router and client differently

Issues at each layer

Transport layerCross layer optimization is required for increasing TCP performance

The new enhanced TCP should work with the existing TCP

Adaptive transport protocols required for an integrated WMN

Adaptive Rate Control Protocol (RCP) is need for real time delivery

Issues at each layer

Application layerMake existing Internet applications work under architecture of WMNs

Application protocols for distributed information sharing

Unique applications that utilize the advantages of WMNs

Practical Implementations

Various academic test-bed’s exist at universities like Carnegie Mellon, MIT, UIUC, Georgia Tech

Various Industrial leaders have already released products or are working on WMNs. Companies include Microsoft Research (MSR), MeshNetworks, Intel, Nortel etc.

City wide Wi-Fi WMNs are deployed or planned at cities like Las Vegas and Philadelphia.

Practical Implementations (Cont.)

Current implementation at Las Vegas

Conclusions

WMNs reduces complexity of network deployment and maintenance

WMNs require minimal investment

Allows users to access Internet anywhere, anytime

Existing WMNs prove that performance of WMNs is far below then expected

All protocols layers need to be improved. Cross layer design required for optimal performance

WMNs are promising technology for next generation wireless networking but still more research is required.