Xiuzhen Cheng cheng@gwu

1. Xiuzhen Chengcheng@gwu.edu Csci332MAS Networks – Challenges and State-of-the-Art Research – Wireless Mesh Networks

2. Introduction • In conventional wireless networks eachhost sends it packets to a central router. • In WMN Nodes  Mesh Routers and Clients • Each node operates as a host. In additioneach node also forwards packets on behalfof other nodes. These nodes may not be inthe direct transmission range of theirdestination. Mesh architecture. • Gateway/Bridge functionalities in MeshRouters  Easy integration with other typeof networks.

3. Mesh Routers • Routing functions • Basic 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 router • Built 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

4. Mesh Clients • Have necessary functions for mesh netorking • Can work as routers without gateway/bridge functions • Have only one wireless interface • Compared to mesh routers • Simpler hardware platform and software • Simpler construction • Have higher variety of devices: laptops PDAs, IP phone, etc.

5. WMN Architectures • Infrastructure/Backbone WMNs • Mesh routers form an infrastructure for clients that connect to them. • Most commonly used • Community and neighborhood networks • Client WMNs • Client nodes form the actual network and perform routing functionalities. • Peer-to-peer networks among client devices • No mesh routers is needed • One types of radios for all clients • Increased requirements such as routing and self-configuration are placed • Hybrid WMNs • The combination of infrastructure and client meshing • Most applicable

6. Infrastructure/Backbone WMNs (1/3)

7. Client WMNs

8. Hybrid WMNs

9. Characteristics • Multihop wireless network • Extend 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 nodes • Mesh 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

10. Compared to Ad Hoc Netoworks • Wireless infrastructure/backbone • More reliable, higher coverage • Integration • For both wireless and wired clients • Dedicated routing and configuration • Load on end-users are decreased • Multiple radios • Better performance • Mobility • Mesh routers usually do not move

11. 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

12. broadband homenetworking • Compared to WiFi • Better coverage • Flexible • Direct communication

13. Community Networking

14. Enterprise Networking

15. Factors Influencing Network Performance • Radio techniques • Scalability • Mesh connectivity • Broadband and QoS • Compatibility andinter-operability • Security • Ease of use

16. Factors influencing network performance (contd.) • Link level factors/issues: • Links have intermediate loss rates • Node distance is not strongly correlated withloss rate • Links have non-bursty loss patterns • High signal strength Low loss rate • Optimum 802.11 bit-ratesignificant lossrate • Most significant factor  Multi-path fading

17. Issues at each layer • Physical layer • New wideband transmission schemesrequired to achieve higher transmission ratein a larger area. • Multiple-antenna systems are complex andcostly. • To utilize the advanced features provided byphysical layer, higher layer protocols (esp.MAC layer) need to be carefully designed.

18. Issues at each layer • MAC layer • Scalability issues in multi-hop ad hocnetworks • MAC protocol for ad hoc network cannot beused in WMN because of several differences • Advance bridging functions required • Multi-channel MAC protocols for multipletransceiver based radio cannot be used asthey are costly • Development of MAC protocol with multipleQoS metrics like delay, packet loss, jitter

19. Issues at each layer • Network layer • New scalable routing protocols required • Integrating multiple performance metricsinto a routing protocol • Routing protocol for multicast applications • Cross-layer design between MAC androuting protocol • Routing protocol that treats mesh routerand client differently

20. Issues at each layer • Transport layer • Cross layer optimization is required forincreasing TCP performance • The new enhanced TCP should work with theexisting TCP • Adaptive transport protocols required for anintegrated WMN • Adaptive Rate Control Protocol (RCP) is needfor real time delivery

21. Issues at each layer • Application layer • Make existing Internet applications workunder architecture of WMNs • Application protocols for distributedinformation sharing • Unique applications that utilize theadvantages of WMNs

22. Practical Implementations • Various academic test-bed’s exist atuniversities like Carnegie Mellon, MIT,UIUC, Georgia Tech • Various Industrial leaders have alreadyreleased products or are working on WMNs.Companies include Microsoft Research(MSR), MeshNetworks, Intel, Nortel etc. • City wide Wi-Fi WMNs are deployed orplanned at cities like Las Vegas andPhiladelphia.

23. Practical Implementations (Cont.) • Current implementation at Las Vegas

24. Conclusions • WMNs reduces complexity of network deploymentand maintenance • WMNs require minimal investment • Allows users to access Internet anywhere, anytime • Existing WMNs prove that performance of WMNs isfar below then expected • All protocols layers need to be improved. Crosslayer design required for optimal performance • WMNs are promising technology for next generationwireless networking but still more research isrequired.