1. Xiuzhen Cheng cheng@gwu.edu
Csci332 MAS Networks – Challenges and State-of-the-Art Research – Wireless Mesh Networks
Xiuzhen Cheng

2. 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.

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 Client WMNs Hybrid 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. A superset of Ad Hoc Networks
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 and inter-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 with loss rate
Links have non-bursty loss patterns
High signal strength  Low loss rate
Optimum bit-rate significant loss rate
Most significant factor  Multi-path fading

17. Issues at each layer Physical layer
New 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.

18. Issues at each layer MAC layer
Scalability 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

19. Issues at each layer Network layer
New 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

20. Issues at each layer Transport layer
Cross 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

21. Issues at each layer Application layer
Make existing Internet applications work under architecture of WMNs
Application protocols for distributed information sharing
Unique applications that utilize the advantages of WMNs

22. 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.

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

24. 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.