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

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 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

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.

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

Infrastructure/Backbone WMNs (1/3)

Client WMNs

Hybrid WMNs

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

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

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

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 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.

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

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

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

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

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.