Wireless Mesh Networks
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Presentation Transcript
Introduction • Wireless mesh network architecture • Why Wireless mesh network? • When Wireless mesh networks? • Routing background • Problems in existing routing protocols • Problems in frequency allocation
Wireless Mesh Networks • A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. • Wireless mesh networks often consist of • mesh clients • mesh routers • Mesh routers contain additional routing functionality due to the presence of wireless interface card in them • Nodes have two functions: • Generate/terminate traffic • Route traffic for other nodes
Characteristics of Wireless mesh networks • Multihop Wireless network. • Support for adhoc networking and capability of self forming, self healing and self organization. • Mobility dependence on the type of mesh node. • Multiple types of network access. • Dependence of power consumption constraints on the type of mesh nodes
Why WMN? • Multi-hop wireless network • Support for ad-hoc networking, and capability of self-forming, self healing and self organization. • Multiple types of network access • Mobility dependence on the type of mesh nodes • Compatibility and interpretability with existing wireless technologies
Compatibility and inter operatability with existing wireless networks • Dedicated routing and configuration • Mobility
Types of WMN • Infrastructure/ Backbone WMN • Client WMN • Hybrid WMN
Infrastructure/Backbone WMN • Mesh routers form an mesh infrastructure among themselves. • Provides backbone for clients and enables integration of WMNs with existing wireless networks and Internet through gateway/bridge functionalities. • Clients connect to mesh router with wireless link or Ethernet
Client WMN • Client nodes constitute peer-to-peer network, and perform routing and configuration functionalities as well as provide end-user applications to customers, ”mesh routers are not required” • Multi-hop routing. • Client nodes have to perform additional functions such as routing and self-configuration.
Hybrid WMN • A combination of infrastructureandclient meshing. • Infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX, cellular, and sensor networks; • Mesh clients can access the network through mesh routers as well as directly meshing with other mesh clients. • The routing capabilities of clients provide better connectivity and coverage
Protocol Design • Physical Layer • Mac Layer • Network Layer • Transport Layer • Application Layer
Physical Layer • Orthogonal frequency multiple access (OFDM) has significantly increased the speed of IEEE 802.11 from 11 mbps to 54 mbps. • Ultra-wide band (UWB) can achieve much higher rate for short-distance applications. • MIMO can increase system capacity by three times or even more. • Frequency agile or cognitive radios can achieve much better spectrum utilization.
MAC Layer Differences between WMNs MACs and Wireless Networks MACs • MACs for WMNs are concerned with more than one hop communication • MAC must be distributed and collaborative, and must work for multipoint-to-multipoint communication. • Network self-organization is needed for better collaboration between neighboring nodes and nodes in multi-hop distances. • Mobility affects the performance of MAC.
Routing Layer Features of routing protocol for WMNs: • Multiple Performance Metrics • Hop-count is not an effective routing metric. • Other performance metrics, e.g., link quality and round trip time (RTT), must be considered. • Scalability • Routing setup in large network is time consuming. • Node states on the path may change. • Scalability of routing protocol is critical in WMNs.
Routing Layer • Robustness • WMNs must be robust to link failures or congestion. • Routing protocols need to be fault tolerant with link failures and can achieveload balancing. • Adaptive Support of Both Mesh Routers and Mesh Clients • Mesh routers : minimal mobility, no constraint of power consumption, routing is simpler • Mesh clients : mobility, power efficiency, routing is complicated • Need to design a routing protocol that can adaptively support both mesh routers and mesh clients.
Transport layer: research issues • Cross-layer Solution to Network Asymmetry • Routing protocol can select an optimal path for both data and ACK packets. • MAC layer and error control may need to treat TCP data and ACK packets differently. • Adaptive TCP • WMNs will be integrated with the Internet and various wireless networks such as IEEE 802.11, 802.16, 802.15, etc. • Same TCP is not effective for all networks. • Applying different TCPs in different networks is a complicated and costly approach, and cannot achieve satisfactory performance.
Application layer Applications supported by WMNs: • Internet Access • Advantages of WMNs: low cost, higher speed, and easy installation. • Distributed Information Storage and Sharing • Data sharing between nodes within WMNs • Query/retrieve information located in distributed database servers. • Information Exchange across Multiple Wireless Networks. • Cellular phone talks Wi-Fi phone through WMNs, • Wi-Fi user monitors the status of wireless sensor networks.
WMN Standards • WPAN: Bluetooth, Zigbee • WiFi: 802.11a, b, g, n • WiMAX: 802.16
WMN Standards • IEEE 802.16a WMAN Mesh • “mesh mode” in addition to the point-to-multipoint(PMP) mode defined in IEEE 802.16. • Operating in the licensed and unlicensed lower frequencies of 2–11 GHz, allowing non-line-of-sight (NLO) communications, spanning up to a 50 km range. • Supporting multihop communications.
WMN Standards • 802.11s WLAN Mesh • Multi-hop capability added to 802.11g/a/b • Auto configure on power up • Multi-channel multi-radio operation • Topology discovery • MAC Path selection protocol • Modified forwarding for QOS and mesh control
Routing Layer Features of routing protocol for WMNs: • Multiple Performance Metrics • Hop-count is not an effective routing metric. • Other performance metrics, e.g., link quality and round trip time (RTT), must be considered. • Scalability • Routing setup in large network is time consuming. • Node states on the path may change. • Scalability of routing protocol is critical in WMNs.
When WMN? • Broadband home networking • Community and neighborhood networking • Enterprise networking • Wireless mesh networks • Transportation systems • Building automation • Health and medical systems • Security surveillance systems
Mesh vs. Ad-Hoc Networks Ad-Hoc Networks Wireless Mesh Networks • Multihop • Nodes are wireless, possibly mobile • May rely on infrastructure • Most traffic is user-to-user • Multihop • Nodes are wireless, some mobile, some fixed • It relies on infrastructure • Most traffic is user-to-gateway
Mesh vs. Sensor Networks Wireless Mesh Networks Wireless Sensor Networks • Bandwidth is generous (>1Mbps) • Some nodes mobile, some fixed • Normally not energy limited • Resources are not an issue • Most traffic is user-to-gateway • Bandwidth is limited (tens of kbps) • In most applications, fixed nodes • Energy efficiency is an issue • Resource constrained • Most traffic is user-to-gateway
Ad Hoc Networks • An ad-hoc network is a wireless local area network (LAN) that is built spontaneously as devices connect. • Instead of relying on a base station to coordinate the flow of messages to each node in the network, the individual network nodes forward packets to and from each other.
Contd… • Formed by wireless hosts which may be mobile. • Don’t need a pre-existing infrastructure/backbone. • Routes between nodes pottentially contain multiple hopes.
Why MANET?? • Ease, speed of deployment • Decreased dependence on infrastructure. • Can be used in many scenerios where deployment of wired network is impossble • Lots of military applications
History of Ad Hoc networks • In situations where networks are constructed and destructed in ad-hoc manner, mobile ad-hoc networking is an excellent choice. • The idea of mobile ad-hoc or packet radio networks has been under development since 1970s. Since the mid-90s, when the definition of standards such as IEEE802.11 (what we think of as WiFi or just 802.11) helped cause commercial wireless technology to emerge, mobile ad-hoc networking has been identified as a challenging evolution in wireless technology.
Characteristics of Ad Hoc networks • Every node is responsible for forwarding packets to other nodes • Nodes themselves implement security function among themselves • Topology changes continuously as nodes are highly mobile. • Purpose Specific • Dynamic • No master-slave relationship (Every node is a router)
Types of MANET’s • Fully symmetric environment • Asymmetric characteristics • Asymmetric responsibilities
Fully symmetric environment • All nodes have identical capabilities and respoonsibilities
Asymmetric capabilities • Transmission range and radios may differ • Battery life at different nodes may differ • Processing capacity may be different at different nodes • Speed of movement different
Asymmetric responsibilities • Only some nodes may route packets • Some nodes may act as leader for nearby nodes e.g. cluster haed
Other variants • Traffic characteristics may differ (bandwidth,realibility, unicast/multicast/broadcast ) • Mobility patterns may be different (Little/ Highly mobile) • Mobility characteristics may differ (speed, direction of movement, pattern of movement)
Challenges • Limited wireless transmission range • Broadcast nature of wireless medium • Packet losses due to transmission errors • Environmental issues • Mobility induced route changes • Mobility induced packet losses • Battery constraints
Characteristics of Ad Hoc networks • Connectivity among the hosts changes with time • Nodes are low power devices, low CPU process capability, and low memory. • Due to above reasons; the existing routing protocols are highly unstable.
Routing protocols • Proactive: • Determine route independent of traffic pattern • Used in traditional wired network • Reactive: • Discover/ maintain routes only if needed.
Tradeoff of proactive vs reactive • Proactive has low while reactive has high latency • Reactive have low overhead while proactive have high overhead
Metrics for Ad Hoc routing • Number of hops • Distance • Latency • Load balancing for congested loads • cost
Wireless Standards for Mobile Ad Hoc networks • 802.11b • 802.11a • 802.11g • 802.11n
8002.11b • Developed in July 1999 • Maximum bandwidth=11 Mbps • Uses 2.4 GHZ Frequency range • Low cost
802.11a • Developed in 2001 • Maximum bandwidth= 54 Mbps • Uses 5 GHZ frequency band • Much faster than 802.11b
802.11g • Developed in 2003 • Modified version of 802.11b • Maximum bandwidth =54Mbps • Uses frequency range=2.4 GHZ
802.11n • Used for faster and long distance communication • Not formally published and approved yet.
Applications • Personal area network • Civilian environment • Emergency operations • Sensor networks
