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Mesh Networks

Mesh Networks

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Mesh Networks

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  1. Mesh Networks By Ian F. Akyildiz at al.

  2. Overview • Introduction • Network Architectures • Characteristics • Application Scenarios • Critical factors • Research Issues

  3. Introduction • Wireless mesh networks (WMN) is an emerging new technology. • WMNs are a type of ad hoc networks but at the same time diversify the capabilities of ad hoc networks and hence ad hoc networks can be thought of as a subset of WMNs • WMNs consists of nodes that are mesh routers and clients. • Nodes in an WMN self-organize to form a network, automatically establishing and maintaining mesh connectivity, creating in effect an ad hoc network • Conventional nodes (e.g., desktops, laptops, PDAs, PocketPCs, phones, etc.) equipped with Network Interface cards (NICs) connect directly to mesh routers.

  4. Introduction… • Mesh routers have gateway/bridge functionalities which enable the integration of WMNs with various existing wireless networks such as cellular, sensor, Wi-Fi, WiMAX (World-wide interoperabilty for microwave access) networks. • Industrial working groups are working on specifications for mesh networking. • Working groups IEEE 802.11, IEEE 802.15, and IEEE 802.16 have established subgroups to focus on standards for WMNs

  5. Example of mesh routers based on different embedded systems (a) PowerPC and (b) Advanced Risc Machines(ARM). Mesh routers can have multiple wireless interfaces Example of mesh clients: Laptop, PDA, WiFi IP phone and Wi-Fi RFID reader

  6. WMN Network Architecture • A mesh router can have multiple wireless interfaces built on same or different wireless technologies • Compared with a conventional wireless router, a mesh router can have same coverage with much lower transmission power through multi-hop communications. • The MAC protocol can be enhanced with better scalabilty in a multi-hop mesh environment (e.g., multiple channels can be used along multiple paths)

  7. WMN Architectures… • Infrastructured Backbone WMNs: • Mesh routers form an infrastructure for clients that connect to them. • Backbone can be constructed using various types of radio technologies, in addition to the widely used 802.11 technologies. • Mesh routers form self-healing and self-configuring topology among themselves. • Community and neighborhood networks can be built using infrastructure meshing. Mesh routers are placed on top of the roof of houses in a neighborhood which serve as access points for clients • Typically two types of radios are used in the routers, one for backbone communication and one for client communication

  8. Infrastructured/Backbone WMN architecture Infrastructured/Backbone Wireless mesh network

  9. WMN Architectures… • Client WMNs: • In this architecture, client nodes constitute the actual network to perform the routing and configuration functionalities. • This architecture is basically an ad hoc network • Mesh routers are not required for this architecture • These networks are formed generally using one type of radios on devices

  10. Client WMN architecture Client WMN architecture

  11. WMN architectures… • Hybrid WMNs: • It is the result of combining infrastructure and client meshing. • Clients can access the network through mesh routers as well as directly meshing with other clients. • The infrastructure part provides connectivity to other networks such as Internet, Wi-Fi LANs, etc; routing capability of the clients provide improved connectivity and coverage inside the WMN. • This architecture provides flexibility

  12. Hybrid WMN Architecture Hybrid WMN architecture

  13. Characteristics of WMNs • It is a Multi-hop wireless network: • Helps extend coverage range of current wireless networks • Can help provide non-line-of-sight connectivity without direct line-of-sight links. • Supports ad hoc networking • Mobility dependence: • Mesh routers usually have minimal mobility, whereas clients are mobile or stationary. • Multiple types of network access: • Support for both backhaul access to Internet and other networks as well as support for peer-to-peer communication.

  14. Characteristics of WMNs… • Dependence of power-consumption constraints on the type of mesh nodes. • Mesh routers usually do not have power-constraints • However, mesh clients may require power efficient protocols • Compatibility and interoperability with existing wireless networks. • For example, WMNs built based on IEEE 802.11 technologies must be capable of supporting both mesh capable and conventional Wi-Fi clients.

  15. Differences between WMNs and ad hoc networks • Wireless infrastructure/backbone: • WMNs have backbone mesh routers, which provides large coverage, connectivity and robustness. • ad hoc networks depend on individual contribution of end users which may not be reliable. • Integration: • WMNs enable integration of various existing networks, thus enabling the clients to access the services provided by other networks. • Dedicated routing and configuration: • In ad hoc networks, end user devices also perform routing and configuration functionalities for all other nodes whereas in WMNs mesh routers perform these functionalities and hence load on the end users is decreased.

  16. Differences between WMNs and ad hoc networks… • Multiple radios: • Mesh routers can be equipped with multiple radios to perform routing and access functionalities. This improves the capacity of the network. • In ad hoc networks these two functions are performed on the same channel and hence the performance decreases. • Mobility: • In ad hoc networks connectivity depends on the movement of end user devices. • In WMNs however, connectivity depends on mesh routers which generally do not move.

  17. Some Application Scenarios • Broadband home networking: • This is currently realized through IEEE 802.11 WLANs • One problem with this is the location of the access points. A house usually has many dead zones. • Installing multiple access points is expensive because of Ethernet wiring from access points to backhaul network access modem or hub. • Even if multiple access points are installed, communication between end nodes under two access points has to go all the way back to the access hub. • Under WMN, the access points must be replaced by wireless mesh routers with mesh connectivity established among them. • Dead zones can be eliminated by adding more mesh routers, changing location of routers or adjusting power levels of mesh routers.

  18. WMN for broadband home networking WMN for broadband home networking

  19. Some Application Scenarios… • Community and neighborhood networking: • Common network access is currently based on cable or DSL modem connected to Internet. • The last hop is wireless by connecting a wireless router to a cable or DSL modem. • Even if information need to be shared within the community, all traffic must flow through Internet. • Only a single path may be available for one home to access the Internet or communicate with neighbors. • WMNs mitigate the above disadvantages

  20. WMN for Community and neighborhood networking WMN for Community and neighborhood networking

  21. Some Application Scenarios… • Enterprise networking: • Can be a small network within an office, a medium size network for all offices in an entire building, or a large-scale network among offices in multiple buildings. • WMNs are suitable for such networks because they can grow easily.

  22. WMN for Enterprise networking Enterprise networking

  23. Some Application Scenarios… • Metropolitan area networks (MAN): • Compared to wired networks, wireless mesh MAN is economic alternative to broadband networking especially in underdeveloped regions. • Wireless Mesh MANs can cover much larger area than a home, enterprise, building, or community networks.

  24. WMN based MAN WMN based MAN

  25. Some Application Scenarios… • Transportation Systems: • Instead of limiting IEEE 802.11 (commercialized under WiFi) or 802.16 (commercialized under WiMax) access to stations and stops, mesh networking technology can extend access to busses, ferries and trains. • This will support convenient passenger information services, remote monitoring of in-vehicle surveillance video and driver communications. • For this, a high-speed mobile backhaul from a vehicle to the Internet and mobile mesh network in the vehicle should be supported.

  26. WMN for transportation system WMN for transportation system

  27. Some Application Scenarios… • Building Automation Control Network (BACnet): • WMN can be useful for controlling and monitoring various electrical devices including power, lights, elevators, airconditioners, etc.

  28. Building Automation Control Network(BACnet): Figure 11

  29. Some Application Scenarios… • Health and medical systems: • In hospital environment, monitoring and diagnosis data need to be processed and transmitted from room to room for various purposes. WMNs can be useful in such situations • Security surveillance systems: • WMNs can be used for surveillance systems for enterprise buildings, shopping malls, grocery stores, etc.

  30. Open Research Issues • Physical layer • New schemes other than OFDM (orthogonal Frequency Division Multiplexing) and UWB (Ultra-wide Band) need to be designed to achieve higher transmission rate in large area networks. • To best utilize the advanced features of the physical layer, higher layer protocols, especially MAC protocols need to be carefully designed.

  31. Open Research Issues… • MAC Layer • Classical MAC protocols are limited to one-hop communication, while WMNs have to deal with multi-hop communication. • For example, the hidden terminal problems is an issue in multi-hop wireless LANs • Novel MAC protocols need to be discovered to utilize the various types of protocols supported at the physical layer. • Due to the difference between WMNs and ad hoc networks, protocols designed for ad hoc networks may not work well for WMNs.

  32. Open Research Issues… • MAC Layer …. • Multi-channel MAC: can be implemented on several hardware platforms • Multi-channel single transceiver MAC : • One transceiver on a radio is preferred approach to minimize cost. Only one channel is active at a time at each network node • Multi-channel multi-transceiver MAC: • A radio includes multiple RF front-end chips and baseband processing modules to support several simultaneous channels • On top of the physical layer, there is only one MAC layer to coordinate the functions of multiple channels. How to design efficient MAC protocol for this type of physical layer is a research issue. • Multi-radio MAC: • A node has multiple radios, each with its own MAC and Physical layers • A virtual MAC layer on top of MAC layer is needed to coordinate communication in all channels

  33. Open Research Issues… • Network Layer • Scalability is the most important issue in designing routing protocols for WMNs. • Hierarchical routing protocols can only partially solve this problem. • Many applications need multicasting capability, for example, video distribution in a community network. So, new protocols that suit WMNs need to be designed. • When multi-radio or multi-channel wireless mesh nodes are considered, new routing protocols are needed for the following reasons: • The routing protocol not only needs to select a path but also the most appropriate channel or radio along the path • Cross-layer design becomes necessary because change of a routing path involves the channel or radio switching in a mesh node.

  34. Open Research Issues… • Transport layer: • As we saw earlier, since classical TCP versions do not differentiate losses due to congestions and non-congestions, performance of TCP can degrade in a wireless network environment. So, new approaches at the Transport layer are needed. • Enhancing TCP only in the context of wireless network environment is not enough because nodes in a mesh network would also communicate with nodes in the Internet. • Application layer: • Internet access • distributed information storage and sharing within WMNs • This does not require backhaul access to the Internet. • Information exchange across multiple wireless networks

  35. Topics for Survey Paper • Location management in cellular networks • Position based routing protocols for MANETs • Reactive (on-demand) routing protocols for MANETs • Location service. • Secure Routing in MANETs • TCP over wireless networks • Routing in Sensor networks • Securing sensor networks • Localization in sensor networks • Group communication in VANETs • Secure authenticated message delivery in VANETs • Routing protocols for MANETs • Routing in Mesh networks • Channel assignment in Mesh networks • Channel assignment in cognitive networks