CHAPTER 12: WIRELESS MESH NETWORKS I. F. Akyildiz Broadband & Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute

CHAPTER 12:CHAPTER 12:

WIRELESS MESH NETWORKS

I. F. AkyildizI. F. Akyildiz

Broadband & Wireless Networking LaboratoryBroadband & Wireless Networking Laboratory

School of Electrical and Computer EngineeringSchool of Electrical and Computer Engineering

Georgia Institute of TechnologyGeorgia Institute of Technology

Tel: 404-894-5141; Fax: 404-894-7883 Tel: 404-894-5141; Fax: 404-894-7883

Email: [email protected]: [email protected]

Web: http://www.ece.gatech.edu/research/labs/bwnWeb: http://www.ece.gatech.edu/research/labs/bwn

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The term 'wireless mesh networks' describes wireless The term 'wireless mesh networks' describes wireless networks in which each node can communicate directly networks in which each node can communicate directly with one or more peer nodes. with one or more peer nodes.

The term 'mesh' originally used to suggest that all nodes The term 'mesh' originally used to suggest that all nodes were connected to all other nodes, but most modern were connected to all other nodes, but most modern meshes connect only a sub-set of nodes to each other. meshes connect only a sub-set of nodes to each other.

Still, this is quite different than traditional wireless Still, this is quite different than traditional wireless networks, which require centralized access points to networks, which require centralized access points to mediate the wireless connection. mediate the wireless connection.

Even two 802.11b nodes that are side-by-side in Even two 802.11b nodes that are side-by-side in infrastructure mode must send data to each other infrastructure mode must send data to each other through the access point. through the access point.

Wireless Mesh NetworksWireless Mesh NetworksI.F. Akyildiz, et.al., “Wireless Mesh Networks; A I.F. Akyildiz, et.al., “Wireless Mesh Networks; A Survey”, Survey”, Computer Networks Journal, March Computer Networks Journal, March 2005.2005.

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Wireless Mesh Networks

Nodes are comprised of mesh routers and mesh clients.

Each node operates not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations.

A WMN is dynamically self-organized and self-configured, with the nodes in the network automatically establishing and maintaining mesh connectivity among themselves

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Wireless Mesh Networks

Extend the range and link robustness of existing Wi-Fi’s by Extend the range and link robustness of existing Wi-Fi’s by allowing mesh-style multi-hoppingallowing mesh-style multi-hopping

A user finds a nearby user and hops through it - or possibly A user finds a nearby user and hops through it - or possibly multiple users - to get to the destinationmultiple users - to get to the destination

Every user becomes a relay point or router for network trafficEvery user becomes a relay point or router for network traffic

Mesh networks consist of multiple wireless devices equipped with Mesh networks consist of multiple wireless devices equipped with

COTS802.11 a/b/g cards that work in ad-hoc fashionCOTS802.11 a/b/g cards that work in ad-hoc fashion

802.11 capable antennas placed on rooftops allow a large area 802.11 capable antennas placed on rooftops allow a large area coveragecoverage

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Network ArchitectureNetwork Architecture

WMNs consist of two types of nodes: WMNs consist of two types of nodes: Mesh Routers and Mesh ClientsMesh Routers and Mesh Clients. .

A wireless mesh router contains additional A wireless mesh router contains additional routing functions to support mesh networking.routing functions to support mesh networking.

It is equipped with multiple wireless interfaces It is equipped with multiple wireless interfaces built built

on either the same or different wireless access on either the same or different wireless access technologies.technologies.

A wireless mesh router can achieve the same A wireless mesh router can achieve the same coverage as a conventional router but with much coverage as a conventional router but with much lower transmission power through multi-hop lower transmission power through multi-hop communications.communications.

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WMN COMPONENTS

Examples of mesh routers based on different embedded

systems: (a) PowerPC and (b) Advanced Risc Machines (ARM)

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WMN COMPONENTS

Examples of mesh clients: (a) Laptop, (b) PDA,

(c) Wi-Fi IP Phone and (d) Wi-Fi RFID Reader.

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WMN COMPONENTSWMN COMPONENTS

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WMN COMPONENTSWMN COMPONENTS

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Wireless Mesh Wireless Mesh NetworksNetworks

Conventional nodes (e.g., desktops, laptops, PDAs, Conventional nodes (e.g., desktops, laptops, PDAs, PocketPCs, phones, etc.) equipped with wireless PocketPCs, phones, etc.) equipped with wireless network interface cards (NICs) can connect directly network interface cards (NICs) can connect directly to wireless mesh routers. to wireless mesh routers.

Customers without wireless NICs can access WMNs Customers without wireless NICs can access WMNs by by

connecting to wireless mesh routers through, e.g., connecting to wireless mesh routers through, e.g., Ethernet.Ethernet.

Thus, WMNs will greatly help users be always-on-Thus, WMNs will greatly help users be always-on-line line

anywhere anytime. anywhere anytime.

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Wireless Mesh Wireless Mesh NetworksNetworks

Moreover, the gateway/bridge functionalities in mesh Moreover, the gateway/bridge functionalities in mesh routers enable the integration of WMNs with various routers enable the integration of WMNs with various existing wireless networks such as cellular, wireless existing wireless networks such as cellular, wireless sensor, wireless-fidelity (Wi-Fi), worldwide inter-sensor, wireless-fidelity (Wi-Fi), worldwide interoperability for microwave access (WiMAX) networks.operability for microwave access (WiMAX) networks.

Consequently, through an integrated WMN, users of Consequently, through an integrated WMN, users of existing networks are provided with otherwise existing networks are provided with otherwise impossible services of these networks.impossible services of these networks.

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Network Architecture Network Architecture ClassificationClassification

1. INFRASTRUCTURE MESHING1. INFRASTRUCTURE MESHING

2. CLIENT MESH NETWORKING2. CLIENT MESH NETWORKING

3. HYBRID MESH NETWORKING3. HYBRID MESH NETWORKING

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INFRASTRUCTURE MESHINGINFRASTRUCTURE MESHING

This includes mesh routers that form an This includes mesh routers that form an infrastructure for clients that connect to them. infrastructure for clients that connect to them.

This can be built using various types of radio This can be built using various types of radio

technologiestechnologies The mesh routers form a mesh of self-The mesh routers form a mesh of self-

configuring, self-healing links among configuring, self-healing links among themselves. themselves.

With gateway functionality, mesh routers can With gateway functionality, mesh routers can be connected to the Internet.be connected to the Internet.

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..

It provides backbone for conventional clients and It provides backbone for conventional clients and enables integration of WMNs with existing enables integration of WMNs with existing wireless networks, through gateway/bridge wireless networks, through gateway/bridge functionalities in mesh routers.functionalities in mesh routers.

Conventional clients with Ethernet interface can Conventional clients with Ethernet interface can be connected to mesh routers via Ethernet links.be connected to mesh routers via Ethernet links.

For conventional clients with the same radio For conventional clients with the same radio technologies as mesh routers, they can directly technologies as mesh routers, they can directly communicate with mesh routers.communicate with mesh routers.

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If different radio technologies are used, clients mustIf different radio technologies are used, clients must communicate with the base stations that have Ethernet connections communicate with the base stations that have Ethernet connections to mesh routers. to mesh routers.

These are the most commonly used.These are the most commonly used.

For example, community and neighborhood networks can be built For example, community and neighborhood networks can be built using infrastructure meshing. using infrastructure meshing.

The mesh routers are placed on the roof of houses in aThe mesh routers are placed on the roof of houses in a neighborhood, which serve as access points for users inside the neighborhood, which serve as access points for users inside the homes and along the roads. homes and along the roads.

Typically, two types of radios are used in the routers, i.e., for Typically, two types of radios are used in the routers, i.e., for backbone communication and for user communication, respectively. backbone communication and for user communication, respectively.

The mesh backbone communication can be established using long-range The mesh backbone communication can be established using long-range communication techniques including directional antennas.communication techniques including directional antennas.

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Client WMNsClient WMNs Client meshing provides peer-to-peer networks among client devices. Client meshing provides peer-to-peer networks among client devices.

Client nodes constitute the actual network to perform routing and Client nodes constitute the actual network to perform routing and configuration functionalities as well as providing end-userconfiguration functionalities as well as providing end-user

applications to customers. applications to customers.

A mesh router is not required for these types of networks. A mesh router is not required for these types of networks.

A packet destined to a node in the network hops through multiple A packet destined to a node in the network hops through multiple nodes to reach the destination. nodes to reach the destination.

They are formed using one type of radios on devices. They are formed using one type of radios on devices.

Moreover, the requirements on end-user devices is increased when Moreover, the requirements on end-user devices is increased when compared to infrastructure meshing; the end-users have to perform compared to infrastructure meshing; the end-users have to perform additional functions such as routing and self-configuration.additional functions such as routing and self-configuration.

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Client WMNsClient WMNs

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HYBRID WMNsHYBRID WMNs

This architecture is the combination of This architecture is the combination of infrastructure and infrastructure and client meshing.client meshing.

Mesh clients can access the network through mesh routers Mesh clients can access the network through mesh routers asas

well as directly meshing with other mesh clients. well as directly meshing with other mesh clients.

While the infrastructure provides connectivity to other While the infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX, cellular, and networks such as the Internet, Wi-Fi, WiMAX, cellular, and sensor networks; the routing capabilities of clients provide sensor networks; the routing capabilities of clients provide improved connectivity and coverage inside the WMN.improved connectivity and coverage inside the WMN.

The hybrid architecture will be the most applicable case!!!The hybrid architecture will be the most applicable case!!!

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Hybrid WMNs

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CHARACTERISTICSCHARACTERISTICS

Multi-hop Wireless NetworkMulti-hop Wireless Network

Support for Ad Hoc Networking, and Capability Support for Ad Hoc Networking, and Capability of Self-Forming, Self-Healing, and Self-Organizationof Self-Forming, Self-Healing, and Self-Organization

Mobility Dependence on the Type of Mesh NodesMobility Dependence on the Type of Mesh Nodes Multiple Types of Network AccessMultiple Types of Network Access

Dependence of Power-Consumption Constraints on the Dependence of Power-Consumption Constraints on the Type of Mesh NodesType of Mesh Nodes

Compatibility and Interoperability with Existing Compatibility and Interoperability with Existing Wireless NetworksWireless Networks

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WMNs vs AD HOC WMNs vs AD HOC NetworksNetworks

Dedicated Routing and Configuration:Dedicated Routing and Configuration:

In ad-hoc networks, end-user devices also perform In ad-hoc networks, end-user devices also perform routing and configuration functionalities for all other routing and configuration functionalities for all other nodes. nodes.

However, WMNs contain mesh routers for these However, WMNs contain mesh routers for these functionalities.functionalities.

Hence, the load on end-user devices is significantly Hence, the load on end-user devices is significantly

decreased, which provides lower energy consumption decreased, which provides lower energy consumption and high-end application capabilities to possibly mobile and high-end application capabilities to possibly mobile and energy constrained end-users. and energy constrained end-users.

Moreover, the end-user requirements are limited which Moreover, the end-user requirements are limited which decreases the cost of devices that can be used in decreases the cost of devices that can be used in WMNs.WMNs.

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Multiple Radios:Multiple Radios: * Mesh routers can be equipped with multiple radios to perform * Mesh routers can be equipped with multiple radios to perform routing and access functionalities. routing and access functionalities.

* This enables separation of two main types of traffic in the wireless * This enables separation of two main types of traffic in the wireless domain. domain.

* While routing and configuration traffic is performed between mesh * While routing and configuration traffic is performed between mesh routers, access to the network from end-users can be carried in a routers, access to the network from end-users can be carried in a different radio. different radio.

* This significantly improves the capacity of the network. * This significantly improves the capacity of the network.

* On the other hand, these functionalities are performed in the same * On the other hand, these functionalities are performed in the same channel in ad-hoc networks constraining the performance.channel in ad-hoc networks constraining the performance.

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Mobility:Mobility: Since ad-hoc networks provide routing using the end-user Since ad-hoc networks provide routing using the end-user

devices, devices, the network topology and connectivity depends on the the network topology and connectivity depends on the

movement movement of users. of users.

This imposes additional challenges to routing protocols as This imposes additional challenges to routing protocols as well as network configuration and deployment.well as network configuration and deployment.

Since mesh routers provide the infrastructure in WMNs, theSince mesh routers provide the infrastructure in WMNs, the coverage of the WMN can be engineered easily. coverage of the WMN can be engineered easily.

While providing continuous connectivity throughout the While providing continuous connectivity throughout the network, network,

the mobility of end-users is still supported, without the mobility of end-users is still supported, without compromising compromising

the performance of the network.the performance of the network.

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Compatibility:Compatibility: WMNs contain many differences when compared to ad hoc WMNs contain many differences when compared to ad hoc networks.networks.

Ad hoc networks can be considered as a subset of WMNs. Ad hoc networks can be considered as a subset of WMNs.

More specifically, the existing techniques developed for ad-hoc More specifically, the existing techniques developed for ad-hoc networks are already applicable to WMNs.networks are already applicable to WMNs.

As an example, through the use of mesh routers and routing-As an example, through the use of mesh routers and routing- capable end-users, multiple ad hoc networks can be supported capable end-users, multiple ad hoc networks can be supported in WMNs, but with further integration of these networks.in WMNs, but with further integration of these networks.

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Application ScenariosApplication Scenarios

1. Broadband Home Networking:1. Broadband Home Networking: Realized through IEEE 802.11 WLANsRealized through IEEE 802.11 WLANs

Problem Problem location of the access points. location of the access points.

Homes have many dead zones without service coverage. Homes have many dead zones without service coverage.

Solutions based on site survey are expensive and not practical for home networking, Solutions based on site survey are expensive and not practical for home networking, while installation of multiple access points is also expensive and not convenient while installation of multiple access points is also expensive and not convenient because of Ethernet wiring from access points to backhaul network access modem or because of Ethernet wiring from access points to backhaul network access modem or hub. hub.

Moreover, communications between end nodes under two different access points have Moreover, communications between end nodes under two different access points have to go all the way back to the access hub. to go all the way back to the access hub.

Not an efficient solution, especially for broadband networking.Not an efficient solution, especially for broadband networking.

Mesh networking can resolve all these issues in home networking. Mesh networking can resolve all these issues in home networking.

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Broadband Home Networking

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2. Community and Neighborhood Networking:2. Community and Neighborhood Networking: In a community, the common architecture for network access is based on cable In a community, the common architecture for network access is based on cable

or DSL connected to the Internet, and the last-hop isor DSL connected to the Internet, and the last-hop is wireless by connecting a wireless router to a cable or DSL modem.wireless by connecting a wireless router to a cable or DSL modem.

This type of network access has several drawbacks:This type of network access has several drawbacks: * Even if the information must be shared within a community or * Even if the information must be shared within a community or neighborhood, all traffic must flow through Internet. neighborhood, all traffic must flow through Internet. This significantly reduces network resource utilization. This significantly reduces network resource utilization.

* Large percentage of areas in between houses is not covered by wireless * Large percentage of areas in between houses is not covered by wireless services. services.

* An expensive but high bandwidth gateway between multiple homes or * An expensive but high bandwidth gateway between multiple homes or neighborhoods may not be shared and wireless services must be set up neighborhoods may not be shared and wireless services must be set up individually. As a result, network service costs may increase. individually. As a result, network service costs may increase.

* Only a single path may be available for one home to access the Internet * Only a single path may be available for one home to access the Internet or communicate with neighbors. or communicate with neighbors.

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Community Networking

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3. Enterprise Networking:3. Enterprise Networking:

Within an office or all offices in an entire building, or among offices in Within an office or all offices in an entire building, or among offices in multiple buildings.multiple buildings.

IEEE 802.11 WLANs are widely used in various offices currently. However, IEEE 802.11 WLANs are widely used in various offices currently. However, they are still isolated islands.they are still isolated islands.

Connections among them are achieved through wired Ethernet Connections among them are achieved through wired Ethernet (still costly)(still costly) In addition, adding more backhaul access modems only increases capacity In addition, adding more backhaul access modems only increases capacity

locally, but does not improve robustness to link failures, network locally, but does not improve robustness to link failures, network congestion and other problems of the entire enterprise network.congestion and other problems of the entire enterprise network.

Multiple backhaul access modems can be shared by all nodes in the entire Multiple backhaul access modems can be shared by all nodes in the entire network, and thus improve the robustness and resource utilization of network, and thus improve the robustness and resource utilization of enterprise networks. enterprise networks.

WMNs can grow easily as the size of enterprise expands.WMNs can grow easily as the size of enterprise expands.

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Enterprise Networking

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Metropolitan Area Networks:Metropolitan Area Networks: The physical-layer transmission rate of a node in WMNs is much higher The physical-layer transmission rate of a node in WMNs is much higher

than that in any cellular networks, e.g., an IEEE 802.11g node can transmit than that in any cellular networks, e.g., an IEEE 802.11g node can transmit at a rate of 54 Mbps. at a rate of 54 Mbps.

Moreover, the communication between nodes in WMNs does not rely on a Moreover, the communication between nodes in WMNs does not rely on a wired backbone. wired backbone.

Compared to wired networks, e.g., cable or optical networks, Compared to wired networks, e.g., cable or optical networks, wireless mesh MAN is an economic alternative to broadband networking,wireless mesh MAN is an economic alternative to broadband networking, especially in underdeveloped regions.especially in underdeveloped regions.

Wireless mesh MAN covers a potentially much larger area thanWireless mesh MAN covers a potentially much larger area than home, enterprise, building, or community networks.home, enterprise, building, or community networks.

Thus, the requirement on the network scalability by wireless mesh MANThus, the requirement on the network scalability by wireless mesh MAN is much higher than that by other applications.is much higher than that by other applications.

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Metropolitan Area Networks

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METROPOLITAN AREA NETWORKS

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Transportation Systems:Transportation Systems:

Instead of limiting IEEE 802.11 or 802.16 access to stationsInstead of limiting IEEE 802.11 or 802.16 access to stations and stops, mesh networking technology can extend access intoand stops, mesh networking technology can extend access into buses, ferries, and trains. buses, ferries, and trains.

Thus, convenient passenger information services, remote monitoring Thus, convenient passenger information services, remote monitoring of in-vehicle security video, and driver communications can be of in-vehicle security video, and driver communications can be supported. supported.

To enable such mesh networking for a transportation system, two keyTo enable such mesh networking for a transportation system, two key techniques are needed: the high-speed mobile backhaul from a vehicletechniques are needed: the high-speed mobile backhaul from a vehicle (car, bus, or train) to the Internet and mobile mesh networks (car, bus, or train) to the Internet and mobile mesh networks within the vehicle.within the vehicle.

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Transportation Systems

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Building Automation: In a building, various electrical devices including power, light, elevator, air In a building, various electrical devices including power, light, elevator, air

conditioner, etc., need to be controlled and monitored. conditioner, etc., need to be controlled and monitored.

Currently this task is accomplished through standard wired networks, which is very Currently this task is accomplished through standard wired networks, which is very expensive due to the complexity in deployment and maintenance of a wired expensive due to the complexity in deployment and maintenance of a wired network.network.

Recently Wi-Fi based networks have been adopted to reduce the cost of such Recently Wi-Fi based networks have been adopted to reduce the cost of such networks. networks.

However, this effort has not achieved satisfactory performance yet, because However, this effort has not achieved satisfactory performance yet, because deployment of Wi-Fis for this application is still rather expensive due to wiring of deployment of Wi-Fis for this application is still rather expensive due to wiring of Ethernet.Ethernet.

If BACnet (Building Automation and Control Networks) access points are replaced by If BACnet (Building Automation and Control Networks) access points are replaced by mesh routers, the deployment cost will be significantly reduced. mesh routers, the deployment cost will be significantly reduced.

The deployment process is also much simpler due to the mesh connectivity The deployment process is also much simpler due to the mesh connectivity among wireless routers.among wireless routers.

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Building Automation

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Health and Medical Systems:Health and Medical Systems:

In a hospital or medical center, monitoring and diagnosis data need to be In a hospital or medical center, monitoring and diagnosis data need to be processed and transmitted from one room to another for various purposes. processed and transmitted from one room to another for various purposes.

Data transmission is usually broadband, since high resolution medical images andData transmission is usually broadband, since high resolution medical images and various periodical monitoring information can easily produce a constant and large various periodical monitoring information can easily produce a constant and large volume of data.volume of data.

Traditional wired networks can only provide limited network access to certainTraditional wired networks can only provide limited network access to certain fixed medical devices. fixed medical devices.

Wi-Fi based networks must rely on the existence of Ethernet connections, which Wi-Fi based networks must rely on the existence of Ethernet connections, which may cause high system cost and complexity but without the abilities to eliminate may cause high system cost and complexity but without the abilities to eliminate dead spots.dead spots.

However, these issues do not exist in WMNs.However, these issues do not exist in WMNs.

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Security Surveillance Systems:Security Surveillance Systems:

As security is turning out to be a very high concern, security As security is turning out to be a very high concern, security surveillance systems become a necessity for enterprise surveillance systems become a necessity for enterprise buildings, shopping malls, grocery stores, etc. buildings, shopping malls, grocery stores, etc.

In order to deploy such systems at locations as needed, WMNs In order to deploy such systems at locations as needed, WMNs are a much more viable solution than wired networksare a much more viable solution than wired networks

to connect all devices. to connect all devices.

Since still images and videos are the major traffic flowing in the Since still images and videos are the major traffic flowing in the network, this application demands much higher network network, this application demands much higher network capacitycapacity

than other applications.than other applications.

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Critical Factors Influencing Critical Factors Influencing Network PerformanceNetwork Performance

1. Radio Techniques:1. Radio Techniques:Typical examples:Typical examples:

* Directional and smart antennas* Directional and smart antennas

* MIMO systems, * MIMO systems, (Key Technology for IEEE 802.11n) (Key Technology for IEEE 802.11n)

* Multi-radio/multi-channel systems* Multi-radio/multi-channel systems * Reconfigurable radios* Reconfigurable radios

* Frequency agile/cognitive radios and * Frequency agile/cognitive radios and

* Even software radios* Even software radios

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2. Scalability2. Scalability 3. Mesh Connectivity 3. Mesh Connectivity 4. Broadband and QoS 4. Broadband and QoS

5. Compatibility and Inter-5. Compatibility and Inter-OperabilityOperability

6. Security6. Security 7. Ease of Use7. Ease of Use

Critical Factors Critical Factors Influencing Network Influencing Network PerformancePerformance

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MAC LAYERMAC LAYER

Differences between WMNs MACs and the Differences between WMNs MACs and the Wireless Networks MACsWireless Networks MACs

* * MACs for WMNs are concerned with more than one hop MACs for WMNs are concerned with more than one hop communicationcommunication

* MAC must be distributed, needs to be collaborative, and must * MAC must be distributed, needs to be collaborative, and must work for multipoint-to-multipoint communication.work for multipoint-to-multipoint communication. * Network self-organization is needed for better collaboration * Network self-organization is needed for better collaboration

between between neighboring nodes and nodes in multi-hop distances. neighboring nodes and nodes in multi-hop distances.

* Mobility affects the performance of MAC.* Mobility affects the performance of MAC.

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SINGLE CHANNEL SINGLE CHANNEL MACsMACs

Improving Existing MAC ProtocolsImproving Existing MAC Protocols

MAC protocols are proposed for multi-hop WMNs by enhancing MAC protocols are proposed for multi-hop WMNs by enhancing existingexisting

MAC protocols.MAC protocols.

For example, in an IEEE 802.11 mesh networks, these schemes usuallyFor example, in an IEEE 802.11 mesh networks, these schemes usuallyadjust parameters of CSMA/CA, e.g., contention window size, and adjust parameters of CSMA/CA, e.g., contention window size, and

modify modify backoff procedures.backoff procedures.

However, these solutions only achieve a low end-to-end throughput, However, these solutions only achieve a low end-to-end throughput, because they cannot significantly reduce the probability of because they cannot significantly reduce the probability of

contentions contentions among neighboring nodes.among neighboring nodes.

As long as contention occurs frequently, whichever method is taken to As long as contention occurs frequently, whichever method is taken to modify backoff or contention resolution procedures, the end-to-end modify backoff or contention resolution procedures, the end-to-end throughput will still be significantly reduced due to the accumulating throughput will still be significantly reduced due to the accumulating

effect effect on the multi-hop path. on the multi-hop path.

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Cross-layer design with advanced physical layer techniquesCross-layer design with advanced physical layer techniques

1. MACs based on Directional Antennas1. MACs based on Directional Antennas Eliminate exposed nodes if antenna beam is assumed to be Eliminate exposed nodes if antenna beam is assumed to be

perfect. perfect.

Due to the directional transmission, more hidden nodes areDue to the directional transmission, more hidden nodes are produced.produced.

Also face other difficulties such as cost, system complexity, Also face other difficulties such as cost, system complexity, and practicality of fast steerable directional antennas.and practicality of fast steerable directional antennas.

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Proposing Innovative MAC Protocols:Proposing Innovative MAC Protocols:

Determined by their poor scalability in an ad hoc multi-hop network, Determined by their poor scalability in an ad hoc multi-hop network, random access protocols such as CSMA/CA are not an efficient solution. random access protocols such as CSMA/CA are not an efficient solution.

Thus, revisiting the design of MAC protocols based on TDMA or CDMA is Thus, revisiting the design of MAC protocols based on TDMA or CDMA is indispensable. indispensable.

To date, few TDMA or CDMA MAC protocols are available for WMNs, To date, few TDMA or CDMA MAC protocols are available for WMNs, probably because of two factors: probably because of two factors:

* The complexity and cost of developing a distributed and cooperative * The complexity and cost of developing a distributed and cooperative MAC with TDMA or CDMA. MAC with TDMA or CDMA.

* The compatibility of TDMA (or CDMA) MAC with existing MAC * The compatibility of TDMA (or CDMA) MAC with existing MAC protocols. protocols.

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2. MACs with Power Control

They reduce exposed nodes, especially in a dense They reduce exposed nodes, especially in a dense network, network,

using low transmission power, and thus, improve the using low transmission power, and thus, improve the

spectrum spatial reuse factor in WMNs.spectrum spatial reuse factor in WMNs.

However, hidden nodes may become worse because However, hidden nodes may become worse because lower lower

transmission power level reduces the possibility of transmission power level reduces the possibility of detecting detecting

a potential interfering node. a potential interfering node.

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For example, in IEEE 802.16, the original MAC For example, in IEEE 802.16, the original MAC protocol protocol

is a centralized TDMA scheme, but a distributed is a centralized TDMA scheme, but a distributed TDMA TDMA

MAC for IEEE 802.16 mesh is still missing.MAC for IEEE 802.16 mesh is still missing.

In IEEE 802.11 WMNs, how to design a In IEEE 802.11 WMNs, how to design a distributed distributed

TDMA MAC protocol overlaying CSMA/CA is an TDMA MAC protocol overlaying CSMA/CA is an interesting but a challenging problem!!!interesting but a challenging problem!!!

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Multi-Channel MACsMulti-Channel MACs

Multi-Channel Single-Transceiver MAC:Multi-Channel Single-Transceiver MAC: If cost and compatibility are the concern, one transceiver on a radio is If cost and compatibility are the concern, one transceiver on a radio is

a preferred hardware platform. a preferred hardware platform.

Since only one transceiver is available, only one channel is active at a Since only one transceiver is available, only one channel is active at a time in each network node.time in each network node.

However, different nodes may operate on different channels However, different nodes may operate on different channels simultaneously.simultaneously.

To coordinate transmissions between network nodes under this To coordinate transmissions between network nodes under this situation, protocols such as the multi-channel MAC and the situation, protocols such as the multi-channel MAC and the

seed-slotted channel hopping (SSCH) scheme are needed. seed-slotted channel hopping (SSCH) scheme are needed.

SSCH is actually a virtual MAC protocol, since it works on top of IEEE SSCH is actually a virtual MAC protocol, since it works on top of IEEE 802.11 MAC and does not need changes in the IEEE 802.11 MAC.802.11 MAC and does not need changes in the IEEE 802.11 MAC.

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Multi-Channel Multi-Transceiver Multi-Channel Multi-Transceiver MACsMACs

A radio includes multiple parallel RF front-end A radio includes multiple parallel RF front-end chips and baseband processing modules to chips and baseband processing modules to support several simultaneous channels.support several simultaneous channels.

On top of the physical layer, only one MAC On top of the physical layer, only one MAC layer module is needed to coordinate the layer module is needed to coordinate the functions of multiple channels. functions of multiple channels.

To date, no multi-channel multi-transceiver To date, no multi-channel multi-transceiver MAC protocol has been proposed for WMNs.MAC protocol has been proposed for WMNs.

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Multi-Radio MACsMulti-Radio MACs The network node has multiple radios each with its The network node has multiple radios each with its own MAC and physical layers. own MAC and physical layers. Communications in these radios are totally independent.Communications in these radios are totally independent. Thus, a virtual MAC protocol such as the multi-radio Thus, a virtual MAC protocol such as the multi-radio unification protocol (MUP) is required on top of MAC unification protocol (MUP) is required on top of MAC to coordinate communications in all channels. to coordinate communications in all channels. In fact, one radio can have multiple channels in this In fact, one radio can have multiple channels in this case. case. However, for simplicity of design and application, a However, for simplicity of design and application, a single fixed channel is usually applied in each radio.single fixed channel is usually applied in each radio.

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MAC LAYER-Open Research MAC LAYER-Open Research IssuesIssues

Scalable Single-Channel MACs:Scalable Single-Channel MACs:

The scalability issue in multi-hop ad hoc networks has The scalability issue in multi-hop ad hoc networks has not been fully solved yet.not been fully solved yet.

Most of existing MAC protocols only solve partialMost of existing MAC protocols only solve partial problems of the overall issue, but raise other problems. problems of the overall issue, but raise other problems.

To make the MAC protocol really scalable, new To make the MAC protocol really scalable, new distributed and collaborative schemes must be distributed and collaborative schemes must be

proposed proposed to ensure that the network performance (e.g., to ensure that the network performance (e.g., throughput and even QoS parameters such as delay and throughput and even QoS parameters such as delay and delay jitter) will not degrade as the network size delay jitter) will not degrade as the network size increasesincreases..

\\

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Scalable Multi-Channel MACsScalable Multi-Channel MACs

Multi-channel MAC protocols for radios with multiple transceivers have not been thoroughly explored, possibly due to the relatively high cost of such radios.

However, as the cost goes down, a multi-channel multi-transceiver MAC will be a rather promising solution for WMNs.

It is obvious that a multi-channel MAC protocol can achieve higher throughput than a single-channel MAC.

However, to really achieve spectrum efficiency and improve the per-channel throughput, the scalable MAC protocol needs to consider the overall performance improvement in multiple channels.

Thus, developing a scalable multi-channel MAC is a more challenging task than a single-channel MAC.

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MAC/Physical Cross-Layer DesignMAC/Physical Cross-Layer Design

When advanced physical layer techniques, such as MIMO and cognitive radios, are used, novel MAC protocols, especially multi-channel MAC, need to be proposed to utilize the agility provided by the physical layer.

Network Integration in the MAC LayerNetwork Integration in the MAC Layer

Mesh routers in WMNs are responsible for integration of various wireless

technologies.

Thus, advanced bridging functions must be developed in the MAC layer so that

different wireless radios, such as IEEE 802.11, 802.16, 802.15, etc., can

seamlessly work together.

Reconfigurable/software radios and the related radio resource management

schemes may be the ultimate solution to these bridging functions.

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MAC Protocol Implementation.MAC Protocol Implementation.

The functions of a MAC protocol are distributed in software, firmware,

and hardware.

Modifying functions in the firmware or hardwareis much more complicated and costly than doing that in software.

A solution to this problem is to develop a new MACprotocol architecture in which the proposed new MAC functionscan be completely implemented in the software.

Currently, several IEEE 802.11 chipset manufacturers have eliminated

firmware in their MAC implementation architecture, and the hardware of

some MAC chipsets is software programmable like a software defined radio

(SDR).

With such an architecture, a true software MAC. can be implemented.

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Routing LayerRouting Layer

Optimal routing protocol for WMNs must capture the following Optimal routing protocol for WMNs must capture the following features:features:

Multiple Performance Metrics.Multiple Performance Metrics.

* Many existing routing protocols use minimum hop-count as a * Many existing routing protocols use minimum hop-count as a performance metric to select the routing path. performance metric to select the routing path.

* This has been demonstrated to be ineffective in many situations. * This has been demonstrated to be ineffective in many situations.

* For example, when a link on the minimum hop-count path has bad * For example, when a link on the minimum hop-count path has bad quality or experiences congestion, it becomes a bottleneck to the quality or experiences congestion, it becomes a bottleneck to the end-to-end throughput. end-to-end throughput.

* To solve this problem, other performance metrics, e.g., link * To solve this problem, other performance metrics, e.g., link quality and round trip time (RTT), must be considered in the quality and round trip time (RTT), must be considered in the routing protocol.routing protocol.

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Scalability.Scalability.

Setting up a routing path in a very large wirelessSetting up a routing path in a very large wirelessnetwork may take a long time. network may take a long time.

Furthermore, even when the path is established,Furthermore, even when the path is established,the node states on the path may change. the node states on the path may change.

Thus, it is critical to have a scalable routing Thus, it is critical to have a scalable routing protocol in WMNs.protocol in WMNs.

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Robustness.Robustness.

* * To avoid service disruption, WMNs must be To avoid service disruption, WMNs must be robust to link failures or congestion. robust to link failures or congestion. * Thus, routing protocols need to be fault * Thus, routing protocols need to be fault tolerant with link failures and can achieve tolerant with link failures and can achieve load balancing.load balancing.

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Adaptive Support of Both Adaptive Support of Both Mesh Routers and Mesh Clients.Mesh Routers and Mesh Clients.Considering the minimal mobility and no constraint of powerConsidering the minimal mobility and no constraint of powerconsumption in mesh routers, a routing protocol much simpler consumption in mesh routers, a routing protocol much simpler than ad hoc network routing protocols can be developed for than ad hoc network routing protocols can be developed for mesh routers.mesh routers.

However, the routing protocol for mesh clients is usually However, the routing protocol for mesh clients is usually complicated due to the support of mobility and power complicated due to the support of mobility and power efficiency.efficiency.

Consequently, it is necessary to design a routing protocolConsequently, it is necessary to design a routing protocolthat can adaptively support both mesh routers and mesh that can adaptively support both mesh routers and mesh clients.clients.

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Routing Protocols with Various Performance Metrics:Routing Protocols with Various Performance Metrics:

LQSR aims to select a routing path according to link quality metrics. LQSR aims to select a routing path according to link quality metrics.

Three performance metrics, i.e., expected transmission count (ETX), per-Three performance metrics, i.e., expected transmission count (ETX), per-hop RTT, and per-hop packet pair are implemented separately in LQSR. hop RTT, and per-hop packet pair are implemented separately in LQSR.

The performance of the routing protocol with these three performanceThe performance of the routing protocol with these three performancemetrics is compared with the method using the minimum hop-count.metrics is compared with the method using the minimum hop-count.

For stationary nodes in WMNs, ETX achieves the bestFor stationary nodes in WMNs, ETX achieves the bestperformance, while the minimum hop-count method outperforms the three performance, while the minimum hop-count method outperforms the three link quality metrics when nodes are mobile.link quality metrics when nodes are mobile.

This result illustrates that the used link quality metrics This result illustrates that the used link quality metrics are still not enough for WMNs when mobility is concerned.are still not enough for WMNs when mobility is concerned.

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Routing LayerRouting LayerMulti-Radio Routing:Multi-Radio Routing:

Multi-radio per node is a preferred architecture in the network Multi-radio per node is a preferred architecture in the network layer, because the capacity can be increased without modifying layer, because the capacity can be increased without modifying The MAC protocol. The MAC protocol.

A multi-radio LQSR (MR-LQSR) is proposed A multi-radio LQSR (MR-LQSR) is proposed where a new performance metric, called weighted cumulative where a new performance metric, called weighted cumulative Expected transmission time (WCETT), is incorporated. Expected transmission time (WCETT), is incorporated.

WCETT takes into account both link quality metric and the WCETT takes into account both link quality metric and the minimum hop-count and achieves good tradeoff between delay and minimum hop-count and achieves good tradeoff between delay and throughput. throughput.

MR-LQSR assumes that all radios on each node are tuned to non-MR-LQSR assumes that all radios on each node are tuned to non-interfering channels with the assignment changing infrequently.interfering channels with the assignment changing infrequently.

In other words, MR-LQSR relies on the MAC layer to perform In other words, MR-LQSR relies on the MAC layer to perform channel selection. channel selection.

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Multi-Path RoutingMulti-Path Routing * * The main objectives of using multi-path routing are to perform The main objectives of using multi-path routing are to perform better load balancing and to provide high fault tolerance.better load balancing and to provide high fault tolerance. * Multiple paths are selected between source and destination.* Multiple paths are selected between source and destination. * When link is broken on a path due to a bad channel quality or * When link is broken on a path due to a bad channel quality or mobility another path in the set of existing paths can be chosen.mobility another path in the set of existing paths can be chosen. * Thus, without waiting for setting up a new routing path, the * Thus, without waiting for setting up a new routing path, the end-to-end delay, throughput, and fault tolerance can be improved. end-to-end delay, throughput, and fault tolerance can be improved. * However, given a performance metric, the improvement depends on * However, given a performance metric, the improvement depends on the availability of node-disjoint routes between source and the availability of node-disjoint routes between source and destinationdestination * Another drawback of multi-path routing is its complexity* Another drawback of multi-path routing is its complexity * As a result, how to design a cost-effective multi-path routing * As a result, how to design a cost-effective multi-path routing protocol with appropriate performance metrics needs further study.protocol with appropriate performance metrics needs further study.

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Hierarchical Routing:

In hierarchical routing, a certain self-organization scheme is employed to group network nodes into clusters.

Each cluster has one or more cluster heads.

Nodes in a cluster can be one or more hops away from thecluster head.

Since connectivity between clusters are needed, some nodescan communicate with more than one cluster and work as a gateway.

Routing within a cluster and routing between clusters may usedifferent mechanisms.

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Routing LayerRouting LayerHierarchical Routing:

For example, inter-cluster routing can be a proactive protocol, while intra-cluster routing can be on demand.

When the node density is high, hierarchical routing protocols tend toachieve much better performance because of less overhead, shorteraverage routing path, and quicker set-up procedure of routing path.

However, the complexity of maintaining the hierarchy may compromisethe performance of the routing protocol.

Implementation difficulty, because a node selected as a cluster head may not necessarily have higher processing capability and channel capacity than the other nodes.

Unless being intentionally designed so, the cluster head may becomea bottleneck.

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Geographic Routing:Geographic Routing:

Compared to topology-based routing schemes, geographic routing schemesforward packets by only using the position information of nodes in the vicinityand the destination node.

Thus, topology change has less impact on the geographic routing than otherrouting protocols.

Early geographic routing algorithms are a type of single-path greedyrouting schemes in which packet forwarding decision is made based onthe location information of current forwarding node, its neighbors,and the destination node.

However, all greedy routing algorithms have a common problem, i.e., delivery is

not guaranteed even if a path exists between source and destination.

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Geographic Routing:Geographic Routing:

Partial flooding and keeping the past routing information can help to guarantee delivery.

However, these approaches increase communication overhead and lose

the stateless property of single-path greedy routing.

In order to keep the stateless property and guarantee delivery, planar-graph based geographic routing algorithms are proposed recently.

However, these algorithms usually have much higher communication overhead than single-path greedy routing algorithms.

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EXISTING ROUTING SOFTWARE IMPLEMENTATIONSEXISTING ROUTING SOFTWARE IMPLEMENTATIONS

The Mobile Mesh software is covered by the GNU General Public License (Version 2).The Mobile Mesh software is covered by the GNU General Public License (Version 2). TBRPFTBRPF, or Topology Broadcast based on Reverse-Path Forwarding, is a proactive, link-state , or Topology Broadcast based on Reverse-Path Forwarding, is a proactive, link-state

routing protocol designed for mobile ad-hoc networks, which provides hop-by-hop routing along routing protocol designed for mobile ad-hoc networks, which provides hop-by-hop routing along minimum hop paths to each destination. It seems it is patent-protected unless it becomes a IETF minimum hop paths to each destination. It seems it is patent-protected unless it becomes a IETF standard.standard.

OSPFOSPF is a link-state routing protocol. It is designed to be run internal to a single Autonomous is a link-state routing protocol. It is designed to be run internal to a single Autonomous System. Each OSPF router maintains an identical database describing the Autonomous System's System. Each OSPF router maintains an identical database describing the Autonomous System's topology. From this database, a routing table is calculated by constructing a shortest-path tree.topology. From this database, a routing table is calculated by constructing a shortest-path tree.

GNU ZebraGNU Zebra is free software that manages TCP/IP-based routing protocols. It is released as part is free software that manages TCP/IP-based routing protocols. It is released as part of the GNU Project, and is distributed under the GNU General Public License. It supports BGP-4 of the GNU Project, and is distributed under the GNU General Public License. It supports BGP-4 protocol as described in RFC1771 (A Border Gateway Protocol 4) as well as RIPv1, RIPv2, and protocol as described in RFC1771 (A Border Gateway Protocol 4) as well as RIPv1, RIPv2, and OSPFv2.OSPFv2.

LocustWorldLocustWorld develops a free bootable CD solution based on the AODV protocol, and also develops a free bootable CD solution based on the AODV protocol, and also develops and sells a complete ready-to-deploy MeshBox running its software, most (but not all) develops and sells a complete ready-to-deploy MeshBox running its software, most (but not all) of which is available under the GPL. The MeshBox and mesh software have been used in a of which is available under the GPL. The MeshBox and mesh software have been used in a number of community networks in the UK.number of community networks in the UK.

4g 4g MeshCubeMeshCube. The German company 4G Mobile Systems has developed a tiny MeshCube running . The German company 4G Mobile Systems has developed a tiny MeshCube running Debian Linux on a MIPS processor, using MITRE Mobile Mesh routing software. This is a ready-Debian Linux on a MIPS processor, using MITRE Mobile Mesh routing software. This is a ready-to-deploy gateway with both a wireless and a wired interface. With a power consumption of 4W to-deploy gateway with both a wireless and a wired interface. With a power consumption of 4W (and potentially lower), it is ideal for deployment with an autonomous sustainable power (and potentially lower), it is ideal for deployment with an autonomous sustainable power source.source.

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Routing Layer- Open Research Routing Layer- Open Research IssuesIssues

Scalability.Scalability.

Hierarchical routing protocols can only partially solve thisHierarchical routing protocols can only partially solve thisproblem due to their complexity and difficulty of management.problem due to their complexity and difficulty of management.

Geographic routing relies on the existence of GPS or similar positioningGeographic routing relies on the existence of GPS or similar positioningtechnologies, which increases cost and complexity of WMNs.technologies, which increases cost and complexity of WMNs.

Thus, new scalable routing protocols need to be developed.Thus, new scalable routing protocols need to be developed.

Better Performance Metrics.Better Performance Metrics.

New performance metrics need to be developed. New performance metrics need to be developed.

Also, it is necessary to integrate multiple performance metrics Also, it is necessary to integrate multiple performance metrics into a routing protocol so that the optimal overall performanceinto a routing protocol so that the optimal overall performanceis achieved.is achieved.

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Routing Layer - Open Research Routing Layer - Open Research IssuesIssues

Routing/MAC Cross-Layer Design.Routing/MAC Cross-Layer Design.

A routing protocol needs to interact with the MAC layer in order toA routing protocol needs to interact with the MAC layer in order toimprove its performance. improve its performance.

Adopting multiple performance metrics from layer-2 into routing protocols Adopting multiple performance metrics from layer-2 into routing protocols is an example. is an example.

However, interaction between MAC and routing layers is so closeHowever, interaction between MAC and routing layers is so closethat merely exchanging parameters between them is not adequate.that merely exchanging parameters between them is not adequate.

Merging certain functions of MAC and routing protocols is a promising Merging certain functions of MAC and routing protocols is a promising approach. approach.

It is particularly meaningful for multi-radio or multi-channel routing, It is particularly meaningful for multi-radio or multi-channel routing, because the channel/radio selection in the MAC layer can help the pathbecause the channel/radio selection in the MAC layer can help the pathselection in the routing layer.selection in the routing layer.

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Routing Layer- Open Research Routing Layer- Open Research IssuesIssues

Hybrid Routing.Hybrid Routing.

In WMNs, mesh routers and mesh clients In WMNs, mesh routers and mesh clients have have

different constraints in power efficiency and different constraints in power efficiency and mobility. mobility.

Thus, a new routing protocol is needed to Thus, a new routing protocol is needed to adaptively support hybrid nodes: mesh adaptively support hybrid nodes: mesh

routers routers and mesh clients. and mesh clients.

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Transport LayerTransport Layer

Reliable Data TransportReliable Data Transport

* * TCP variants TCP variants * New transport protocols.* New transport protocols.

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TRANSPORT PROTOCOLSTRANSPORT PROTOCOLS

TCP Variants:TCP Variants: Non-Congestion Packet Losses.Non-Congestion Packet Losses. The classical TCPs do not differentiate congestion and non-The classical TCPs do not differentiate congestion and non- congestion losses. congestion losses.

As a result, when non-congestion losses occur, the network As a result, when non-congestion losses occur, the network throughput quickly drops due to unnecessary congestion throughput quickly drops due to unnecessary congestion avoidance.avoidance.

In addition, once wireless channels are back to the normal In addition, once wireless channels are back to the normal operation, the classical TCP cannot be recovered quickly.operation, the classical TCP cannot be recovered quickly.

Feedback mechanism can be used to differentiate different Feedback mechanism can be used to differentiate different packet losses.packet losses.

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TRANSPORT PROTOCOLSTRANSPORT PROTOCOLS

Unknown Link FailureUnknown Link FailureLink failure occurs frequently in mobile ad hoc networks,since all nodes are mobile.

As far as WMNs are concerned, link failure is not as criticalas in mobile ad hoc networks, because the WMN infrastructure avoid the issue of single-point-of-failure.

However, due to wireless channels and mobility in mesh clients, link failure may still happen.

To enhance TCP performance, link failure needs to be detected.

One possible approach is to include a link failure notification scheme in the transport protocol.

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TRANSPORT TRANSPORT PROTOCOLSPROTOCOLS

Network Asymmetry.Network Asymmetry.

Network asymmetry is defined as the situation where the forward direction of a network is significantly different from the reverse direction in terms of bandwidth, loss rate, and latency

Since TCP is critically dependent on ACK, so its performance can be severely impacted by network asymmetry.

Schemes such as ACK filtering, ACK congestion control, etc., are proposed to solve the network asymmetry problem

However, whether they are applicable to WMNs needs investigation.

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Large RTT Variations. In WMNs, mesh routers and mesh clients are connected as an ad hoc network, so dynamic change of routing path is common.

Considering mobility, variable link quality, traffic load,

and other factors, the change may be frequent and may cause large variations of RTT.

This will degrade the TCP performance, because the

normal operation of TCP relies on a smooth measurement of RTT.

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New Transport ProtocolsNew Transport Protocols::

To further improve performance of transport protocols,To further improve performance of transport protocols,researchers have started to develop entirely newresearchers have started to develop entirely newtransport protocols. transport protocols.

The ad hoc transport protocol (ATP) is proposed for ad hoc The ad hoc transport protocol (ATP) is proposed for ad hoc networks. networks.

Transmissions in ATP are rate-based, and quick start is used Transmissions in ATP are rate-based, and quick start is used for initial rate estimation. for initial rate estimation.

The congestion detection is a delay-based approach, and thus The congestion detection is a delay-based approach, and thus ambiguity between congestion losses and non-congestion losses ambiguity between congestion losses and non-congestion losses

is is avoided. avoided.

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New Transport ProtocolsNew Transport Protocols::

Moreover, in ATP, there is no retransmission timeout, and Moreover, in ATP, there is no retransmission timeout, and congestion control and reliability are decoupled. congestion control and reliability are decoupled.

By using an entirely new set of mechanisms for reliable data By using an entirely new set of mechanisms for reliable data transport, new transport protocol like ATPtransport, new transport protocol like ATPachieves much better performance (e.g., delay, throughput,achieves much better performance (e.g., delay, throughput,and fairness) than the TCP variants.and fairness) than the TCP variants.

However, for WMNs, an entirely new transport protocol is not However, for WMNs, an entirely new transport protocol is not Favorable solution. Favorable solution.

WMNs will be integrated with the Internet and many otherWMNs will be integrated with the Internet and many otherwireless networks, and thus, transport protocols for WMNs wireless networks, and thus, transport protocols for WMNs needs to be compatible with TCPs in such networks.needs to be compatible with TCPs in such networks.

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Real-Time DeliveryReal-Time Delivery

RCP protocols can be classified into two types: additive-increaseRCP protocols can be classified into two types: additive-increasemultiplicative-decrease (AIMD)-based or equation-based.multiplicative-decrease (AIMD)-based or equation-based.

An adaptive detection rate control (ADTFRC) scheme for mobile An adaptive detection rate control (ADTFRC) scheme for mobile ad ad

hoc networks hoc networks an end-to-end multi-metric joint detection an end-to-end multi-metric joint detection approach approach

is developed for TCP-friendly rate control schemes.is developed for TCP-friendly rate control schemes.

To really support real-time delivery for multimedia To really support real-time delivery for multimedia traffic, the accuracy of the detection approach is still traffic, the accuracy of the detection approach is still insufficient. insufficient.

Also all non-congestion packet losses due to differentAlso all non-congestion packet losses due to differentproblems are processed in the same way, whichproblems are processed in the same way, whichmay degrade the performance of the rate control scheme. may degrade the performance of the rate control scheme.

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TRANSPORT PROTOCOLS-TRANSPORT PROTOCOLS-OPEN RESEARCH ISSUESOPEN RESEARCH ISSUES

Cross-layer Solution to Network Asymmetry.Cross-layer Solution to Network Asymmetry.

All problems of TCP performance degradation are actually All problems of TCP performance degradation are actually related to protocols in the lower layers. related to protocols in the lower layers.

For example, it is the routing protocol that determines the For example, it is the routing protocol that determines the path for both TCP data and ACK packets. path for both TCP data and ACK packets.

To avoid asymmetry between data and ACK packets, it is To avoid asymmetry between data and ACK packets, it is desired for a routing protocol to select an optimal path for both desired for a routing protocol to select an optimal path for both data and ACK packets.data and ACK packets.

Moreover, the link layer performance directly impacts packet Moreover, the link layer performance directly impacts packet loss ratio and network asymmetry. loss ratio and network asymmetry.

In order to reduce the possibility of network asymmetry, the In order to reduce the possibility of network asymmetry, the MAC layer and error control may need to treat TCP data and MAC layer and error control may need to treat TCP data and ACK packets differently. ACK packets differently.

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TRANSPORT PROTOCOLS-TRANSPORT PROTOCOLS-OPEN RESEARCH ISSUESOPEN RESEARCH ISSUES

Adaptive TCP.Adaptive TCP.

WMNs will also be integrated with the Internet andWMNs will also be integrated with the Internet andvarious wireless networks such as IEEE 802.11, 802.16, 802.15, various wireless networks such as IEEE 802.11, 802.16, 802.15, etc. etc.

The characteristics of these networks may be significantlyThe characteristics of these networks may be significantlyheterogeneous due to different network capacity and behaviors of heterogeneous due to different network capacity and behaviors of error control,error control,

MAC, and routing protocols. Such heterogeneity renders the same MAC, and routing protocols. Such heterogeneity renders the same TCP ineffective for all networks. TCP ineffective for all networks.

Applying different TCPs in different networks is a complicatedApplying different TCPs in different networks is a complicatedand costly approach, and cannot achieve satisfactory performanceand costly approach, and cannot achieve satisfactory performance

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Application LayerApplication Layer

Internet Access.Internet Access.

Various Internet applications provide important timely Various Internet applications provide important timely information to people,make life more convenient, and information to people,make life more convenient, and

increase increase work efficiency and productivity.work efficiency and productivity.

In a home or small/medium business environment, the most In a home or small/medium business environment, the most popular network access solution is still DSL or cable modem popular network access solution is still DSL or cable modem along with IEEE 802.11 access points. along with IEEE 802.11 access points.

However, comparing with this approach, WMNs have many However, comparing with this approach, WMNs have many potential advantages: low cost, higher speed, and easy potential advantages: low cost, higher speed, and easy installation.installation.

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Distributed Information Storage and SharingDistributed Information Storage and Sharing..

Backhaul access to the Internet is not necessary in this type ofBackhaul access to the Internet is not necessary in this type ofapplications, and users only communicate within WMNs.applications, and users only communicate within WMNs.

A user may want to store high-volume data in disks owned by otherA user may want to store high-volume data in disks owned by otherusers, download files from other users' disks based on peer-to-users, download files from other users' disks based on peer-to-Peer networking mechanism, and query/retrieve information Peer networking mechanism, and query/retrieve information

located located in distributed database servers. in distributed database servers.

Users within WMNs may also want to chat, talk on the video Users within WMNs may also want to chat, talk on the video phones, and play games with each other.phones, and play games with each other.

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Information Exchange across Multiple Wireless Information Exchange across Multiple Wireless Networks.Networks.

For example, a cellular phone may want to talk For example, a cellular phone may want to talk to to

a Wi-Fi phone through WMNs, or a user on a Wi-a Wi-Fi phone through WMNs, or a user on a Wi-Fi Fi

network may expect to monitor the status in network may expect to monitor the status in various various

sensors in a wireless sensor networks.sensors in a wireless sensor networks.

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Three research directions:Three research directions:

1. Improve Existing Application Layer Protocols.1. Improve Existing Application Layer Protocols.

Due to ad hoc and multi-hop wireless network architecture of Due to ad hoc and multi-hop wireless network architecture of WMNs, protocols in the lower layers cannot provide perfect supportWMNs, protocols in the lower layers cannot provide perfect supportfor the application layer. for the application layer.

For example, as perceived by the application layer,For example, as perceived by the application layer,packet loss may not always be zero, packet delay may be variable packet loss may not always be zero, packet delay may be variable with a large jitter, etc. Such problems may fail many Internet with a large jitter, etc. Such problems may fail many Internet applications that work smoothly in a wired network. applications that work smoothly in a wired network.

Therefore, existing application layer protocols need to be improved.Therefore, existing application layer protocols need to be improved.

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2. Propose New Application Layer Protocols for 2. Propose New Application Layer Protocols for Distributed Information Sharing.Distributed Information Sharing.

Currently, many peer-to-peer protocols are available Currently, many peer-to-peer protocols are available forfor

information sharing on the Internet. information sharing on the Internet.

However, these protocols cannot achieve a However, these protocols cannot achieve a satisfactorysatisfactory

performance in WMNs, since WMNs have much performance in WMNs, since WMNs have much different different

characteristics than the Internet. characteristics than the Internet.

New application layer protocols need to be developed.New application layer protocols need to be developed.

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3. Develop Innovative Applications for 3. Develop Innovative Applications for WMNs.WMNs.

Such applications must bring tremendous Such applications must bring tremendous benefitsbenefits

to users, and cannot achieve best performance to users, and cannot achieve best performance without WMNs.without WMNs.

Such applications will enable WMNs to be a Such applications will enable WMNs to be a unique networking solution instead of just unique networking solution instead of just

another another option of wireless networking.option of wireless networking.

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Mobility Mobility ManagementManagement

Centralized mobility management schemes are not applicable in Centralized mobility management schemes are not applicable in WMNs.WMNs.

Thus, a distributed mobility management scheme is needed for Thus, a distributed mobility management scheme is needed for WMNs. WMNs.

However, because of the existence of a backbone network a However, because of the existence of a backbone network a distributed scheme for WMNs can be simpler than that for distributed scheme for WMNs can be simpler than that for mobile ad hoc networks. mobile ad hoc networks.

How to take advantages of the network backbone to design a How to take advantages of the network backbone to design a light-weight distributed mobility management scheme for WMNs light-weight distributed mobility management scheme for WMNs needs further investigation.needs further investigation.

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Mobility Mobility ManagementManagement

Location service is a desired feature by WMNs. Location service is a desired feature by WMNs.

Location information can enhance the performance of MAC andLocation information can enhance the performance of MAC androuting protocols. routing protocols.

It can help to develop promising location-related applications.It can help to develop promising location-related applications.

Proposing accurate or efficient algorithms for location service is still Proposing accurate or efficient algorithms for location service is still an open research topican open research topic

Mobility management is closely related to multiple layers of Mobility management is closely related to multiple layers of network network

protocols, the development of multi-layer mobility management protocols, the development of multi-layer mobility management schemes is another interesting research topic. schemes is another interesting research topic.

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Power ManagementPower Management

The goal of power management in WMNs varies with network nodes. The goal of power management in WMNs varies with network nodes.

Usually, mesh routers do not have a constraint on power consumption; Usually, mesh routers do not have a constraint on power consumption; power management aims to control connectivity, interference, spectrum power management aims to control connectivity, interference, spectrum spatial-reuse, and topology.spatial-reuse, and topology.

In contrast to mesh routers, mesh clients may expect protocols to be power In contrast to mesh routers, mesh clients may expect protocols to be power efficient. efficient.

For example, some mesh clients are IP phones or even sensors; power For example, some mesh clients are IP phones or even sensors; power efficiency is the major concern for them. efficiency is the major concern for them.

Thus, it is quite possible that some applications of WMNs require power Thus, it is quite possible that some applications of WMNs require power management to optimize both power efficiency and connectivity, which management to optimize both power efficiency and connectivity, which

results results in a complicated problem.in a complicated problem.

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Network MonitoringNetwork MonitoringThe statistics in the MIB (management information base) of mesh nodes, The statistics in the MIB (management information base) of mesh nodes, especially mesh routers, need to be reported to one or several servers in especially mesh routers, need to be reported to one or several servers in order to continuously monitor the network performance. order to continuously monitor the network performance.

In addition, data processing algorithms in the performance monitoring In addition, data processing algorithms in the performance monitoring software on the server analyze these statistical data and determine software on the server analyze these statistical data and determine potential abnormality.potential abnormality.

Based on the statistical information collected from MIB, data Based on the statistical information collected from MIB, data processing algorithms can also accomplish many other functions such processing algorithms can also accomplish many other functions such as network topology monitoring.as network topology monitoring.

To reduce overhead, schemes for efficient transmission of network To reduce overhead, schemes for efficient transmission of network monitoring information are expected.monitoring information are expected.

In addition, in order to accurately detect abnormal operation and quickly In addition, in order to accurately detect abnormal operation and quickly derive network topology of WMNs, effective data processing algorithms derive network topology of WMNs, effective data processing algorithms need to be developed.need to be developed.

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SECURITYSECURITY

WMNs lack efficient and scalable security solutions, WMNs lack efficient and scalable security solutions, because their security is easier to be compromised due because their security is easier to be compromised due to: to: distributed network architecture, vulnerability of distributed network architecture, vulnerability of channels and nodes in the shared wireless medium, and channels and nodes in the shared wireless medium, and dynamic change of network topology.dynamic change of network topology.

Different attacks in several protocol layersDifferent attacks in several protocol layerscan easily fail the network.can easily fail the network.

Attacks may occur in the routing protocolAttacks may occur in the routing protocolsuch as advertising wrong routing updates.such as advertising wrong routing updates.

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SECURITYSECURITY

The attacker may sneak into the network, impersonateThe attacker may sneak into the network, impersonatea legitimate node, and does not follow the required a legitimate node, and does not follow the required specifications of a routing protocol. specifications of a routing protocol.

Same types of attacks as in routing protocols may also Same types of attacks as in routing protocols may also occur in MAC protocols. occur in MAC protocols.

For example, the backoff procedures and NAV forFor example, the backoff procedures and NAV forvirtual carrier sense of IEEE 802.11 MAC may be virtual carrier sense of IEEE 802.11 MAC may be misused by some attacking nodes, which cause the misused by some attacking nodes, which cause the network to be always congested by these malicious network to be always congested by these malicious nodes.nodes.

Attackers may also sneak into the network by misusingAttackers may also sneak into the network by misusingthe cryptographic primitives.the cryptographic primitives.

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SECURITYSECURITY

In a cryptographic protocol, the exchange of information In a cryptographic protocol, the exchange of information among users occurs frequently. among users occurs frequently.

The users employ a fair exchange protocol which depends on a The users employ a fair exchange protocol which depends on a trusted third party. trusted third party.

However, this trusted party is not available in WMNs due to lack of However, this trusted party is not available in WMNs due to lack of infrastructure.infrastructure.

A widely accepted counter-attack measure is authenticationA widely accepted counter-attack measure is authenticationand authorization. and authorization.

For wireless LANs, this is taken care of by authentication, For wireless LANs, this is taken care of by authentication, authorization, and accounting (AAA) services directly over the access authorization, and accounting (AAA) services directly over the access point or via gateways.point or via gateways.

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SECURITYSECURITY

However, AAA is performed through a centralized serverHowever, AAA is performed through a centralized serversuch as RADIUS (remote authentication dial-in user service). such as RADIUS (remote authentication dial-in user service).

Such a centralized scheme is not applicable in WMNs.Such a centralized scheme is not applicable in WMNs.

Moreover, security key management in WMNs is much more difficult Moreover, security key management in WMNs is much more difficult thanin wireless LANs, because there is no central authority,thanin wireless LANs, because there is no central authority,trusted third party or server to manage security keys.trusted third party or server to manage security keys.

Key management in WMNs need to be performed in a distributed but Key management in WMNs need to be performed in a distributed but secure way. secure way.

Therefore, a distributed authentication and authorizationTherefore, a distributed authentication and authorizationscheme with secure key management needs to be proposed forscheme with secure key management needs to be proposed forWMNs.WMNs.

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SECURITYSECURITY

To further ensure security of WMNs, two more strategiesTo further ensure security of WMNs, two more strategiesneed to be considered: embedding security mechanism into network need to be considered: embedding security mechanism into network protocols such as secure routing and MAC protocols orprotocols such as secure routing and MAC protocols ordeveloping security monitoring and response systems to detect developing security monitoring and response systems to detect attacks monitor service disruption, and respond quickly to attacks.attacks monitor service disruption, and respond quickly to attacks.

For a secure networking protocol, a multi-protocol layer security For a secure networking protocol, a multi-protocol layer security scheme is desired, because security attacks occur simultaneously in scheme is desired, because security attacks occur simultaneously in different protocol layers. different protocol layers.

For a security monitoring system, a cross-layer For a security monitoring system, a cross-layer framework also needs to be developed. framework also needs to be developed.

How to design and implement a practical security system, including How to design and implement a practical security system, including cross-layer secure network protocols and various intrusion detection cross-layer secure network protocols and various intrusion detection algorithms, is a challenging research topic.algorithms, is a challenging research topic.

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Cross-Layer DesignCross-Layer Design

The methodology of layered protocol design does not The methodology of layered protocol design does not necessarily lead to an optimum solution.necessarily lead to an optimum solution.

This is particularly the case in WMNs due toThis is particularly the case in WMNs due tounreliable physical links, dynamic network topology,unreliable physical links, dynamic network topology,distributed network architecture, etc.distributed network architecture, etc.

The physical channel in WMNs is variable in terms of The physical channel in WMNs is variable in terms of capacity, bit error rate, etc. capacity, bit error rate, etc.

Although different coding, modulation, and error control Although different coding, modulation, and error control schemes can be used to improve the performance of the schemes can be used to improve the performance of the physical channel, there is no way to guaranteephysical channel, there is no way to guaranteefixed capacity, zero packet loss rate, or reliable fixed capacity, zero packet loss rate, or reliable connectivity.connectivity.

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In order to provide satisfactory network performance, MAC,In order to provide satisfactory network performance, MAC,routing, and transport layer protocols need to interactivelyrouting, and transport layer protocols need to interactivelywork together with the physical layer.work together with the physical layer.

In WMNs, because of the ad hoc feature, network topologyIn WMNs, because of the ad hoc feature, network topologyconstantly changes due to mobility and link failures.constantly changes due to mobility and link failures.

Such a dynamic network topology impacts multiple protocol Such a dynamic network topology impacts multiple protocol layers.layers.

Thus, in order to improve the protocol efficiency, cross-layer Thus, in order to improve the protocol efficiency, cross-layer designdesign

become indispensable, as discussed before in the openbecome indispensable, as discussed before in the openresearch issues of different protocol layers.research issues of different protocol layers.

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Cross-layer design can be performed in two ways.Cross-layer design can be performed in two ways.

1. Improve the performance of a protocol layer1. Improve the performance of a protocol layer by considering parameters in other protocol layers.by considering parameters in other protocol layers.

Typically, parameters in the lower protocol layers are reported toTypically, parameters in the lower protocol layers are reported to higher layers, e.g., the packet loss rate in the MAC layer can higher layers, e.g., the packet loss rate in the MAC layer can be reported to the transport layer so that a TCP protocol is ablebe reported to the transport layer so that a TCP protocol is able to differentiate congestion from packet loss;to differentiate congestion from packet loss; e.g., physical layer can report the link qualitye.g., physical layer can report the link quality to a routing protocol as an additional performance metricsto a routing protocol as an additional performance metrics for the routing algorithms. for the routing algorithms.

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2. Merge several protocols into one component, e.g., in ad hoc 2. Merge several protocols into one component, e.g., in ad hoc networks, MAC and routing protocols can be combined into one networks, MAC and routing protocols can be combined into one protocol in order to closely consider their interactions. protocol in order to closely consider their interactions.

The advantage of the first way is that it does not totally abandonThe advantage of the first way is that it does not totally abandonthe transparency between protocol layers. the transparency between protocol layers.

However, the second way can achieve much betterHowever, the second way can achieve much betterperformance through closer interaction between protocols.performance through closer interaction between protocols.

Certain issues must be considered when carrying outCertain issues must be considered when carrying outcross-layer protocol design: cross-layer protocol design:

Cross-layer design have risks due to loss of protocol layer Cross-layer design have risks due to loss of protocol layer abstraction,incompatibility with existing protocols, unforeseen abstraction,incompatibility with existing protocols, unforeseen impact on the future design of the network, and difficulty in impact on the future design of the network, and difficulty in maintenance and management.maintenance and management.

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Academic Research Academic Research TestbedsTestbeds

Carnegie-Mellon University's mobile ad hoc network Carnegie-Mellon University's mobile ad hoc network testbed. testbed.

It consists of 7 nodes: 2 stationary nodes, 5 car mounted nodes It consists of 7 nodes: 2 stationary nodes, 5 car mounted nodes that drive that drive

around the testbed site, and 1 car mounted roving node that around the testbed site, and 1 car mounted roving node that enters and enters and

leaves the site. leaves the site.

Packets are routed between the nodes using the DSR protocol Packets are routed between the nodes using the DSR protocol which also which also

integrates the ad hoc network into the Internet via a gateway. integrates the ad hoc network into the Internet via a gateway.

They experiment with the network behavior under different levels They experiment with the network behavior under different levels of of

traffic load, including audio and video streams, and designingtraffic load, including audio and video streams, and designingprotocol enhancements to provide these streams with QoS protocol enhancements to provide these streams with QoS

promises. promises.

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Interesting results were observed in the experiments at CMU:Interesting results were observed in the experiments at CMU:

Local (i.e., link layer) retransmission algorithms is aLocal (i.e., link layer) retransmission algorithms is acritical part of any multihop ad hoc network. critical part of any multihop ad hoc network.

If the retransmission algorithms implemented above the linkIf the retransmission algorithms implemented above the linklayer, it must be adaptive in order to accommodate network layer, it must be adaptive in order to accommodate network congestion and periods of high contention in the wireless congestion and periods of high contention in the wireless channel. channel.

Delivering routing protocol control packets as rapidly as Delivering routing protocol control packets as rapidly as possiblepossible

is important for high end-to-end performance, and this implies is important for high end-to-end performance, and this implies that packets with routing implications should be scheduled for that packets with routing implications should be scheduled for transmission ahead of users data packets.transmission ahead of users data packets.

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MIT's RoofnetMIT's Roofnet

This is an experimental multi-hop 802.11b mesh network.This is an experimental multi-hop 802.11b mesh network.

It consists of about 50 wireless nodes to interconnect the EthernetIt consists of about 50 wireless nodes to interconnect the Ethernetnetworks (with Internet gateways) in apartments in Cambridge, MA.networks (with Internet gateways) in apartments in Cambridge, MA.

A primary feature of Roofnet is that it requires no configuration orA primary feature of Roofnet is that it requires no configuration orplanning.planning.

One consequence of an unplanned network is that each node can route One consequence of an unplanned network is that each node can route packets through any of a large number of neighbors, but the radio packets through any of a large number of neighbors, but the radio link to each neighbor is often of marginal quality; finding the best link to each neighbor is often of marginal quality; finding the best multi-hop routes through a rich mesh of marginal links turns out to multi-hop routes through a rich mesh of marginal links turns out to be a challenge. be a challenge.

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MIT's RoofnetMIT's Roofnet

The average TCP throughput and latency of all Roofnet nodes to The average TCP throughput and latency of all Roofnet nodes to their nearest gateway were measured in April 2004. their nearest gateway were measured in April 2004.

When 1 hop is considered for 18 nodes, the average throughput and When 1 hop is considered for 18 nodes, the average throughput and latency are 357.2 Kbytesps and 9.7 ms.latency are 357.2 Kbytesps and 9.7 ms.

However, when 4 hops are considered for 7 nodes, the average However, when 4 hops are considered for 7 nodes, the average throughput is only 47.3 Kbytesps and the average latency is 43.0 ms.throughput is only 47.3 Kbytesps and the average latency is 43.0 ms.

The low multihop throughput reflects the problem typical in all 802.11 The low multihop throughput reflects the problem typical in all 802.11 MAC based multihop networks.MAC based multihop networks.

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SUNY Stony BrookSUNY Stony Brook

It is 4-node multi-channel 802.11b testbed. It is 4-node multi-channel 802.11b testbed.

Each node is equipped with 2 cards whose channels were determined Each node is equipped with 2 cards whose channels were determined based on the load-aware channel assignment algorithm. based on the load-aware channel assignment algorithm.

The multi-channel network achieves 2.63 times the throughput as The multi-channel network achieves 2.63 times the throughput as compared to the single channel network. compared to the single channel network.

The number of non-overlapping channels in 802.11b standard,The number of non-overlapping channels in 802.11b standard,i.e. 3, is the limiting factor for this performance. i.e. 3, is the limiting factor for this performance.

The performance, however, does not reach 3 times of the single-The performance, however, does not reach 3 times of the single-channel network performance because of the inter-channel channel network performance because of the inter-channel interference that cannot be completely eliminated.interference that cannot be completely eliminated.

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Substantial interference was observed between two 802.11b cardsplaced on the same machine despite operating on non-overlappingchannels.

In addition, the degradation due to inter-channel interferencewas found independent of the guard band.

One way to reduce the interference is to use USB cards instead ofPCI/PCMCIA cards and place them side-by-side in similar configuration as in Orinoco AP-1000 access points.

Another possibility is to equip cards with external antennas andplace the external antennas slightly away from each other.

Yet another option is to use the upcoming Engim chipsets which solve the interference problem at RF-level.

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California Institute for Telecommunications and Information California Institute for Telecommunications and Information Technology (Cal-(IT)^2)Technology (Cal-(IT)^2)

A basic Wi-Fi MAC development platform called CalRADIO-IA basic Wi-Fi MAC development platform called CalRADIO-I

This is a Wi-Fi research and development device that consists of a This is a Wi-Fi research and development device that consists of a TI 5410 DSP, a 16-bit stereo CODEC, external Flash and SRAM TI 5410 DSP, a 16-bit stereo CODEC, external Flash and SRAM memories, and support of a RF LAN module.memories, and support of a RF LAN module.

It provides a convenient platform for development of RF radiosIt provides a convenient platform for development of RF radiosfrom the physical layer up to the application layer.from the physical layer up to the application layer.

The key benefit of the board is that all aspects of the MACThe key benefit of the board is that all aspects of the MACare coded in C language and, therefore, are altered easilyare coded in C language and, therefore, are altered easilyfor research in queueing, security, power management, MIMO, for research in queueing, security, power management, MIMO, cognitive radio, and so forth. cognitive radio, and so forth.

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It also utilizes basic Symbol Technologies' Wi-Fi testIt also utilizes basic Symbol Technologies' Wi-Fi testboard as the base for modifying board and re-spinning to board as the base for modifying board and re-spinning to

incorporate incorporate New features.New features.

CalRADIO-I is evolving into a CalRADIO-II develop platform CalRADIO-I is evolving into a CalRADIO-II develop platform withwith

basic DSP board and multiple RF front-end modules such asbasic DSP board and multiple RF front-end modules such as802.11x, 802.16, cell and general RF. 802.11x, 802.16, cell and general RF.

This will eventually allow the capability of publishing This will eventually allow the capability of publishing standards in standards in

software/firmware and hardware.software/firmware and hardware.

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The Broadband and Wireless Network (BWN) Lab at Georgia TechThe Broadband and Wireless Network (BWN) Lab at Georgia Tech

The WMN, called BWN-Mesh, consists of 15 IEEE 802.11b/g based The WMN, called BWN-Mesh, consists of 15 IEEE 802.11b/g based mesh routers, among which several of them are connected to the next mesh routers, among which several of them are connected to the next generation Internet testbed (also available in the BWN Lab) as generation Internet testbed (also available in the BWN Lab) as backhaul access to the Internet. backhaul access to the Internet.

The testbed consists of laptops and desktops equipped with IEEEThe testbed consists of laptops and desktops equipped with IEEE802.11b and IEEE 802.11g cards located in various rooms on the floor 802.11b and IEEE 802.11g cards located in various rooms on the floor Where the BWN Lab resides. Where the BWN Lab resides.

By changing the topology of the network, experimentsBy changing the topology of the network, experimentsinvestigating the effects of inter-router distance, backhaul placement investigating the effects of inter-router distance, backhaul placement And clustering are performed along with mobility experiments using the And clustering are performed along with mobility experiments using the Laptops in the testbed. Laptops in the testbed.

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BWN-Mesh Testbed at Georgia Tech

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Moreover, experiments with existing protocols (i.e., TCP,Moreover, experiments with existing protocols (i.e., TCP,

AODV, and IEEE 802.11g as transport, routing, and MAC protocols) AODV, and IEEE 802.11g as transport, routing, and MAC protocols)

for BWN-Mesh testbed have demonstrated that these protocols do for BWN-Mesh testbed have demonstrated that these protocols do

not perform well in terms of end-to-end delay and throughput in not perform well in terms of end-to-end delay and throughput in

WMNs. WMNs.

Currently, the research is focused on adaptive protocols for Currently, the research is focused on adaptive protocols for transport transport

layer, routing and MAC layers and their cross-layer design. layer, routing and MAC layers and their cross-layer design.

These protocols are developed and evaluated on the BWN-Mesh These protocols are developed and evaluated on the BWN-Mesh

testbed. testbed.

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The approaches being explored in the BWN lab are not merely The approaches being explored in the BWN lab are not merely

limited to Wi-Fi mesh networks but also applicable for wireless limited to Wi-Fi mesh networks but also applicable for wireless

sensor networks (WSNs) and wireless sensor and actor networkssensor networks (WSNs) and wireless sensor and actor networks

(WSANs). (WSANs).

Thus, the BWN-Mesh testbed is integrated with the alreadyThus, the BWN-Mesh testbed is integrated with the already

existing BWN Sensor Network Testbed, which consists of MICA existing BWN Sensor Network Testbed, which consists of MICA

motes, with TinyOS distributed software operating system, and motes, with TinyOS distributed software operating system, and

light, temperature, acoustic actuator, magnometer, and light, temperature, acoustic actuator, magnometer, and

accelerometer sensors. accelerometer sensors.

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In align with this effort, BWN Lab is also trying to In align with this effort, BWN Lab is also trying to integrate the current Wi-Fi mesh networks with integrate the current Wi-Fi mesh networks with

other other wireless networks such as WiMAX. wireless networks such as WiMAX.

Consequently, this integrated testbed will enable Consequently, this integrated testbed will enable the the

design and evaluation of protocols applicable to design and evaluation of protocols applicable to heterogeneous wireless networks including WMNs, heterogeneous wireless networks including WMNs,

next next Generation Internet, WSNs, WSANs, and WiMAX.Generation Internet, WSNs, WSANs, and WiMAX.

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Industrial PracticeIndustrial Practice

Microsoft Research Lab (MSR)Microsoft Research Lab (MSR)

It implements ad-hoc routing and link quality measurement in It implements ad-hoc routing and link quality measurement in a a

software module called the mesh connectivity layer (MCL).software module called the mesh connectivity layer (MCL).

Architecturally, MCL is a loadable Windows driver. Architecturally, MCL is a loadable Windows driver.

It implements a virtual network adapter, so that the ad-hoc It implements a virtual network adapter, so that the ad-hoc network appears as an additional (virtual) network link to network appears as an additional (virtual) network link to

the rest the rest of the system. of the system.

MCL routes by using a modified version of DSR called LQSR. MCL routes by using a modified version of DSR called LQSR.

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MCL is a routing protocol well-suited for low MCL is a routing protocol well-suited for low mobility, mobility,

unconstraint power consumption and small unconstraint power consumption and small diameter networks.diameter networks.

The MCL driver implements an interposition layer The MCL driver implements an interposition layer between the link layer and the network layer. between the link layer and the network layer.

To higher layer software, MCL appears to be just To higher layer software, MCL appears to be just another Ethernet link, albeit a virtual link. another Ethernet link, albeit a virtual link.

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No modification to either network stack is required.No modification to either network stack is required.

Network layer functionality (for example ARP, DHCP, and Network layer functionality (for example ARP, DHCP, and Neighbor Neighbor

Discovery) works fine. Discovery) works fine.

Ad-hoc routing runs over heterogeneous link layers.Ad-hoc routing runs over heterogeneous link layers.

Microsoft's implementation supports Ethernet-like physical link Microsoft's implementation supports Ethernet-like physical link layers layers

(e.g., IEEE 802.11 and 802.3) but the architecture (e.g., IEEE 802.11 and 802.3) but the architecture accommodates accommodates

link layers with arbitrary addressing and framing conventions.link layers with arbitrary addressing and framing conventions.

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INTEL:Low-cost and low-power access point prototypes have Low-cost and low-power access point prototypes have been developed to enable further research onbeen developed to enable further research onsecurity, traffic characterization, dynamic routing and security, traffic characterization, dynamic routing and configuration, and QoS problems. configuration, and QoS problems.

A demonstration was discussed in various occasions, A demonstration was discussed in various occasions, consisting of a consisting of a

collection of Centrino laptop computers and IXP425 network collection of Centrino laptop computers and IXP425 network processor based routers running AODV and 802.11b MACprocessor based routers running AODV and 802.11b MACprotocols. protocols.

The testbed results confirm that 802.11 MAC limits fullThe testbed results confirm that 802.11 MAC limits fullexploitation of multihop throughput. exploitation of multihop throughput.

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As a means to enhance multihop throughput, it advocates spatial As a means to enhance multihop throughput, it advocates spatial reuse through carrier sensing threshold tuning. reuse through carrier sensing threshold tuning.

Another potential solution experimented was the concept ofAnother potential solution experimented was the concept ofheterogeneous networks: an 802.11 mesh network comprised of 4 heterogeneous networks: an 802.11 mesh network comprised of 4 high-end nodes, such as Intel XScale based nodes, is overlaid on a high-end nodes, such as Intel XScale based nodes, is overlaid on a 50-sensor node (motes) network scattered throughout a large 50-sensor node (motes) network scattered throughout a large conference room. conference room.

Sensor data can enter and exit the 802.11 backbone at multiple Sensor data can enter and exit the 802.11 backbone at multiple interchanges (the XScale nodes) in order to bypass the interchanges (the XScale nodes) in order to bypass the intermediate sensors. intermediate sensors.

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NORTEL:NORTEL: A peer-to-peer architecture—with smart antennas, integrated routers and A peer-to-peer architecture—with smart antennas, integrated routers and

adaptive routing and security capabilities—to backhaul data wirelessly to adaptive routing and security capabilities—to backhaul data wirelessly to wired broadband networks. This minimizes the need for expensive wired wired broadband networks. This minimizes the need for expensive wired backhaul connections, such as T1 lines. backhaul connections, such as T1 lines.

Nortel Networks Wireless Mesh Network solution is comprised of three main Nortel Networks Wireless Mesh Network solution is comprised of three main network elements: network elements: – Wireless Access Point 7220 (Wireless AP)Wireless Access Point 7220 (Wireless AP)

The Wireless AP performs traffic collection and distribution functions for The Wireless AP performs traffic collection and distribution functions for traffic within the Community Area Network (CAN) and incorporates: traffic within the Community Area Network (CAN) and incorporates: routing and wireless transit functions; security functions for validating routing and wireless transit functions; security functions for validating connections to other Wireless APs; security functions for controlling connections to other Wireless APs; security functions for controlling access by user devices; and low-cost advanced antenna designs for access by user devices; and low-cost advanced antenna designs for extended reach, simplified deployment and reliability.extended reach, simplified deployment and reliability.

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Industrial PracticeIndustrial Practice– Wireless Gateway 7250Wireless Gateway 7250

The Wireless Gateway advertises reachability for one or more IP subnets The Wireless Gateway advertises reachability for one or more IP subnets assigned to Wireless LAN CAN subscribers and network entities. assigned to Wireless LAN CAN subscribers and network entities.

– In addition, the Wireless Gateway hides Wireless LAN-specific mobility In addition, the Wireless Gateway hides Wireless LAN-specific mobility and provides data security for the mesh transit links (between Wireless and provides data security for the mesh transit links (between Wireless AP 7220s).AP 7220s).

– Optivity Network Management SystemOptivity Network Management SystemThe Optivity Network Management System provides centralized facilities The Optivity Network Management System provides centralized facilities for monitoring and managing network operations, including discovery for monitoring and managing network operations, including discovery and visualization of Wireless AP 7220 and Wireless Gateway 7250, fault and visualization of Wireless AP 7220 and Wireless Gateway 7250, fault management, and real-time performance metrics.management, and real-time performance metrics.

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NORTEL

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MeshNetworks'MeshNetworks'

Initial attempt to commercializing mesh technology was its Quadrature Initial attempt to commercializing mesh technology was its Quadrature Division multiple access (QDMA) radio platform. Division multiple access (QDMA) radio platform.

The QDMA radio is designed for mobile ad hoc broadband networking.The QDMA radio is designed for mobile ad hoc broadband networking.

It uses multi-channel MAC and PHY to overcome the effects of Doppler It uses multi-channel MAC and PHY to overcome the effects of Doppler shifting, rapid Raleigh fading and multipath encountered in a mobile system. shifting, rapid Raleigh fading and multipath encountered in a mobile system.

The MeshNetworks' scalable routing protocol is implemented above QDMA The MeshNetworks' scalable routing protocol is implemented above QDMA radios. radios.

The scalable routing technology utilizes a hybrid ad hoc routing algorithm The scalable routing technology utilizes a hybrid ad hoc routing algorithm that combines both proactive and reactive routing techniques. that combines both proactive and reactive routing techniques.

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To adapt the routing protocol to a given radio platform, adaptive To adapt the routing protocol to a given radio platform, adaptive Transmission protocol (ATP) is implemented to tightly bind the scalable Transmission protocol (ATP) is implemented to tightly bind the scalable routing protocol to the underlying radio platform. routing protocol to the underlying radio platform.

MeshNetworks provides a software-only overlay solution that lets native MeshNetworks provides a software-only overlay solution that lets native 802.11b clients in existing networks work in mesh-mode. 802.11b clients in existing networks work in mesh-mode.

While it will not add any mobile broadband capabilities beyond what While it will not add any mobile broadband capabilities beyond what 802.11b 802.11b

can already support, it will extend the range and link robustness ofcan already support, it will extend the range and link robustness of

existing Wi-Fi Networks by allowing mesh-style multi-hopping. existing Wi-Fi Networks by allowing mesh-style multi-hopping.

Security features in MeshNetworks' QDMA-based systems includeSecurity features in MeshNetworks' QDMA-based systems includea hardware firewall on a chip that makes it impossible for aa hardware firewall on a chip that makes it impossible for aclient to access somebody else's packets. client to access somebody else's packets.

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Tropos NetworksTropos Networksemploys a cellular Wi-Fi network architecture to supportemploys a cellular Wi-Fi network architecture to support““infrastructure mesh” networking, using its a infrastructure mesh” networking, using its a layer-3 network operating system (NOS) called Tropos Sphere,layer-3 network operating system (NOS) called Tropos Sphere,that runs on standard 802.11 hardware and software. that runs on standard 802.11 hardware and software.

Tropos Sphere operates on every (small sized) Tropos Wi-Fi cell Tropos Sphere operates on every (small sized) Tropos Wi-Fi cell and contains the key communications, path selection, and and contains the key communications, path selection, and

security security functions that allow the Wi-Fi cells to inter-operate and form a functions that allow the Wi-Fi cells to inter-operate and form a completely wireless network like a wireless routed LAN. completely wireless network like a wireless routed LAN.

Tropos uses a lightweight control protocol for supporting a large Tropos uses a lightweight control protocol for supporting a large number of Wi-Fi cells.number of Wi-Fi cells.

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It uses a proprietary predictive path optimization protocol to improve end-It uses a proprietary predictive path optimization protocol to improve end-user throughput and continuously optimize performance to compensate for user throughput and continuously optimize performance to compensate for the changing RF environment. the changing RF environment.

This protocol is called predictive wireless routing protocol (PWRP), which is This protocol is called predictive wireless routing protocol (PWRP), which is analogous to traditional wired routing protocols such as OSPF). analogous to traditional wired routing protocols such as OSPF).

However, PWRP does not use routing tables or rely on hop-count only to However, PWRP does not use routing tables or rely on hop-count only to select transmission paths. select transmission paths.

Rather, it compares packet error rates and other network conditions to Rather, it compares packet error rates and other network conditions to determine the best path at a given moment.determine the best path at a given moment.

Since the system is largely a layer-3 solution that relies on the standard Since the system is largely a layer-3 solution that relies on the standard 802.11802.11

MAC protocol for a large mesh network, many of the throughput MAC protocol for a large mesh network, many of the throughput performance impairments remain unresolved.performance impairments remain unresolved.

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INDUSTRIAL INDUSTRIAL PRACTICEPRACTICE

PacketHop's Core Technology PacketHop's Core Technology (SRI International Lab)(SRI International Lab)

It consists of a network controller, performing It consists of a network controller, performing gateway, QoS, security, and roaming functions,gateway, QoS, security, and roaming functions,a network management system, and the Windows a network management system, and the Windows software for ad hoc mesh routing.software for ad hoc mesh routing.

This is largely a layer-3 solution that runs on This is largely a layer-3 solution that runs on 802.11 and multi-mode broadband radios.802.11 and multi-mode broadband radios.

PacketHop is in collaboration with Nortel to PacketHop is in collaboration with Nortel to complement Nortel's “infrastructure mesh” solution complement Nortel's “infrastructure mesh” solution with its ad hoc meshing capability.with its ad hoc meshing capability.

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Kiyon Inc.,Kiyon Inc.,

is in field trials with building automation is in field trials with building automation and “small office home office'' (SOHO) customers and “small office home office'' (SOHO) customers of its broadband wireless mesh routers. of its broadband wireless mesh routers.

Its technology is a layer-2/3 solution that Its technology is a layer-2/3 solution that implements a hybrid CSMA/CA and distributed implements a hybrid CSMA/CA and distributed TDMA MAC protocol atop an 802.11g/a physical TDMA MAC protocol atop an 802.11g/a physical layer. layer.

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This is tightly coupled with a multi-metric “Attribute Routing'' This is tightly coupled with a multi-metric “Attribute Routing'' protocol, aiming at high and steady multihop throughput in a mesh protocol, aiming at high and steady multihop throughput in a mesh network. network.

As the new generation 802.11 radios adopt the soft MAC As the new generation 802.11 radios adopt the soft MAC approach, e.g., Atheros, Broadcom and more recently Intel, Kiyon's approach, e.g., Atheros, Broadcom and more recently Intel, Kiyon's enhanced MAC/routing protocols can be implemented in host enhanced MAC/routing protocols can be implemented in host software and downloaded into these standard 802.11 chipsets at software and downloaded into these standard 802.11 chipsets at runtime.runtime.

Kiyon supports both infrastructure and client mesh, stationary or Kiyon supports both infrastructure and client mesh, stationary or mobile wireless networks.mobile wireless networks.

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Several routers form a broadband backbone of the network. Several routers form a broadband backbone of the network.

Each of the routers is equipped with Kiyon's routing and MAC Each of the routers is equipped with Kiyon's routing and MAC protocol software plus a standard IEEE 802.11g/a radio.protocol software plus a standard IEEE 802.11g/a radio.

For client access to the broadband backbone, several options For client access to the broadband backbone, several options can be adopted. can be adopted.

The first option is called the “wired host route”, in which The first option is called the “wired host route”, in which a client can connect to the backbone via an Ethernet connection.a client can connect to the backbone via an Ethernet connection.

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Any IP capable devices (e.g., a RFID reader, BACnet controller or Any IP capable devices (e.g., a RFID reader, BACnet controller or database server) can be connected to the wireless network this way.database server) can be connected to the wireless network this way.

No software modification on the client is required.No software modification on the client is required.

The second option is called the “wireless host route”, in which a The second option is called the “wireless host route”, in which a client device connects to the wireless network via a wireless LAN client device connects to the wireless network via a wireless LAN interface such as an 802.11 b/g/a NIC. interface such as an 802.11 b/g/a NIC.

In this arrangement, the client is “homed” on one of the routers in In this arrangement, the client is “homed” on one of the routers in the network that satisfies the defined routing metric, such as signal the network that satisfies the defined routing metric, such as signal strength.strength.

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The client has the option to run Kiyon's software or not.The client has the option to run Kiyon's software or not.

With Kiyon's software, a client becomes a full function router. With Kiyon's software, a client becomes a full function router.

Without Kiyon's software, a client device running standard Without Kiyon's software, a client device running standard 802.11 station software can originate and terminate traffic.802.11 station software can originate and terminate traffic.

Mobility of client devices is supported in both cases.Mobility of client devices is supported in both cases.

The third option is a form of hierarchical network, in which The third option is a form of hierarchical network, in which a number of standard 802.11 access points serve as the a number of standard 802.11 access points serve as the access layer for client devices. access layer for client devices.

Each of these access points is attached to one of the Each of these access points is attached to one of the backbone routers via an Ethernet connection.backbone routers via an Ethernet connection.

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Standard ActivitiesStandard Activities

IEEE 802.11 Mesh NetworksIEEE 802.11 Mesh Networks

Currently, IEEE 802.11 wireless networks can achieve a Currently, IEEE 802.11 wireless networks can achieve a peak rate of 11 Mbps (802.11b) and 54 Mbps peak rate of 11 Mbps (802.11b) and 54 Mbps

(802.11a/g).(802.11a/g).

Also under development is a high-bandwidth extension Also under development is a high-bandwidth extension to to

the current Wi-Fi standard. the current Wi-Fi standard.

Researchers expect 802.11n to increase the speed ofResearchers expect 802.11n to increase the speed ofWi-Fi connections by 10 to 20 times. Wi-Fi connections by 10 to 20 times.

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Although many home users will not benefit from the Although many home users will not benefit from the additional speed right away, because of limits onadditional speed right away, because of limits ontheir cable or DSL connections, enterprises are hoping the their cable or DSL connections, enterprises are hoping the technology will allow them to reduce the burden of laying technology will allow them to reduce the burden of laying and maintaining Ethernet cabling throughout the building.and maintaining Ethernet cabling throughout the building.

There are many academic testbeds and commercial There are many academic testbeds and commercial deployment of mesh networks using IEEE 802.11 wireless deployment of mesh networks using IEEE 802.11 wireless LAN technology. LAN technology.

However, mesh networking is at the same stage as However, mesh networking is at the same stage as wireless wireless

LANs were in the early 1990's; they are expensiveLANs were in the early 1990's; they are expensiveand proprietary. and proprietary.

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To become commoditized, the economic pressures are driving the standard To become commoditized, the economic pressures are driving the standard processes. processes.

Furthermore, protocols for 802.11 ad hoc mode are insufficient for multi-Furthermore, protocols for 802.11 ad hoc mode are insufficient for multi-hop and mesh networking, because of lack of scalability in the MAC hop and mesh networking, because of lack of scalability in the MAC

protocol, protocol, resulting in poor network performance. resulting in poor network performance.

A working group within IEEE 802.11, called 802.11s, has been formed A working group within IEEE 802.11, called 802.11s, has been formed recently to standardize the extended service Set (ESS). recently to standardize the extended service Set (ESS).

802.11s aims to define a MAC and PHY layers for meshed networks that 802.11s aims to define a MAC and PHY layers for meshed networks that extended coverage with no single point of failure. extended coverage with no single point of failure.

In such networks, 802.11 cellular wireless LAN access points relay In such networks, 802.11 cellular wireless LAN access points relay information from one to another in a router-like hop-by-hop fashion.information from one to another in a router-like hop-by-hop fashion.

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As users and access points are added, the capacity increases, As users and access points are added, the capacity increases, as in the Internet, giving rise to a scalable and redundant as in the Internet, giving rise to a scalable and redundant architecture. architecture.

Early discussions in this working group include definition of Early discussions in this working group include definition of WMNs,WMNs,

usage cases, QoS, architecture specifications, security, usage cases, QoS, architecture specifications, security, routing routing

protocols,and development of new MAC protocols. protocols,and development of new MAC protocols.

Several task groups have been formed to tackle these issues. Several task groups have been formed to tackle these issues.

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Standard ActivitiesStandard ActivitiesWi-Fi mesh networking can be implemented in two basic modes: Wi-Fi mesh networking can be implemented in two basic modes:

infrastructure and client meshing.infrastructure and client meshing.

The former is an infrastructure ESS mesh, in which access points are The former is an infrastructure ESS mesh, in which access points are

interconnected through wireless links that enable automatic topology interconnected through wireless links that enable automatic topology

learning and dynamic path configuration.learning and dynamic path configuration.

Clients are associated with access points and need not be aware Clients are associated with access points and need not be aware

of the mesh.of the mesh.

Infrastructure meshing creates wireless backhaul mesh among access Infrastructure meshing creates wireless backhaul mesh among access

points or wireless routers. points or wireless routers.

This reduces system backhaul costs while increasing network This reduces system backhaul costs while increasing network

coverage and reliability. coverage and reliability.

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To provide an IEEE 802.11 ESS Mesh, 802.11s will define an To provide an IEEE 802.11 ESS Mesh, 802.11s will define an

architecture and protocol based on the IEEE 802.11 MAC to create architecture and protocol based on the IEEE 802.11 MAC to create

an IEEE 802.11 wireless distribution system (WDS) that supports an IEEE 802.11 wireless distribution system (WDS) that supports

both broadcast/multicast and unicast delivery at the MAC layer both broadcast/multicast and unicast delivery at the MAC layer

using radio-aware metrics over self-configuring multi-hop topologies. using radio-aware metrics over self-configuring multi-hop topologies.

From the view of access points, the infrastructureFrom the view of access points, the infrastructure

meshing also forms an ad hoc network among access points.meshing also forms an ad hoc network among access points.

The other mode of meshing, i.e. client meshing, is a layer-3The other mode of meshing, i.e. client meshing, is a layer-3

ad hoc IBSS (independent basic service set), in which all devices ad hoc IBSS (independent basic service set), in which all devices

operate in ad hoc mode in a flat network, using IP routing.operate in ad hoc mode in a flat network, using IP routing.

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There is no distinction between access points and client.

Client meshing enables wireless peer-to-peer networks to form between and among client devices and does notrequire any network infrastructure to be present.

In this case, clients can hop through each other to reach other clients in the network.

To maximize the benefit that meshing can offer, both modes should

be supported simultaneously and seamlessly in a single network

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Standard ActivitiesStandard ActivitiesIEEE 802.15 Mesh Networks

IEEE 802.15.3a standard is based on MultiBand OFDM Alliance (MBOA)'s physical layer that uses ultra wide band (UWB) to reach up to 480 Mbps.

A competing proposal of a Direct Sequence-UWB (DS-UWB) claims support for up to 1.3 Gbps.

It is intended for high throughput personal area networking (PAN) that has communication distances of around 10 meters (or less), with applications in home networking space, with imminent wireless extensions to USB, IEEE 1394, and with the capability to address the convergence of PC, consumer electronicsand IP mobile phones.

Vendors planning to produce 802.15.3a products have formed the WiMedia Alliance, a branding and testing organizationthat will certify standards compliance.

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UWB networks hold many advantages over other wireless UWB networks hold many advantages over other wireless networks, such as covert communications, low power and cost networks, such as covert communications, low power and cost requirement, accurate location information, and extra high requirement, accurate location information, and extra high bandwidth. bandwidth.

However, the communication range is rather short. However, the communication range is rather short.

Mesh networks have been predicted to be the killer applicationMesh networks have been predicted to be the killer applicationfor UWB radio systems. for UWB radio systems.

A new MAC proposed by MBOA, which deviates substantially from A new MAC proposed by MBOA, which deviates substantially from the original IEEE 802.13a MAC proposal, has addedthe original IEEE 802.13a MAC proposal, has addedstrong support for mesh networking and mobility, paving the waystrong support for mesh networking and mobility, paving the wayfor UWB to enter the enterprise network. for UWB to enter the enterprise network.

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The MBOA MAC uses piconet structure, combined The MBOA MAC uses piconet structure, combined with with

a decentralized resource-handling ability to allow a decentralized resource-handling ability to allow forfor

the reservation of timeslots for 802.15.3-like TDMA the reservation of timeslots for 802.15.3-like TDMA for high priority connections requiring determinism for high priority connections requiring determinism while assigning contention-based, best-effort while assigning contention-based, best-effort

access access periods.periods.

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IEEE 802.15.4 is intended for telemetry with low data rate,IEEE 802.15.4 is intended for telemetry with low data rate,long battery life and low device cost requirements. long battery life and low device cost requirements.

The ZigBee Alliance is developing higher-level protocols that will The ZigBee Alliance is developing higher-level protocols that will run run

over 802.15.4 MAC and PHY layers that operate in unlicensed bands over 802.15.4 MAC and PHY layers that operate in unlicensed bands worldwide. worldwide.

Raw data rates of 250Kbps can be achieved at 2.4GHz (16 Raw data rates of 250Kbps can be achieved at 2.4GHz (16 channels), 40Kbps at 915MHz (10 channels), and 20Kbps at 868MHz channels), 40Kbps at 915MHz (10 channels), and 20Kbps at 868MHz (1 channel). (1 channel).

The transmission distance is expected to range from 10 to 75 The transmission distance is expected to range from 10 to 75 meters, depending on power output and environmental meters, depending on power output and environmental characteristics. characteristics.

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The ZigBee network layer supports multinetwork topologies The ZigBee network layer supports multinetwork topologies including including

star, cluster tree, and mesh. star, cluster tree, and mesh.

In a mesh topology, a special node called coordinator is responsible In a mesh topology, a special node called coordinator is responsible for starting the network and for choosing key network parameters. for starting the network and for choosing key network parameters.

The routing algorithm uses a request-response protocol to eliminate The routing algorithm uses a request-response protocol to eliminate sub-optimal routing. sub-optimal routing.

Recently a new working group, i.e., IEEE 802.15.5, is established toRecently a new working group, i.e., IEEE 802.15.5, is established todetermine the necessary mechanisms in the physical and MAC layers determine the necessary mechanisms in the physical and MAC layers to enable mesh networking in wireless PANs.to enable mesh networking in wireless PANs.

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IEEE 802.16 Mesh Networks

While IEEE 802.11 networks fulfill the need for data servicesin a local area (i.e. last several hundreds of feet), IEEE 802.16 aims at serving the broadband wireless access in metropolitan Area networks (i.e., last mile), supporting point-to-multipoint connection oriented QoS communications to extend fiber optic backbones.

The original 802.16 standard operates in the 10-66 GHz frequency band and requires line-of-sight towers.

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The 802.16a extension, ratified in January 2003, uses a lower frequency of 2-11 GHz, enabling nonline-of-sight connections.

With 802.16a, carriers will be able to connect more customers to

a single tower and substantially reduce service costs.

To allow consumers to connect to the Internet while moving at

vehicular speeds, researchers are developing an extension to IEEE

802.16 standard called 802.16e.

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Standard ActivitiesStandard ActivitiesTo enhance the 802.16 mesh, several proposals have been To enhance the 802.16 mesh, several proposals have been submitted to the standard committee. submitted to the standard committee. A group within 802.16, the Mesh Ad Hoc committee, isA group within 802.16, the Mesh Ad Hoc committee, isinvestigating ways to improve the performance of mesh investigating ways to improve the performance of mesh networking.networking.It is understood that only a small amount of meshing is required It is understood that only a small amount of meshing is required to see a large improvement in the coverage of a single base to see a large improvement in the coverage of a single base station. station.

More importantly, the following issues are considered More importantly, the following issues are considered in specifying the 802.16 mesh MAC protocol:in specifying the 802.16 mesh MAC protocol: * avoiding hidden terminal collisions,* avoiding hidden terminal collisions, * selection of links,* selection of links, * synchronization,* synchronization, * power versus data rate tradeoffs, and* power versus data rate tradeoffs, and * greater routing-MAC interdependence.* greater routing-MAC interdependence.

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ADVANTAGES OF WMNsADVANTAGES OF WMNs Price: Price:

802.11 radios have become quite cheap, but the radios are often still among 802.11 radios have become quite cheap, but the radios are often still among the most expensive elements of such a network. The fact that each mesh the most expensive elements of such a network. The fact that each mesh node runs both as a client and as a repeater potentially means saving on the node runs both as a client and as a repeater potentially means saving on the number of radios needed and thus the total budget.number of radios needed and thus the total budget.

Ease and simplicity: Ease and simplicity:

If you have a box that is pre-installed with wireless mesh software and uses If you have a box that is pre-installed with wireless mesh software and uses standard wireless protocols such as 802.11b/g, the setup is extremely standard wireless protocols such as 802.11b/g, the setup is extremely simple. Since routes are configured dynamically, it is often enough to simply simple. Since routes are configured dynamically, it is often enough to simply drop the box into the network, and attach whatever antennas are required drop the box into the network, and attach whatever antennas are required for it to reach one or more existing neighboring nodes (assuming that we can for it to reach one or more existing neighboring nodes (assuming that we can solve the issue of IP address allocation).solve the issue of IP address allocation).

Organization and business models:Organization and business models:

The decentralized nature of mesh networks lends itself well to a The decentralized nature of mesh networks lends itself well to a decentralized ownership model wherein each participant in the network decentralized ownership model wherein each participant in the network owns and maintains their own hardware, which can greatly simplify the owns and maintains their own hardware, which can greatly simplify the financial and community aspects of the system.financial and community aspects of the system.

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ADVANTAGES OF WMNsADVANTAGES OF WMNs

Network robustness:Network robustness:

The character of mesh topology and ad-hoc routing promises greater The character of mesh topology and ad-hoc routing promises greater stability in the face of changing conditions or failure at single nodes, stability in the face of changing conditions or failure at single nodes, which will quite likely be under rough and experimental conditions.which will quite likely be under rough and experimental conditions.

Power: Power:

The substrate nodes of a mesh network can be built with extremely The substrate nodes of a mesh network can be built with extremely low power requirements, meaning that they can be deployed as low power requirements, meaning that they can be deployed as completely autonomous units with solar, wind, or hydro power. completely autonomous units with solar, wind, or hydro power.

Power generating units are typically connected to points of Power generating units are typically connected to points of infrastructure and human presence. infrastructure and human presence.

This makes them valid locations for network nodes. This makes them valid locations for network nodes.

As a secondary benefit, the presence of integrated network nodes As a secondary benefit, the presence of integrated network nodes within power networks may allow for better monitoring and within power networks may allow for better monitoring and management.management.

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ADVANTAGES OF WMNsADVANTAGES OF WMNs

Integration:Integration:

Mesh hardware is typically small, noiseless, and easily Mesh hardware is typically small, noiseless, and easily encapsulated in weatherproof boxes. encapsulated in weatherproof boxes.

This means it also integrates nicely outdoors as well as in This means it also integrates nicely outdoors as well as in human housing.human housing.

Reality fit: Reality fit:

Reality rarely comes as a star, ring, or a straight line. In Reality rarely comes as a star, ring, or a straight line. In difficult terrain -- be that urban or remote -- where not difficult terrain -- be that urban or remote -- where not every user can see one or few central points, chances are every user can see one or few central points, chances are one can see one or more neighboring users.one can see one or more neighboring users.

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FURTHER ADVANTAGESFURTHER ADVANTAGES

Provides a value-added entry into the high-speed wireless packet and data Provides a value-added entry into the high-speed wireless packet and data business business

Utilizes 802.11 technology—the interface of choice for high-speed wireless Utilizes 802.11 technology—the interface of choice for high-speed wireless packet data. packet data.

Offers high-speed wireless packet data access across a wider coverage area Offers high-speed wireless packet data access across a wider coverage area Today's cellular systems do not provide the bandwidth available in WLANs. Today's cellular systems do not provide the bandwidth available in WLANs. Today's isolated hotspot 802.11 deployments do not satisfy user desire for Today's isolated hotspot 802.11 deployments do not satisfy user desire for

ubiquitous access or for mobility. ubiquitous access or for mobility. Emergence of small-form factor terminals with 802.11 wireless interfaces Emergence of small-form factor terminals with 802.11 wireless interfaces

means impending demand for adding mobility to WLAN packet data means impending demand for adding mobility to WLAN packet data services. services.

Minimizes cost of capital, installation and commissioning Minimizes cost of capital, installation and commissioning Utilizes low-cost 802.11 technology. Utilizes low-cost 802.11 technology. Uses wireless links for backhaul to eliminate costs associates with Uses wireless links for backhaul to eliminate costs associates with

installation of wired interconnect. installation of wired interconnect.

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FURTHER ADVANTAGESFURTHER ADVANTAGES

Auto-configuration algorithms in Wireless Access Point eliminate costs Auto-configuration algorithms in Wireless Access Point eliminate costs associated with engineering and organization of the wireless backhaul associated with engineering and organization of the wireless backhaul network. network.

Minimizes cost of operations Minimizes cost of operations Uses wireless links for backhaul to eliminate costs associated with Uses wireless links for backhaul to eliminate costs associated with

ongoing leasing of facilities. ongoing leasing of facilities. Auto-configuration, self-organizing and self-healing are intrinsic to the Auto-configuration, self-organizing and self-healing are intrinsic to the

Wireless Mesh Network solution Wireless Mesh Network solution Centralized OAM&P minimizes staffing requirements. Centralized OAM&P minimizes staffing requirements. Highly flexible in terms of capacity, coverage and availability Highly flexible in terms of capacity, coverage and availability Increasing capacity, coverage and/or availability simply means Increasing capacity, coverage and/or availability simply means

deploying more Wireless Access Points. deploying more Wireless Access Points. Wireless Access Points maybe deployed indoors or outdoors. Wireless Access Points maybe deployed indoors or outdoors.

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Ugly TruthsUgly Truths

1. 1. Radio is a shared medium and forces everyone to stay silent Radio is a shared medium and forces everyone to stay silent while one person holds the stage. while one person holds the stage.

Wired networks, on the other hand, can and do hold multiple Wired networks, on the other hand, can and do hold multiple simultaneous conversations.simultaneous conversations.

2. In a single radio ad hoc mesh network, the best you can do is 2. In a single radio ad hoc mesh network, the best you can do is (1/2)^^n at each hop. (1/2)^^n at each hop.

So in a multi hop mesh network, the max available bandwidth So in a multi hop mesh network, the max available bandwidth available to you degrades at the rate of 1/2, 1/4, 1/8. available to you degrades at the rate of 1/2, 1/4, 1/8.

By the time you are 4 hops away the max you can get is 1/16 of By the time you are 4 hops away the max you can get is 1/16 of the total available bandwidth. the total available bandwidth.

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3. That does not sound too bad when you are putting together a 3. That does not sound too bad when you are putting together a wireless sensor network with limited bandwidth and latency wireless sensor network with limited bandwidth and latency considerations. considerations.

It is DISASTROUS if you wish to provide the level of It is DISASTROUS if you wish to provide the level of latency/throughput people are accustomed to with their wired latency/throughput people are accustomed to with their wired networks. networks.

Consider the case of just 10 client stations at each node of a 4 hop Consider the case of just 10 client stations at each node of a 4 hop mesh network. mesh network.

The clients at the last rung will receive -at best- 1/(16,0000) of the The clients at the last rung will receive -at best- 1/(16,0000) of the total bandwidth at the root. total bandwidth at the root.

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4. Why has this not been noticed as yet? 4. Why has this not been noticed as yet?

Because first there are not a lot of mesh networks around and second, they Because first there are not a lot of mesh networks around and second, they have not been tested under high usage situations. have not been tested under high usage situations.

Browsing and email do not count. Browsing and email do not count.

Try video - where both latency and bandwidth matter - or VOIP where the Try video - where both latency and bandwidth matter - or VOIP where the bandwidth is a measly 64Kbps but where latency matters. bandwidth is a measly 64Kbps but where latency matters.

Even in a simple 4 hop ad hoc mesh network with 10 clients, VOIP phones will Even in a simple 4 hop ad hoc mesh network with 10 clients, VOIP phones will not work well beyond the first or second hop – the latency and jitter caused by not work well beyond the first or second hop – the latency and jitter caused by CSMA/CA contention windows (how wireless systems avoid collisions) will be CSMA/CA contention windows (how wireless systems avoid collisions) will be unbearable.unbearable.

Mesh networks are a great concept. But the challenge lies in managing the Mesh networks are a great concept. But the challenge lies in managing the dynamics of mesh networks so users receive an acceptable level of dynamics of mesh networks so users receive an acceptable level of performance in terms of both latency and throughput. performance in terms of both latency and throughput. It is time to focus on solving some real problems to make mesh networks scale It is time to focus on solving some real problems to make mesh networks scale and provide stable performance. and provide stable performance.

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Is this a Is this a Disruptive Technology?Disruptive Technology?

In its vision of WLANs and wireless access networks In its vision of WLANs and wireless access networks

of the very near future, Mesh Networks sees every of the very near future, Mesh Networks sees every

client device also becoming a relay point or router for client device also becoming a relay point or router for

network traffic.network traffic. One immediate benefit is that such networks can in One immediate benefit is that such networks can in

effect see around corners. effect see around corners. Even line-of-sight network technologies like 802.11 Even line-of-sight network technologies like 802.11

can become non-line-of-sight - almost overnight if can become non-line-of-sight - almost overnight if

Mesh Networks can deliver what it is promising. Mesh Networks can deliver what it is promising. And the next-generation networks the company is And the next-generation networks the company is

building will also power mobile broadband services. building will also power mobile broadband services.

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What is a What is a Disruptive Disruptive Technology? Technology?

"In real-world terms, it has to meet at least two of "In real-world terms, it has to meet at least two of

three criteria:three criteria:

Be ten times cheaper than any alternative, have ten Be ten times cheaper than any alternative, have ten

times higher performance, and ten times higher times higher performance, and ten times higher

functionality. All three is best." functionality. All three is best." There are two parts to Mesh Networks' supposedly There are two parts to Mesh Networks' supposedly

disruptive technology. disruptive technology.

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WMNs as Disruptive WMNs as Disruptive TechnologyTechnology

One is QDMA (quad-division multiple access), a One is QDMA (quad-division multiple access), a

proprietary radio technology developed for and proprietary radio technology developed for and

currently used by WMNs.currently used by WMNs.

QDMA's most notable characteristics are that it is IP QDMA's most notable characteristics are that it is IP

from end to end and supports high-speed mobile from end to end and supports high-speed mobile

broadband access and infrastructure-free "ad hoc broadband access and infrastructure-free "ad hoc

peer-to-peer networking." peer-to-peer networking."

The company claims it can deliver up to 6 Mbps to The company claims it can deliver up to 6 Mbps to

each user in a QDMA wireless network.each user in a QDMA wireless network.

The technology also has built-in GPS capabilities and The technology also has built-in GPS capabilities and

QoS (quality of service) for IP voice and video. QoS (quality of service) for IP voice and video.

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REMARKSREMARKS

For QoS in the strict sense, there are doubts. For QoS in the strict sense, there are doubts.

But for Video and Data with a certain bandwidth, But for Video and Data with a certain bandwidth, they will take they will take off in wireless as the physical wireless capacity becomes really off in wireless as the physical wireless capacity becomes really broadband and reliable for mobile end users.broadband and reliable for mobile end users.

Because, currently, GSM/GPRS systems are widely usedBecause, currently, GSM/GPRS systems are widely used here for data and multimedia (to a certain degree, such as small here for data and multimedia (to a certain degree, such as small video, image and sound captures with the camera of the cellular video, image and sound captures with the camera of the cellular phone) communication, although its data rate is very low GPRSphone) communication, although its data rate is very low GPRS data rates were around 14.4-20 data rates were around 14.4-20

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REMARKSREMARKS

However, the interest of the people and the However, the interest of the people and the success in the implementation draws big success in the implementation draws big companies' attention. companies' attention.

Especially the future application of Mesh networks Especially the future application of Mesh networks is considered to realize Mobile WiFi by integrating is considered to realize Mobile WiFi by integrating Mesh Enabled Architecture (MEA) architecture with Mesh Enabled Architecture (MEA) architecture with 802.11 access points. 802.11 access points.

MEA consists of wireless cards, cheap mesh MEA consists of wireless cards, cheap mesh wireless routers, portable wireless routers, and wireless routers, portable wireless routers, and intelligent access pointsintelligent access points

IFA’05 ECE6610

Wireless Mesh NetworksWireless Mesh NetworksCase StudiesCase Studies

Medford, OR (70,000 people)Medford, OR (70,000 people)

24 square miles – broadband 24 square miles – broadband communicationscommunications

ROI – 8 months possibleROI – 8 months possible

$770,000 to install$770,000 to install

Garland, TX (221,000 people)Garland, TX (221,000 people)

57 square miles – broadband 57 square miles – broadband communications communications

Cost Avoidance – subscription fees / cell Cost Avoidance – subscription fees / cell towerstowers

Documents

CHAPTER 12: WIRELESS MESH NETWORKS I. F. Akyildiz Broadband & Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute