12/09/2004 1

Daniela Maniezzo, UCLA Gianluca Villa, Politecnico di MilanoMario Gerla, UCLA

A “Smart” MAC-A “Smart” MAC-Routing Protocol for Routing Protocol for

WLAN Mesh NetworksWLAN Mesh Networks

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WLAN MESH Network – IEEE 802.11s

Distribution SystemDistribution System(DS)(DS)

WLAN MeshWLAN Mesh

Mesh LinksMesh Links802.11 MAC/PHY802.11 MAC/PHY

802.11 BSS802.11 BSS

802.11 ESS802.11 ESS

L2 Switch

Mesh PortalMesh Portal

Mesh APMesh AP

Mesh APMesh AP

STASTA

L3 Router

Portal

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WLAN Mesh definitions

•A WLAN Mesh is an IEEE 802.11-based Wireless Distribution System (WDS) which is part of a Distribution System, consisting of a set of two or more Mesh Access Point interconnected via IEEE 802.11 wireless links and communicating via the WLAN Mesh Services.

•A WLAN Mesh supports automatic topology learning and dynamic path selection (including across multiple hops).

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Usage Models

Office

Bedroom

Den

Internet

Mesh AP

Mesh SoftAP PCs Mesh AP CE Devices

Non-MeshClients

Home Network

Non-meshclients

Soft Mesh AP

Small Enterprise

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Usage Models (cont’d)

• In the digital home and small/medium usage models, the primary purposes for the mesh network are to create low-cost, easily deployable, high performance wireless coverage throughout the home. – The mesh network should help to eliminate RF dead-

spots. – The mesh network should be self-configuring to allow

for easy deployment and management .– Mesh APs will mostly be dedicated infrastructure

devices, but some PCs may also participate as Mesh APs in the network.

– STAs may be a combination of PCs, laptops, PDAs, printers, telephones and other devices commonly found in an home/office environment.

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Usage Models (cont’d)

Inside APOutside APInside APOutside AP

Large enterprise usage model.

University Campus

Community Area

Park Area

University Campus

Community Area

Park Area

University Campus

Community Area

Park Area

Campus/ Community Network

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Usage Models (cont’d)• Wireless mesh networks can provide cost effective

campus wide coverage for faculty and students. The university avoids cabling and trenching which are costly and disruptive. Students and faculty can enjoy the convenience of data connectivity over the entire campus.

• Community Area Network (residential Internet Access). Community–based wireless internet access built on wireless mesh networks may be used as an alternative to dial-up, DSL, or cable modem service.– Local programming / advertising can be targeted to

interest groups within the neighborhood. – Internet service can be provided inside and outside the

home, and extended to coffee shops, corner stores, recreational areas and local schools.

– Community area mesh networks can be used to offer data services to municipalities or public safety initiatives.

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Usage Models (cont’d)

Public Safety Public Access: Urban Streets

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Usage Models (cont’d)

• Incident Scene relates to fire/police/emergency personnel responding to an incident scene. Communications are mostly outdoors but may include communicating with first responders inside buildings.

• Urban Street. Groups of people will use VoIP and data-centric services in the HotSpot scenario.

At pedestrian speed there will be low mobility and no topology changes of the mesh backbone.

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Usage Models (cont’d)

Car2Car: Danger Warning

Car2Car: Data/Telematics applications

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Usage Models (cont’d)• Data/Telematics applications. Car-2-var communication

enables data applications in cars in urban or rural scenarios where no full WLAN coverage is available. Typical applications are – telematics applications for traffic or parking management. – In traffic jam scenarios gaming, chatting …

• Danger Warning. Car to car (Car2Car) communication enables active safety measures. Danger warnings can be transported on an ad hoc network of cars using 802.11 mesh technology, i.e. informing succeeding cars of accidents or other blockings of the road ahead. The scenario is characterized by highly mobile stations. The Physical Layer required to support such high speeds will be standardized by 802.11p. However, the mesh networking aspects have to be covered by 802.11s. The Mesh network is subject to frequent topology changes and constant neighbor discovery. All routes and connections have to be set up in a very short time. On the other hand only a small amount of data has to be delivered, however, the delay has to be as small as possible.

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IEEE 802.11s: necessity of a joint MAC Routing

• If the destination station is not associate to the same AP of the source station, the AP does not forward the packet to all the APs in the ESS but the packet is sent along the APs path to reach the destination station.

• It is a multi-hop ad-hoc network between the APs in the same ESS.

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“SMART”: Smart Antenna MAC-Routing Protocol

AP1

AP2

AP3 AP4

• Using directional antenna we can create parallel paths.

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“SMART”: Smart Antenna MAC-Routing Protocol

(cont’d)• Node i chooses node j as relay node to reach a

destination d• If node i knows that the communication with the

neighbor j would interfere with an ongoing communication

• i queries the Routing Table checking for an alternative next hop to reach the final destination.

Thanks to the available routing information, the MAC protocol will not defer a transmission. The packet will be send thought a path that not interfere with the on going communications.

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AP a

AP b

AP c

AP f

AP d

AP e

APa has a packet to transmit to APf

Ongoingcommunication

“SMART”: an example

Even if the primary selected path to

reach the destination is goes

trough APb, APa will choose an

alternative path transmitting the packet to APd

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Work in progress

• We are validating the idea via simulations.

• We are thinking to QoS extensions for 802.11s.