Advanced Network Technologies Laboratory

MobiMESH – Wireless Mesh Network Architecture and TestbedMobiMESH – Wireless Mesh Network Architecture and Testbed

Wireless Mesh networks represent the future in wireless networking technology.

The advantages they bring include: - low deployment costs - high available bandwidth - access for standard and advanced clients - mobility management - Integration with heterogeneous networks (Internet)

Possible associated clients include:

Cellular Phones PDA Video Camera Laptop

It has been demonstrated that Minimum Hop Routing does not offer the best performance in ad hoc and mesh networks.

The rate adaptation algorithm implemented in IEEE 802.11 devices often changes the transmission rate, according to the environment; routing should account for that behaviour.

In fact if AR1 sends traffic to AR2, a Shortest Path routing algorithm would send it over the 11Mb/s link; yet if traffic is sent over the two 54Mb/s links, available thorughput would be around 27Mb/s, much higher than the other.

MobiMESH WMN Testbed features:

- standard IEEE 802.11b/g wireless interfaces- commercial IEEE 802.11b/g wireless routers

- OLSR mobile ad hoc routing protocol- OLSR Unik implementation (www.olsr.org)

MobiMESH ArchitectureMobiMESH Architecture

WMN EnhancementsWMN Enhancements

- We are currently adapting the architecture in order to support multi radio devices. - The introduction of multiradio devices involves carefully assigning the frequencies over the network, in order to minimize interference.- Routing must be modified in order to support multi interface devices: we are implementing modifications to the OLSR routing protocol in order to solve the isotonicity problem.

Radio environment aware routing metrics are currently being added to the MobiMESH prototype.

Such metrics rely on information coming from the drivers (MadWifi drivers for Atheros chipsets).

RoutingRouting

Multi Radio DevicesMulti Radio Devices

Performance in a mesh network can be greatly enhanced by employing multiple radio interfaces on the access routers.

Routers equipped with multiple interfacescan transimt and receive at the same time achieving a higher throughput.

The new Access Router, currently under development, features:

- multiple (up to 4) radio interfaces- x86 (Geode) based architecture- Linux based firmware- low cost

A. Capone, S. Napoli, A. PollastroA. Capone, S. Napoli, A. PollastroPolitecnico di Milano, Dip. di elettronica e informazione, ItalyPolitecnico di Milano, Dip. di elettronica e informazione, Italy

www.elet.polimi.it/upload/antlabwww.elet.polimi.it/upload/antlab

MobiMESH DemonstrationMobiMESH Demonstration

ConnectivityConnectivity

Once a client is connected to the Access network, it canaccess services provided by the network and it can communicate with other clients.

Possible applications include:- audio/video streaming- data transfers- instant messaging- real time applications (games,...)

Internet AccessInternet Access

Clients have access to the Internet thorugh gateway entities. The same happens with other networks based on different technologies, provided that a suitable gateway is created.

MobiMESH also supports multiple gateways; exploiting OLSR functionalities, clients access the Internet through the closest gateway.

Multihop routing negatively affects throughput performance: wireless routers can't transmit and receive at the same time!

UDP performs better than TCP because of retransmissions

Thanks to channel orthogonality, interference can be minimized, reachingthe same throughput as infrastructure IEEE 802.11 (case 1, 17Mb/s).

Throughput is severely reduced when the flow employs twice the same radio channel (case 2, 6.5 Mb/s)

ThroughputThroughput Multihop RoutingMultihop Routing Mobility DelayMobility Delay

We have measured how much time a UDP flow remains idle when a client moves from an AR to another.

This has been measured sending UDP traffic from the client and measuring the received throughput on the core network during handover.

The average Mobility Delay is around 2800ms. The majority of this time (64%) is due to OLSR implementation problems; in fact

the OLSR implementation gives low priority to HNA messages, which are exploitedby MobiMESH to propagate handover information.

Advanced Network Technologies Laboratory

www.elet.polimi.it/upload/antlabwww.elet.polimi.it/upload/antlab A. Capone, S. Napoli, A. PollastroA. Capone, S. Napoli, A. PollastroPolitecnico di Milano, Dip. di elettronica e informazione, ItalyPolitecnico di Milano, Dip. di elettronica e informazione, Italy

To Gateway

To Client