Purdue University Wireless Mesh Network Testbed
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Mesh@Purdue
Purdue University Wireless Mesh Network Testbed |
MAP is an experimental wireless mesh network testbed at Purdue University. Wireless mesh networks (WMNs) have been proposed as an effective solution for ubiquitous last-mile broadband access. WMNs are characterized by static mesh routers connected by wireless links to each other, each providing connectivity to end hosts. The cost and deployability of WMNs make them particularly attractive for providing last-mile broadband access in rural and suburban areas. The main difference between WMNs and other multi-hop wireless networks such as mobile ad-hoc networks and sensor networks are that the routers in WMNs are static and typically not power-constrained. This shifts the focus of routing from dealing with mobility to finding high throughput routes. MAP currently consists of 32 nodes and is capable running in both 802.11a or 802.11b/g mode. MAP has been recently enhanced with multi-radio support for higher capacity.
A testbed allows us to study many practical issues in deploying such networks as well as to serve as a vehicle to test and refine theoretical ideas to improve their practical applicability.
Routers: Our wireless mesh routers are based on HP Pentium small form factor desktops, Dell Pentium 4 small desktops, and Dell Pentium II machines.
| MAP mesh router |
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Radios: The wireless cards used in the system are of 3 types. We have 5 Orinoco Silver 802.11b PCMCIA cards, 8 Senao Prism 2.5 802.11b PCMCIA cards, and 8 Atheros 521X based 802.11 a/b/g miniPCI cards.
| Atheros 802.11 a/b/g Card | Prism 2.5 Senao Card | Orinoco Wavelan Card |
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Antennas: We use 2dBi omnidirectional rubber duck antennas with RP-TNC and MMCX connectors on most of the wireless nodes. A portion of our network which operates outdoor and serves to interconnect the indoor portions of our network also uses directional antennas. Our antennas are connected to the wireless card through low loss pigtails to minimize interference between multiple radios on a single node.
| Directional antennas in MAP | Omnidirectional antennas in MAP |
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Adapters: Since neither PCMCIA or miniPCI cards can be directly used in PCI interfaces on the meshrouters, we use PCMCIA-to-PCI and miniPCI-to-PCI adapters
| PCMCIA-PCI Adapter | miniPCI-PCI Adapter |
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We have tried out various routing protocols in our testbed over various projects. We have used the OLSR multi-hop routing protocol to route packets between wireless nodes in the testbed. OLSR has support for Internet connectivity by allowing gateways to send HNA packets. A mesh router can choose between gateways using a measurement based metric. OLSR uses the ETX metric to find high throughput routes among nodes in MAP. We have also deployed the AODV routing protocol which worked well but originally did not have the ETX route selection features. We modified it with such features and proactive gateway discovery and also used it in our projects.
Each router is also connected through an Ethernet interface to facilitate code updates, changes to routing protocols, and debugging when the wireless interface is misconfigured. The process of finding the Ethernet side IP addresses of nodes is automated through a reporting agent since the IP addresses can change due to DHCP.
We are developing and testing several applications on MAP. MAP can be used first and foremost for Internet access. For this purpose we have a mobile ad hoc network testbed consisting of 5 laptops and 16 Compaq IPAQ PDAs. These devices are used as clients for the mesh network and connect to the mesh routers through 802.11b Orinoco cards. MAP can also be used for other interesting applications such as video streaming, multicast, media sharing etc.
MAP was initially deployed in early 2005 on the 2nd floors of the MSEE and EE buildings in Purdue University. The network is continuously growing. An overhead view of the current network (image courtesy Google Maps) and a schematic of the initial deployment in MSEE and EE buildings is shown below. The current network consists of 32 nodes and more are being deployed/upgraded continuously.
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Our aim is to extend the MAP network to a large portion of the campus so that we can study additional exciting real-world issues in the design and deployment of wireless mesh networks.
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The initial testbed is seeded by support from the Purdue Research Foundation. Additional funding for the testbed development is from the National Science Foundation under grant CNS-0626703. The research conducted on the testbed is in part supported by the National Science Foundation under grants ANI-0338856 and CNS-0626703.
Last updated: July 15th, 2008.