1 / 18

A New Opportunity Has Arrived!

Stony Brook Mesh Router: Architecting a Multi-Radio Multihop Wireless LAN Samir R. Das (Joint work with Vishnu Navda, Mahesh Marina and Anand Kashyap) Computer Science Department SUNY at Stony Brook samir@cs.sunysb.edu http://www.cs.sunysb.edu/~samir. A New Opportunity Has Arrived!.

Lucy
Download Presentation

A New Opportunity Has Arrived!

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Stony Brook Mesh Router:Architecting a Multi-RadioMultihop Wireless LANSamir R. Das(Joint work with Vishnu Navda, Mahesh Marina and Anand Kashyap)Computer Science DepartmentSUNY at Stony Brooksamir@cs.sunysb.eduhttp://www.cs.sunysb.edu/~samir

  2. A New Opportunity Has Arrived! • Linksys WRT54G access point/router runs Linux. User programmable. Decent processor and memory. Costs $70. • Several router platforms provide multiple PC/mini-PCI/PCI card interfaces. Decent processor and memory. Can run FreeBSD/Linux. Costs $250-$400. • What a systems researcher can do with all these?

  3. Access Points Clients Wired Backbone Ethernet Stony Brook Wireless Router • Traditional Wireless LAN needs “wired” connectivity to access points. • Deployment slow and expensive, particularly for wide area.

  4. Get rid of the wires! Access Points/ Mesh Routers • Use a mesh routing backbone. • Clients can associate with any access point/router. Complete transparency. • Multiple radio interfaces on each router assigned to different bands/channels. Clients Wired Backbone Ethernet

  5. Architectural Choices • Clients run on infrastructure mode. • Associate to a nearby AP. • Unaware of the wireless backbone. • Use WDS (wireless distribution system) for inter-AP communication. • Use a routing protocol for inter-AP routing. • Link state-based routing. • Choice of link cost metric? • Multiple radios on each AP • Channel assignment problem.

  6. Routing • Layer 2 handoff triggers routing updates. Mesh network cloud of APs

  7. Routing • Handoff delay with Prism2-based cards and HostAP driver = 240ms at L2 + 28ms per hop at L3. Mesh network cloud of APs

  8. Multihop Relaying Performance with Multiple Channels TCP throughput • Setup: 802.11b prism2-based cards. HostAP driver. Relaying on WDS links. • Gains over single channel not always spectacular. • Suspect radio leakage. Base case: 1 hop throughput 5.5 Mbps

  9. Channel Assignment Problem: Observations and Approaches • Channel switching takes time (~100ms) in COTS hardware • Rule out dynamic approaches. • Statically? Semi-dynamically? • Channel assignment is a topology control problem. • Two neighboring node can talk only when they have a radio on a common channel. • Ideally, one should jointly solve channel assignment and routing. • Our approach: Assign channels to radios to minimize interference (objective), but preserve original topology (constraint).

  10. Conflict Graph-based Greedy Algorithm • Visits nodes in a certain order and assigns channels to radios such that all links from this node gets a channel. • Channel selection based on a greedy heuristic. • Maintain a conflict graph on the side to model interference. Compute the heuristic on this graph. • Centralized; but can be distributed. 3 nodes 2 radios/node 3 non-overlapping channels

  11. Conflict Graph-based Greedy Algorithm • Visits nodes in a certain order and assigns channels to radios such that all links from this node gets a channel. • Channel selection based on a greedy heuristic. • Maintain a conflict graph on the side to model interference. Compute the heuristic on this graph. • Centralized; but can be distributed. 3 nodes 2 radios/node 3 non-overlapping channels

  12. Conflict Graph-based Greedy Algorithm • Visits nodes in a certain order and assigns channels to radios such that all links from this node gets a channel. • Channel selection based on a greedy heuristic. • Maintain a conflict graph on the side to model interference. Compute the heuristic on this graph. • Centralized; but can be distributed. 3 nodes 2 radios/node 3 non-overlapping channels

  13. Conflict Graph-based Greedy Algorithm • Visits nodes in a certain order and assigns channels to radios such that all links from this node gets a channel. • Channel selection based on a greedy heuristic. • Maintain a conflict graph on the side to model interference. Compute the heuristic on this graph. • Centralized; but can be distributed. 3 nodes 2 radios/node 3 non-overlapping channels

  14. The Devil is in the Model • Interference model (used in objective) • Current model: Two links on the same channel with a common node interferes. Nothing else interferes. • Future: Model overlapping channels and radio leakage. Model interference beyond one hop. Factor in load? • What to optimize? Minimize max interference. Maximize no. of concurrent transmissions. • Topology (used as a constraint) • Current model: Preserve the original topology. • Future: Use the sub-topology actually used by routing.

  15. Can iterative approaches helpin lieu of joint optimization? • Convergence? • Practicality? Routing Influences interference Influences topology Channel Assignment

  16. Random Graph-based Simulations • 50 nodes. Dense network. • 12 independent channels.

  17. Several orders of magnitude 9.5 x NS-2 Simulations • 50 node. Dense network. • MAC layer capacity with Poisson traffic on each link.

  18. Summary • Extend infrastructure-mode WLAN to a mesh network. • Complete client transparency. • Handoff driven routing update. • Multiple radio on each router. Channel assignment problem.

More Related