1 / 38

Grid: Scalable Ad-Hoc Wireless Networking

Grid: Scalable Ad-Hoc Wireless Networking. Douglas De Couto http://pdos.lcs.mit.edu/grid. A. F. D. B. E. C. G. J. I. H. Goal: Networks out of Chaos. Ad hoc Applications. Temporary, fast setup Emergencies & events Rooftop networks No wires, trenches, etc. Developing communities

sydney-beard
Download Presentation

Grid: Scalable Ad-Hoc Wireless Networking

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. Grid: Scalable Ad-Hoc Wireless Networking Douglas De Couto http://pdos.lcs.mit.edu/grid

  2. A F D B E C G J I H Goal: Networks out of Chaos

  3. Ad hoc Applications • Temporary, fast setup • Emergencies & events • Rooftop networks • No wires, trenches, etc. • Developing communities • Cheap, incremental, automatic

  4. A F D B E C G J I H Direct Contact Scales Badly “Hello J!”

  5. A F D B E C G J I H Solution: Multi-hop Forwarding “A to J: Hello!”

  6. Design Challenges • Finding routes • Cope with mobile nodes • Conserving battery power • Coping with malicious/faulty nodes • Scaling to large networks

  7. Completed Research • Scalable routing: • Geographic forwarding • Distributed P2P location database • Low-power forwarding • Understanding capacity limits • Avoiding malicious nodes • Current research: link selection

  8. System Status • Software distributions for • Linux, BSD • PC, iPaq • Works with unmodified Internet software • Two Grid nets deployed • In-building network • Rooftop network

  9. LCS Grid Net 5 5 6 5 6 5 5 5 6 5 6 6 5 6 5 5 5 • 17 static nodes on 5th/6th floors • A dozen iPaq hand-helds wired gateway

  10. Roof-Top Grid Net 6 5 4 3 2 1 LCS

  11. Geographic forwarding (GF) C’s radio range A D F C G B E • Packets addressed to idG,locationG • Next hop is chosen from neighbors to move packet geographically closer to destination location • Per-node routing overhead constant as network size (nodes, area) grows • Requires location service, which adds overhead

  12. Grid Location Service (GLS) overview E H L B D J G A “D?” I F K C Each node has a few servers that know its location. 1. Node D sends location updates to its servers (B, H, K). 2. Node J sends a query for D to one of D’s close servers.

  13. GLS’s Spatial Hierarchy level-0 level-1 level-2 level-3 All nodes agree on the global origin of the grid hierarchy

  14. sibling level-0 squares s n s s s s sibling level-1 squares s s sibling level-2 squares s s 3 servers per node per level • s is n’s successorin that square. • (Successor is the node with “least ID greater than” n )

  15. location query path Queries search for destination’s successors s n s s s s Each query step: visit n’s successor at increasing levels, until location server found s s s1 x s2 s s3

  16. GF + GLS performs well Grid DSR Number of nodes Biggest network simulated: 600 nodes, 2900x2900m (4-level grid hierarchy) Fraction of data packets delivered successfully • Geographic forwarding is less fragile than source routing. • DSR queries use too much b/w with > 300 nodes.

  17. GLS properties • Spreads load evenly over all nodes • Degrades gracefully as nodes fail • Queries for nearby nodes stay local • Per-node storage and communication costs grow slowly as the network size grows: O(log n), n nodes • More details: Li et al, Mobicom 2000

  18. A F D B E C G J I H Does Grid Find Useful Paths?

  19. A F D B E C G J I H Mistake: Shortest-Path Routes A’s max range

  20. Link Quality Isn’t Bi-modal

  21. Route metrics • How to select good routes? • Compare metrics • Good metric: expected total packet transmissions • Want to mimimize • Route metric = sum of link metrics • Fight strong bias towards shortest paths • While penalizing longer paths

  22. Obstacles to Better Routing • Want to detect and avoid lossy links, but… • Loss rate masked by 802.11 re-sends • Changes quickly with time, motion

  23. How to find loss rate? • Signal strength?

  24. Current Work • Trying to directly measure loss rates • Route broadcast packets • Long time constants • 802.11 protocol beacons? • Requires driver integration

  25. Grid Summary • Grid routing protocols are • Self-configuring • Easy to deploy • Scalable http://www.pdos.lcs.mit.edu/grid

  26. End Of TalkDemo

  27. Access Point Application: Smart Devices Remote Control Print Share E-Mail Internet

  28. Application: Rooftop Nets School/Homework Server Internet Access Game server

  29. Application: Disaster Services • Disaster may have damaged phone system &c • Want to avoid N2 plans for N services to communicate

  30. A B C D F G Topology Distribution Scales Badly 1. “C can reach A and B.” 3. Data from F to B. 2. “D can reach A, B, and C.”

  31. A F D B E C G Geographic Forwarding Scales Well “Send towards latG / lonG.” Latitude Longitude

  32. A F D B E C G Location Database DB 2. “Where is G?” 1. “G is at latG / lonG” Latitude Longitude

  33. Distributed Location Database • Each node is DB for a few other nodes • How to find a node’s location server(s)? • Every node has an unchanging ID • hash(ID) maps ID to position in unit square

  34. G’s Location Server is a Point I H x hash(G) = 0.1,0.9 G (0,0)

  35. Spatial Grid Hierarchy All nodes agree on the global origin of the Grid hierarchy

  36. Multiple Servers per Node c b a G

  37. Lookups Expand in Scope c b a G ? A

  38. Grid Protocol Overhead Grows Slowly Protocol Overhead (packets per second) Number of nodes • Protocol packets include: Grid update, Grid query/reply.

More Related