net_non-traditional-routing-or.ppt

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  • Multirate Multradio
  • spend a little more time on the 240 x. 121. say this is just for the median, and it’s a factor of 2!
  • possible question – why are there only 7 forwarders.(just say we thin out...)
  • lower is better. right circle – using lots of longer links, sum them up and it’s 25%. so, like ex 1, using lots of long links. zeros: before many packets made no progress, with exor at least some.

Transcript

  • 1. Network Routing: Link Metrics and Non-Traditional Routing Y. Richard Yang 2 / 26 /200 9
  • 2. Admin.
    • Homework 3
    • Project proposal:
      • March 6 by email to [email_address] and richard.alimi@yale.edu
  • 3. Recap: Routing Protocols
    • Proactive protocols
      • distance vector
        • e.g., DSDV
      • link state
      • link reversal
        • e.g., partial link reversal, TORA
    • Reactive (on-demand) protocols
      • DSR
      • AODV
    A E D C B F 2 2 1 3 1 1 2 5 3 5
  • 4. Recap: ETX
    • ETX: The predicted number of data transmissions required to successfully transmit a packet over a link
    • Link loss rate = p
    • Expected number of transmissions
  • 5. ETX Performance DSDV DSR
  • 6. Problems of ETX
    • ETX does not handle multirate 802.11 networks
    • ETX does not work out well when nodes have multiple radios that can operate at different channels
  • 7. Extending ETX: Multirate
    • In a multirate environment, need to consider link bandwidth:
      • packet size = S, Link bandwidth = B
      • each transmission lasts for S/B
    “ Routing in Multi-radio, Multi-hop Wireless Mesh Network,” Richard Draves, Jitendra Padhye, and Brian Zill. Mobicom 2004.
  • 8. Extending ETX: Multirate
    • Add ETTs of all links on the path
    • Use the sum as path metric
    • Interpretation: pick a path with the lowest total network occupation time
      • Q: under what condition is SETT the network occupation time?
  • 9. Problem of SETT
    • In networks with multiple channels/radios, SETT does not consider channel reuse
    2.66 ms 3 Mbps 2.66 ms 6 Mbps Path SETT Throughput Red-Red Red - Blue
  • 10. Observation
    • Interference reduces throughput
      • throughput of a path is lower if many links are on the same channel
      • path metric should be worse for non-diverse paths
  • 11. Extending SETT for Multiple Channels
    • Group links on a path according to channel
      • assumes links on the same channel interfere with one another
      • pessimistic for long paths
    • Add ETTs of links in each group
    • Find the group with largest sum (BG-ETT)
      • this is the “bottleneck” group
      • too many links, or links with high ETT (“poor quality” links)
    • Use this largest sum as the path metric
      • Lower value implies better path
  • 12. BG-ETT Example 0 5.33 ms 5.33 ms 1.5 Mbps 1.33 ms 4 ms 4 ms 2 Mbps 2.66 ms 2.66 ms 2.66 ms 3 Mbps Path Blue Sum Red Sum BG-ETT Throughput All-red 1 Blue Red-Blue
  • 13. BG-ETT May Select Long Paths
  • 14. Path Metric: Putting it all together
    • SETT favors short paths
    • BG-ETT favors channel diverse paths
    • β is a tunable parameter
    • Higher value: more preference to channel diversity
    • Lower value: more preference to shorter paths
  • 15. Implementation and such
    • Implemented in a source-routed, link-state protocol, Multi-Radio Link Quality Source Routing (MR-LQSR)
      • Nodes discover links to its neighbors, measure quality of those links
      • link information floods through the network
        • each node has “full knowledge” of the topology
        • sender selects “best path”
        • packets are source routed using this path
    • Measure loss rate and bandwidth
      • loss rate measured using broadcast probes similar to ETX
        • updated every second
      • bandwidth estimated using periodic packet-pairs
      • updated every 5 minutes
  • 16. Evaluations
  • 17. Median Throughput (Baseline, single radio)
  • 18. Median Throughput (Baseline, two radios)
  • 19. Impact of β value
  • 20. Summary
    • Link metrics are still an active research area, in particular, due to interactions with (channel, spatial) diversity
  • 21. Summary: Traditional Routing
    • So far, all routing protocols in the framework of traditional wireline routing
      • a graph representation of underlying network
        • point-to-point graph, edges with costs
      • select a lowest-cost route for a src-dest pair
      • commit to a specific route before forwarding
      • each node forwards a received packet as it is to next hop
    • Problems: don’t fully exploit path (spatial) diversity and wireless broadcast opportunities
  • 22. Motivating Scenario: I
  • 23. Motivating Scenario: II
    • Traditional routing picks a single route, e.g., src -> B -> D -> dst
    • Packets received off path are useless
    Motivating question: can we take advantage of transmissions that reach unexpectedly far or unexpectedly short?
  • 24. Motivating Scenario: III
    • Src A sends 1 packet to dst B; src B sends packet 3 to dst A
    • The network needs to transmit 4 packets
    • Motivating question: can we do better?
    A B R
  • 25. Motivating Scenario: III
    • If R has both packets 1 and 3, it can combine them and explore coding and broadcast nature of wireless
    A B R
  • 26. Outline
    • Admin.
    • Link metrics
    • Non-traditional routing
      • motivation
      • network coding: exploiting network broadcast
  • 27. Network Coding
    • We have covered source coding (FEC, compression)
    • The new approach uses opportunistic network coding
    • goal: increase the amount of information that is transported
  • 28. Opportunistic Coding: Basic Idea
    • Each node looks at the packets available in its buffer, and those its neighbors’ buffers
    • It selects a set of packets, computes the XOR of the selected packets, and broadcasts the XOR
  • 29. Opportunistic Coding
  • 30. Outline
    • Admin.
    • Link metrics
    • Non-traditional routing
      • motivation
      • network coding: exploiting network broadcast
      • opportunistic routing
  • 31. Key Issue in Opportunistic Routing Key Issue: opportunistic forwarding may lead to duplicates.
  • 32. Extreme Opportunistic Routing (ExOR)
    • Basic idea: avoid duplicates by scheduling
    • Instead of choosing a fix sequential path (e.g., src->B->D->dst), the source chooses a list of forwarders (a forwarder list in the packets) using ETX-like metric
      • a background process collects ETX information via periodic link-state flooding
    • Forwarders are prioritized by ETX-like metric to the destination
  • 33. ExOR: Forwarding
    • Group packets into batches
    • The highest priority forwarder transmits when the batch ends
    • The remaining forwarders transmit in prioritized order
      • each forwarder forwards packets it receives yet not received by higher priority forwarders
      • status collected by batch map
  • 34. Batch Map
    • Batch map indicates, for each packet in a batch, the highest-priority node known to have received a copy of that packet
  • 35. ExOR: Example N0 N3 N1 N2
  • 36. ExOR: Stopping Rule
    • A nodes stops sending the remaining packets in the batch if its batch map indicates over 90% of this batch has been received by higher priority nodes
      • the remaining packets transferred with traditional routing
  • 37. Evaluations
    • 65 Node pairs
    • 1.0MByte file transfer
    • 1 Mbit/s 802.11 bit rate
    • 1 KByte packets
    • EXOR bacth size 100
    1 kilometer
  • 38. Evaluation: 2x Overall Improvement
    • Median throughputs: 240 Kbits/sec for ExOR,
    • 121 Kbits/sec for Traditional
    Throughput (Kbits/sec) 1.0 0.8 0.6 0.4 0.2 0 0 200 400 600 800 Cumulative Fraction of Node Pairs ExOR Traditional
  • 39. OR uses links in parallel
    • Traditional Routing
    • 3 forwarders
    • 4 links
    • ExOR
    • 7 forwarders
    • 18 links
  • 40. OR moves packets farther
    • ExOR average: 422 meters/transmission
    • Traditional Routing average: 205 meters/tx
    Fraction of Transmissions 0 0.1 0.2 0.6 ExOR Traditional Routing 0 100 200 300 400 500 600 700 800 900 1000 Distance (meters) 25% of ExOR transmissions 58% of Traditional Routing transmissions
  • 41. Comments: ExOR
    • Pros
      • takes advantage of link diversity (the probabilistic reception) to increase the throughput
      • does not require changes in the MAC layer
      • can cope well with unreliable wireless medium
    • Cons
      • scheduling is hard to scale in large networks
      • overhead in packet header (batch info)
      • batches increase delay
  • 42. Outline
    • Admin.
    • Link metrics
    • Non-traditional routing
      • motivation
      • network coding: exploiting network broadcast
      • opportunistic routing
        • ExOR
        • MORE
  • 43. MORE: MAC-independent Opportunistic Routing & Encoding
    • Basic idea:
      • Replace node coordination with network coding
      • Trading structured scheduler for random packets combination
    • Previous network coding technique is for inter-flow
    • MORE is for intra-flow network coding
  • 44. Basic Idea: Source
    • Chooses a list of forwarders (e.g., using ETX)
    • Breaks up file into K packets (p1, p2, …, pK)
    • Generate random packets
    • MORE header includes the code vector [c j1 , c j2 , …c jK ] for coded packet p j ’
  • 45. Basic Idea: Source
  • 46. Basic Idea: Forwarder
    • Check if in the list of forwarders
    • Check if linearly independent of new packet with existing packet
    • Re-coding and forward
  • 47. Basic Idea: Destination
    • Decode
    • Send ACK back to src if success
  • 48. Key Practical Question: How many packets does a forwarder send?
    • Compute zi: the expected number of times that forwarder i should forward each packet
  • 49. Computes z s Compute z s so that at least one forwarder that is closer to destination is expected to have received the packet : Єij: loss probability of the link between i and j
  • 50. Compute z j for forwarder j
    • Only need to forward packets that are
      • received by j
      • sent by forwarders who are further from destination
      • not received by any forwarder who is closer to destination
  • 51. Compute z j for forwarder j
    • To guarantee at least one forwarder closer to d receives the packet
  • 52. Evaluations
    • 20 nodes distributed in a indoor building
    • Path between nodes are 1 ~ 5 hops in length
    • Loss rate is 0% ~ 60%; average 27%
  • 53. Throughput
  • 54. Problem of MORE?
  • 55. Mesh Networks API So Far Network Forward correct packets to destination PHY/LL Deliver correct packets
  • 56. Motivation S D 10 -3 BER 10 -3 BER 0% 0% 570 bytes; 1 bit in 1000 incorrect  Packet loss of 99% R1 R2
  • 57. Implication S D 99% (10 -3 BER) 99% (10 -3 BER) 0% 0% Opportunistic Routing  50 transmissions Loss Loss R1 R2
  • 58. Outline
    • Admin.
    • Link metrics
    • Non-traditional routing
      • motivation
      • network coding: exploiting network broadcast
      • opportunistic routing
        • ExOR
        • MORE
        • MIXIT
  • 59. New API PHY + LL Deliver correct symbols to higher layer Network Forward correct symbols to destination
  • 60. What Should Each Router Forward? D S P1 P2 P1 P2 P1 P2 R1 R2
  • 61. What Should Each Router Forward? D S P1 P2
    • Forward everything  Inefficient
    • Coordinate  Unscalable
    P1 P2 P1 P2 R1 R2 P1 P2 P1 P2
  • 62. Symbol Level Network Coding Forward random combinations of correct symbols D S P1 P2 P1 P2 P1 P2 R1 R2
  • 63. Symbol Level Network Coding Routers create random combinations of correct symbols … … R1 R2 D … … … …
  • 64. Symbol Level Network Coding Solve 2 equations Destination decodes by solving linear equations R1 R2 D … …
  • 65. Symbol Level Network Coding Routers create random combinations of correct symbols … … R1 R2 D … … … …
  • 66. Symbol Level Network Coding Solve 2 equations Destination decodes by solving linear equations R1 R2 D … …
  • 67. Destination needs to know which combinations it received Use run length encoding Original Packets Coded Packet
  • 68. Destination needs to know which combinations it received Original Packets Coded Packet Use run length encoding
  • 69. Destination needs to know which combinations it received Original Packets Coded Packet Use run length encoding
  • 70. Destination needs to know which combinations it received Original Packets Coded Packet Use run length encoding
  • 71. Destination needs to know which combinations it received Use run length encoding
  • 72. Symbol-level Network Coding Original Packets Coded Packet Forward random combinations of correct symbols R1
  • 73. Symbol-level Network Coding Original Packets Coded Packet Forward random combinations of correct symbols R1
  • 74. Symbol-level Network Coding Original Packets Coded Packet Forward random combinations of correct symbols R1
  • 75. Symbol-level Network Coding Original Packets Coded Packet Forward random combinations of correct symbols R1
  • 76. Evaluation
      • Implementation on GNURadio SDR and USRP
      • Zigbee (IEEE 802.15.4) link layer
      • 25 node indoor testbed, random flows
      • Compared to:
        • Shortest path routing based on ETX
        • MORE: Packet-level opportunistic routing
  • 77. Throughput Comparison Throughput (Kbps) CDF 2.1x 3x Shortest Path MORE MIXIT
  • 78. Backup Slides
  • 79. Motivation for a Better Metric
  • 80. Implementation and such
    • Modify DSDV or DSR
    • Example evaluation:
      • in DSDV w/ ETX, route table is a snapshot taken at end of 90 second warm-up period
      • in DSR w/ ETX, source waits additional 15 sec before initiating the route request
  • 81. Where do the gains come from? 1.5x Throughput (Kbps) CDF Shortest Path MORE MIXIT without concurrency Take concurrency away from MIXIT
  • 82. Where do the gains come from? Throughput (Kbps) CDF Shortest Path MORE MIXIT Take concurrency away from MIXIT