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Opportunistic Routing in Multi-hop Wireless Networks. Shunyuan Ye 12/16/05. Paper. "EXOR: Opportunistic Multi-Hop Routing for Wireless Networks“, Sanjit Biswas and Robert Morris, In Proc. of ACM/SIGCOMM 2005. Outline. Introduction Basic idea Protocol design details Measurements

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paper
Paper
  • "EXOR: Opportunistic Multi-Hop Routing for Wireless Networks“, Sanjit Biswas and Robert Morris, In Proc. of ACM/SIGCOMM 2005
outline
Outline
  • Introduction
  • Basic idea
  • Protocol design details
  • Measurements
  • Conclusion
traditional routing
Traditional routing
  • Identify a route, forward over links
  • Abstract radio to look like a wired link
radios aren t wires
Radios aren’t wires
  • Packet is broadcast
  • Reception is probabilistic
opportunistic routing
Opportunistic routing
  • Motivation
    • Exploiting probabilistic broadcast
  • Goal
    • High throughput and network capacity
  • ExOR
    • Extremely opportunistic routing
outline1
Outline
  • Introduction
  • Basic idea
  • Protocol design details
  • Measurements
  • Conclusion
why exor good
Why ExOR good?
  • Assumes independent losses
  • Traditional routing: 1/0.25 + 1 = 5 tx
  • ExOR: 1/(1-(1-0.25)^4) + 1 = 2.5 tx
basic idea
Basic idea
  • Probability falls off gradually with distance
  • Traditional route through N2, N4
  • EXOR exploits lucky long receptions
  • Node closest to the dst has highest priority
outline2
Outline
  • Introduction
  • Basic idea
  • Protocol design details
  • Measurements
  • Conclusion
protocol design
Protocol Design
  • Source’s behavior
  • Intermediate nodes’ behavior
  • Destination behavior
source s behavior
Source’s behavior
  • Collects enough packets of the same destination to form a batch
    • ExOR operates on batches of packets for efficiency
  • Selects a set of nodes to be candidate forwarders, and includes the prioritized list in the overhead of every packet
priority ordering
Priority ordering
  • Goal: nodes “closest” to the destination send first
  • Higher delivery probability, closer to the destination
priority ordering 2
Priority ordering (2)
  • ETX=1/(delivery probability)
  • Sort by ETX metric to dst
  • Nodes periodically flood ETX “link state” measurement
protocol design1
Protocol Design
  • Source’s behavior
  • Intermediate nodes’ behavior
  • Destination behavior
forwarders behavior 1
Forwarders’ behavior (1)
  • How can a node know whether it is one of the forwarders or not?
  • Check the forwarder list in the overhead of the received packet
    • If the node finds itself in the list, buffer the packet and keep state of this batch
    • If no, discard the packet
forwarders behavior 2
Forwarders’ behavior (2)
  • How can a node know whether the packet it receives has also been received by a node with higher priority or not?
  • ExOR designs a “batch map” to record, for every packet in the batch, the highest-priority node known to have received that packet.
batch map example
Batch map example
  • src generates a batch map before tx
  • src inserts the batch map into the overhead of every packet in this batch
batch map example1
Batch map example
  • When N1 first receives a packet from src, it keeps the batch map in local
  • N1 updates its batch map when receiving new packets of this batch
batch map example2
Batch map example
  • N2 receives packets from src, so it doesn’t know that N1 has received packet 1 and 2
batch map example3
Batch map example
  • After scr finished transmission, N2 begins to broadcast packets it received
  • N1 also received these packets and then update its local batch map
batch map example4
Batch map example
  • src updates its local map and gets into know that all the packets in the batch has been received by dst or intermediate nodes, no acknowledge is needed.
forwarders behavior 3
Forwarders’ behavior (3)
  • How can a node know when is its turn to transmit?
  • ExOR add a “fragment size” and “fragment number” in the overhead of every packet.
    • Fragment size: number of packets the node has to send
    • Fragment no. : the index of the sending packet in the fragment
fragment example
Fragment example
  • N2’s fragment size is 2 and fragment no. is 1 for packet 3 and 2 for packet 2
forwarding estimate
Forwarding estimate
  • When N1 receives packet 3 from N2, it knows that there is still one packet N2 has to send, then N1 can estimate the time to forwarding its fragment
protocol design2
Protocol Design
  • Source’s behavior
  • Intermediate nodes’ behavior
  • Destination behavior
destination s behavior
Destination’s behavior
  • Actually destination is the last intermediate node and has the highest priority.
  • After the finish of src’s transmission. Destination sends out ten packets only including the batch map, to inform other nodes about the packets it has received
outline3
Outline
  • Introduction
  • Basic idea
  • Protocol design details
  • Measurements
  • Conclusion
exor 2x overall improvement
Exor: 2x overall improvement
  • Median throughputs: 240Kbit/s for ExOR

121Kbit/s for Traditional

conclusion
Conclusion
  • ExOR achieves 2x throughput improvement
  • Future work will focus on:
    • Choosing best 802.11 bit rate
    • Cooperation between simultaneous flows