SignalStrengthAware Routing in Ad hoc Networks

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Signal-Strength-Aware Routing in Ad hoc Networks

• Abhinav Gupta
• Ian Wormsbecker
• Carey Williamson
• Dept. of Computer Science
• University of Calgary

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Ad hoc Networks

• An ad hoc network is dynamically formed when two
  or more mobile hosts with wireless capability
  come into transmission range of each other
• Advantage of ad hoc networks
• Can be set up on-the-fly
• Requires no existing infrastructure

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Ad hoc Network
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Objectives

• Implementation of Signal-strength-aware AODV
• Study the effect of AODV routing, user mobility,
  and number of hops on TCP throughput.
• Study the effectiveness of rate-based-pacing of
  TCP (TCP-RBP)

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AODV Operation
Data
Data
RREQ
Source
RERR
RREP
Destination
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Ad hoc On-Demand Distance Vector Routing Protocol
(AODV)

• Reactive in operation
• Route discovery and maintenance using control
  packets (RREQ, RREP, RERR and HELLO)
• The route freshness determined using sequence
  numbers associated with the control packets.

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AODV UU

• Implementation carried out in user-space.
• Consists of 3 kernel modules and some user space
  modules.
• Uses Netfilter hooks for packet mangling from
  kernel space to user space.
• Packets analyzed in user-space to trigger AODV
  events.
• Packets are queued on to user-space using libipq
  which communicates with ip_queue, standard queue
  handler for IPv4.

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AODV Modules
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Signal-strength-aware AODV

• Rationale Dont allow route freshness to be
  determined solely on the basis of sequence
  numbers
• Checks signal strength of control packets coming
  from adjacent Mobile Host to before it creates,
  updates or deletes routes.
• Signal strength of control packets determined by
  link_strength module and used by aodv_socket to
  choose whether or not to let the packet through.

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Variation of Signal Strength
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Operation

• If the packet is a broadcast or is intended for
  the current host, then it is handled as usual by
  Linux.
• If the packet is not intended for the current
  host and a route exists, it is forwarded to the
  next hop.
• If no route exists, the packet is dropped.
• If the packet is generated by the local host, it
  is buffered in user-space, and a route discovery
  initiated and routed to next hop when a route is
  found.

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Locally Generated Packet
Packet
NF_IP_LOCAL_OUT
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Experimental Environment

• Redhat Linux 8.0 (kernel 2.4.18-14)
• 5 laptops
• 3 IBM Thinkpads (Processor P4)
• 2 Compaq Evos (Processor P3)
• Cisco Aironet 350 PCMCIA Wireless Cards
• Netperf and Netserver used as source and sink for
  TCP traffic.
• Kernel Probes added to TCP code to monitor the
  TCP statistics
• Airopeek Sniffer used to count the control packets

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Testbed Topology
Node1 Running netserver
Node2
Node3
Node5 Running netperf
Node4
Airopeek Sniffer
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Routing Discovery Time (ms)
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Round Trip Time
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TCP Throughput (Mbps)
Slow Speed 0.33 m/s Fast Speed 1.0m/s
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Routing Overhead
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TCP rate-based-pacing (TCP RBP)

• Rationale Spread-out the TCP Packets in time
  to improve TCP performance
• InterPacketDelayRTT/(CurrentWindowV)
• Performed simulations and experiments with Reno
  TCP and RBP TCP
• Related Work
• 1 Z.Fu et al, The Impact of Multi-hop
  Wireless Channel on TCP Throughput and Loss,
  Proceedings of IEEE INFOCOM03, San Francisco,
  April 2003
• 2 J.Ke and C.Williamson, Towards a Rate-Based
  TCP Protocol for the Web, Proceedings of MASCOTS
  2000, San Francisco, pp. 36-45, October 2000

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TCP rate-based-pacing
Packet
Packet
Packet
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Simulations Results (TCP-RBP)
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Experimental Results

• TCP Throughput (Mbps)

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Conclusions

• Signal-strength-aware AODV is a good choice for
  ad hoc networks because of low overhead and good
  performance
• Design choices made for signal-strength-aware
  AODV were effective
• Performance of RBP TCP is highly sensitive to
  channel contention and AODV routing dynamics
• Simulation results should be interpreted with
  caution, unless validated against experimental
  measurements

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Thank You!
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Contributions

• Provides a working implementation of
  signal-strength-aware AODV
• Demonstrates the functionality and performance of
  the protocol
• Presents empirical measurements of TCP throughput
  in multi-hop wireless ad hoc network
• Evaluates the effectiveness of TCP
  rate-based-pacing in an experimental setting