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High Throughput Route Selection in Multi-Rate Ad Hoc Wireless Networks. Dr. Baruch Awerbuch, David Holmer, and Herbert Rubens. Johns Hopkins University. Department of Computer Science. www.cnds.jhu.edu/archipelago. Overview. Problem: Route selection in multi-rate ad hoc network

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high throughput route selection in multi rate ad hoc wireless networks

High Throughput Route Selection in Multi-RateAd Hoc Wireless Networks

Dr. Baruch Awerbuch, David Holmer, and Herbert Rubens

Johns Hopkins University

Department of Computer Science

www.cnds.jhu.edu/archipelago

overview
Overview
  • Problem:

Route selection in multi-rate ad hoc network

  • Traditional Technique:

Minimum Hop Path

  • New Technique:

Medium Time Metric (MTM)

  • Goal:

Maximize network throughput

what is multi rate
What is Multi-Rate?
  • Ability of a wireless card to automatically operate at several different bit-rates

(e.g. 1, 2, 5.5, and 11 Mbps)

  • Part of many existing wireless standards

(802.11b, 802.11a, 802.11g, HiperLAN2…)

  • Virtually every wireless card in use today employs multi-rate
advantage of multi rate
Advantage of Multi-Rate?
  • Direct relationship between communication rate and the channel quality required for that rate
  • As distance increases, channel quality decreases
  • Therefore: tradeoff between communication range and link speed
  • Multi-rate provides flexibility

1 Mbps

2 Mbps

5.5 Mbps

11 Mbps

Lucent Orinoco 802.11b card ranges using

NS2 two-ray ground propagation model

ad hoc network single rate example
Ad hoc Network Single Rate Example
  • Which route to select?

Destination

Source

ad hoc network single rate example1
Ad hoc Network Single Rate Example
  • Which route to select?
  • Source and Destination are neighbors! Just route directly.

Destination

Source

multi rate network example
Multi-rate Network Example
  • Varied Link Rates

Destination

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

multi rate network example1
Multi-rate Network Example
  • Varied Link Rates

Destination

Throughput = 1.04 Mbps

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

multi rate network example2
Multi-rate Network Example
  • Varied Link Rates

Destination

Throughput = 1.15 Mbps

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

multi rate network example3
Multi-rate Network Example
  • Varied Link Rates
  • Min Hop Selects Direct Link
    • 0.85 Mbps

Destination

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

multi rate network example4
Multi-rate Network Example
  • Varied Link Rates
  • Min Hop Selects Direct Link
    • 0.85 Mbps effective
  • Highest Throughput Path
    • 2.38 Mbps effective

Destination

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

multi rate network example5
Multi-rate Network Example
  • Under Mobility
  • Min Hop
    • Path Breaks
  • High Throughput Path
    • Reduced Link Speed
    • Reliability Maintained
    • More “elastic” path

Destination

X

Source

11 Mbps

5.5 Mbps

2 Mbps

1 Mbps

challenge to the routing protocol
Challenge to the Routing Protocol
  • Must select a path from Source to Destination
  • Links operate at different speeds
  • Fundamental Tradeoff
    • Fast/Short links = low range = many hops/transmissions to get to destination
    • Slow/Long links = long range = few hops/transmissions
minimum hop path traditional technique
Minimum Hop Path(Traditional Technique)
  • A small number of long slow hops provide the minimum hop path
  • These slow transmissions occupy the medium for long times, blocking adjacent senders
  • Selecting nodes on the fringe of the communication range results in reduced reliability
how can we achieve high throughput
How can we achieve high throughput?
  • Throughput depends on several factors
    • Physical configuration of the nodes
    • Fundamental properties of wireless communication
    • MAC protocol
wireless shared medium
Wireless Shared Medium
  • Transmission blocks all nearby activity to avoid collisions
  • MAC protocol provides channel arbitration

Carrier Sense Range

Carrier Sense Range

1

2

transmission duration
Transmission Duration

4.55 Mbps

3.17 Mbps

1.54 Mbps

0.85 Mbps

Medium Time consumed to transmit 1500 byte packet

hops vs throughput
Hops vs. Throughput
  • Since the medium is shared, adjacent transmissions compete for medium time.
  • Throughput decreases as number of hops increase.

1

2

3

effect of transmission
Effect of Transmission

Source

Destination

X

X

X

X

X

X

X

1

2

3

4

5

6

7

8

Request to Send (RTS)

Clear to Send (CTS)

DATA

ACK

analysis
Analysis
  • General Model of ad hoc network throughput
    • Multi-rate transmission graph
    • Interference graph
    • Flow constraints
  • General Throughput Maximization Solution is NP Complete
  • Derived an optimal solution under a full interference assumption
new approach medium time metric mtm
New Approach: Medium Time Metric (MTM)
  • Assigns a weight to each link proportional to the amount of medium time consumed by transmitting a packet on the link
  • Existing shortest path protocols will then discover the path that minimizes total transmission time
mtm example
MTM Example

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11

= 2.5

2.5ms

4.55 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example1
MTM Example

11 Mbps

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11 + 11

= 5.0

2.5ms

2.5ms

2.36 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example2
MTM Example

11 Mbps

11 Mbps

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11 + 11 + 11

= 7.5

2.5ms

2.5ms

2.5ms

1.57 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example3
MTM Example

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11 + 11 + 11 + 11

= 10.0

2.5ms

2.5ms

2.5ms

2.5ms

1.18 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example4
MTM Example

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11 + 11 + 11 + 11 + 11

= 12.5

2.5ms

2.5ms

2.5ms

2.5ms

2.5ms

0.94 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example5
MTM Example

11 Mbps

Source

Destination

1 Mbps

Path Medium Time Metric (MTM)

Path Throughput

Link Rate

11 + 11 + 11 + 11 + 11 + 11

= 15

2.5ms

2.5ms

2.5ms

2.5ms

2.5ms

2.5ms

0.78 Mbps

1

0.85 Mbps

13.9ms

= 13.9

mtm example6
MTM Example

Medium Time Usage

Link Throughput

Destination

4.55 Mbps

11 Mbps

2.5ms

3.17 Mbps

5.5 Mbps

3.7ms

1.54 Mbps

2 Mbps

7.6ms

0.85 Mbps

1 Mbps

13.9ms

Source

Path Medium Time Metric (MTM)

Path Throughput

11 Mbps

5.5 Mbps

1

0.85 Mbps

13.9ms

= 13.9 ms

2 Mbps

1 Mbps

mtm example7
MTM Example

Medium Time Usage

Link Throughput

Destination

4.55 Mbps

11 Mbps

2.5ms

3.17 Mbps

5.5 Mbps

3.7ms

1.54 Mbps

2 Mbps

7.6ms

0.85 Mbps

1 Mbps

13.9ms

Source

Path Medium Time Metric (MTM)

Path Throughput

5.5 + 2

11 Mbps

= 11.3 ms

1.04 Mbps

3.7ms

7.6ms

5.5 Mbps

1

0.85 Mbps

13.9ms

= 13.9 ms

2 Mbps

1 Mbps

mtm example8
MTM Example

Medium Time Usage

Link Throughput

Destination

4.55 Mbps

11 Mbps

2.5ms

3.17 Mbps

5.5 Mbps

3.7ms

1.54 Mbps

2 Mbps

7.6ms

0.85 Mbps

1 Mbps

13.9ms

Source

Path Medium Time Metric (MTM)

Path Throughput

11 + 2

1.15 Mbps

2.5ms

7.6ms

= 10.1 ms

5.5 + 2

11 Mbps

= 11.3 ms

1.04 Mbps

3.7ms

7.6ms

5.5 Mbps

1

0.85 Mbps

13.9ms

= 13.9 ms

2 Mbps

1 Mbps

mtm example9
MTM Example

Medium Time Usage

Link Throughput

Destination

4.55 Mbps

11 Mbps

2.5ms

3.17 Mbps

5.5 Mbps

3.7ms

1.54 Mbps

2 Mbps

7.6ms

0.85 Mbps

1 Mbps

13.9ms

Source

Path Medium Time Metric (MTM)

Path Throughput

11 + 11

= 5.0 ms

2.5ms

2.5ms

2.38 Mbps

11 + 2

1.15 Mbps

2.5ms

7.6ms

= 10.1 ms

5.5 + 2

11 Mbps

= 11.3 ms

1.04 Mbps

3.7ms

7.6ms

5.5 Mbps

1

0.85 Mbps

13.9ms

= 13.9 ms

2 Mbps

1 Mbps

advantages
Advantages
  • It’s an additive shortest path metric
  • Paths which minimize network utilization, maximize network capacity
    • Global optimum under complete interference
    • Single flow optimum up to pipeline distance (7-11 hops)
    • Excellent heuristic in even larger networks
  • Avoiding low speed links inherently provides increased route stability
disadvantages
Disadvantages
  • MTM paths require more hops
    • More transmitting nodes
      • Increased contention for medium
      • Results in more load on MAC protocol
      • Only a few percent reduction under the simulated conditions
    • Increase in buffering along path
      • However, higher throughput paths have lower propagation delay
sounds great but
Sounds great but…
  • Do faster paths actually exist?
    • There needs to be enough nodes between the source and the destination to provide a faster path
    • Therefore performance could vary as a function of node density
    • When density is low: MTM = Min Hop
mtm throughput increase under 802 11mac
MTM Throughput IncreaseUnder 802.11MAC

-NS2 Network Simulations

-20 TCP Senders and receivers

-Random Waypoint mobility (0-20m/s)

-DSDV Protocol modified to find MTM path

mtm oar throughput increase over min hop 802 11
MTM + OAR Throughput Increaseover Min Hop + 802.11

-NS2 Network Simulations

-20 TCP Senders and receivers

-Random Waypoint mobility (0-20m/s)

-DSDV Protocol modified to find MTM path

slide39

Thank You!

Questions??

Herb Rubens

herb@cs.jhu.edu

More Information:

http://www.cnds.jhu.edu/networks/archipelago/