Isolation of Wireless Ad hoc Medium Access Mechanisms under TCP

1
Isolation of Wireless Ad hoc Medium Access
Mechanisms under TCP

• Ken Tang,Mario Correa,Mario Gerla Computer
  Science Department,UCLA

2
Introduction

• For mobile computing to be successful, an obvious
  layer, the MAC layer, must be efficient in
  channel access and reservation
• Provide the insights into the design of
  contemporary wireless, ad hoc random access MAC
  layer protocols

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Wireless MAC Protocols

• CSMACarrier Sense Multiple Access
• MACAMultiple Access with Collision Avoidance
• MACAW
• FAMAFloor Acquisition Multiple Access
• IEEE 802.11

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CSMA,FAMA,and MACA

• CSMA solely uses carrier sense
• FAMA utilizes carrier sense with RTS/CTS control
  frames
• MACA digresses from the carrier sensing of FAMA
  and instead ops for packet sensing

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MACAW and IEEE 802.11

• MACAW adds on top of MACA link-level ACKs, among
  other features
• IEEE 802.11 coalesces FAMA, link-level ACKs and
  collision avoidance

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Experimental configuration

• Consider several topologies(Fig1Fig4)
• Channel bandwidth are 2Mbps
• Transmission and propagation delays are modeled
• Processing delay is negligible

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Experimental Topologies
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Experimental Topologies
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Experimental configuration

• Each node has a 25-packet MAC layer buffer pool
• Scheduling of packet transmission is FIFO

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Hidden Terminal

• Topology is as figure 2
• node_1 is in radio range of node_0 and node_2
• node_0 and node_2 are not within reception range
  of each other
• Connections are set up from node 0 to node 1 and
  node 2 to node 1

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Exposed Terminal

• Topology is as figure 3
• node_0 is in range of node_1
• node_3 is in range of node_2
• node_1 is in range of both node_0 and node_2
• node_2 is in range of both node_1 and node_3
• Connection are 1 to 0 and 2 to 3

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Simulation platform

• OS FreeBSD 2.2.4
• Simulation code GloMoSim
• Traffic type FTP with infinite backlog at each
  source node
• TCP packet fix at 1460B
• TCP connection starts uniformly, distributed
  between 0 to 10 sec

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Results

• PSMA and CSMA works best overall compared to
  CSMA/CA
• RTS/CTS control frames assist to provide fairness
  to the network
• ACKs in general improve the cumulative throughput
  of the network environment
• The combination that works best is
  CSMA/CA/RTS/CTS/ACK

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Conclusion

• CSMA/CA/RTS/CTS/ACK provide the best overall
  network service under general terms
• CSMA/CA/RTS/CTS/ACK is exactly the IEEE 802.11
  standard with virtual carrier sense enabled