TCPIP Performance over 3G Wireless Links with Rate and Delay Variation Mun Choon Chan and Ramachandr

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TCP/IP Performance over 3G Wireless Links with
Rate and Delay VariationMun Choon Chan and
Ramachandran RamjeeACM MOBICOM 2002
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Motivation

• TCP performance degrades with loss links,
  especially in multiple packet losses case
• Mechanisms in 3G to mitigate the effects of
  losses
• Local link layer retransmission
• RLP/RLC ensure loss probability of less than 1
• Channel state based scheduling
• Available rate depends on signal to noise ratio
• Expense increased delay and rate variation
• Consequence ACK compression

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Some Experiment Results
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Some Experiment Results (more)

• ACK packet size is 52bytes
• ACK transmission time on the uplink is 528/8
  52ms
• Interack spacing of less than 52ms is a result of
  uplink delay variation

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Motivation (more)

• ACK compression is BAD
• Burst release of data packets
• gt congestion at bottleneck link
• gt multiple packet losses
• gt poor TCP throughput

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ACK Regulator

• Goal
• To achieve saw-tooth congestion window behavior
  even in presence of varying delay and rate
• Method
• By controlling the buffer overflow process in
  bottle-neck link
• ACK Regulator regulates the ACK flow back to the
  TCP source

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Flow Diagram with ACK Regulator
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Simulation / Results

• Variable Delay
• Measuring throughput as delay increases from 20ms
  to 100ms
• TCP Reno decreased by 30
• TCP Sack decreased by 19
• TCP Reno/Sack with ACK regulator decreased by
  only 8

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Simulation / Results

• Variable Bandwidth
• Same buffer size
• TCP Reno decreased as expected
• TCP Sack just as good as ACK regulated flows
• Variable buffer size
• At buffer size 5, ACK regulated flows are 40
  better that Sack

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Simulation / Results

• Variable Bandwidth and Delay
• Throughput, ACK regulated
• 20 30 better than TCP Reno
• 5 10 better than TCP Sack
• RTT, ACK regulated
• Up to 48 larger

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Conclusions

• ACK Regulator is able to increase TCP Reno and
  TCP Sack performance
• ACK Regulator delivers the same high throughput
  irrespective whether the TCP source is Reno or
  Sack
• ACK Regulator showed robust high throughput
  across different buffer size