An Adaptive TCP Protocol for Lossy Mobile Environment

1
An Adaptive TCP Protocol for Lossy Mobile
Environment

Choong Seon Hong Feb. 27, 2003
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Contents

• Introduction
• Related Works
• TCP HACK
• Our Proposal Extended TCP HACK
• Conclusions and Future Work

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Introduction

• TCP is a transport layer protocol designed for
  the wired links.

Slow-start algorithm is triggered after packet
loss is detected

• It incurs end-to-end performance degradation in
  wireless environments where packet loss is very
  high.

4
Related Works

• Indirect TCP(I-TCP) A.Bakre 1995
• Mobile TCP (M-TCP) K.Brown 1997
• Optimized TCP between MH and BS, No caching at BS
• Explicit bad-state notification (EBSN) N.Vaidya
  1999
• Partial ACK from BS
• Snoop protocol H.Balakrishnan 1995
• New Snoop protocol Jian-Hao Hu 2000
• Two- layer hierarchical cache scheme (MSC and BS)
• TCP HACKTCP Header Checksum Option R.K.Balan
  2001

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Introduction(contd)

• Drawbacks using Performance Enhancing Proxies
  (PEPs)
• The intermediary will become the bottleneck
• Add the third point of failure besides the
  endpoints themselves
• Cannot handle encrypted traffic
• Asymmetric routing

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Strengths and Drawbacks of Existing Solutions
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TCP HACK

• TCP HACK (Header Checksum option) is a novel
  mechanism proposed to improve original TCP in
  lossy link.
• It cannot work well when the ACK packets are also
  corrupted much.
• Proposing an Extended TCP HACK.

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TCP HACK(contd)

• Data portion is usually much larger than header
  portion
• Corruptions are far more likely in data portion
• Packets with corrupted headers are unlikely to
  reach destination

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TCP HACK(contd)
TCP Header Checksum option
TCP Header Checksum ACK option
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TCP Sender
TCP HACK(contd)
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TCP HACK(contd)
TCP Receiver
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TCP HACK(contd)
ACK Processing
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Proposed SolutionExtended TCP HACK

• The special ACK in TCP HACK may be lost.
• Extended TCP HACK
• Add a buffer in the TCP receiver(denoted
  s_buffer)
• Save all sequence numbers into s_buffer
• these sequence numbers are recovered from those
  packets transmitted in the same window
• Send special ACK to the sender containing all the
  sequence numbers in the s_buffer.
• Sequence numbers in the s_buffer will be cleared
  if the retransmitted packets are received
  correctly or the timers are expired.

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Extended TCP HACK(contd)
Kind14
Length4

• 1s complement checksum of TCP header and
  pseudo-IP header

TCP Header Checksum option
Kind16
Length Variable
1st 32-bit sequence number of corrupted segment
to resend
1st 32-bit sequence number of corrupted segment
to resend
2nd 32-bit sequence number of corrupted segment
to resend
.
nth 32-bit sequence number of corrupted segment
to resend
Extended TCP header Checksum ACK option
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Extended TCP HACK(contd)

• The segments with sequence A, C and E are data
  corrupted but their headers can be recovered.
• The segment with sequence B is correct
• The segment with sequence D is corrupted in the
  header.

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Extended TCP HACK(contd)
The process of extended TCP HACK when receiving
the segment with sequence number B
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Extended TCP HACK(contd)
The process of extended TCP HACK when receiving
the segment with sequence number C
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Extended TCP HACK(contd)
The process of extended TCP HACK when receiving
the segment with sequence number E
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Extended TCP HACK(contd)
The process of extended TCP HACK when receiving
the retransmitted segment with sequence number A
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Extended TCP HACK(contd)
TCP Sender
Modifications to the TCP sender
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Extended TCP HACK(contd)
TCP Receiver
Modifications to the TCP receiver
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Extended TCP HACK(contd)

• ACK Processing

Modification to the ACK processing
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Simulation Model
Simulation
Parameters (simulation tool
OPNET modeler v8.0) Bandwidth of wireless link
384Kbytes MSS 536bytes Burst length 3
packets size of
s_buffer 40Byte
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Simulation Results(2/2)
Throughput for various packet loss rates when
corrupting on both directions
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Conclusions and Future Work

• With our proposal, we can enhance the performance
  of TCP HACK in situations where not only the
  data on the forward path are corrupted much, but
  also the ACKs on the inverse path susceptible to
  packet corruption.
• Simulation results proved the efficiency of our
  proposal.
• More simulations should be done to test our
  extended TCP HACK.
• Studying on SCTP as streaming protocol in the
  wireless environment

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Questions?
cshong_at_khu.ac.kr