Improving the Performance of SCTP over Wireless Networks

1
Improving the Performance of SCTP over Wireless
Networks

• Zhongwei Zhang and Lu Jin
• Department of Mathematics and Computing

WITSP'06 5th Workshop on the Internet,
Telecommunication and Signal Processing, 11-13th,
Dec 2006, Hobart
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Outline

• Motivation
• Introducing SCTP
• What is SCTP
• Features of SCTP
• Modification of SCTP
• Modification of the Protocol
• Design of a Fuzzy Logic Estimator
• Simulation
• Simulated wireless network
• Experiment scenarios
• Conclusion

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Motivation

• Two popular transmission protocols (TCP and UDP)
  are
• Initially designed for wired networks
• Suffering the head-of-line blocking
• Use one IP address.
• Vulnerable to network failures and DoS attacks
• A transmission protocol for Wireless networks
• Communication is characterized by higher
  transmission errors,
• Network or route failures are more likely.
• Denial-of-services SYN attacks

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SCTP

• SCTP is Stream Control Transmission Protocol, a
  reliable transport protocol
• Designed within IETF SIGTRAN working group for
  telephone signalling over IP networks (VoIP).
• Multistreaming to fix up the TCPs Head-of-line
  blocking
• Multihoming to handle network failures
• Association to prevent the DoS attacks

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SCTP vs TCP vs UDP
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SCTP Association vs TCP connection
Four-way handshake
Three-way handshake
SYN J
INIT
INIT-ACK
SYN K, ACK J1
COOKIE_ECHO
ACK K1
COOKIE_ACK
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Multi-streams and multi-homing
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SCTP Features

• SCTP offers several advantages. (Performance)
• Unordered delivery of packets, like UDP
• Multistreaming
• Avoiding Header Of Line Blocking --- Most
  important at the application level are SCTPs
  multistreaming of boundary-preserved messages,
• Multihoming Any SCTP host can establish multiple
  interfaces, each identified by a separate IP
  address
• Fault tolerance if one of these addresses
  fails, the destination host can be reached
  through an alternative interface.
• Selective acknowledgements (SACKS)
• Security (Security)
• Resistance to flooding and masquerade attacks

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Problems with SCTP

• The problems
• Since each stream has a cost and an overhead to
  maintain, we must carefully decide the number
• A current SCTP scheme that uses the same number
  of streams every time is inappropriate.
• No methods to determine the number of streams
• If we can determine the optimal number of streams
  and set the optimal number of stream dynamically,
  SCTP will be able to get maximum performance
  without wasting valuable resources

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Modification to SCTP

• Factors affecting the SCTPs performance
• Receiver buffer size
• Link error rate
• Round trip time
• Observations
• If throughput is constrained by the senders
  congestion window, it is useless to add
  additional streams
• Within congestion window size, more streams are
  needed if receiver buffer is smaller, as link
  error rate is higher, and as RTT is shorter.
• An optimal number estimation is added before the
  SCTP association is made.
• The estimator can be implemented as fuzzy logic
  referring system based on the above observations.

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FL optimal number estimator
N
?
Link error rate
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NS2 Simulation

• SCTP patch for the NS2 has been contributed by a
  group at the University of Delware1.
• The simulated network

Internet
X
AP
AP
A
Y
B
C
Z
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Experiment Scenarios

• The fuzzy logic based optimal number estimator is
  used for each scenarios.
• Before the SCTP association is made, the
  estimator determines an optimal number based on
  the current parameters of underlying networks.
• Scenario 1
• This scenario run 100 simulations in which the
  receiver buffer size change from 5KB to 40KB
• Scenario 2
• This scenario run 100 simulation in which the
  Round trip time (RTT) ranging from 25ms to 100ms
  (satellite)
• Scenario 3
• This scenario run 100 simulation in which the
  link error rate change from 0.1 (wired networks)
  to 10(wireless networks).

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Goodput vs. Buffer Size
For different receiver buffer sizes, Modified
SCTP with an estimated optimal number always give
the best performance.
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Goodput vs. RTT
For different round trip times, modified SCTP
with an estimated optimal number always generate
no worse throughput, but certainly better than
TCP (SCTP with one stream)
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Goodput vs. Link Error Rate
For different link error rates, modified SCTP
with an estimated optimal number of streams
always perform the best, comparing with the SCTP
with a fixed number of streams.
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Related works

• WiSE from CERCOM, Italy
• This work improves SCTP for wireless networks by
  inferring whether losses are due to congestions
  or radio channel errors.2
• From CUNY Graduate Center, USA.
• This works improves SCTP performance by
  overcoming the small window syndrome resulting
  from the MAC layer when the SCTP receiver side
  window is small.3
• Commercial SCTP products
• Cisco implemented SCTP as a part of IP Transfer
  Point (ITP) product family, and was distributed
  in the Cisco IOS Software Releases 12.2
• Signalware NextGen This software uses SCTP as
  the transport protocol to enable voice and data
  networks to converge, and allows carriers to
  offer enhancements such as Voice over the
  Internet and Internet call waiting.

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Conclusion and future works

• Concluding remarks
• SCTP can achieve a better performance than
  TCP-Reno and TCP-SACK over the wireless networks.
• SCTP with an estimator of the optimal number of
  streams always outperforms the SCTP with a fixed
  number of streams in terms of throughput.
• Three improvements have been made to the SCTP
  patch for NS2 simulator
• Future directions
• In the future, we may use SCTP in Wireless Mobile
  Wireless Ad Hoc Networks (MANET)
• Combining our approach with other strategies
  which tackle the SCTP congestion control to
  further improve SCTP performance in the wireless
  environment.

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References

• SCTP pact for NS2, University fo Delaware,
  http//pel.cis.udel.edu
• Fracchia et al, A WiSE Extension of SCTP for
  Wireless Networks, IEEE 2005 Conference on
  Communication.
• G. Ye et al, SCTP Congestion Control Performance
  in Wireless Multi-Hop Networks, IEEE