TCPPeach: A New Congestion Control Scheme for Satellite IP Networks

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TCP-Peach A New Congestion Control Scheme
forSatellite IP Networks

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• Date09/27

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Author Source

• Author
• Akyildiz, I.F. Morabito, G. Palazzo, S
• Source
• Networking, IEEE/ACM Transactions onVolume 9, 
  Issue 3,  June 2001 Page(s)307 - 321

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Outline

• Introduction
• TCP-Peach
• Sudden Start
• Rapid Recovery
• Simulation Result
• Conclusion

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Introduction

• In satellite networks, TCP throughput decreases
  because
• the long propagation delays
• high link error rates
• In this paper, we introduce TCP-Peach, a new
  congestion control scheme for satellite networks
  which is an end-to-end solution to improve the
  throughput performance in satellite networks.

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The Performance Problem with Long Propagation
Delay

• In the beginning of a new connection, the sender
  enters the Slow Start Phase to probe the
  availability of bandwidth , the time required by
  the Slow Start to reach a bit rate B is

RTT Round Trip Time l average packet length
expressed in bits B Bit Rate
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Table 1. DURATION OF THE SLOW START
PHASE FOR LEO, MEO, AND GEO
SATELLITES (With average Packet Size
(l)1Kbytes)
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Proposed solutions for the performance problems
of Slow Start in long propagation delay networks

• Increasing Initial Window (IIW)
• TCP Spoofing
• TCP Splitting
• Fast Start

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The throughput of IW1 and IW4 with BER0
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The throughput of IW1 and IW4 with BER10-4
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TCP Spoofing

• A router near the source sends back ACKs for TCP
  packets in order to give the source the illusion
  of a short delay path.
• TCP Spoofing has some problems
• The router must analyze TCP header. But current
  router just analyze IP header. So it exceed its
  ability.
• TCP Spoofing requires ACKs to flow through the
  same path as data.
• If IP (Data Field) encryption is used, the scheme
  cannot be applied.

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TCP Splitting

• TCP connection is divided into multiple
  connections.
• This solution has the same problems as TCP
  spoofing with the exception of Problem 2 .

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Fast Start

• The basic idea of the Fast Start is to reuse the
  values of the transmission rate from the recent
  past.
• The TCP packets transmitted during this Fast
  Start period are carried by low-priority IP
  packets.

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Fast Start (Cont.)

• Fast Start has some Problems
• The transmitted low-priority packets carry new
  information to the receiver, thus, they are still
  data packets, and if they are lost, then they
  must be recovered.
• Fast Start can be used only if for the same path.
  This requires that within a short time the same
  server (sender) transfers several files to the
  same user (receiver), which may often not be the
  case.

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The performance problem with Error Rate

• TCP was initially developed for wire-line
  networks where the link error rate is low, such
  that the majority of the packet losses is due to
  network congestions.
• Satellite networks have several orders of
  magnitude higher error rates than the wire-line
  networks.

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The performance problem with Error Rate (Cont.)

• In other paper, the author suggest to decouple
  error control and congestion control
• TCP would then be responsible only for congestion
  control while the error control is handled by the
  link layer.
• The link layers of all sub-networks composing the
  Internet need to be redesigned.

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TCP-Peach
TCP-Peach
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Dummy Packets

• Low priority packets generated by the sender as a
  copy of the last transmitted data packet. (They
  do not carry any new information.)
• The sender uses dummy packets to probe the
  availability of the network resources.

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Sudden Start

• The sudden start algorithm is executed at the
  beginning of a new connection in order to avoid
  the low throughput performance of slow start.
• For the sender, an ACK for a dummy packet is the
  sign that there are still unused resources in the
  network.
• During the sudden start the sender transmits one
  data packet and (rwnd 1) dummy packets.

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Sudden Start (Cont.)

• In this phase, the sender will increase its
  congestion window, cwnd, by one packet each time
  it receives an ACK for a dummy packet.
• At the end of the sudden start algorithm, the
  transmission rate for the new connection suddenly
  jumps from (1/RTT) to (nAbsorbed/RTT) .
• The cwnd reaches rwnd within 2RTTs.

The number of dummy packets the network is able
to absorb
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Comparison of TCP-Peach and TCP-Reno in the
beginning of a new connection (rwnd64 packets)
The cwnd of TCP-Reno reaches rwnd within 7RTT
The cwnd of TCP-Peach reaches rwnd within 2RTT
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Rapid Recovery

• Objective Solving the throughput degradation
  problem due to link errors.
• When a packet loss is detected through ndup
  duplicate ACKs, the original Fast Retransmit
  scheme is used.
• After completing the Fast Retransmit scheme, we
  apply the Rapid Recovery scheme .

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Rapid Recovery (Cont.)

• The rapid recovery algorithm first keeps the fast
  recovery conservative assumption that all packet
  losses are due to network congestion.
• Accordingly, the TCP sender halves cwnd.
• If the packet loss is due to link errors, the
  dummy packets will reach the receiver and be
  acknowledged to the sender, which will increase
  cwnd.

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Rapid Recovery
nDummy is Double of Current cwnd which is at
begin of Rapid Recovery
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The Behavior of Rapid Recovery with RTT0.26Secs
Packet Loss due to Link Error
½ RTT
Last for 1RTT
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Simulation Experiments

• N20 , rwnd64 packets
• Earth Station buffer K50 packets, RTT500ms
• tsimulation 500secs

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Goodput performance comparison of TCP-Peach and
TCP-Reno for different values of Ploss
(c1300packets/sec)
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Goodput performance comparison of TCP-Peach and
TCP-Reno for different values link capacity C
(Ploss10-2)
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Transmission of files of S 50 segments average
goodput
TCP-Peach
TCP-Reno
IIW
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Fairness evaluation in heterogeneous scenario
RTTX500ms(satellite link)
RTTY200ms(terrestrial Link) PLOSS,X0, 10-4,
10-3, 10-2 PLOSS,Y0 NM5 K50packets Rwnd64pack
ets
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Fairness evaluation in heterogeneous scenario
Homogeneous scenario
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CONCLUSION

• TCP-Peach is based on the use of dummy packets
  that do not carry any new data to the receiver.
• TCP-Peach requires the routers along the
  connection to implement some priority mechnism at
  the IP layer.
• TCP-Peach contains two new algorithms Sudden
  Start Rapid Recovery
• TCP-Peach improves the goodput performance and
  fairness in satellite networks