Energy Consumption of TCP Reno, Newreno, and SACK in Multi-Hop Wireless Network

1
Analysis of Energy Consumption of TCP Reno,
Newreno, and SACK in Multi-Hop Wireless Network
Thesis Defense of Harkirat Singh
2
Outline

• Motivation
• TCP Mechanism
• Energy Model
• Experiment Methodology
• Experiment Results
• Conclusion

3
Motivation

• Wireless devices need to be
• Reliable
• Light Weight
• Wireless links are error prone, low bandwidth
  etc.
• TCP connection suffers long idle time hence low
  throughput
• How is Power consumed in a wireless node?

4
Lucent 802.11 Silver (11 Mbps) WaveLAN DSSS PC
Card Characteristics INFOCOM01

• Radio States Transmit, receive, idle, sleep

Power (Idle) 780mW
Power (Sleep) 50mW
Idle / Sleep
Ack
Data
Recv
Xmt
Power (Xmt) 1478mW
Power (Recv) 900mW
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TCP Mechanism

• TCP is a sliding window protocol with built in
  self-clocking and congestion control algorithm
• Slow start
• Congestion avoidance
• Fast retransmit
• Fast recovery
• TCP Tahoe implements first three
• TCP Reno, Newreno and SACK have all four

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Slow start

• Slow start is used during initial phase of a
  connection or after retransmission timeout
  (Probing the network)
• It is also known as additive increase and
  multiplicative decrease
•  
•  
•  

cwnd1 cwnd2 cwnd4 cwnd8
Sender Receiver
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Fast retransmit and recovery

• TCP receiver generates ack for next expected
  packet
• In the event of packet loss or reordering,
  receiver Acks last in-sequence pkt received
• TCP sender retransmits first unacknowledged
  packet after 3 dup_acks without waiting for
  retransmit timer to go off
• ssthresh min (cwnd, rcv advertised window) / 2
• Send missing pkt and set cwnd 3
• Inflate cwnd till retransmitted pkt is acked
• Deflate the window, enter Congestion Avoidance

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Congestion Avoidance

• When cwnd gt ssthresh TCP invokes Congestion
  Avoidance
• cwnd 1/cwnd (for each ack)
• In other words cwnd is incremented (cwnd) by
  one per round trip time
• It is conservative approach to increase cwnd as
  name suggests
• When congestion is detected (by timeout), TCP
  slows down and invokes slow start

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Evolution of TCP window
Fast retransmit and recovery
Slow start
Congestion avoidance
Congestion Window
Time
10
Evolution of cwnd
Outstanding Data
Time
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TCP Newreno

• TCP Reno is optimized for single packet loss in a
  window, multiple pkt loss degrades the
  performance
• TCP Newreno enhances the performance in the event
  of multiple pkt drop without having SACK
• Introduces new variable Partial ACK
• When fast retransmit is invoked record the
  highest sequence number transmitted as Recover
• When all of the data up to and including Recover
  is acknowledged TCP exits fast recovery
• Avoids invocation of Fast retransmit in quick
  succession

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Sender
Receiver
0 .. 61
14
7 .. 14
7 .. 13
cwnd 8
New round
14 dup Acks
0 .. 131
15 .. 28
15 .. 28
14
cwnd 15
New round
14, 29 .. 34
14
29 .. 34
cwnd 10
cwnd 21
Receiver generates Ack 29, sender exits Fast
recovery and adjust inflated cwnd and enters
Congestion avoidance
0 .. 281
cwnd 7
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TCP SACK

• SACK Data structure
• Recover and Partial ack as Newreno
• Receiver informs non-contiguous data
• Receiver can reflects max of three SACK blocks
• Sender maintains a queue of segments that have
  been transmitted but not yet acknowledged,
  Scoreboard
• SACK is invoked in the event of three dup_acks
• Sender can judiciously send new packet or
  retransmit packet to fill hole at receiver

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TCP SACK Data Structures

• struct tcpcb
• struct sackhole snd_holes

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SACK Example
Senders queue
Receivers queue
1
2
3
4
5
6
1
2
ACK 1 SACK 2
1
3
4
5
6
2
3
4
ACK 1 SACK 3,2
1
4
5
6
6
2
3
5
ACK 1 SACK 5,3,2
1
4
6
HOLES AT RCVR
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Evolution of ACK received by TCP-SAC Sender
   
3 dup_ack
Sequence Number
Time
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TCP Protocols Summary
Partial ACK Recv holes details Modified Recv
RENO NO NO NO
NEWRENO YES NO NO
SACK YES YES YES
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Outline

• Motivation
• TCP Mechanism
• Energy Model
• Experiment Methodology
• Experiment Results
• Conclusion

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Energy consumption of a node
Packet Reception Processing Packet
Processing Transmission
Idle Period
Current
PTX
PRX
Idle Current Consumption Pidle
Time
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Energy Model

• Total energy (E) can be represented as
• PTX is energy spent for transmission
• tTX is time spent in transmission
• tRX is negligible so can be eliminated
• Assume average connection throughput is ?
  bytes/sec and the transmission speed is r
  bytes/sec we can write

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Goals

• Awake node during ideal time consume unnecessary
  power
• Power off nodes during idle period this gives
  lower bound of Total Energy consumption though
  not realistic call it Idealized Energy
• Alternatively during idle period node is asleep
  and in the event of a pkt node is awoken up by
  radio

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Goals contd.

• Investigate the Energy consumption of TCP
  variants (Total Energy vis-à-vis Idealized
  Energy)
• TCP connection characteristic in wireless
  revisited
• Low bandwidth connection
• Higher BER
• Mobility
• These leads to longer Idle time
• Hence TCP sender can sleep!!

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Evolution of TCP Sequence
Idle connection
Sequence Number
Time
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Outline

• Motivation
• TCP Mechanism
• Energy Model
• Experiment Methodology
• Experiment Results
• Conclusion

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Test Bed

• Three hop wireless ad hoc network
• Each laptop equipped with Lucent 11 Mbps WaveLAN
  card Running FreeBSD 4.3
• SACK is implemented based on RFC 2018
• Dummynet used for packet loss and delay
• Energy measurement at sender using HP 34401A
  multimeter and VeePro software

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Energy Measurement

• Two multimeters simultaneously used for measuring
  Radio and Total Node Power
• Multimeter takes current measurement with a
  granularity of 1 millisecond
• Multimeter dumps data to different laptop
• Integration of current voltage over connection
  time gives total Energy

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Workload, Factors, and Metrics

• TTCP used as a constant workload generator - 5 MB
  
• Error 1, 5 and 10
• RTT 15, 40, 70, 100 and 130 msec
• Reordering 1 and 5
• Burst Error 85 for 1 sec every 12 sec
• MTU 512 and 1500

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A typical run ..
Pkt
Router generates Loss and Delay (DUMMYNET)
Pkt
Start TTCP
Start LossDelay script
Pkt
Start TTCP server
Start multimeter
Stop
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Energy Consumed by Node
Current (mA)
Idealized Energy
Simultaneous measurement of Energy consumed by
the radio
Time (msec)
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Metrics

• Total Energy/bit ( E ) measured in Joules/bit.
  This includes the energy consumed while the
  sender is idle
• Idealized Energy/bit ( EI ) measured in
  Joules/bit. This measure excludes the idle time
  energy and thus more closely approximates the
  cost of the various protocols
• Goodput in kbps

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Outline

• Motivation
• TCP Mechanism
• Energy Model
• Experiment Methodology
• Experiment Results
• Conclusion

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Experiment Results Burst Loss
 
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Burst loss
Energy
Goodput
NEWRENO-Total
Sack-Total
SACK
Goodput (kbps)
Energy (Joules e-6/Bit)
Reno
SACK-Ideal
NEWRENO-Ideal
Average RTT (msec)
Average RTT (msec)
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Random uniform Loss
 
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1 Packet Loss
Total Energy
Idealized Energy
RENO512
SACK512
SACK512
Total Energy (Joules e-6/Bit)
Idealized Energy (Joules e-6/Bit)
SACK1500
RENO512
SACK1500
NEWRENO1500
Average RTT(msec)
Average RTT(msec)
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5 Packet Loss
Total Energy
Goodput
RENO1500
NEWRENO1500
SACK512
SACK1500
RENO512 NEWRENO512
Total Energy (Joules e-6/Bit)
Goodput (Kbps)
SACK1500
SACK512
RENO512 NEWRENO512
RENO1500
Average RTT(msec)
Average RTT(msec)
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TCP Reno, Newreno and SACK (Thruput)
Average Thruput 5 Packet Loss, MTU 1500
SACK
Newreno
Thruput (bps)
Reno
Time
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10 Packet Loss
Total Energy
Idealized Energy
SACK1500
SACK1500
Total Energy (Joules e-6/Bit)
Idealized Energy (Joules e-6/Bit)
NEWRENO1500
SACK512
NEWRENO512
Average RTT(msec)
Average RTT(msec)
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Loss Experiment Summary - (mtu 512)
1 Loss 5 Loss 10 Loss
Goodput SACK SACK SACK
Total Energy SACK SACK SACK
Idealized Energy Reno Newreno Newreno
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Packet Reordering
 
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Goodput Packet Reordering
1 Packet reorder 5
Packet reorder
SACK
SACK512 1500
1500
512
NEWRENO
NEWRENO
1500
Goodput (Kbps)
Goodput (Kbps)
1500
512
512
Average RTT(msec)
Average RTT(msec)
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1 Packet Reordering
Total Energy
Idealized Energy
RENO512
NEWRENO512
NEWRENO512
RENO512
Idealized Energy (Joules e-6/Bit)
Total Energy (Joules e-6/Bit)
SACK512
SACK512
Average RTT(msec)
Average RTT(msec)
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5 Packet Reordering
Total Energy
Idealized Energy
RENO
512
1500
NEWRENO
NEWRENO512
1500
512
Total Energy (Joules e-6/Bit)
Idealized Energy (Joules e-6/Bit)
NEWRENO1500
SACK512 1500
SACK512 1500
Average RTT(msec)
Average RTT(msec)
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Discussion

• SACK outperforms in most of the cases (Burst
  Loss, Random uniform Loss and Packet Reordering)
• Does SACK help YES/NO
• Higher Goodput at the cost of extra processing
• SACK has higher Idealized Energy

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Discussion contd.
Total Energy vs Goodput

• Energy a 1 / Goodput
• Idealized Energy is a
• factor of Protocol

E a 1/?
Energy (Joules e-6/Bit)
Goodput (Kbps)
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Discussion contd.
Timeouts (Loss case)

• At higher loss all protocols perform
• alike
• SACK512 leads to lesser timeouts
• SACK - No timeout in reordering
• case, Reno gt Newreno

SACK1500
Average Number of Timeouts
RENO512
NEWRENO512
SACK512
Loss
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Related Work

• TCP Energy based on simulation
• We measured energy using a wireless test-bed and
  a real TCP/IP stack (FreeBSD)
• Metrics considered were Total Energy, ratio of
  successful transmission to total number of
  transmission
• Total as well as Idealized energy (Processing
  energy)

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Conclusion

• Awake Energy a 1 / Goodput
• Idealized Energy is a factor of Complexity of the
  Protocol
• Channel conditions are important in selection of
  particular Protocol
• SACK is not suitable for nodes with low Idle
  Energy
• SACK has lower Total Energy and Idealized Energy
  under Packet reordering

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Questions??
Thank You