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8/8/2019 Improving Tcp Ip Performance Over Wireless Network
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Improving TCP/IP Performance overImproving TCP/IP Performance overThird Generation Wireless Networks:Third Generation Wireless Networks:M C Chan andM C Chan and RamchandranRamchandran RamjeeRamjee
Bell Labs, Lucent TechnologiesBell Labs, Lucent Technologies
Guided by Shivanth M P
Latha . V Roll No : 60
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AgendaAgenda
y Introduction
y
Windows Regulatory Performance of long-lived TCP flows
y Short-flow differentiation
y
Conclusion
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IntroductionIntroduction2G wireless 2.5G wireless 3G wireless
Phone calls
Voice mailSimple emails
Phone /fax
Voice mailLarge emails
Web browse
Navigation
New updates
Phone/fax
Global roamingLarge emails
High speed web
Video-conferencing
Speed: 10 kb/sec Speed 64-144 Kb/sec Speed:144 kb-2mb/sec
Download 3 min mp3
31-41 min
Download 3 min mp3
6-9 min
Download 3 min mp3
11 sec-1.5 min
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Introduction cont.Introduction cont.
y TCP is most widely used
y Windows regulator that Maximizes
throughput for all buffer sizes (important
metric for long flows)
y Scheduling algorithm to reduce transfer
latency for short flow
y Exploiting user diversity is important
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Simplified 3G networkSimplified 3G network
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TCPTCP WINDOWWINDOW--INGING
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Ack RegulatorAck Regulator
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Windows RegulatorWindows Regulator
Wi = Ni+Yi+1 ------------------- (1)
Yi+1 < Wi ---- ----------------------(2)
Yi+B >= Wi ------------------------ (3)
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Windows RegulatorWindows Regulator--static (WRS)static (WRS)
y On Enqueue of each Ack
Set W=B
Send Ack to sourceWRSAlgorithm
Wi = B and Yi >0 fulfills equation 3
If B
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Windows Regulator Dynamic(WRD)Windows Regulator Dynamic(WRD)
On Dequeue of each data packetY=Y+1
On Enqueue of each Ack packet
Y=Y-1set W=Y+B
Transmit Ack to source
WRD Algorithm
W = Y + B ------ fulfills Equation 3
If B=0, it underflows & violates Equation 2
As W(wrd) >=W(wrs), throughput W/RTT is better for wrd
than wrs
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Windows Regulator withWindows Regulator withAAck Buffer(WRB)ck Buffer(WRB)
On dequeue of each data packet
Y=Y+1
If there is an ack stored in ack buffer then
W=Y+B+Ba
Transmit ack to source
On Enqueue of each ack set
Y=Y+1
W=Y+B+Ba
if W B then no
acks are sent to TCP source.
Ba is ack buffer in reverse direction
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Throughput vs. buffer size(single user)Throughput vs. buffer size(single user)
For TCP selective
ack:
AR performs better
than WRS and DT
WRD is close to
max with Buffer
>15
WRB outperformsall others
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Throughput vs. Buffers Multiple usersThroughput vs. Buffers Multiple users
Similar to Single user
Except AR outperforms
WRD
Absolute performance is
better with multiple users.
8 users are similar to 4
users except gap between
AR and WRD widens.
WRB still performs best.
WRD is best considering
RTT tradeoff.
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Throughput vs. Wired LatencyThroughput vs. Wired Latency
For D < 70ms, WRS is better
than DT. It is degrading>70ms
For D400ms, WRD/WRB are worse
than DT
Increasing RLP buffer sizewill help AR,WRD,WRB
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ThroughputThroughput VsVs LossLossRandom Loss
AR,WRB,WRD perform well for
small amount but start degrading
after 10-3
After 10-2 all algorithms have same
low perf as random error is
dominant factor
Congestion loss
AR,WRB perform better than DT
below congestion loss rate 10-3
WRD/WRS performs poorly thanDT
AR/WRB don't degrade as they
have ack buffer to provide fast
feedback
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Comparison SummaryComparison Summary
y DT and WRS cannot adapt to the large rate anddelay variation in wireless channel
y AR adapts well to the large variations but doesnot perform well with latency as estimation
errors cause throughput degradey WRD performs well against latency but poorly
against congestion loss
y WRB is best and robust against latency andpacket loss
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SchedulingScheduling
y Intra-user scheduling
SFP : short flow priority algorithm
Short flow/Long flow based on data transfer
Reclassification short->long->short
y Inter-user scheduling
PF: Priority Fair queuing
PF-SP: priority fair with Strict PriorityPF-RP: priority fair with Rate priority
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PF schedulerPF scheduler
y Each user reports measured channelconditions to the PF scheduler (RNC)
y User with best channel is selected to
transmit in different time slot, better thanround robin but unfair
y PF weight the current rate achievable byaverage rate received by user and selectuser i with maximum Ri/Ai ,where Ri isthe rate achievable by user andAi isaverage rate .
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PFPF--SP SchedulerSP SchedulerLet set of short flows be SLet set of long flows be L
If S is non empty
select user I with largest Ri
Else ifL is non Empty
select user with largest Ri/Ai
Update Ai for all usersPF-SP SchedulerAlgorithm
y Short flows have higher priority
y It is unfair to long flow.
y Average rate for each user is
maintain over all short and long flows
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PFPF--RP schedulerRP scheduler
Better balance between minimizingShort term latency and fairness
It relatively sacrifices fairness to users
with long flows
Latency reduction improves with more
no of users
Run PF and user i is selected
Run Pf-SP and user j is selected
If Ri>Rj
select user i
else
select user j
Update Ai for all usersThe PF-RP algorithm
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Performance comparisonPerformance comparison
2 users with SNR +4dB and 2
users with -4dB
PF/SFP has better latency
under 15 KB file transferthan PF/FIFO
PF-SP and PF-RP can exploit
differences in channel
conditions
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Performance comparison cont.Performance comparison cont.
All 4 users with same -4dB SNR
PF-SP performs worst for all file
sizes
PF and PF-RP is better than PF-
FIFO
PF/SFP is always better than
PF/FIFO
PF-SP is better or worse than PFdepending on channel condition
PF-RP is the most robust
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ConclusionConclusion
y WRS a common algorithm used in wired
routers perform poorly
y WRB which adapts wireless channel conditions
and performs ack regulation improves 100%over DT
y PF-RP/SFP provides robust performance over
different user channel conditions. 54% over
PF/FIFO
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ReferencesReferences
1 M C Chan and Ramchandran RamjeeImproving TCP/IP performance over Thirdgeneration Wireless networks
Infocom , IEEE 20082 M C Chan and Ramchandran
Ramjee:TCP/IP performance over 3Gwireless link with rate and delay variation
ACM mobicom ,IEEE,2002
3 Wikipedia.org
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Q &A
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