Download Analysis of TCP flows in the Surfnet network Bachelor

How to Identify
the Speed Limiting Factor
of a TCP Flow
E2EMON 2006
Vancouver
Mark Timmer
April 3, 2006
Co-authors:
Pieter-Tjerk de Boer and Aiko Pras
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Contents
•
•
•
•
•
•
•
Motivation
Related work
Possible factors
Overview: identifying the limiting factors
One factor in-depth
Measurement results
Conclusions
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Motivation
•
Surfnet: 1 Gbit
•
Upgrades still useful?
•
Approach: Identify speed limiting factor
10 Gbit
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Related work
• Y. Zhang, L. Breslau, V. Paxson, and S. Shenker,
“On the characteristics and origins of internet flow rates”,
Proceedings of SIGCOMM’02
• M. Siekkinen, G. Urvoy-Keller, E.W. Biersack, and T. En-Najjary,
“Root cause analysis for long-lived tcp connections”,
Proceedings of CoNEXT’05
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Speed limiting factors of a TCP flow
application
application
(sender)
(receiver)
TCP
(receiver)
TCP
(sender)
network
(network layer, link
layer, physical layer)
application
layer
TCP
layer
network
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Overview: identifying the limiting factors
Data repository of packet traces
• Information directly available:
– Arrival time
– IP header (source, destination)
– TCP header (port numbers, sequence number,
acknowledgment number, size of receive window)
• Information calculated:
– Number of outstanding bytes
– Achieved throughput
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Application layer limitations (1)
Slow sender limitation
A
B
idle period
data
data
data
ack
ack
Identification
– Measure idle period percentage
– Careful when receive window is empty
data
data
data
Note:
We only consider flows
measured at the sending side
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Application layer limitations (2)
Slow receiver limitation
A
B
=30)
ack (rwnd
data (leng
th=30)
=0)
ack (rwnd
=30)
ack (rwnd
Identification
– Measure how often the
receive window decreases
data (leng
th=30)
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Application layer limitations (3)
Application protocol limitation
A
B
=150)
ack (rwnd
data (leng
t
data (leng h=30)
t
data (leng h=30)
th=30)
h=0)
ack (lengt =4)
h
ack (lengt
data (leng
t
data (leng h=30)
t
data (leng h=30)
th=30)
h=0)
ack (lengt =4)
h
ack (lengt
Identification
– Measure how often an ACK
contains data
Note:
We only consider flows
sending data one-way
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E2EMON, April 3, 2006
How to Identify the Speed Limiting Factor of a TCP Flow
Network limitation (1)
#outstanding bytes
Limited by loss / retransmission
‘TCP Friendly formula’
BW 
MSS c
RTT p
time
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Network limitation (2)
Limited by delay
– Large buffers
– Entire receive window stored
– Injecting more packets
more delay
extra
data
throughput of bottleneck link 
extra delay
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E2EMON, April 3, 2006
How to Identify the Speed Limiting Factor of a TCP Flow
TCP buffers limitations
The receive buffer limitation
B
B
=100)
ack (rwnd
60 bytes
=30)
ack (rwnd
data (leng
t
data (leng h=10)
data (leng th=10
th=10)
=30)
ack (rwnd rwnd=30)
ack (
data (le
data (lengngth=10)
t
data (leng h=10)
th=10)
=30)
ack (rwnd 30)
=
ack (rwndd
ata (length
=10)
A
60 bytes
rwnd full
rwnd full
A
The send buffer limitation
data (leng
t
data (leng h=20)
t
data (leng h=20)
th=20)
=100)
ack (rwnd 100)
=
ack (rwnddat
a (length=
20)
data (leng
t
h
=
20)
data (leng
th=20)
=100)
ack (rwnd 100)
=
ack (rwnd
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E2EMON, April 3, 2006
How to Identify the Speed Limiting Factor of a TCP Flow
In-depth: the receive window limitation
• Peaks
t1 t2
t3 t4
rwnd full
receive
window
receive
window
rwnd full
#outstanding bytes
A
time
B
=30)
ack (rwnd
data (leng
t
data (leng h=10)
data (leng th=10
th=10)
=30)
ack (rwnd rwnd=30)
ack (
data (leng
data (leng th=10)
t
data (leng h=10)
th=10)
=30)
ack (rwnd 30)
=
ack (rwndd
ata (length
=10)
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Measurement results
Category
% flows
% bytes
Undetermined
20 – 40
10 – 20
Network
20 – 30
30 – 40
0 – 10
0 – 10
Receive buffer
10 – 15
10 – 20
Slow sender
20 – 30
20 – 40
Slow receiver
0–5
0–5
Application protocol
0 – 10
0–1
Send buffer
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Conclusions
• Upgrading network still useful
• However, many flows limited by buffers
• Recommentations:
– Perform statistical analyses
– Develop tool to ‘fix’ TCP-buffer limited flows
– Detect changes of limiting factor in time
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How to Identify the Speed Limiting Factor of a TCP Flow
E2EMON, April 3, 2006
Questions?
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