Empirically Characterizing the
Buffer Behaviour of Real
Devices
Luis Sequeira
Julián Fernández-Navajas
Jose Saldana
Luis C...
Index
I. Introduction and Related Works
II. Test Methodology
• Test Procedure
• Methodology

III. Experimental Results
• W...
Index
I. Introduction and Related Works
II. Test Methodology
• Test Procedure
• Methodology

III. Experimental Results
• W...
Introduction and Related Works
• Packet size varies for different Internet
services and applications:
• VoIP, web, FTP, vi...
Introduction and Related Works
• In access network capabilities are lower than
the ones available in the backbone; this
im...
Introduction and Related Works
• Mid and low-end routers normally do not implement
advanced traffic management techniques....
Introduction and Related Works
• Most Internet routers use FIFO, but there exist
other techniques to manage drop-tail buff...
Introduction and Related Works
• Relationship between router buffer size and
link utilization:
Excessive amount of memory
...
Index
I. Introduction and Related Works
II. Test Methodology
• Test Procedure
• Methodology

III. Experimental Results
• W...
Test Procedure

It may be a device
or a network
Test Procedure
UDP Packets of different size are used
to determine if buffer size is in bytes or
in packets

to produce a ...
Test Procedure

Traffic is captured here
Test Procedure
Input rate
Buffer of the
“System Under Test”

Input rate > output rate

Output rate
Test Procedure
Input rate
Buffer of the
“System Under Test”

Input rate > output rate

Buffer fills

Output rate
Test Procedure
Filling the buffer

Input rate
i

2
1

Output rate
Test Procedure
Time to fill the buffer

First loss

Input rate
i

2
1

Packet i leaves the
buffer

Error
Time to fill and ...
Methodology
• Physical Access:
Counting the
number of
packets in the
queue in the
moment that a
packet arrives to
the buff...
Methodology
• Remote Access:
If the delay of a
packet in the
buffer can be
determined, then
the variations of
this delay c...
Methodology
Input rate

Method 1: Physical Access

Time when the packet
i arrived to the buffer

i

2

• Buffer size is de...
Methodology
Input rate

Method 1: Physical Access

Buffer gets empty

• Buffer size is determined for each packet as follo...
Methodology
Input rate

Method 1: Physical Access

Time when the
packet i leaves
the buffer

• Buffer size is determined f...
Methodology
Input rate

Method 1: Physical Access

Queue

Count packets

Queue

• Buffer size is determined for each packe...
Methodology
Method 2: Remote Access

It will completly
fill the buffer

Input rate
i

2
1

Dropped
packets

Output rate
Methodology
Method 2: Remote Access

Input rate

It will completly
fill the buffer

i

2

𝑅 𝑓𝑖𝑙𝑙

1

Output rate
Time to f...
Methodology
Method 2: Remote Access

Input rate

Time to fill and
empty the buffer
𝑅 𝑜𝑢𝑡

𝑅 𝑓𝑖𝑙𝑙

i

Output rate
It appear...
Methodology
Estimation of the size:
Time to fill
the buffer

Time to fill and to
empty the buffer
Index
I. Introduction and Related Works
II. Test Methodology
• Test Procedure
• Methodology

III. Experimental Results
• W...
Wired Scenario
• In this case we want to test
the accuracy of our method
when there is no possibility
of physical access t...
Wired Scenario
A Particular buffer behaviour:

Linksys WAP54G

Groups of dropped packets

3COM 4500
Wired Scenario
A Particular buffer behaviour:

• It has been observed in the wired
and wireless tested:
• when the buffer ...
Wired Scenario
• Three different amounts of
bandwidth have been used in
order to flood the buffer.
• We see that the accur...
Wireless Scenario
• Variations of the output
rate in wireless network
generate error growth.
• While filling rate is relat...
Wireless Scenario
• We have compared the two
methods when there is
physical access to the SUT.
• The presented results are...
Index
I. Introduction and Related Works
II. Test Methodology
• Test Procedure
• Methodology

III. Experimental Results
• W...
Conclusions
• Two methods have been presented in order to analyze the
technical and functional characteristics of commerci...
Conclusions
• A particular buffer behaviour has been observed for a device: once
the buffer is full, it does not accept ne...
Upcoming SlideShare
Loading in...5
×

Empirically Characterizing the Buffer Behaviour of Real Devices

106

Published on

Luis Sequeira, Julian Fernandez-Navajas, Jose Saldana, Luis Casadesus, Jose Ruiz-Mas, "Empirically Characterizing the Buffer Behaviour of Real Devices," Proc. International Symposium on Performance Evaluation of Computer and Telecommunication Systems SPECTS 2012, July 8-11, 2012, Genoa, Italy. ISBN: 978-1-4673-2235-5.

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
106
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
1
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Transcript of "Empirically Characterizing the Buffer Behaviour of Real Devices"

  1. 1. Empirically Characterizing the Buffer Behaviour of Real Devices Luis Sequeira Julián Fernández-Navajas Jose Saldana Luis Casadesus Communication Technologies Group (GTC) Aragón Institute of Engineering Research (I3A) University of Zaragoza, Spain
  2. 2. Index I. Introduction and Related Works II. Test Methodology • Test Procedure • Methodology III. Experimental Results • Wired Scenario • Wireless Scenario IV. Conclusions
  3. 3. Index I. Introduction and Related Works II. Test Methodology • Test Procedure • Methodology III. Experimental Results • Wired Scenario • Wireless Scenario IV. Conclusions
  4. 4. Introduction and Related Works • Packet size varies for different Internet services and applications: • VoIP, web, FTP, video streaming, online games, etc. • Traffic behaviour has to be taken into account for the design of network devices: • Constant bit rate traffic • Bursty traffic • Different number of frames into each burst
  5. 5. Introduction and Related Works • In access network capabilities are lower than the ones available in the backbone; this implies that some network points become critical bottlenecks • Bottlenecks may also appear at critical points of high-performance networks.
  6. 6. Introduction and Related Works • Mid and low-end routers normally do not implement advanced traffic management techniques. • They always use buffers as a traffic regulation mechanism. • Buffer size becomes an important design parameter • Buffer can be measured in different ways: • Maximum number of packets it can store • Amount of bytes • Queuing time limit (ms)
  7. 7. Introduction and Related Works • Most Internet routers use FIFO, but there exist other techniques to manage drop-tail buffers, e.g. Random Early Detection (RED). • These techniques, in conjunction with buffer size, mainly define the buffer behaviour and how traffic is affected by it.
  8. 8. Introduction and Related Works • Relationship between router buffer size and link utilization: Excessive amount of memory latency increase Small amount of memory packet loss increase • Characterization of buffer behaviour is interesting when trying to improve link utilization.
  9. 9. Index I. Introduction and Related Works II. Test Methodology • Test Procedure • Methodology III. Experimental Results • Wired Scenario • Wireless Scenario IV. Conclusions
  10. 10. Test Procedure It may be a device or a network
  11. 11. Test Procedure UDP Packets of different size are used to determine if buffer size is in bytes or in packets to produce a buffer overflow in the SUT All packets have a unique ID
  12. 12. Test Procedure Traffic is captured here
  13. 13. Test Procedure Input rate Buffer of the “System Under Test” Input rate > output rate Output rate
  14. 14. Test Procedure Input rate Buffer of the “System Under Test” Input rate > output rate Buffer fills Output rate
  15. 15. Test Procedure Filling the buffer Input rate i 2 1 Output rate
  16. 16. Test Procedure Time to fill the buffer First loss Input rate i 2 1 Packet i leaves the buffer Error Time to fill and to emtpy the buffer Output rate
  17. 17. Methodology • Physical Access: Counting the number of packets in the queue in the moment that a packet arrives to the buffer. Traffic may be captured here packet delay packet loss interarrival packet time input and output buffer rate filling buffer rate captures script BUFFER SIZE
  18. 18. Methodology • Remote Access: If the delay of a packet in the buffer can be determined, then the variations of this delay can give us useful information for estimating buffer size. Traffic may be captured here packet delay packet loss interarrival packet time input and output buffer rate filling buffer rate captures script BUFFER SIZE
  19. 19. Methodology Input rate Method 1: Physical Access Time when the packet i arrived to the buffer i 2 • Buffer size is determined for each packet as follows: for all packets in out-capture, a shell script looks for the incoming time in in-capture and counts in out-capture the number of packets between incoming time and the time stamp registered in out- capture, finally the buffer size is estimated as the average of all these values. 1 Output rate
  20. 20. Methodology Input rate Method 1: Physical Access Buffer gets empty • Buffer size is determined for each packet as follows: for all packets in out-capture, a shell script looks for the incoming time in in-capture and counts in out-capture the number of packets between incoming time and the time stamp registered in out- capture, finally the buffer size is estimated as the average of all these values. i Output rate
  21. 21. Methodology Input rate Method 1: Physical Access Time when the packet i leaves the buffer • Buffer size is determined for each packet as follows: for all packets in out-capture, a shell script looks for the incoming time in in-capture and counts in out-capture the number of packets between incoming time and the time stamp registered in out- capture, finally the buffer size is estimated as the average of all these values. i Output rate
  22. 22. Methodology Input rate Method 1: Physical Access Queue Count packets Queue • Buffer size is determined for each packet as follows: for all packets in out-capture, a shell script looks for the incoming time in in-capture and counts in out-capture the number of packets between incoming time and the time stamp registered in out- capture, finally the buffer size is estimated as the average of all these values. i Output rate
  23. 23. Methodology Method 2: Remote Access It will completly fill the buffer Input rate i 2 1 Dropped packets Output rate
  24. 24. Methodology Method 2: Remote Access Input rate It will completly fill the buffer i 2 𝑅 𝑓𝑖𝑙𝑙 1 Output rate Time to fill the buffer
  25. 25. Methodology Method 2: Remote Access Input rate Time to fill and empty the buffer 𝑅 𝑜𝑢𝑡 𝑅 𝑓𝑖𝑙𝑙 i Output rate It appears in the receiver
  26. 26. Methodology Estimation of the size: Time to fill the buffer Time to fill and to empty the buffer
  27. 27. Index I. Introduction and Related Works II. Test Methodology • Test Procedure • Methodology III. Experimental Results • Wired Scenario • Wireless Scenario IV. Conclusions
  28. 28. Wired Scenario • In this case we want to test the accuracy of our method when there is no possibility of physical access to the SUT. • We obtained the buffer size using method 1 with physical access. Next, the estimations obtained using method 2 are compared with previous results, and the relative error is obtained.
  29. 29. Wired Scenario A Particular buffer behaviour: Linksys WAP54G Groups of dropped packets 3COM 4500
  30. 30. Wired Scenario A Particular buffer behaviour: • It has been observed in the wired and wireless tested: • when the buffer is completely full, no more packets are accepted, it will be called upper limit. • The buffer does not accept new packets until a certain amount of memory is available, it will be called lower limit. • In this moment the filling process begins again. • Although this behaviour has some similarities with Random Early Detection (RED) but it is not the same: • There is not probability for dropping an incoming packet.
  31. 31. Wired Scenario • Three different amounts of bandwidth have been used in order to flood the buffer. • We see that the accuracy of the buffer size estimation using the method 2 is high. In addition, the error diminishes as input rate grows. • The results are less accurate but they are still acceptable. • The results using smaller packets are less accurate so we have not presented them. (packet size = 1500 bytes)
  32. 32. Wireless Scenario • Variations of the output rate in wireless network generate error growth. • While filling rate is relatively constant, the emptying rate shows variations for the highest bandwidths. The WiFi access point switches from higher to lower speeds depending on the status of the radio channel
  33. 33. Wireless Scenario • We have compared the two methods when there is physical access to the SUT. • The presented results are the ones obtained using packets of 1500 bytes, since they are the most accurate. • Method 1 is the most accurate estimation so it has been used to compare with method 2.
  34. 34. Index I. Introduction and Related Works II. Test Methodology • Test Procedure • Methodology III. Experimental Results • Wired Scenario • Wireless Scenario IV. Conclusions
  35. 35. Conclusions • Two methods have been presented in order to analyze the technical and functional characteristics of commercial buffers of different devices, or even networks. • This characterization is important, taking into account that the buffer may modify traffic characteristics, and may also drop packets. • The methodology can be used if there is physical access to the “System Under Test”, but it is also useful, with certain limitations, for measuring a remote system. • Tests using commercial devices have been deployed in two different scenarios, using wired and wireless networks.
  36. 36. Conclusions • A particular buffer behaviour has been observed for a device: once the buffer is full, it does not accept new packets until a certain space is again available. • The results show that accurate results of the buffer size can be obtained when there is physical access to the “System Under Test”. • In case of having no direct access to the system, an acceptable estimation can also be obtained if the input rate is more than three times the output rate. In this case, big packets have to be used for the tests. • As future work the method has to be improved in order to minimize the error, especially when measuring wireless devices.
  1. A particular slide catching your eye?

    Clipping is a handy way to collect important slides you want to go back to later.

×