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Transcript of Overhearing Aided Redundancy Elimination in Multi Rate...
Mobile Network and Communications Lab.
Overhearing‐Aided Redundancy Elimination in Multi‐Rate Wireless
Networks10 August 2013
Youngjun Shim, Gwangwoo Park, Insun Jang, and Sangheon Pack
{yjshim, kwoo17, zerantoss, shpack}@korea.ac.krMNC Lab.
Korea UniversitySeoul, Korea
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Mobile Network and Communications Lab.
Contents
• Introduction– Redundancy Elimination– Problems in terms of using RE in WNs
• Overhearing‐Aided Redundancy Elimination– Concept of OARE– Operation of OARE
• Future Works• Conclusions
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Mobile Network and Communications Lab.
To deal with the data explosion
• Mobile data explosion– Congest data traffic conditions in the wireless infrastructure networks
• Redundancy Elimination– A method to reduce network traffic load– It adapts a protocol independent approach– Designed for WAN optimization (between two middleboxes) [1]
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Continue…
Mobile Network and Communications Lab.
Redundancy Elimination
• Network‐level Redundancy Elimination (RE)– Compare real byte‐strings to reduce (or to encode) redundant traffic
– To encode a packet, the sender has to know the receiver’s cache information
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Mobile Network and Communications Lab.
Problems of RE in WNs
• Cache information synchronization– In wired networks (devices are fixed) it is relatively easy
– In wireless networks (mobile terminals can move and they are frequently disconnected) it is hard
• Alternative approaches– Request cache information before encoding a packet– MTs frequently update own cache information
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lead to a significant overhead
Mobile Network and Communications Lab.
Overhearing‐Aided RE• Exploits broadcast nature of wireless medium
– MT can overhear other MT’s packets – We can compute overhearing probability depending on the transmission mode in multi‐rate environment
– Overhearing probability implies MT’s cache information
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3 42
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Cached by overhearing
Mobile Network and Communications Lab.
Overview of OARE• Simple operation
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Compare the incoming packet and the cache table
For k, 1 ≤k ≤iIf fp(chunk) == fp(ck)Then chunk redundant chunkend
Mobile Network and Communications Lab.
Possibility of overhearing• The transmission mode means the
channel condition of MT – The PER can be computed depending
on the transmission mode [2] and we can regard ‘1‐PER’ as the overhearing probability
• The channel condition in multi‐rate wireless networks can be modeled as a finite‐state Markov chain (FSMC) [3]– md* can be computed by adapting the
transition probability with md and the time difference where the current mode of MT d is md
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overhearing probability overhear
, ( , , )r d im m r d current cp f m m t t
Mobile Network and Communications Lab.
Encoding and decoding• Decision of encoding
– If is higher than a pre‐defined threshold δ, the BS encode a packet
• Failure of decoding at the MT– Because transmission errors when the MT d overheard and replacement of chunks in the fingerprint table at the MT
– The MT d should respond with a NAK, and the BS retransmitsredundant chunks without encoding
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overhear,r dm mp
Mobile Network and Communications Lab.
Future works• Select a proper threshold δ to
optimize OARE– When δ is low
the BS encodes more packets and much traffic can be saved
the decoding failure is high and more retransmissions can occur
– When δ is high the BS encodes less packets and
sufficient traffic reduction cannot be achieved
it can minimize the decoding failure
• Carry out extensive simulation and analytical study– To verify the effectiveness of OARE in terms of the bandwidth
savings and the cost minimization
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Encoding rate (BS) vs. Decoding rate (MT)
Mobile Network and Communications Lab.
Conclusion• OARE is a efficient method to use RE in multi‐rate wireless
networks– The RE technique can be applied efficiently in WNs by exploiting
broadcast nature – It is suitable for the most of WNs which provide the multi‐rate
environment– Consequentially, the redundant traffic can be effectively reduced
• Low overhead and scalable – Does not maintain individual MT’s information
BS maintains only transmitted chunk information– It minimizes the cache synchronization overhead
No explicit synchronization information– It can adapt to the variation of MT’s channel condition
Analytical model is used to analyze MT’s channel condition
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Mobile Network and Communications Lab.
Reference• [1] N. Spring and D. Wetherall. A Protocal‐Independent Technique
for Eliminating redundant Network Traffic. In Proc. ACM SIGCOMM 2000, Aug. 2000.
• [2] Q. Liu, S. Zhou, and G. B. Giannakis. Queuing with Adaptive Modulation and Coding over Wireless Links: Cross‐Layer Analysis and Design. IEEE Transaction on Wireless Communications, 4(3):1142‐1153, May 2005.
• [3] H. S. Wang and N. Moayeri. Finite‐state Markov channel – A useful model for radio communication channels. IEEE Transaction on Vehicular Technology, 44(1):163‐171, Feb. 1995.
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