Download - Communication Latency
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Latency minimization
in data communication
Presented By: Ishita Akhter
Date: 11/07/2013
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Introduction: Latency Overview
Latency Sources
Latency background
Latency research motivations
The research project
Intended timeline
Tasks performed
Current simulation setup
Observations
Discussions
Future targets
Conclusions
References
Presentation topics
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Definition
Delay between a command and corresponding reaction
Prominently used in Psychology, Biology, Computer Science,
Communication Networking etc.
Focus of current discussion is Communication Latency
The time duration of exchanging a packet (APDU) within a
communication network
One-way delay or RTT (Round Trip Time)
Example evident inSlow audio/video transmission, lateresponse in gaming commands, delayed arrival of data files
etc.
Introduction: Latency Overview
Source:
o D. Delaney, T. Ward and S. McLoone, "On consistency and network latency in distributed interactive
applications: A survey-Part I," Presence: Teleoperators & Virtual Environments, vol. 15, no. 2, pp. 218-234,
2006.
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Processing Delay: Preparation time on each arriving packet, before being queued (Typically within srange)
Queuing Delay: Waiting time for processed packet to be transmitted into the physical link
(Expressed as, QD =Used memory
Packet processing speed, Typically within s - ms range)
Transmission delay: Transfer time for all bits of a packet into the start of physical link (Expressed as, TD
= 1Interface speed , Typically within s - ms range) Propagation delay: Travelling time for packet all through the physical link towards destination node
(Expressed as, SPD =Packet travelling distance
Propagation speed , Typically within ms range)
Figure: Communication network scenario
Latency Sources
Source:
o J. F. Kurose and W. R. Keith, Computer Networking: A Top-Down Approach, Essex: Pearson, 2013.
o ONPATH Technologies, "White Papers - Physical layer switching," 2013. [Online]. Available:
http://www.onpathtech.com/assets/WhitePapers/ONPATHLatencyWP.pdf. [Accessed 20 6 2013].
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Earliest latency observationdelay in repetitive sound generationof volcano eruptions (19121916)
Latency observation within circuit-switched telephone networks(1930s1960s)
Latency investigation in packet-switched communications (1970spresent)
Network performance issues over the last thirty years
Table: Comparison of network performance issues
Recent latency-oriented researches focus on measurement,estimation, possible solutions etc.
Latency background
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Latency effects
Reduced efficiency in real-time interactivity
Data congestion and loss of information
Complicates relevant system/application design
Overall network performance degraded
Less favourable user experience
General latency improvement policies
Better hardware with lesser processing times
Congestion control mechanisms to downsize queuing
Better compression techniques for faster transmission
Relocating network equipment to reduce propagation time
Latency research motivations
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Latency investigation schemes
End-to-end latency measurements
Wireless network latency estimations
Online gaming latency dimensions
Miscellaneous latency observations (IPV6, channel,positioning, satellite, telemedicine etc.)
Significant latency improvement initiatives
Remote access latency minimization
Mobile environment latency improvements
Packet-switching latency enhancements
Developing low-latency communication mechanisms/systems
Latency research motivations (cont.)
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Latency-based research mostly around layer- 3 (Network layer)
Insignificant latency observation for layers 1 & 2 (physical &
data link layer)
Effects on latency with physical layer modulation schemes-
unexplored initiative in physical layer
Latency by MAC header processing-not observed for data
link layer
Latency due to data coding techniques-still offering scopes of
in-depth observations
Not enough attempts to relate energy consumption and latency
Not enough observation of individual layer latencies
Latency research motivations (cont.)
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Project title
Latency minimization in data communications
Primary directive
Investigating latency in first 3 OSI reference model layers
Initial attempt
Spectral efficiency & latency relation in physical layer
Simulator tool
Simulink by Mathworks
The research project
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Research directives Timeline
Literature review on communication latency in
OSI layers
Month(s) 1- 2: (November 2012
December 2012)
Selecting research project focus areas andfinalizing on tasks & tools to be used
Month(s) 3 - 4: (January 2013February 2013)
Building-up skills on software for system
simulations, e.g. Simulink
Month(s) 5 - 6: (March 2013April
2013)
Designing & simulating systems on different
modulation schemes
Month(s) 6 - 10: (May 2013August
2013)
Experimenting with the developed systems,
possible paper publication
Month(s) 11- 12: (September 2013
October 2013)
Preparation for the PhD conversion Month(s) 13: (November 2013)
Intended timeline
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Literature review on latency publications
Research project defining
Finalizing on tasks & tools
Building-up software skills
Designing & simulating on different modulation schemes
Tasks performed
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System components: Source, transmitter, ideal/noisy channel, receiver,destination, result scopes, BER calculator and delay calculator
Simulated systems: OOK, ASK, BPSK & BFSK
Experimental setup
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Transmitted modulated signal
= (), 1(), 0 Signal passes through communication channel, reaches receiver side as
received signal
= , + , , = noise signal is multiplied with a reference unit-energy wave = () (),
to become = Integrating for the period (0, Tb), where Tb= bit transmission time, to
get signal,= Integrated signal passes through the decision device, compared to
threshold
if > , bit detected as 1 and if < , bit detected as 0
Experimental setup (contd.)
Source:
o R. C. T. Lee, M. C. Chiu and J. S. Lin, "Digital Modulation Techniques," in Communications Engineering:
Essentials for Computer Scientists and Electrical Engineers, 2008, pp. 135-188.
o D. Silage, "Bandpass Modulation and Demodulation," in Digital Communication Systems Using MATLAB andSimulink, Bookstand Pub., 2009.
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Observations
Figure: Example of delay comparison
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Initial observation
Component-by-component approach showing delay for
ideal/noisy channels
Non-coded information transmission/reception performed forsingle-level modulation schemes
Delay seen at demodulation, specifically just before integration
Simulating with ideal software blocks provide no delay
Further results expected with ongoing system-build up using
higher order modulations
Observations (contd.)
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Modulationscheme
Constellationpoints (M= 2k)
Bit transmissionrate (k)
Spectral efficiency(bps/Hz)
Delay(Samples)
OOK 2 1 1 1
ASK 2 1 1 1
BPSK 2 1 1 1
BFSK 2 1 1 1
Discussions
Systems simulated have the same spectral efficiency, exhibiting same amount of
delay
Same results obtained for both noisy/ideal channels (component-by-component
approach)
Delay possibly in order to detect transient behaviour of incoming signal Default simulator blocksets solve systems ideally with numerical method
Further designs are being developed with modulation schemes having higher
spectral efficiencies and additional coding components
Source:
o S. Tomazic, "Spectral Efficiency," in Encyclopedia of Wireless and Mobile Communications, 2008, pp. 1095-
1099.o Mathworks, Simulink documentation, 2012.
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Latency observation by
Building higher-order modulation systems & observing
spectral efficiency and latency relation
Inclusion & observation of latency in MAC layer processing
Observation of system energy consumptions in relation with
latency
Relate above observations with established findings on
network layer
Future targets
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Addressed issues so far
Defined latency, its sources
Provided latency research background/history
Explained latency-based research motivations Summarized the research project, along with
intended workplan/timeline
Elaborated on tasks performed
Explained experimental setup, observations andrelated discussions
Described future targets within the scope of theproject
Conclusion
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Questions/comments??
Thankyou
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References
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