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Highlights from Geddes/PNSol public workshop on network performance engineering.
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Fundamentals of Network Performance Engineering
Dr Neil Davies Predictable Network Solutions Ltd
Peter Thompson Predictable Network Solutions Ltd
Martin Geddes
Martin Geddes Consulting Ltd
© 2013 All Rights Reserved
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Dr Neil Davies Co-founder, Predictable Network Solutions Ltd
Ex: University of Bristol (23 years).
Former technical head of joint university/research institute (SRF/PACT).
Peter Thompson CTO, Predictable Network Solutions Ltd
Ex: GoS Networks, U4EA, SGS-Thomson, INMOS & Universities of Bristol, Warwick and Cambridge.
Authority on technical and commercial issues of converged networking.
Martin Geddes Founder, Martin Geddes Consulting Ltd
Ex: BT, Telco 2.0, Sprint, Oracle, Oxford University.
Thought leader on future of telecommunications industry.
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Dr Neil Davies Co-founder, Predictable Network Solutions Ltd
Ex: University of Bristol (23 years).
Former technical head of joint university/research institute (SRF/PACT).
Peter Thompson CTO, Predictable Network Solutions Ltd
Ex: GoS Networks, U4EA, SGS-Thomson, INMOS & Universities of Bristol, Warwick and Cambridge.
Authority on technical and commercial issues of converged networking.
Martin Geddes Founder, Martin Geddes Consulting Ltd
Ex: BT, Telco 2.0, Sprint, Oracle, Oxford University.
Thought leader on future of telecommunications industry.
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The only ex-ante network performance engineering company in the world.
• New mathematical performance techniques.
• Performance assessment methodology.
• World’s first network contention management solution.
Consultancy on the future of telecoms and the Internet.
• Business model innovation.
• Technology & product ideation.
• Organisation development.
• Public & private workshops.
This presentation is taken from the content for
Fundamentals of Network Performance Workshop
For information on locations and timing of public events visit
www.sustainablebroadband.com
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Overview
What is “Network
Performance Engineering”?
3 Basic Concepts
G, S and V Implications: Broadband,
LTE, SDN, NFV
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What is
networking?
• Networking is inter-process communications – What matters is enabling computation
• We only care about the effects visible to the computation processes – We don’t per se care about
technologies, mechanisms or policies.
• The only visible effect of the network to the computation processes is (paradoxically) to lose and delay data!
Networking is a
statistical “game of chance”
• We’re sharing a fixed and finite transmission resource through statistical multiplexing
• Good outcomes come from – many “good coincidences”
– few “bad coincidences”
• In the game of chance, networks have some choices over what to lose and delay
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What is “Network Performance Engineering?”
• Network performance engineering is about delivering good enough outcomes…
– Acceptable quality of experience (QoE) to user
– Low cost to network operator
• …and managing the trade-offs in achieving these…
• …by tipping the odds in the game of chance in favour of lower cost and higher QoE
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Overview
What is “Network
Performance Engineering”?
3 Basic Concepts
G, S and V Implications: Broadband,
LTE, SDN, NFV
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Three essential concepts of network performance engineering
1. Loss and delay accumulate along a path
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The raw data we want to work with is end-to-end path delay, because that’s what
the computation processes experience.
Three essential concepts of network performance engineering
1. Loss and delay accumulates along a path
2. What matters is the distribution of loss and delay
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This is the simplest view of probability
distribution, but is of limited help managing
performance
Cumulative view allows (de)composition of loss
and delay along the path. Can isolate performance
issues to specific network elements and links.
We are most interested in the “tails” and their
structure. These are what cause application QoE failure, and whose mitigation drives cost.
Three essential concepts of network performance engineering
1. Loss and delay accumulates along a path
2. What matters is the distribution of loss and delay
3. A model of causality: decompose and predict
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How can you know what kind of intervention will address your QoE or cost issue, and what its effect will be?
Is there another way of looking at this data that will help us to select the right intervention and predict its effect?
Overview
What is “Network
Performance Engineering”?
3 Basic Concepts
G, S and V Implications: Broadband,
LTE, SDN, NFV
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Sort by packet size: a clear structure
emerges
Example packet delay: what is it comprised of?
Look at how there is this boundary line. Packets on the line experienced a network where all buffers were empty; those above
had to wait for other traffic in buffers. Note that the difference in delay along this dotted line is
related only to packet size.
Transit time of hypothetical zero
length packet
Geographic delay G
Every packet experienced a structural delay due to the
speed of light, routing lookup overheads.
Serialisation delay S
Packets with bigger payloads experience more structural delay: as they are being duplicated by each network element it takes longer
to turn the packet into a bitstream, and back again into a packet.
Variable contention delay
V
The remainder of the delay is not structural, but is induced by applying a demand load to
the shared transmission supply. We have choices over
how we allocate this delay.
Geographic delay
Serialisation delay
Variable contention delay
G
S
V
All delay is (everywhere and always) comprised of these
three basic elements.
Network technology or design
Link rate
Scheduling
G
S
V
Once we understand their contribution to QoE and cost, we can measure and manage the right thing!
Ideas like “jitter” conflate delay from V and S, along with loss. Measure the wrong thing, and you manage the wrong thing.
Packets whose delay is on this line are experiencing no contention, even though their delays are varying due to packet size. We would measure “jitter”, but attempts to manage it
would be futile.
Summary (thus far)
1. Measure paths… not points.
2. Analyse distributions… not averages.
3. Extract structure… for understanding and prediction.
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Note that these simple principles are not common practise in network performance engineering today.
(That’s why you should do business with us.)
Overview
What is “Network
Performance Engineering”?
3 Basic Concepts
G, S and V Implications: Broadband,
LTE, SDN, NFV
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So what? Broadband
Megabits/second are an insufficient measure: G and V matter too.
The broadband market is not being regulated correctly!
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Example: Two different ADSL providers in the same location, with same measured “speed”
Great for gaming Useless for gaming
So what? LTE
• Cellular will never be as good as low-spec ADSL – G and V are too high
– Has implications for real-time media, gaming
• Nothing in 3G/4G standards and networks supports consistent loss and delay (i.e. managing V) – Yet this is needed for real-time
value added services
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Downstream delay over a 3G connection
Too much variability for TCP to work well.
So what? SDN and NFV
Software Defined Networking (SDN) resource model is restricted to the arbitrary concept of “bandwidth”.
– So can’t ask for the right G, S and V loss and delay characteristics.
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Delays measured across UK Internet exchange
Bad virtualisation is likely to be the result!
“Bandwidth” is too weak a proxy for what matters in network performance
For further information on network performance engineering
download white papers at
www.pnsol.com/publications.html
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For further insight, webinars and workshops
sign up for
Future of Communications email newsletter
www.martingeddes.com
Neil Davies [email protected]
Peter Thompson [email protected]
Martin Geddes [email protected]
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