This document introduces network performance engineering and discusses three key concepts: 1) loss and delay accumulate along a network path, 2) the distribution of loss and delay is important, not just averages, and 3) loss and delay can be decomposed into geographic (G), serialisation (S), and variable contention (V) components. It argues this framework provides insights into broadband, LTE, SDN, and NFV that current approaches overlook by focusing on throughput over end-to-end quality of experience. Predictable Network Solutions and Martin Geddes Consulting aim to advance the practice of network performance engineering.

1. 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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2. 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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3. 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.

4. 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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5. Overview
What is
“Network
Performance
Engineering”?
3 Basic
Concepts
G, S and V
Implications:
Broadband,
LTE, SDN, NFV
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SOLUTIONS

6. 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!

7. 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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8. 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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9. Overview
What is
“Network
Performance
Engineering”?
3 Basic
Concepts
G, S and V
Implications:
Broadband,
LTE, SDN, NFV
PREDICTABLE
NETWORK
SOLUTIONS

10. Three essential concepts of
network performance engineering
1. Loss and delay accumulate along a path
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11. The raw data we want to work with is
end-to-end path delay, because that’s what
the computation processes experience.

12. 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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13. This is the simplest view
of the probability
distribution, but it is of
limited use for
managing performance

14. Cumulative view allows
(de)composition of loss
and delay along the path:
can isolate performance
issues to specific network
elements and links.

15. We are most interested
in the “tails” and their
structure: these are
what cause application
QoE failure, and whose
mitigation drives cost.

16. 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?

17. Is there another way of looking at this data
that will help us to select the right
intervention and predict its effect?

18. Overview
What is
“Network
Performance
Engineering”?
3 Basic
Concepts
G, S and V
Implications:
Broadband,
LTE, SDN, NFV
PREDICTABLE
NETWORK
SOLUTIONS

19. Sort by packet size:
a clear structure
emerges

20. Example packet
delay: what is it
comprised of?

21. Transit time of
hypothetical zero
length packet
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.

22. Geographic delayG
Every packet experienced a
structural delay due to the
speed of light, routing
lookup overheads.

23. Serialisation delayS
Packets with bigger payloads experience more 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.

24. 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.

25. Geographic delay
Serialisation delay
Variable contention
delay
G
S
V
All delay is (everywhere and
always) comprised of these
three basic elements.

26. 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!

27. 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.

28. 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.)

29. Overview
What is
“Network
Performance
Engineering”?
3 Basic
Concepts
G, S and V
Implications:
Broadband,
LTE, SDN, NFV
PREDICTABLE
NETWORK
SOLUTIONS

30. 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

31. 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
– 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.

32. 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

33. For further information on
network performance engineering
download white papers at
www.pnsol.com/publications.html
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34. For further insight, webinars
and workshops
sign up for
Future of Communications
email newsletter
www.martingeddes.com

35. Neil Davies
Neil.Davies@pnsol.com
Peter Thompson
Peter.Thompson@pnsol.com
Martin Geddes
mail@martingeddes.com
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