1. science
2. social science
3. anthropology

THE SERVICE RELIABILITY
ECOSYSTEM
©M ichael Tor tor ella, Ph. D.
M anaging Dir ector
Assur ed Networ ks, LLC
THEME
SDN/NFV NETWORK RELIABILITY
STANDARDS CAN’T BE SENSIBLY
CONSTRUCTED UNLESS YOU FIRST
KNOW WHAT
SERVICE RELIABILITY TARGETS YOU
ARE TRYING TO MEET
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 2
OVERVIEW
Ser vice examples
Customer s want r eliable ser vices
Ther e is a language for talking about ser vice
r eliability
Ther e is a theor y and a set of engineer ing
pr inciples suppor ting r eliable ser vices
Ser vice r eliability r equir ements come fir st!
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 3
OVERVIEW
Ser vice r eliability r equir ements ar e
abstr acted fr om any r equir ements for
r eliability of ser vice deliver y infr astr uctur e
(SDI) and its elements
The r eliability char acter istics of the SDI
deter mine the how r eliable the ser vice it
suppor ts will be
The or der in which you do things matter s!
Ecosystem diagr am
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 4
TELECOM SERVICE
EXAMPLES
Voice telephony ser vice



POTS networ k
Connectionless networ ks
M obile
Inter net access ser vice


TCP/ IP W AN backbone
Local access var ies
+
+
+
+
Dial-up
DSL
TV Cable
Optical
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 5
TELECOM SERVICE
EXAMPLES
Var ious enter tainment ser vices

M ost mediated by the Inter net
Complex combinations of ser vices



Video teleconfer encing
Point-of-sale cr edit appr oval
M obile banking
Peer -to-peer ser vices
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 6
CUSTOMERS WANT
RELIABLE SERVICES
PC M agazine r eliability r atings of ISPs


Inter net access ser vice “outages”
Upload and download speeds
Customer r eliability complaints about mobile
ser vices



Dr opped calls
Echo
Slow data
Ver izon FiOS adver tising “the fastest and
most r eliable Inter net”
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 7
SERVICE RELIABILITY
LANGUAGE
Tr ansactions
Ser vice failur e classifications accor ding to
tr ansaction phases



Accessibility
Continuity/ Fulfillment
Release
Requir ements for these ar e based on
systems engineer ing under standing of
customer needs and desir es for satisfactor y
tr ansactions in each ser vice
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 8
SERVICE RELIABILITY
ENGINEERING PRINCIPLES
Ser vice failur e modes can be catalogued
Ser vice failur e mechanisms and failur e
causes ar e events or omissions in the SDI
Congestion is always a factor in SDIs


Economically unr easonable to pr ovision an SDI
for ever y possible ser vice demand
W hen SDI elements fail, a level of ser vice
demand that might have been suppor table if
ever ything wer e wor king pr oper ly will lead to
incr eased congestion
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 9
SERVICE RELIABILITY
ENGINEERING PRINCIPLES
So if you want to under stand how r eliable
your ser vice is,


M ake a r eliability model to r elate the fr equency
and dur ation of ser vice failur es and outages to
the fr equency and dur ation of events or
omissions in the SDI and/ or
Collect and analyze accessibility,
continuity/ fulfillment, and r elease data
+ DPM appr oach is followed by many ser vice pr ovider s
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 10
SERVICE RELIABILITY
ENGINEERING PRINCIPLES
And if you want to know what r eliability
r equir ements you should put on your SDI
and its elements, “wor k the model
backwar ds”
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 11
VOICE TELEPHONY
EXAMPLE
 Voice telephony (VT) is the ability to speak with
another par ty beyond shouting distance
 VT was fir st deliver ed on an analog networ k


Panel, step-by-step, cr ossbar switching
Twisted pair , coax, micr owave tr anspor t
 In the 1 9 6 0 s-1 9 7 0 s, VT began to be pr ovided on a
digital networ k

Seamless tr ansition to
+ Electr onic switching
+ SONET/ SDH, OC-3 -1 2 -4 8 -2 9 2 , and many other digital
tr anspor t systems
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 12
VOICE TELEPHONY
EXAMPLE
Nobody noticed! Customer s don’t know or
car e what technology you ar e using to
pr ovide their ser vice
This impor tant pr inciple means that ser vice
r eliability r equir ements ar e invar iant with
r espect to the natur e of the SDI you use to
deliver the ser vice
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 13
VOICE TELEPHONY
EXAMPLE
 “Car r ier gr ade” ser vice accessibility has always been
claimed to be ≥ 0 .9 9 9 9 9 (“5 nines”)


Does not account for delays
No local – toll distinction
 “Car r ier gr ade” ser vice continuity objective was “no
mor e than 2 5 0 DPM ” (for exponentially-distr ibuted
holding times with a mean of 6 minutes)
 Ser vice r elease failur es wer e so r ar e that no one
car ed
 Some impor tant questions still linger

W as the 2 hour s downtime in 4 0 year s switching system
r equir ement r eally necessar y?
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 14
VOICE TELEPHONY
EXAMPLE
 Reliability model for the POTS networ k based on the
5 -level hier ar chy in the toll networ k


Using cut set – path set methods combined with r enewalr ewar d capacity models for networ k elements
Or iginally, this was for the analog networ k (slide 1 6 )
+ But the str uctur e of the digital networ k was similar
+ W ith digital, loss/ noise/ echo wer e no longer issues so
ser vice fulfillment (slide 8 ) became simpler

Later , signaling r an on a separ ate SS7 networ k
+ So signaling networ k failur es need to be incor por ated also
 AFAIK, a complete POTS r eliability model was never
satisfactor ily car r ied to conclusion


Used “r epr esentative connections” appr oach instead
Gener alized to histogr am of connection types
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 15
VOICE TELEPHONY
LL TOLL HIERARCHY
⋅
⋅
⋅
etc.
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 16
VOICE TELEPHONY
EXAMPLE
VT can also be pr ovided on a TCP/ IP
networ k
Then it is called “VoIP” - but it is still a voice
telephony ser vice
Ser vice r eliability r equir ements ar e the
same!
Accessibility ≥ 0 .9 9 9 9 9
 Continuity ≤ 2 5 0 DPM
 Fulfillment?
 Release again negligible
CQR Emerging Technologies

Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 17
VOICE TELEPHONY
EXAMPLE
W hat kind of TCP/ IP networ k model do you
need to extr act these voice telephony
ser vice r eliability descr iptor s?
“Repr esentative connections” makes no
sense
Simulation models hold pr omise

The gov’t communication folks use these
Need to gr apple with r outer and tr anspor t
systems r eliability/ capacity cur ves
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 18
INTERNET ACCESS
EXAMPLE
The ser vice is the simple ability to connect
to the inter net
Ser vice accessibility is the pr obability that
you can br ing up your home page when you
want

Requir ement? Any page?
Ser vice continuity is the pr obability that your
br owsing session will be inter r upted by loss
of inter net connectivity

Requir ement?
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 19
INTERNET ACCESS
EXAMPLE
Ser vice fulfillment is the pr obability that
per ceptual aspects (delays, video quality,
etc.) of the exper ience ar e “satisfactor y”

Requir ements?
Ser vice r elease is the pr obability that the
inter net connection goes away when you
dismiss it


M aybe not as simple as it used to be because
malwar e continually intr oduces new wr inkles
Requir ements?
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 20
INTERNET ACCESS
EXAMPLE
 Catalog accessibility, continuity, and r elease failur e
modes
 Catalog associated failur e mechanisms and failur e
causes in the TCP/ IP networ k
 One of the r easons for inconclusive discussions
about inter net access ser vice r eliability is that not
ever yone agr ees on the language


Telephone people
IT people
 Standar dization can help her e
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 21
INTERNET ACCESS
EXAMPLE
Reliability models for TCP/ IP networ ks ar e
consider ably mor e complicated
Analytical appr oaches via limit theor ems for
connectionless networ ks with unr eliable
elements
Simulation appr oaches via OpNET, OmNET,
etc.
W hatever model is used, it needs to be
focused on accessibility, continuity, and
r elease at the ser vice level
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 22
CONSEQUENCES OF
INADEQUATE SERVICE
RELIABILITY ENGINEERING
Over pr ovisioning the SDI

Excess CAPEX
Under pr ovisioning the SDI

M or e ser vice failur es than desir able
+ Excess congestion
Failur es in networ k elements make the
networ k look under pr ovisioned for the per iod
of time the outages per sist
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 23
SERVICE RELIABILITY
ECOSYSTEM DIAGRAM
Start
Here
SERVICE
CUSTOMER
NEEDS/DESIRES
SERVICE
RELIABILITY
REQUIREMENTS
MARKETING
ADVERTISING
CQR Emerging Technologies
Roundtable
11 May 2015
SDI
RELIABILITY
MODEL
SDI ELEMENT
RELIABILITY
REQUIREMENTS
EQUIPMENT
SUPPLIERS
SLAs
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 24
SoME BENEFITS OF
STANDARDIZATION
 Pr omote the idea of focusing on the ser vice fir st



Not ever y ser vice pr ovider need offer the same ser vice
r eliability
A ser vice pr ovider can offer differ ent gr ades of ser vice
r eliability
Customer s can make compar isons, analyze SLAs, etc.
 Pr omote a common language acr oss the var ious
stakeholder communities
 Abstr act the ser vice r eliability r equir ements fr om
the SDI element r eliability r equir ements

Rational appr oach to SDI r eliability r equir ements
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 25
Some BENEFITS OF
STANDARDIZATION
Use the ser vice r eliability ecosystem to
establish a pr ocess-based appr oach to SDI
design and pr ovisioning
A clear path for war d for the har d technical
wor k of devising r eliability r equir ements for
SDN/ NFV networ ks and their elements
The next gener ation of telecom engineer s
won’t have to r einvent this wheel

Some “new” “better ” technology will come along
to succeed SDN/ NFV
CQR Emerging Technologies
Roundtable
11 May 2015
THE SERVICE RELIABILITY ECOSYSTEM
©2015 M. Tortorella
Slide 26