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The Evolution of Layered Protocol Stacks The Evolution of Layered Protocol Stacks

The Evolution of Layered Protocol Stacks - PowerPoint Presentation

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The Evolution of Layered Protocol Stacks - PPT Presentation

Leads to an HourglassShaped Architecture Saamer Akhshabi Constantine Dovrolis Georgia Institute of Technology sakhshabiconstantinegatechedu 1 My coauthor Saamer Akhshabi ID: 544326

protocol layer protocols hourglass layer protocol hourglass protocols http waist ipv4 nodes tcp probability udp competition higher node quality

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Slide1

The Evolution of Layered Protocol Stacks Leads to an Hourglass-Shaped Architecture

Saamer Akhshabi Constantine DovrolisGeorgia Institute of Technologys.akhshabi,constantine@gatech.edu

1Slide2

My co-author, Saamer Akhshabi

(Very smart 2nd year PhD student, he could not travel to Toronto)

2Slide3

OutlineMotivationModel descriptionResultsConcluding remarks

3Slide4

Why did we write this paper?Ethernet

Twisted PairSMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

4Slide5

Why is the Internet protocol stack an hourglass?

Why?

-

Random?

-Designed?

-

Emergence

?

Ethernet

Twisted

Pair

SMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

5Slide6

What happens at the “waist” compared to other layers?

Frequent innovationsFrequent

innovations

Conserved (“ossified”)

Ethernet

Twisted

Pair

SMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

6Slide7

How can a new protocol survive at the waist?

X.25SNAEthernet

Twisted

Pair

SMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

ATM

IPv6

7Slide8

What about “Future Internet” those architectures?

Will these architectures also evolve to an hourglass in few years?How to make them more “evolvable”?So that they can better accommodate innovation?So that no single protocol at the waist “kills” all competitors

NDN

XIA

MpbilityFirst

Nebula

?

8Slide9

OutlineMotivationModel: EvoArch

ResultsConclusions9Slide10

Two DisclaimersEvoArch is only an abstraction of protocol stacksEvoArch

does not capture many practical aspects and protocol-specific or layer-specific semanticsEvoArch is certainly not the only model, or “the correct model”, for the emergence of hourglass-shaped network architecturesModels should be judged based on their assumptions, parsimony and predictions10Slide11

Model description

Protocols as nodes

Protocol dependencies as

edges

Products:

P(u)

Substrates:

S(u)

Layer of u: l

(u)

Layered acyclic network

u

Every layer provides a service

L

1

4

3

2

11Slide12

The value of a protocolThe value of a protocol depends on the value of its productsProtocols with valuable products are more valuable

1

1

5

2

5

3

1

1

1

1

1

1

12Slide13

The generality of a layerEthernet

Twisted PairSMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

As we go higher in the stack:

Protocols become less general – they offer more specialized services

The probability that a protocol is used by next-layer’s protocols decreases

13Slide14

Generality as a probability

We introduce a parameter called

generality vector s

s(l) : probability that new node at layer l+1 chooses each node at layer l as substrate

s(l) decreases as we go higher in protocol stack

s

(1) = 0.9

s

(3) = 0.5

s

(L-1) = 0.1

14Slide15

Competition between protocolsTwo protocols at the same layer compete if they offer similar servicesi.e., if they have large overlap in their products

HTTP competes with FTP due to several overlapping productsTCP does not compete with UDP because they have minimal service overlap TCP

UDP

HTTP

FTP

15Slide16

Modeling competition

If c = 3/5u competes with

q and w

q does not

compete with w

q

u

w

Let C(u) be set of competitors of u

Node w competes with u if

c: competition threshold

16Slide17

When does a protocol “die”?Protocols can become extinct due to competition with other protocolsFor example, HTTP services cover the set of services provided by FTP

Competition from HTTP has led to FTP’s demiseHTTP

FTP

17Slide18

Modeling protocol deathsA node u dies if its value is significantly less than the value of its strongest (i.e., maximum value) competitor.

z: mortality parameter

18Slide19

Cascade deathsu is w’s competitor

Suppose that w dies due to competition with u (r=3/7)21

4

2

7

2

1

3

1

1

1

1

1

1

1

1

q

u

w

If a node w dies, its products also die if their only substrate is w. This can lead to

cascade deaths.

19Slide20

Protocol birthsBasic birth processNumber of new nodes at given time is a small fraction of total number of nodes in network at that time.

New nodes assigned randomly to layersDeath-regulated birth processThe birth rate at a layer is regulated by the death rate in that layerDiscussed later20Slide21

Summary of EvoArchDiscrete-time modelTime advances in

rounds Each round includesbirth of new nodescompetition among nodes at the same layerpotentially, death of some nodes Key parametersGenerality vector s

Competition threshold cMortality parameter z

21Slide22

OutlineMotivationModel DescriptionResults

Emergence of hourglass structures Controlling the location/width of the waistEvolutionary kernelsProtocol differencesConclusions22Slide23

Hourglass shapeThe network forms an hourglass structure over timeThe waist usually occurs at layer 5 or 6.

L = 10c = 3/5

z

= 1

s(l) = 1-l/L

23Slide24

Hourglass Resemblance Metricw(l) : width of layer l

Minimum occurs at layer bX = {w(l), l = 1, . . . b} Y = {w(l), l = b, . . .L}Mann-Kendall statistic for monotonic trend on the sequences X and Y: coefficients τX

and τY

H = (

τ

Y –

τX)/2

H=1 when widths first decrease and then increase (monotonically)

Width

Layer number

w(1)

w(2)

w(b)

w(

b+1

)

W(L)

24Slide25

RobustnessHigh hourglass scores under a wide range of parameters

25Slide26

Why does EvoArch generatehourglass-shaped networks?

Small generality Low competition (local)Low death probabilityLarge

generality

Frequent

competition

Protocols have similar

substrates &

values

Low death probability

Generality close to 50%

Few protocols

with many products

Most other protocols die

26Slide27

How can we get a wider waist?As γ increases

Location of the waist moves to higher layersWidth of waist increases27

γ is the layer at which the generality

is 50%

L

ayer

number

γ

0.5

s(l)Slide28

Evolutionary kernels 28Slide29

How can a kernel die?Normalized value of a node: value divided by maximum possible value at that round

If several nodes appear at the next higher layer, andkernel fails to quickly acquire those new possible products,

someone else may do so..29Slide30

Death-regulated birth process?What if the birth probability in a layer is regulated by the death probability in that layer?

30

It

becomes practically

impossible to replace kernels Slide31

What if protocols differ in term of a “quality factor”?The “quality factor” can be interpreted broadly

Performance, Extent of deployment, Reliability or security, Incremental improvements,etc

31Slide32

Effects of quality factorWe still get an hourglassLower part of hourglass is smaller in size

only high quality nodes survive at the lower partKernels are often NOT the highest quality protocols32Slide33

OutlineMotivationModel DescriptionResults

Concluding remarks33Slide34

What does this mean for the Internet architecture?New way to think about (and teach) Internet’s hourglass architectureNew way to think about “ossification” of protocols at the waist

Parameterized model for TCP/IP stack: Two protocols compete when their service overlap is more than 70%A protocol survives only if its value is more than 90% of its strongest competitor’s valueDeath-regulated births 34Slide35

What does this mean for IPv4 vs IPv6?

IPv6 has same products but lower extent of deployment (i.e., lower “quality factor”)IPv6 would find it easier to compete w IPv4 if:It had some distinct products that IPv4 does not haveUnfortunately, it only offers more addressesIPv6 would face easier adoption if it was not presented as “IPv4 replacement” but as “the second network-layer protocol”35Slide36

What does this mean for future Internet architectures?Hourglass structures should be expected if these new architectures evolve/competeDesigners should strive for wider waist

More diverse waist -> more evolvable architectureEvoArch: as the waist moves higher, it also becomes widerHow to push the waist to a higher layer?See highly relevant paper:L. Popa, A.

Ghodsi, and I. Stoica

. HTTP as the Narrow Waist of the Future Internet. In ACM

SIGCOMM

HotNets, 2010

36Slide37

From Networking to Network ScienceHourglass effect in development of embryos

Hourglass effect in organization structuresHourglass effect in innate immune system37Slide38

38Thanks to Todd Streelman (School of Biology, Georgia Tech)

Soojin Yi (School of Biology, Georgia Tech)National Science Foundation (NSF)