The Evolution of Layered Protocol Stacks - PowerPoint Presentation

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

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

2Slide3

OutlineMotivationModel descriptionResultsConcluding remarks

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Where does this work come from?Ethernet

Twisted PairSMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

Modeling

study of the

Internet protocol stack (architecture) and

its

evolution

…

…

…

…

4Slide5

Why is it an hourglass?

Why

?

-Random?

-Designed?

-

Emergence

?

Ethernet

Twisted

Pair

SMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

…

…

…

…

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

Frequent

innovations

Frequent

innovations

Conserved (“ossified”)

Ethernet

Twisted

Pair

SMTP

HTTP

Thunderbird

Silverlight

Firefox

PPP

Coaxial

Cable

IPv4

UDP

TCP

RTP

Optical

Fiber

MPlayer

…

…

…

…

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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

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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

?

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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

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The value of a protocolThe value of a protocol depends on the value of its products

Protocols with valuable products are more valuable example TCP, HTTP

1

1

5

2

5

3

1

1

1

1

1

1

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The generality of a layer

EthernetTwisted 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

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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

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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

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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

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When does a protocol “die”?Protocols can become extinct due to competition with other protocols

For example, HTTP services cover the set of services provided by FTPCompetition from HTTP has led to FTP’s demise

HTTP

FTP

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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

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Cascade deathsu is w’s

competitorSuppose 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.

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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

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OutlineMotivationModel DescriptionResults

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

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Hourglass shapeThe network forms an hourglass structure over time

The waist usually occurs at layer 5 or 6. L = 10

c = 3/5

z

= 1

s(l) = 1-l/L

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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 τ

X and

τ

Y

H = (

τ

Y

–

τ

X

)/

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)

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RobustnessHigh hourglass scores under a wide range of parameters

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Why does EvoArch generatehourglass-shaped networks?

Small generality Low competition (local)Few deathsLarge

generality

High competition

Protocols have similar products

-similar values

Few deaths

Generality close to 50%

Few protocols

with many products

Most other protocols die

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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,

s

omeone else may do so..

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

?

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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

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Effects of quality factorWe still get an hourglassSlower network growthLower part of hourglass is smaller in size

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

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OutlineMotivationModel DescriptionResults

Concluding remarks33Slide34

What does this mean for the Internet architecture?New way to think about (and teach) Internet’s hourglass architecture

New way to think about “ossification” of protocols at the waistParameterized 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

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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/compete

Designers should strive for wider waistMore 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

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From Networking to Network ScienceHourglass effect in

development of embryosHourglass effect in organization structuresHourglass effect in innate immune system

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