Configurable restoration in overlay networks

Matthew Caesar, Takashi Suzuki

MotivationToday’s internet core has bursty losses

Backbones have low average loss rates (<0.2%), but experience large bursts in loss

Loss durations vary from 10ms to 33.72sec 6 out of 7 providers experienced large outage periods 10-

220sec for 1-2 times per day

Difficult for multimedia applications to recover from repeated loss (e.g. with FEC)Commonly used restoration techniques insufficient

Link layer recovery, MPLS not yet uniformly deployed RON too slow (20 sec), not scalable

real-time recovery desired

“Assessment of VoIP Quality over Internet Backbones,” Markopoulou, Tobagi, Karam (INFOCOM 2002)

ApproachTechnique: Overlay based, real-time recovery

Use Link-state routing Determine link

cost from packet receipt delay

Adaptively dampen, localize route advertisements

text

text

text

text

text

text

Link Cost Advertisements

Link Failure

Probe Packets

text

Link Health Estimation

text

text

text

text

text

text

Link Cost Advertisements

Link Failure

Probe Packets

text

Link Health Estimation

Link Cost Advertisements

Link Failure

Probe Packets

text

Link Failure

Probe Packets

text

Link Health Estimation

Desirable properties: Speed: Low end-to-

end failure time Stability: Few route

oscillations Accuracy: Avoid

reacting to transient failures

Scalability: Low probing/communication overhead

Layer 3

Layer 2

Layer 1

MeasureLink cost

AverageLink cost

UpdateLink cost

Incomingprobe packet

Calculateerror

counter

F()

G()

α

MIMD

Updatethreshold

Routingalgorithm

Phase 1: Detection MechanismGoal: Calculate link cost

Link Cost Estimation (LCE): Estimates failure

probability from packet loss

“Delay-deficit algorithm”

Adaptive Tracking (AT): Filters noise Reacts quickly to

changes

Route Stabilization (RS): Dampens route flaps

RS

AT

LCE

Phase 1: ExampleShow detailed actions of layers

Link Cost Estimation (LCE):

metric representing probability link has failed

spikes result from packet losses

Adaptive Tracking (AT): metric with noise filtered

Route Stabilization (RS): advertised value for link

Setup Link Failure at t=[150s-

170s] Probe every 300ms, 10%

loss

Results First Detection in 0.92s,

next at 5.42 A false positive due to

cold start. Stabilizes in 5 seconds.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50Time [seconds]

Lin

k co

st

Layer 1 (Sm)Layer 2 (Sav)Layer 3 (S)

LCE output

AT output

RS output

Phase 1: Comparison

Compared LCA, RON, and “Oracle-based” routing. Results:

RON requires 4 to 10x more advertisements than LCA

RON’s overhead increases exponentially with probe speed, LCA’s overhead increases linearly

Packet loss has an extreme effect on RON, moderate effect on LCA

LCA can achieve subsecond reactions on most internet links

Number of advertisements required to acheive desired loss rate (0% loss)

0

50

100

150

200

250

0 50 100 150 200

total packets dropped due to failure

tota

l # o

f req

uire

d ad

verti

sem

ents

RON 0%loss

RRAPID 0%loss

Number of advertisments required to acheive desired loss rate (5% loss)

0

1000

2000

3000

4000

5000

0 50 100 150 200 250 300

total packets dropped due to failure

tota

l # o

f req

uire

d ad

verti

sem

ents

RON 5%loss

RRAPID 5%loss

achieve desired

achieve

LCA

LCA

Phase 2: RoutingGoals:

Limit scope of link effects Configurable tradeoff between availability and overhead

Related work:

No existing scheme autonomously scopes dissemination with respect to links

Hierarchy (HIPR, HSR…)

Backbone-based (CEDAR, Span)

Flat no-coordination(LS, DV, DSR, DSDV, TORA, …)

Flat coordinated (AODV, FSR, ZRP)

LSA scoped based on link characteristics?

No Partially No No

Autonomous? No No Yes No

Phase 2: SolutionSolution idea: Autonomously localize LSA propagation

Unstable cost changes propagated locally

Stable changes propagated further

Application can control distance of propagation based on its requirements

Mechanism: Localized Reaction Global level propagates link

existence Local level propagates up to

date link state Create boundary around link Only nodes inside boundary

receive LSAs from link Dynamically resize the boundary

based on link characteristics

D

S

Phase 2: Simulation Results

Compared: Localized Reaction (LR)

Stability-sensitive LR (LRS)

Cost-sensitive LR (LRC) Random Hierarchies (RH)

Performance with heterogeneous link cost

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5Average Path cost

Ov

erh

ea

d

RH

LR

LRC

Performance with heterogeneous link stability

0

5

10

15

20

25

30

0 0.5 1 1.5Average Path Cost

Ov

erh

ea

d

RH

LRS

Flooding smaller, more stable costs further improves performanceHowever, LR not appropriate for all environments

Works best for large, heterogeneous

Conclusions

1. Can achieve sub-second reactions on most links with reasonable stability Congested links increase reaction time Can react well on most internet links

2. Localization of route updates Scoping state dissemination with

respect to links improves performance in heterogeneous network

Can achieve resiliency close to link-state with fraction of overhead