Configurable restoration in overlay networks

1. Configurable restoration in overlay networks Matthew Caesar, Takashi Suzuki

2. Motivation • Today’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)

3. Approach • Technique: Overlay based, real-time recovery • Use Link-state routing • Determine link cost from packet receipt delay • Adaptively dampen, localize route advertisements • Desirable properties: • Speed: Low end-to-end failure time • Stability: Few route oscillations • Accuracy: Avoid reacting to transient failures • Scalability: Low probing/communication overhead

4. LCE Phase 1: Detection Mechanism • Goal: • 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 AT RS

5. Phase 1: Example LCE output AT output RS output • Show 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.

6. achieve Phase 1: Comparison LCA • 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 achieve desired LCA

7. Phase 2: Routing • Goals: • Limit scope of link effects • Configurable tradeoff between availability and overhead • Related work: •  No existing scheme autonomously scopes dissemination with respect to links

8. Phase 2: Solution • Solution 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 S D

9. Phase 2: Simulation Results • Compared: • Localized Reaction (LR) • Stability-sensitive LR (LRS) • Cost-sensitive LR (LRC) • Random Hierarchies (RH) • Flooding smaller, more stable costs further improves performance • However, LR not appropriate for all environments • Works best for large, heterogeneous

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