Yashar Ganjali

Sprint Advanced Technology Lab.August 5, 2003

Link Failures in IP Networks:Link Failures in IP Networks:A Closer LookA Closer Look

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Previous Work

Link Failures

UnplannedMaintenance

Individual Link Failures

Shared: Router Related, Optical Related, …

70 % of Unplanned

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Our Work

• Goal: gaining a deeper understanding of the causes & characteristics of link failures

• How: – Using SONET alarm logs– Focusing on high failure

links/periods

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IS-IS Failures, Feb. 2003

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Number of Failures per Day

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Zoom In

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Zoom In (Cont’d)

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High Failure Periods

1. Periods with a large number of failures (HNP)

2. Periods in which a large percentage of links are down (HDP)

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Number vs. Duration of Failures

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High Failure Periods

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Periods with High Number of Failures

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High Failure Periods (Cont’d)

• We can also classify high failure periods based on spatial distribution of the links failing in those periods.

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Spatial DistributionJune 17, 2003

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Spatial DistributionFeb. 26, 2003

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Links with High Duration of Failures

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Links with High Number of Failures

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Matching IS-IS Failures with SONET alarms (SLOS)

IS-IS Failure % Matched IS-IS Failure % Matched

STK.Feb-Jun.2003 0.58 STK.Feb-Jun.2003-NM-NRR 0.65

STK.Feb-Jun.2003-HDL 0.68 STK.Feb-Jun.2003-NM-NRR-HDL 0.85

STK.Feb-Jun.2003-HDP 0.19 STK.Feb-Jun.2003-NM-NRR-HDP 0.65

STK.Feb-Jun.2003-HNL 0.77 STK.Feb-Jun.2003-NM-NRR-HNL 0.84

STK.Feb-Jun.2003-HNP 0.56 STK.Feb-Jun.2003-NM-NRR-HNP 0.78

STK.Feb-Jun.2003-NM 0.61 STK.Feb-Jun.2003-NM-RR 0.29

STK.Feb-Jun.2003-NM-HDL 0.69 STK.Feb-Jun.2003-NM-RR-HDL 0.00

STK.Feb-Jun.2003-NM-HDP 0.28 STK.Feb-Jun.2003-NM-RR-HDP 0.07

STK.Feb-Jun.2003-NM-HNL 0.81 STK.Feb-Jun.2003-NM-RR-HNL 0.16

STK.Feb-Jun.2003-NM-HNP 0.65 STK.Feb-Jun.2003-NM-RR-HNP 0.26

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Preliminary Results• About 58% of all failures match with a

SLOS alarm.• High Failure Links have a higher

correlation with SLOS alarms (85%)• Router Related Failures show much

less correlation than other classes (0-29%).

• Periods with high number of failures show more correlation than periods with high duration of failures.

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Unmatched SLOS alarms

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Matching SLOS alarms• Problem: A large percentage (45%) of

SLOS alarms do not correspond to any IS-IS failures

• Solution: Remove links which are not up or links which go down for ever

• Result: Less than 2% of SLOS alarms do not correspond to any IS-IS failures

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Matching IS-IS Failures & SONET alarms

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Unmatched SLOS alarms(considering removed links)

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Unmatched SLOS alarms• Spread over time

• Almost half of them have a matching alarm (SLOS <-> SLOS cleared)

• Minimum time between SLOS and SLOS cleared is 9 seconds.

• More investigation???

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Research Direction• High Failure Periods: Study cascading

effects, spatial distribution of failures• High Failure Links: Predicting future

failures based on passed ones.• Network Availability: How do failures

affect network availability?

• ???

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You always pass failures on the way

to success!

You always pass failures on the way

to success!

Thank you!

Thank you!

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Spatial-Temporal Correlation of Failures

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Spatial-Temporal Correlation of Failures