Download AI Approaches to Network Fault Management

AI Approaches to Network
Fault Management
Andrew Learn
29 Nov 2001
1
Outline
• Fault Management Process
• AI Approaches
– Expert Systems
– Neural Networks
– Case-based Reasoning
2
Network Faults
• Hardware
– Wear and tear
– Cut cables
– Improper installation
• Software
– Incorrect design
– Bugs
– Incorrect data (e.g. routing tables)
3
Fault Management Process
1.
2.
3.
4.
5.
Collect alarms
Filter and correlate alarms
Diagnose faults
Restoration and repair
Evaluate effectiveness
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1. Collect Alarms
• Types of alarms
– Physical: Failure in communication
• e.g. loss of signal, CRC failure
– Logical: Statistical values exceed threshold
• e.g. number of packets dropped
• Communication with components
– Control protocol: Simple Network Management
Protocol (SNMP)
– Data format: Management Information Base (MIBII, 1990) has ~170 manageable objects
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• Sample MIB Entry
ipInReceives OBJECT-TYPE
SYNTAX Counter
ACCESS read-only
STATUS mandatory
DESCRIPTION
"The total number of input datagrams
received from interfaces, including
those received in error."
::= { ip 3 }
• Sample SNMP “get” call
snmpget netdev-kbox.cc.cmu.edu

public
system.sysUpTime.0
Name: system.sysUpTime.0
Timeticks: (2270351) 6:18:23
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2. Filter and Correlate Alarms
• Filter
– Eliminate redundant alarms
– Suppress noncritical alarms
– Inhibit low-priority alarms in presence of
high-priority alarms
• Correlate
– Analyze and interpret multiple alarms to
assign new meaning (derived alarm)
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3. Diagnose Faults
• May require additional tests/diagnostics
on circuits or components
– Automated or manual
• Analyze all info from alarms, tests,
performance monitoring
• Identify smallest system module that
needs to be repaired or replaced
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4. Restoration and Repair
• Restoration: Continue service in presence of fault
– Switch over to spares
– Reroute around trouble spot
– Restore software or data from backup
• Repair
– Replace parts
– Repair cables
– Debug software
• Retest to verify fault is eliminated
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5. Evaluate Effectiveness
• Questions to answer :
– How often do faults occur?
– How many faults affect service?
– How long is service interrupted?
– How long to repair?
• Provides assessment of:
– Performance of fault management system
– Reliability of equipment
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AI Approaches to Fault Management
• Well-developed approach:
– Expert systems
• New approaches:
– Neural networks
– Case-based reasoning
– Other
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Why AI?
• Need for intelligence
–
–
–
–
Data analysis
Pattern recognition
Clustering and categorization
Problem solving
• Need for automation
– Manual analysis/solution takes time
– Limited manpower
– Limited expertise
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Well-developed approach:
Expert Systems
•
•
Expert systems = Rule-base + Working Memory
Three parts to rules:
1. Context trigger (when should rule be considered)
2. Condition ( if X . . . )
3. Conclusion ( . . . then Y)
•
Used since 1980’s by major telecomm companies
– Bell: Automated Cable Expertise (ACE) system
– GTE: Central Office Maintenance Printout Analysis &
Suggestion System (COMPASS)
– AT&T: Network Management Expert System
(NEMESYS)
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Need for New Approaches
• Weaknesses of expert systems
–
–
–
–
–
Brittle in unforeseen situations
Cannot learn from experience
Hard to maintain (adding/deleting/modifying rules)
Knowledge acquisition bottleneck
Can’t handle incomplete or probabilistic data
• Factors driving new approach
–
–
–
–
Rapidly changing technology
Dynamic network topology
Network complexity
Competition, demand for QoS
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Neural Nets
• Structure: input, hidden, output layers
• Training
– Supervised: Input pattern & desired output
– Unsupervised: Clustering of similar inputs
weights
Input
Output
Hidden
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Neural Nets
• Advantages
– Pattern matching & generalization
– Fast & efficient
– Trainable
– Handles incomplete, ambiguous data
• Disadvantages
– Black box
– Lack of training data
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Neural Net Example
• Example: Alarm correlation in cell
phone networks (Univ of Hannover, Germany)
Maintenance
Center
BS1
Microwave
Links
BS2
Mobile
units
Base
Stations
MC
BSC
Base Station
Controller
Switching
Centers
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Neural Net Example
• Test Results:
– 94 alarms
– 99.76% correct classification with up to 25% noise
BSC
alarms
.
.
ML-1
fault
.
BS-1
alarms
.
.
ML-2
fault
Initial
Cause
.
BS-2
alarms
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Case-Based Reasoning
• Case-based reasoning = matching previous
examples
– Case library: Set of previous faults, diagnoses,
solutions
– Usually based on “trouble ticket” help-desk
databases
• Design considerations:
– What are key attributes of a case?
– What attributes will be used to index & access a
case?
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Case-Based Reasoning
• Advantages
– Easier knowledge acquisition than expert
systems
– Can learn by adding new cases
– Doesn’t require extensive maintenance
• Disadvantages
– Requires time-consuming user interaction
– No help for first-time problems
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Case-Based Reasoning Example
Case 134
Problem Type: Performance
Description: High error rate in comm between POA-SP & DF
No access: Intermittent
Retrieval: Case 103 [Similarity = 0.69]
Description: 64kb line from VendorX drops big datagrams.
Additional Info requested: Is there loss of big datagrams in
ping test? (Result: Yes)
Cause: Link 34 inside Bldg 207 was defective
Solution: Vendor replaced cabling.
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Summary of 3 AI Methods
• Expert systems
– If / then rules
– Well-developed technology
– Brittle, hard to maintain
• Neural networks
– Output = weighted transform of inputs
– Fast pattern matching, robust to noise
– Black box, lack of training data
• Case-based systems
– Trouble-ticket retrieval
– Easy to build, maintain
– Slower diagnosis, takes time to build
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Other Approaches
• Bayesian networks
– Model statistical probabilities and
dependence of faults
• Mobile intelligent agents
– Independent software agents cooperate to
collect info, suggest solutions
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Future Trends
• Proactive fault detection
– Recognizing trouble signs and taking
corrective action before service degrades
• Hybrid systems
– Multiple AI methods integrated
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