ICT SERVICE MANAGEMENT
Lecture 6 — Comprehensive Exam Summary
Chapter 17: Quality Management
Service levels · SLA · Availability & reliability math
Overview
• Service levels — definition, structure, 4 kinds
• Service level agreements (SLA) — contract built around service levels
• Availability/reliability mathematics — MTBF, MTTR, β, composite systems
• High-availability improvement techniques
EXAM TIP: Highly quantitative — bring calculator. Practise: serial/redundant composite availability
with 4 components.
Part 1 — Service Levels
Slide: Service level definition (quantitative minimum)
Service level: Quantitative definition of a MINIMUM quality requirement for one particular aspect of
a service. Must be measurable. Defines minimum (not average). Good provider exceeds the level.
Lecture 6 — ICT Service Management — Page 1
,Quality attributes — ISO/IEC 25002 SQuaRE
Slide: SQuaRE 8 characteristics
• 1. Functional suitability 2. Performance efficiency 3. Compatibility 4. Usability
• 5. Reliability 6. Security 7. Maintainability (internal) 8. Portability (internal)
Common structure of a service level
Slide: The formula — y, x%, p, z
The formula: In at least X% of all measurements of parameter Y, performed over period P, a value
will be obtained of [at least/at most/equal to] Z.
4 formal parameters
• y = service parameter (quantitative, with unit)
• x% = success rate (frequency of meeting threshold)
• p = period (over which measurements collected)
• z = threshold value (=, ≤, ≥, <, >)
Lecture 6 — ICT Service Management — Page 2
, Lecture 6 — ICT Service Management — Page 3
Lecture 6 — Comprehensive Exam Summary
Chapter 17: Quality Management
Service levels · SLA · Availability & reliability math
Overview
• Service levels — definition, structure, 4 kinds
• Service level agreements (SLA) — contract built around service levels
• Availability/reliability mathematics — MTBF, MTTR, β, composite systems
• High-availability improvement techniques
EXAM TIP: Highly quantitative — bring calculator. Practise: serial/redundant composite availability
with 4 components.
Part 1 — Service Levels
Slide: Service level definition (quantitative minimum)
Service level: Quantitative definition of a MINIMUM quality requirement for one particular aspect of
a service. Must be measurable. Defines minimum (not average). Good provider exceeds the level.
Lecture 6 — ICT Service Management — Page 1
,Quality attributes — ISO/IEC 25002 SQuaRE
Slide: SQuaRE 8 characteristics
• 1. Functional suitability 2. Performance efficiency 3. Compatibility 4. Usability
• 5. Reliability 6. Security 7. Maintainability (internal) 8. Portability (internal)
Common structure of a service level
Slide: The formula — y, x%, p, z
The formula: In at least X% of all measurements of parameter Y, performed over period P, a value
will be obtained of [at least/at most/equal to] Z.
4 formal parameters
• y = service parameter (quantitative, with unit)
• x% = success rate (frequency of meeting threshold)
• p = period (over which measurements collected)
• z = threshold value (=, ≤, ≥, <, >)
Lecture 6 — ICT Service Management — Page 2
, Lecture 6 — ICT Service Management — Page 3
