Reliability and Recovery
256 Avaya Application Solutions IP Telephony Deployment Guide
Assessment Methodology and Criteria
The availability of a subsystem is described by the following equation:
where MTBF represents Mean Time Between Failures and MTTR represents Mean Time to
Recover/Repair. MTTR is the time to diagnose, respond, and resume service.
This equation is also sometimes presented in industry literature as the following:
where MTTF is defined as Mean Time to Failure, and equates to (MTBF - MTTR).
Using the above equation, the estimated average annual minutes of downtime experienced due
to a subsystem failure can be expressed as:
(Based on assuming 365.25 days in a year, There are 365.25
×
24
×
60 = 525960 minutes in a
year).
For projecting a enterprise’s total system availability, the sum of annual downtime contributed
from all subsystems is calculated, and then the system availability is estimated by using this
sum.
Note that this formula will result in a crude approximation of availability, as it does not account
for the groups of subsystems whose downtimes overlap.
Definition of Critical Outages and Downtime
The industry recognized criteria used for defining failure, outages and the downtime minutes
experienced is based on the Telecordia (Bellcore) GR-512 Reliability Model requirements for
telecommunications equipment.
Availability
MTBF
MTTR
–
(
)
MTBF
----------------------------------------------
=
Availability
MTTF
(
)
MTTF
MTTR
+
(
)
----------------------------------------------
=
AnnualDowntimeMinutes
1
Availability
–
(
)
525960minutes / year
(
)
×
=
TotalSystemAvailability
1
i
th
SubsystemContributedMinuteDowntime
[
]
i
∑
525960Minutes / Year
------------------------------------------------------------------------------------------------------------------------------------
–
=
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...