Reliability
Issue 3.4.1 June 2005
231
Table 43: Expected range of typical availability
shows the range of availability that is typically
expected of communications systems:
High availability – general design considerations
High availability requires dedicated design diligence at multiple layers and with several
overlapping objectives (
Table 44: Measurements used for assessing availability expectations
).
Not only are failures at the device or subassembly level minimal, but also when there is a
failure, the design itself helps in many ways to alleviate the impact of the failure. For example,
the design tests itself frequently to detect problems before they become customer affecting. The
design isolates subassemblies that are not functioning properly, and runs verification tests on
Table 43: Expected range of typical availability
Availability Downtime
per year
Reliability
level
Who might need this
99.95
4 ½ hours
“Standard”
Generally accepted as the minimum
standard of acceptable downtime for
business
99.99
53 minutes
“High”
Businesses or organizations that
highly depend on their
communication system
99.999+
5 minutes
or less
“Critical”
Hospitals, emergency services,
high-performance call centers,
critical government agencies,
financial institutions
Table 44: Measurements used for assessing availability expectations
Design element
Measurement
Failures of each component and subsystem must
be infrequent
Mean Time between
Failures (MTBF)
System outages must be infrequent
Mean Time between
Outages (MTBO)
When there is a failure or outage:
●
The impact must be minimized and
isolated.
●
Recovery must be speedy.
Mean Time to
Recovery (MTTR)
The system collects its own performance
statistics
Various
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 ...