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Reliability and Recovery
Reliability
Customers need the full reliability of their traditional voice networks, including feature richness
and robustness, and they want the option of using converged voice and data infrastructures.
With the convergence of voice and data applications that run on common systems, a
communications failure could bring an entire business to a halt. Enterprises are looking to
vendors to help them design their converged infrastructure to meet their expected availability
level.
"High availability" communications require the system to work reliably with preexisting transport
infrastructures, and to integrate with a wide variety of external connectivity options. As a result,
the underlying architecture should be designed to support reliable performance at every level.
Avaya Communication Manager running on the Avaya S8700 and the 8300 Media Servers
employs a variety of techniques to achieve this high reliability and availability.
Communication Manager is designed to automatically and continually assess performance, and
detect and correct errors as they occur. The software incorporates component and
subassembly self-tests, error detection and correction, system recovery, and alarm escalation
paths. Its maintenance subsystem manages hardware operation, software processes, and data
relationships.
Employing the TCP/IP packet-based transport architecture allows additional reliability
advantages. One example is the load-sharing and fail-over ability of the principal IP resources
found in the media gateways. The TCP/IP architecture also allows telephones to have a
recovery mechanism of their own, so they can connect to alternate controllers if the link to their
primary gatekeeper is broken.
For large systems, Avaya S8700 Media Servers provide server redundancy, with call preserving
fail-over, on the strength of a Linux operating system. The Avaya S8300 Media Servers can
further enhance redundancy by serving as Local Survivable Processors (LSPs) within networks.
LSPs can take over segments that have been disconnected from their primary call server, and
provide those segments with Avaya Communication Manager operation until the outage is
resolved.
Reliability and availability
The reliability of maintained systems is often expressed in terms of availability, which is defined
as the percentage of time that the system is available to most of the users. The basic formula
for calculating availability is:
where
Mean Time Between Outage (MTBO) measures length of time between outages.
Mean Time To Recovery (MTTR) measures the time to recover from an outage.
230 Avaya Application Solutions IP Telephony Deployment Guide
MTBO
---------------------------------------------- -
A =
MTBO
+
MTTR
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