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High Availability Overview
With the wide deployment of various types of value-added services such as IPTV and video
conference, communication interruption may affect these services and result in serious lost.
Therefore, as the carrier of services, the availability of basic network infrastructures is becoming a
great concern.
In an actual network, increasing fault tolerance capabilities of a system, increasing fault recovery
speed, and reducing impact of faults on services are effective ways to enhance system availability.
Availability Requirements
Availability requirements fall into three levels based on purpose and implementation, as shown in
Table 1-1
Availability requirements
Level
Purpose
Implementation
1
Decrease system software and
hardware faults
z
Hardware: Simplifying circuit design, enhancing
production techniques, and performing reliability tests.
z
Software: Reliability design and test
2
Protect system functions from being
affected if faults occur
Device and link redundancy and deployment of switchover
strategies
3
Enable the system to recover fast
even if system functions are
affected.
Providing fault detection, diagnosis, isolation, and
recovery technologies
Among the availability requirements, the availability requirement of level 1 should be considered
during the design and production process of network devices; the availability requirement of level 2
should be considered at the design of network infrastructure; the availability requirement of level 3
should be met by adopting corresponding high availability technologies during the deployment of a
network according to the network infrastructure and service characteristics. This manual describes
these high availability technologies.
Availability Evaluation
Typically, Mean Time Between Failures (MTBF) and Mean Time to Repair (MTTR) are used to
evaluate the availability of a network.
MTBF
MTBF is the predicted elapsed time between inherent failures of a system during operation. It is
typically in the unit of hours. A higher MTBF means a high availability.
