High Availability Overview; Availability Requirements; Availability Evaluation - HPE FlexNetwork HSR6800 series Configuration Manual

High availability overview

Because communication interruptions can seriously affect widely-deployed value-added services
such as IPTV and video conference, basic network infrastructures must be able to provide high
availability.
The following are the effective ways to improve availability:
•
Increasing fault tolerance.
•
Speeding up fault recovery.
•
Reducing impact of faults on services.

Availability requirements

Table 1 describes a typical availability model that divides availability requirements into different
levels.
Table 1 Availability requirements
Level Requirement
Decrease system software and
1
hardware faults
Protect system functions from being
2
affected if faults occur
Enable the system to recover as fast
3
as possible
Consider level 1 availability requirements during the design and production processes of network
devices.
Consider level 2 availability requirements during network design.
Consider level 3 availability requirements during network deployment, according to the network
infrastructure and service characteristics.

Availability evaluation

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.
MTTR
MTTR is the average time required to repair a failed system. MTTR in a broad sense also involves
spare parts management and customer services.
MTTR = fault detection time + hardware replacement time + system initialization time + link recovery
time + routing time + forwarding recovery time. A smaller value of each item means a smaller MTTR
and a higher availability.
Solution
•
Hardware—Simplified circuit design, enhanced
production techniques, and reliability tests.
•
Software—Reliability design and test.
Device and link redundancy and switchover.
Performing fault detection, diagnosis, isolation, and
recovery technologies.
1