H3C Technologies H3C MSR 50 - Manual (Page 9)

1
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 Solution
1
Decrease system software and
hardware faults
• Hardware—Simplified circuit design, enhanced
production techniques, and reliability tests.
• Software—Reliability design and test.
2
Protect system functions from being
affected if faults occur
Device and link redundancy and switchover.
3
Enable the system to recover as fast
as possible Performing fault detection, diagnosis, isolation, and
recovery technologies.
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.