High Availability Technologies; Fault Detection Technologies - H3C S9500E Series Configuration Manual

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.

High availability technologies

As previously mentioned, increasing MTBF or decreasing MTTR can enhance the availability of a
network. The high availability technologies described in this section meet the level 3 high
availability requirements in the aspect of decreasing MTTR.
High availability technologies can be classified as fault detection technologies or protection
switchover technologies.

Fault detection technologies

Fault detection technologies enable detection and diagnosis of network faults.
•
DLDP and Ethernet OAM are data link layer fault detection technologies.
•
BFD is a generic fault detection technology that can be used at any layer
•
NQA is used for diagnosis and evaluation of network quality
•
Monitor Link and Track work along with other high availability technologies to detect faults
through a collaboration mechanism.
See Table 2 for the details of these technologies.
Table 2 Fault detection technologies
Technology
DLDP
Ethernet OAM
BFD
Introduction
DLDP deals with unidirectional links that may occur in a network. On
detecting a unidirectional link, DLDP, as configured, can shut down the
related port automatically or prompt users to take actions to avoid
network problems.
As a tool monitoring Layer 2 link status, Ethernet OAM is mainly used
to address common link-related issues on the "last mile". You can
monitor the status of the point-to-point link between two directly
connected devices by enabling Ethernet OAM on them.
BDF provides a single mechanism to quickly detect and monitor the
connectivity of links or IP forwarding in networks. To improve network
performance, devices must quickly detect communication failures to
restore communication through backup paths as soon as possible.
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Reference
High Availability
Configuration
Guide/DLDP
Configuration
High Availability
Configuration
Guide/Ethernet
OAM
Configuration
High Availability
Configuration
Guide/BFD
Configuration