H3C Technologies H3C S7500E Series Switches - Manual (Page 13)

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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, 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 into fault detection technologies and protection
switchover technologies.
Fault Detection Technologies
Fault detection technologies enable detection and diagnosis of network faults. CFD, 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 1-2 for the details of these technologies.
Table 1-2 Fault detection technologies
Technology Introduction Reference
CFD
Connectivity Fault Detection (CFD), which conforms to IEEE
802.1ag Connectivity Fault Management (CFM) and ITU-T
Y.1731, is an end-to-end per-VLAN link layer Operations,
Administration and Maintenance (OAM) mechanism used for
link connectivity detection, fault verification, and fault location.
CFD Configuration in
the High Availability
Configuration Guide
DLDP
The Device link detection protocol (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.
DLDP Configuration in
the High Availability
Configuration Guide
Ethernet OAM
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.
Ethernet OAM
Configuration in the
High Availability
Configuration Guide