Juniper E Series Hardware Manual page 35

Guide. In this scheme, an extra line module in a group of identical line modules
provides redundancy in case of line module failure. To use this feature, you need a:
Spare line module
Redundancy midplane
Redundancy I/O module
A redundancy midplane may cover 3–6 slots. It provides additional connectivity
that enables the spare line module to assume control of the I/O module associated
with any failed line module in the redundancy group. The spare I/O module
provides connectivity from the spare line module to the redundancy midplane.
The process by which the system switches to the spare line module is called
switchover . When switchover occurs, the system:
Breaks the connection between the primary I/O module and the primary
1.
line module.
Connects the primary I/O module to the spare line module via the redundancy
2.
midplane and redundancy I/O module.
Protocol processing then takes place on the spare line module.
Figure 15 shows the data flow when a spare line module becomes active.
E-series Overview
19
Redundancy Features