# Unified ISSU Terms

Table 18 defines terms relevant to module behavior during a unified in-service software upgrade.

Table 18: Unified ISSU-Related Terms

Term | Meaning
--- | ---
Cold boot | The SRP module or line module loads diagnostics from the flash file system and runs them. When the diagnostics successfully complete, the operational image is loaded from the flash file system and then cold started.
Cold start | The SRP module or line module is initialized from the loaded operational image. The line modules are reloaded and the configuration is read from flash memory. When the line modules are operational, their configuration data is bulk downloaded and their interfaces become operational.
Cold restart | If the active SRP module fails, the standby SRP module takes the role of active SRP module. When high availability is not configured, the cold restart is similar to the cold start, except that the applications are already loaded into memory on the standby SRP module and ready to be started. The line modules are reloaded.
Warm restart | If the active SRP module fails, the standby SRP module takes the role of active SRP module. Mirrored configuration data as well as any mirrored volatile data are already resident in memory. The line modules continue to forward data (with a small loss of packets when the fabric is switched from the formerly active SRP module to the newly active SRP module). The protocols and other applications re-initialize from the mirrored data and resynchronize communications with the line modules. When resynchronization is completed, the router resumes normal operations, including updates of any routing tables that result from changes that occurred during the warm restart.