The TN792 used on release 7 or later delivers high and critical reliability by coping contents of memory from the primary SPE to a standby SPE. The latter can then take over immediately when the former fails. The TN792 circuit packs require two duplication interfaces (one for primary control carrier and one for standby). This model can be replaced with TN772 duplication interfaces with TN792s, but they must be replaced in pairs. The TN722 does not communicate with a TN792.