The difference I know about these resets are:
Reset 1 & 2 are reset where in the voice calls which are ON would not be effected but the data calls would be dropped.Secondly the unsaved translation/announcement/wake-up requests would not be affected in level 1 /2 reset.

Reset 3 & 4 are the hard reset when the system is powered on the reset 4 is performed where the system boots from the scratch & loads the translation from the storage media tape/ Flash card. reset 4 would drop all the calls & would take its sweet time of around 5-6 min. in flash card system & around 15-20 min. in tape drive system.Any unsaved translation & temporary information would be lost in this reset.
There is also reset 5 which does a ful system check at a very low level & takes more time as compared to other resets.

Reset 1 Effects:
- Stable calls are preserved
- System links and stable feature and service state data are preserved.
- Error and alarm logs are preserved. And almost all alarms are resolved.
- Transient calls are dropped.
- Remote access and system port logins are dropped.
- Apllications links (CDR, AUDIX etc.) are dropped and reestablished.
- MSS activity is aborted.

Reset 2 Effects:
- All system and application links are dropped.
- All calls are dropped.
- Non-translation feature data is lost.
- All hardware components except PNC components are resetted.
- All busied out maintenance objects are released.
- Circuit packs are reinitialized.


Reset 3 effects:
- Same effects as reset 2 plus;
- Emergency transfer is invoked.
- Translations are reloaded from disk or tape.

Reset 4 effects:
- System software is reloaded. (default medium = disk).
- Before the reboot alarm & error logs are saved to disk.
- After reboot alarm & errors logs are reloaded from disk. (Some error information might be incorrect at this moment).
 If this reboot fails your SPE will go down.

Reset 5 Effects:
- More extensive diagnositcs are performed compared to all previous resets.



Rgds,

M.

Thanks....