Sounds like Full Time Reserve Service. Leave at NRD, get gratuity/pension, 30 days in civi street and come back in earning no more than you did when you were in.
However, this means they skim off a slice of your pension because they have set the FTRS pay at certain levels, and that + pension can exceed your in-Service salary. I believe someone has challenged the pension skim-off. Anyone got any details of that case?