Equipment and procedures are necessarily limited in the pre-hospital environment, and EMS professionals are trained to follow a formal and carefully designed decision tree (more commonly referred to as a "protocol") which has been approved by Medical Control. This protocol helps ensure a consistent approach to the most common types of emergencies the EMS professional may encounter. Medical Control may take place on-line, with the EMS personnel having to contact the physician for direction delegation for all Advanced Life Support (ALS) procedures, or off-line, with EMS personnel performing some or all of their ALS procedures on the basis of protocols or 'standing orders'.