In Travco, you will see 3 types of defense calls. These are: 

• Normal defense call
• Permanent defense call
• Defense call in between attacks

Normal defense call

This type of call is used the most. Once the impact time passes the call will automatically vanish from the current called defense and will be put to the database of called defense.

Permanent defense call

This call will be at the active calls until the requested troop count is met. Of course you can manually delete it at anytime. 

Defense call in between attacks

These calls are supposed to catch enemy waves with catapults. You should put in exact impact time of the attack and a length of gap between next wave (delay). It will also automatically move to the defense database once the impact time passes.