Spawn System
The Enemy Spawn Director
The Enemy Spawn Director(ESD) monitors players through a mission, and decides what to spawn, where, and how much based on how well the player is doing. The ESD knows how well a player is doing based on Stress Levels. When the stress you and your squad are under is High, the ESD will consider ending the current encounter faster and will spawn less enemies. When the stress you and your squad are under is Low, the ESD will start spawning more enemies. All of this to try to ensure that you are under a constant and continuous amount of Pressure. By keeping your Pressure Level consistent throughout a mission, the ESD insures that there are never too little enemies and never to many enemies.
Stress
Stress Levels are shared between your squad mates. If your Stress is High or low, it will contribute to how high or low your Squad's Stress Level is. Your personal Stress Level can increase dramatically if you have taken damage, have been incapacitated, have been grabbed, have a low ammo or grenade count, or are low on stims. Stress will also go up over time based on how long you have been in active combat. Your Stress levels will decrease over time as long as you are not doing anything to increase them.
Waves

Progress Monitoring
The ESD monitors how players are progressing in a level. If you are stalling or not progressing