Ujayi Pranayama

Before you undertake the practice of Ujayi pranayama, you must have a good understanding of Udyana bandha.
For that reason, Ujayi breath is best learnt only after you have learnt to lengthen your breath in Visama Vritti pranayama.
In Ujayi pranayama, Udyana bandha is held in during inhalation, so the abdomen is kept still and the chest puffs up. This is somewhat similar to the Taoist practice of reverse abdominal breathing, but as Udyana bandha is also held on the exhalation, the abdomen doesn't moves out at any stage of the practice.
In proper Ujayi breathing, the glottis is partially closed. This help control the flow of air and produces a characteristic sound.
Ujayi breath can be done with Sama Vritti or Visama vritti ratios. It is very energizing, and for this reason is often used in asana practice.