Session types are a formalism for structuring communication based on the notion of
: the structure of a conversation is abstracted as a type which is then used as a basis of validating programs through an associated type discipline. While standard session types have proven to be able to capture many real scenarios, there are cases where they are not powerful enough for describing and validating interactions involving more complex scenarios. In this note, we shall explore two extensions of session types to
in presence of asynchronous communication.