Most network communication based on TCP treats data as an ordered sequence of packets.This ordered-sequence paradigm of TCP is too restrictive when the data is large or is to be distributed to a large number of users.In the data transmission paradigm based on digital fountain codes

obviating the need for ordered data simplifies data delivery.Thus

digital fountain codes are a class of efficient codes which are suitable for reliable communication

and have been widely used in many respects.This paper surveys the principles of a few types of digital fountain codes and their advantages and disadvantages

and investigates their engineering applications.Some key problems needed to be solved in the study of digital fountain codes are pointed out.Finally

the future development and research directions of digital fountain codes are discussed.