Several transport protocols have been designed to provide a richer service to the applications. The two most widely deployed transport protocols on the Internet are the User Datagram Protocol (UDP) and the Transmission Control Protocol (TCP). A third important transport protocol, the Stream Control Transmission Protocol (SCTP) :rfc:`4960` appeared in the early 2000s. It is currently used by some particular applications such as signaling in Voice over IP networks. SCTP was described in the second edition of the e-book.