The Serial Data Transport Protocol (SDTP), described in RFC 1963, is used to transfer serial data over a PPPconnection(Point to Point Protocol). The data can be transmitted synchronously and asynchronously. \nDuring transmission, the SDTP datagrams are encapsulated in Point to Point Protocol (PPP) data packets. The frame length of the SDTP datagram that can be transmitted over a PPP link is determined exclusively by the negotiated maximum frame size and the maximum length of the information field of the encapsulated PPP data packet. Transmission can only take place when SDTP protocol signals that the connection is open.