By default, synchronous serial lines use the High-Level Data Link Control (HDLC) serial encapsulation method, which provides the synchronous framing and error detection functions of HDLC without windowing or retransmission. The synchronous serial interfaces support the following serial encapsulation methods:
"Asynchronous Transfer Mode-Data Exchange Interface (ATM-DXI)
"High-Level Data Link Control (HDLC)
"Frame Relay
"Point-to-Point Protocol (PPP)
"Synchronous Data Link Control (SDLC)
"Switched Multimegabit Data Services (SMDS)
"Cisco Serial Tunnel (STUN)
"X.25-based encapsulations