High-level Data Link Control (HDLC)
The maximum frame size depends on the number of CRC bytes at the end of the frame. It can be shown that for frame sizes of up to 4096 bytes, 2 CRC bytes gives a very high probability that no erroneous frame will be passed as good. For larger frame sizes, up to 16kbytes, a four byte CRC is used. HDLC LAPB is the Link Layer (Level 2 of the OSI model) that is usually used by X.25, the ITU (previously called the CCITT) standard for Packet Switched Networks.