asyhdlc(7tcp)

asyhdlc -- asynchronous High-level Data Link Control (HDLC) protocol module

Description

The asyhdlc module is part of the STREAMS protocol stack used for PPP connections over asynchronous links.

A PPP HDLC packet lacks a CRC checksum and uses a ``transparent code'' for data transmission. asyhdlc performs the following functions on PPP datagrams:

generates (on writing) and validates (on reading) the CRC checksum
performs byte stuffing to achieve data transparency by encoding (on writing) and decoding (on reading) packet data
generates and strips the framing patterns that delimit the start and end of packets
adds (on writing) and removes (on reading) constant address and control bytes if address and control compression is not negotiated
while reading, discards short or long packets and packets with bad checksums, and notifies PPP to allow recovery of compressed TCP headers

See ppp(7) for additional information about the PPP implementation.

References

ppp(7), ppptalk(1M)

RFC 1661