(Microcom Networking Protocol) A family of communications protocols from Microcom, Inc., Norwood, MA, that have become de facto standards for error correction (classes 2 through 4) and data compression (class 5). In 1997, Compaq acquired Microcom.
Class 1: Half-duplex asynchronous transmission.
This is an earlier mode that is no longer used.
Class 2: Full-duplex asynchronous transmission.
Class 3: Full-duplex synchronous transmission
using HDLC framing techniques and 64-byte
blocks. Start/stop bits are stripped.
Class 4: Increased throughput. Shorter headers,
frames up to 256 bytes. Some vendors adjust frame
size based on line quality.
Class 5: Compresses data up to two times.
Class 6: Starts at V.22bis modulation and
switches to V.29 if possible. Uses pseudo-
duplexing ping-pong method for faster
turnaround of V.29 transmission.
Class 7: Compresses data up to three times.
Class 8: Not in use.
Class 9: Adds Piggy-back Acknowledgment** and
selective retransmission for more efficient
data transport. Provides better performance over
variety of links.
Class 10: Adds Adverse Channel Enhancements** for
better transmission on rural, cellular and other
noisy lines.
** Proprietary Microcom techniques.
