User`s guide

100-8006-152G AirborneDirect™ Serial Bridge User’s Guide Page 95
Quatech, Inc. Confidential
TRANSMISSION OF IP DATAGRAMS OVER SERIAL USING
AIRBORNEDIRECT™ SERIAL
Introduction
ASLIP (Airborne Serial Line IP) is a simple packet framing protocol: ASLIP defines a sequence
of characters that frame IP packets on a serial line, and nothing more. It provides no
addressing, packet type identification, error detection/correction or compression mechanisms.
Because the protocol does so little, though, it is usually very easy to implement.
Protocol
The proposed ASLIP protocol defines four special characters:
Character Definition
START 0xC1 (decimal 193)
END 0xC0 (decimal 192)
ESC 0xDB (decimal 219)
• Each data packet sent will begin with the START character.
• Each data packet sent will end with the END character.
• The ESC character is inserted by the transmitter to indicate that the following byte is a
literal data byte. The receiver removes the ESC character and passes the following byte
as data without interpretation.
• If the data packet contains a character the same as the END character a two-byte
sequence of ESC and END is sent instead.
• If the data packet contains a character the same as the START character a two-byte
sequence of ESC and START is sent instead.
• If the data packet contains a character the same as the ESC character a two-byte
sequence of ESC and ESC is sent instead.
• ASLIP is applicable only in data pass-through mode.
• If the data packet contains a START character between a START and END sequence, it
will be treated as an END START sequence i.e. all data preceding the START will be
sent as a data packet and a new data packet will be started.
APPENDIX E
ASLIP PROTOCOL