19.0 Appendix
Below is a brief description of the
Addressed Serial Protocol
specification.
Please see section 8.2 “AT+LCLENC Local Data Encoding” for more information on
how the to enable
Addressed Serial Protocol
.
19.1 Addressed Serial Protocol Specification
Land-Cellular has implemented Addressed Serial Protocol to allow a master station to
communicate with a number of remote stations via 1xRTT. During network activity, the
master station must be able to identify individual remote stations sending data to the
master and in turn be able to direct transmissions to a specific remote station. In order to
provide this addressibility, the following protocol is defined:
All data will be sent encapsulated in HLDC-like frames with the IP address of the
remote station (in standard network byte order) as the first 4 information bytes of
each frame. Application data starts at the 5th byte of the information field of each
frame.
Frame Format:
A summary of the HDLC-like frame structure is shown below. This figure does not
include bits inserted for synchronization (such as start and stop bits for asynchronous
links), nor any bits or octets inserted for transparency. The fields are transmitted from left
to right.
The standard HDLC Address, Control and FCS fields are not used or present.
Flag Field
The Flag Sequence indicates the beginning or end of a frame, and is used for frame
synchronization. The bit stream is examined for the binary sequence 01111110
(hexadecimal 0x7E).
Transparency
An octet stuffing procedure is used. The Control Escape octet is defined as binary
01111101 (hexadecimal 0x7D), most significant bit first.
Each Flag Sequence and Control Escape octet is replaced by a two octet sequence
consisting of the Control Escape octet followed by the original octet XOR'd with
hexadecimal 0x20.
Escaped data is transmitted on the link as follows:
0x7E is encoded as 0x7D, 0x5E (Flag Sequence)
0x7D is encoded as 0x7D, 0x5D (Control Escape)
Protocol Field
