Proxima ASA 7911 - Manual (Page 78)

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The Modem Command Protocol (MCP) is an application layer
protocol by which an External computer may exchange com-
mands, status information, and data with the Serial Adapter over
the Serial Adapter’s RS-232 serial line. Since the protocol is an
application layer protocol, it contains no provision for error
recovery over the serial line. This problem of error recovery is a
layer 2 problem and is handled by the Proxim layer 2 serial
protocol, the PPX-1.
The MCP protocol consists of a set of commands which cause the
Serial Adapter to transmit data, change an operating parameter, or
respond with status information. The MCP protocol is conveyed
over the serial line using the PPX-1 layer two protocol. The
details of the PPX-1 protocol are unrelated to the details of the
MCP protocol.
The PPX-1 protocol used by the Serial Adapter is very similar to
what is used by Proxim’s 900 MHz ProxLink. The MCP proto-
col is designed to be compatible with the 900 MHz product
wherever possible, but because the 2.4 GHz Serial Adapter
contains additional features, uses a different radio, and handles
networking differently, there are significant changes.
PPX-1 is a very simple, unacknowledged protocol. No provision
is made within PPX-1 for error correction (retries, etc). PPX-1
does provide simple error detection through the use of a check
code. The most significant attribute of PPX-1 is it simplicity.
The table below summarizes the features of the PPX-1 layer 2
protocol:
Error Detection 16-bit Checksum
Error Correction None
Suitable Applications Serial line to Serial Adapter is short
Higher layer error correcting
protocol is in use above PPX-1