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 |
