This page describes the TinyOS serial-forwarder protocol. This is probably described in a TEP somewhere as well. http://tinyos.stanford.edu/tinyos-wiki/index.php/Mote-PC_serial_communication_and_SerialForwarder_%28TOS_2.1.1_and_later%29

Communication with serial-forwarder is done over a TCP socket, basically packets over a stream. The server and client identify themselves with a handshake and then start sending messages. Messages are basically sent as Pascal strings - first the length and then the number of bytes specified by the length. The length field is 1 byte, so the maximum number of bytes in a packet is 255. Theoretically it should be possible to send 0 bytes for keep-alive and detecting broken streams, but this might not work in all implementations(TODO check).

In the beginning of the TCP connection the server sends and also expects to receive a protocol version handshake. Most implementations have this hard-coded and an exact match is required. The handshake is 2 bytes in both directions and is a fixed value of "U ". Supposedly the space is the actual protocol version and could differ.

Handshake

The following is a 16 byte packet.