Editing SimTX API (section)

== Design notes ==
* '''Protobuf frames.''' Every message is a protobuf message. On the wire each one is a varint length followed by a <code>ClientFrame</code> or <code>ServerFrame</code>, a message with a single <code>oneof</code>. The recommended approach is to generate bindings from the [[SimTX API/Schema|.proto files]] with <code>protoc</code>. A hand-written codec needs only varints, 32- and 64-bit little-endian values and length-delimited fields; [[SimTX API/Quick start]] shows one in a few dozen lines of Python.
* '''Unknown is not an error.''' A frame whose <code>oneof</code> member a reader does not know, and a field it does not know, are skipped. See [[SimTX API/Compatibility and versioning]].
* '''Rejections are never silent.''' A refused hello gets a [[SimTX API/Packets/ServerHello|ServerHello]] with a status, a refused or ended session a [[SimTX API/Packets/SessionStatus|SessionStatus]] with an error code and a reason, and a failed request an [[SimTX API/Packets/Error|Error]] with its <code>request_id</code>.
* '''Real time.''' Receivers get samples at the rate of the simulation, and transmitters must send samples at the rate they declared. Neither side waits for the other. A client that falls behind loses data.
* '''Simulated reception.''' The IQ a receiver gets includes the propagation, fading, Doppler shift, noise and interference at its location and antenna. See [[Propagation Basics]].