20.3 MI transport

At the lowest level the communication is performed in terms of frame messages.

The layout of each message is:

type PMI_FrameMessage =
 struct
 {
    big uint<4> size : size <= 2048;
    byte[size] payload;
 }

Where size is the length of the payload, measured in bytes. The maximum length of a frame message payload is two kilobytes.