Data transmission protocol method and apparatus

In a system for communicating messages between signal originating equipment and signal receiving equipment in which the signal originating equipment outputs data packets comprising first and second headers and data via single path media, the signal receiving equipment comprising

• a first header detector for detecting a start code field of said first header comprising less than or equal to three bytes and for determining the beginning of the second header,
• a second header capture circuit for evaluating the value of the second header,
• a controller for inhibiting first header detection and for counting bytes of data according to the value of the second header while said first header detection is inhibited, and
• an output for outputing the data bytes.

In a system for communicating messages from signal originating equipment to signal receiving equipment over single path media, a method of forming data packets comprising the steps of

• determining a first header in accordance with a predetermined pattern,
• determining a second header according to a byte count of a data packet to be transmitted,
• transmitting the first header, the second header, and payload comprising the byte count of data in sequence,
• in a first mode of operation fixing the value of the second header upon initialization of a new type of data;
• in a second mode of operation varying the value Of the second header between originating first and next data packets;
• and
• constructing a cyclic redundancy check field from a serial data stream comprising the second header and the payload.

In a system for communicating messages from signal originating equipment to signal receiving equipment over single path media, a method for recovering data from a received signal comprising the steps of

• detecting a first header comprising a first predetermined pattern,
• inhibiting the detection of the first header,
• determining the beginning of a second header,
• determining the value of the second header,
• determining the beginning of a data field,
• counting the bytes of the data field according to the value of the second header and
• outputing the data bytes to user circuits, said inhibiting step preceding said counting step.

Digital signal originating apparatus comprising

• a clock signal generator,
• an idle time signal pattern generator, responsive to the generated clock signal, for generating idle time signal,
• a data packet originator, responsive to a received data signal and the generated clock signal, for originating data packets including overhead, said overhead comprising a start code comprising less than or equal to three bytes of a predetermined data pattern having a Hamming distance of zero, a byte count field of one byte comprising a binary value representation of the number of bytes of data payload of the data packet and a cyclic redundancy check field comprising less than or equal to two bytes and
• a controller for controlling the outputs of the idle time signal pattern generator and the data packet generator, the maximum data transmission rate given by the equation:
• ##EQU3## where B is the baud rate, E is the worst case time base error as a ratio of the baud ram, L is a length of a data payload field of a data packet in bits and O represents overhead in bits, said overhead comprising less than or equal to 48 bits,
• said data packet originator further comprising a configuration memory or storing said predetermined data pattern of said start code and said byte count value and
• a memory interface, coupled to said configuration memory, for varying the stored value of at least one of said predetermined data pattern and said byte count value.