Method and apparatus of providing bit count integrity and synchronous data transfer over a channel which does not preserve synchronization

A method for determining the number of data bits transmitted in a frame of data, said frame of data replaced by an erasure fame comprising fill bits, comprising the steps of:

• identifying said erasure frame, a first data frame received immediately prior to said erasure frame, and a second data frame received immediately after said erasure frame;
• adding a length field corresponding to said first data frame to a predetermined amount corresponding to a frame rate of said second data frame to produce a first value;
• subtracting said first value from said length field corresponding to said second data frame to produce a second value, wherein said second value corresponds to a data rate of said data frame corresponding to said erasure frame;
• adding a pre-determined modulo number to said second value if said second value is a negative number to produce a third value, wherein said third value corresponds to a data rate of said data frame corresponding to said erasure frame;
• and
• calculating the number of data bits transmitted in a data frame corresponding to said erasure frame using said second value if said second value is a positive number and using said third value if said second value is a negative number.

In a communication system, a method of providing a constant rate data stream comprising the steps of:

• receiving a first frame of data, said first frame of data comprising a first number of bits and a first field length value;
• placing said first frame of data in a queue;
• moving a write pointer to indicate a queue position for a next received bit;
• receiving an erasure in place of a second frame of data;
• placing a first number of filler bits in said queue according to said write pointer;
• moving said write pointer to indicate a next bit after a last one of said first number of filler bits in said queue;
• receiving a third frame of data, said third frame of data comprising a third number of bits and a third field length value;
• determining a second number of bits in said second frame of data based on said third number of bits, said first field length value and said third field length value;
• and
• moving, if necessary, said write pointer to a next bit after one of said first number of filler bits in said queue such that an actual number of filler bits equal to said second number of bits has been added to said queue.

An apparatus for providing a constant rate data stream with bit integrity from a series of variable rate frames wherein at least one frame of said series of variable rate frames may be an erasure comprising:

• an adaptation layer in a protocol stack that receives said series of variable rate frames, each frame having a frame length and a frame length value, and where when a first frame is received as an erasure, a corresponding frame length and a corresponding frame length value is unknown, wherein said adaptation layer outputs frame data from each frame of said series of variable rate frames which is not received as said erasure and determines said corresponding frame length of said erasure;
• a first queue that receives said frame data from said adaptation layer;
• a fill generator that produces fill bits;
• and
• a switch that connects an output constant rate bit stream to said first queue to transfer each frame of said series of variable rate frames which is not received as said erasure and that connects said output constant rate bit stream to said fill generator for a period of time necessary to transfer a series of bits having said corresponding frame length of said erasure at a time when data from said first frame would have been transferred if said first frame had not been received as said erasure, wherein said switch may connect said output constant bit stream to said fill generator before said adaptation layer determines said corresponding frame length.

An apparatus that provides synchronization and bit count integrity with minimum delay to a variable rate, frame based, non-error free data stream comprising:

• means for receiving a first frame of data, said first frame of data comprising a first number of bits and a first field length value;
• means for placing said first frame of data in a queue and moving a write pointer to indicate a queue position for a next received bit;
• means for receiving an erasure indication in place of a second frame of data;
• means for placing a first number of filler bits in said queue according to said write pointer and moving said write pointer to indicate a next bit after a last one of said first number of filler bits in said queue;
• means for receiving a third frame of data, said third frame of data comprising a third number of bits and a third field length value;
• means for calculating a second number of bits in said second frame of data based on said third number of bits, said first field length value and said third field length value;
• and
• means for moving, if necessary, said write pointer to indicate a next bit after one of said first number of filler bits in said queue such that an actual number of filler bits equal to said second number of bits has been added to said queue.