Use the foregoing ph extension to describe a message dispatcher that works along the following lines: the dispatcher receives messages from two different channels and the checks the parity of each message. if the parity is wrong, it sends a “nack” (negative acknowledgement” through a reply channel (there is one such channel for each input channel); if the parity is right, it places the received message into a buffer. the buffer may store 10 messages. when the buffer is full, the dispatcher sends the whole contents of the buffer to a processing unit through another channel. no message can be placed into a full buffer.