data at 2 . 4 kbps is to be transmitted over a noisy link having 3 kbps capacity , and made available to isdn - compatible user devices . the 2 . 4 kbps data is multiplexed with its control and synchronization signals in a first rate adapter to generate 3 kbps data , organized into 10 msec frames of 30 bits , and transmitted over the link . the signals received from the link are further adapted in a second rate adapter to form 8 kbps , 10 msec , 80 - bit , v . 110 frames . not all of the data for each 10 msec , 80 - bit frame is available from the corresponding 10 msec , 30 - bit frame . some of the additional data is multiplexed onto plural 30 - bit frames , and becomes available to the current 80 - bit frame by use of a memory . other bits of the additional data is stored in a memory in the second rate adapter , and used to fill in the 80 - bit frames . the 8 kbps data is further rate adapted to 64 kbps by addition of dummy bits .