Abstract: 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.