Adapting to the ISDN-which rate adaption scheme should I use?

The CCITT has standardised two rate adaption protocols for use over the ISDN. V.110 uses a fixed pattern of bits (frame) into which the user´s data bits are fitted. Both synchronous and asynchronous data are supported, together with some end-to-end control signals. V.110 provides neither error detection nor correction facilities and operates only over a B channel using the circuit mode bearer service. V.120 encapsulates the user´s data stream in HDLC frames. Three types of data are supported: asynchronous, HDLC framed synchronous and bit transparent synchronous. Error detection is provided for all types and for the asynchronous and HDLC classes, error correction is available as an option. V.120 can operate over a B channel using the circuit mode or frame relay bearer services or the D channel using frame relay only. Now that V.120 is a stable Recommendation it will start to be provided on TAs sold in Europe. Such TAs will almost certainly be multi-protocol, supporting V.110 as well. They will therefore continue to interwork with older V.110-only equipment whilst also solving the transatlantic compatibility problem