scope:

This European Telecommunication Standard (ETS) specifies a function that allows data communication applications utilizing protocol stacks which include High Level Data Link Control (HDLC) procedures (ITU-T Recommendation X.25, [2]) also to be deployed in a Broadband Integrated Services Digital Network (B-ISDN) environment. The required mapping function specified in this ETS is called "Service Specific Convergence Sublayer for HDLC Applications". This ETS makes use of the fact that the functionality of the HDLC framing, i.e., the flag and abort sequences, the zero-bit insertion, and the Frame Checking Sequence (FCS) can be interpreted as a subset of the services offered by the ATM Adaptation Layer type 5 (AAL 5) as specified in ITU-T Recommendation I.363.5 [1].