the modulo switching of internal connections. 2 division by the generator polynomial X + x2 X + 1 of the 3. B-TE functions: user-user and user-machine dialogue and product multiplied by the content of the header excluding the protocol; interface termination and other layer 1 functions; HEC field. Cell delineation is performed by using the correla- protocol handling for signalling; connection handling to other tion between the header bits to be protected and the relevant equipments; OAM functions. control bits introduced into the header by the HEC. In the 'hunt' state the delineation process is performed by checking bit-by bit whether the HEC coding law is respected (syndrome = zero) 41.4.11.5 Physical layer information flows and interface for the assumed header field. Once such an agreement is found, functions it is assumed to identify a cell boundary and the 'pre-sync' state is entered. In this state the process is confirmed several times Physical layer information flows between the physical medium before the 'synch' state is declared. In the 'synch' state, a (PM), the transmission convergence (TC) sublayer and their ad- certain number of incorrect recognitions of the coding law jacent entities (ATM layer and management plane) are defined as indicates loss of cell delineation causing transition to the 'hunt' are UNI related OAM functions. state once more. (Figure 4.17.) Scrambling will be used to improve the security and robustness of the HEC cell-delineation mechanism. In addition it helps 41.4.12 1.432 B-ISDN User-Network interface, physical layer specification Bit by bit This defines a limited set of Physical Layer interface structures to be applied to the SB and TB reference points. It also covers the Correct HEC physical medium and the transmission system structure that may be used at these interfaces and also addresses the implementation of UNI related OAM functions. Incorrect HEC The main orientation of the recommendation is toward optical SYNCH transmission since this is the preferred physical medium, ho