SAR1a is an instance of MSSAR which is as similar to SAR1 as possible but which is compliant with FAS. It is shown in table 3.
FDL networks used SAR1a. However such networks may also carry cells from standard compliant equipment. In order to inter-operate the assumption is made that the network is performing VPI switching so that the SAR1a information will be carried by the network between FDL/MSSAR endpoints. This only leaves the problem of the PT code-points. To avoid using embarrassing code point values, FDL networks shall always step the assemble field in such a way that no PT code-point with the most significant two bits set shall ever be emitted.
Table 4: Overlap of assemble and PT
