E1 Sa-bits and Sa-byte usage

Hello,

I am trying to get an understanding of how the E1 Sa-bits (for non-CRC) and Sa bytes (CRC) are used by applications.

I have heard (for example) that V5.2 uses one of the Sa-bits, which would imply that it could only run on a non-CRC E1 framing type.

I have also heard that Euro ISDN may require one or more of these bits to be set.

So my questions are:

1. Are these types of requirements (for lack of a better term) "application specific", or are they imposed by the country PTT?

1. I would have expected that any application that cared about these would define both a non-CRC and CRC (i.e., using Sa bytes) implementation. Is this the case?

Any other information or pointers to learn more about this would be greatly appreciated.

Thanks,

Mitchell J. McConnell