I have been told that APC-1466 states enough requirements for the device control interface A, but that we should have requirements for the signalling interfaces B, C, and D before committing ourselves to protocol design. I just don't have the same feeling for detailed requirements in those areas that I have for interface A. I can only think of two requirements: these interfaces must - pass all the signalling content offered to them - do it quickly and reliably. Can anyone get us down to another level of detail? Tom Taylor E-mail: taylor@nortelnetworks.com (internally Tom-PT Taylor) Tel.: +1 613 765 4167 (internally 395-4167) FAX: +1 613 763 7236 (internally 393-7236)