ITU Q.21:1988
ITU Q.21:1988 Systems Recommended For Out-band Signalling
Table of Contents
ANNEXA-Out-bandsignallingsystemsforcarriersystemswith12channelspergroup
A.1TypeI(discontinuoussignals)
A.2TypeII
ANNEXB-Out-bandsignallingsystemsforcarrier
systemswith8channelspergroup